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  • 1.
    Afshari, Davood
    et al.
    School of Mechanical Engineering, Iran University of Science and Technology, Iran .
    Mohammd, Sedighi
    School of Mechanical Engineering, Iran University of Science and Technology, Iran .
    Zuhier, Barsoum
    Department of Aeronautical and Vehicle Engineering, KTH – Royal Institute of Technology, Sweden .
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    An Approach in Prediction of Failure in Resistance Spot Welded Aluminum 6061-T6 under Quasi-static Tensile Test2012In: Proceedings of the Institution of mechanical engineers. Part B, journal of engineering manufacture, ISSN 0954-4054, E-ISSN 2041-2975, Vol. 226, no 6, p. 1026-1032Article in journal (Refereed)
    Abstract [en]

    The aim of this article is to predict the failure load in resistance spot welded aluminum 661-T6 sheets with 2 mm thickness under quasi-static tensile test. Various welding parameters, e.g. welding current, welding time and electrode force are selected to produce welded joints with different quality. The results show that for all the samples in this study only interfacial failure mode was observed in tensile-shear test and no pull-out mode was observed. According to the failure mode, an empirical equation was used for the prediction of failure load based on nugget size and hardness of failure line. Microstructure study has been carried out to investigate microstructural changes in the welded joints. For determination of the minimum hardness, microhardness tests have been carried out to find hardness profiles. The minimum hardness value was observed for a thin layer around the nugget with large and coarse grains. The results show that by using the presented empirical equation, the failure can be predicted with a good agreement only by measuring nugget size.                   .

  • 2.
    Agmell, M.
    et al.
    Lund University, Sweden.
    Ahadi, A.
    Lund University, Sweden.
    Zhou, J. M.
    Lund University, Sweden.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Bushlya, V.
    Lund University, Sweden.
    Stahl, J. -E.
    Lund University, Sweden.
    Modeling subsurface deformation induced by machining of Inconel 7182017In: Machining science and technology, ISSN 1091-0344, E-ISSN 1532-2483, Vol. 21, no 1, p. 103-120Article in journal (Refereed)
    Abstract [en]

    Traditionally, the development and optimization of the machining process with regards to the subsurface deformation are done through experimental method which is often expensive and time consuming. This article presents the development of a finite element model based on an updated Lagrangian formulation. The numerical model is able to predict the depth of subsurface deformation induced in the high- speed machining of Inconel 718 by use of a whisker-reinforced ceramic tool. The effect that the different cutting parameters and tool microgeometries has on subsurface deformation will be investigated both numerically and experimentally. This research article also addresses the temperature distribution in the workpiece and the connection it could have on the wear of the cutting tool. The correlation of the numerical and experimental investigations for the subsurface deformation has been measured by the use of the coefficient of determination, R-2. This confirms that the finite element model developed here is able to simulate this type of machining process with sufficient accuracy.

  • 3. Agmell, Mathias
    et al.
    Ahadi, A
    Zhou, J M
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Bushlya, Volodymyr
    Stahl, J-E
    Modeling Subsurface Deformation Induced by Machining of Inconel 7182017In: Machining science and technology, ISSN 1091-0344, E-ISSN 1532-2483, Vol. 21, no 1, p. 103-120Article in journal (Refereed)
    Abstract [en]

    Traditionally, the development and optimization of the machining process with regards to the subsurface deformation are done through experimental method which is often expensive and time consuming. This article presents the development of a finite element model based on an updated Lagrangian formulation. The numerical model is able to predict the depth of subsurface deformation induced in the high- speed machining of Inconel 718 by use of a whisker-reinforced ceramic tool. The effect that the different cutting parameters and tool microgeometries has on subsurface deformation will be investigated both numerically and experimentally. This research article also addresses the temperature distribution in the workpiece and the connection it could have on the wear of the cutting tool. The correlation of the numerical and experimental investigations for the subsurface deformation has been measured by the use of the coefficient of determination, R2. This confirms that the finite element model developed here is able to simulate this type of machining process with sufficient accuracy.

  • 4.
    Ahmad, Maqsood
    et al.
    Base Engine & Materials Technology, Volvo Group, Gothenburg.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    König, Mathias
    Materials Technology for Basic Engine, Scania CV, Södertälje.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Bending Fatigue Behavior of Blast Cleaned Grey Cast Iron2017In: Residual Stresses 2016: ICRS-10, Materials Research Proceedings 2 (2016), 2017, Vol. 2, p. 193-198Conference paper (Refereed)
    Abstract [en]

    This paper presents a detailed study on the effect of an industrial blast cleaning process on the fatigue behavior of a grey cast iron with regard to the residual stresses and microstructural changes induced by the process. A comparison was also made to the effect of a machining operation which removed the casting skin layer. The blast cleaning process was found to greatly improve the fatigue resistance in both the low and high cycle regimes with a 75% increase in the fatigue limit. Xray diffraction measurements and scanning electron microscopic analyses showed that the improvement was mainly attributed to compressive residual stresses in a surface layer up to 800 μm in thickness in the blast cleaned specimens. The machining also gave better fatigue performance with a 30% increase in the fatigue limit, which was ascribed to the removal of the weaker casting skin layer.

  • 5.
    Albertini, G
    et al.
    Departimento di Fisica e Ingegneria dei Materiali e del Territorio Unverisita Ancona, Italy.
    Giuliani, A
    INFM Universita Ancona, Italy.
    Peng, Ru
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    Manescu, A
    National Rd Institute for Welding amd material testing Universita, Ancona, Italy.
    Ponzetti, A
    NUOVA Jesi.
    Determination of the residual stress in a centrifuge bowl by neutron diffraction2002In: Applied physics.. A,. Materials science & processing, ISSN 0947-8396, Vol. 75Article in journal (Refereed)
  • 6.
    Albertini, G
    et al.
    Dip di Fisica e Ingegneria dei Materiali e del Territorio Universita Ancona Italy.
    Giuliani, A
    INFN Ancona, Italy.
    Peng, Ru
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    Manescu, A
    Intituto di Scienze Fisiche Universita, Ancona, Italy.
    Rustichelli, F
    INFN Ancona, Italy.
    Pozetti, A
    NUOVA MAIP Jesi.
    Neutron diffraction determinatin of rediual stresses in a duplex steel centifuge bowl2002In: Metal 2002,2002, 2002Conference paper (Refereed)
  • 7.
    Albertini, Gianni
    et al.
    Dipartimento di Scienze dei Materiali e della Terra, Universita, Ancona, Italy.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials . Linköping University, The Institute of Technology.
    Manescu, Adrian
    Instituto di Scienze Fisiche, Universita, Ancona, Italy.
    Ponzetti, Araldo
    NUOVA M.A.I.P SpA, Viale Cavalotti n 30, Jesi, Italy.
    Neutron Diffraction Measurement of Residual Stress in a centrifugal Bowl of Duplex Steel2001In: Journal of Neutron Research, ISSN 1023-8166, E-ISSN 1477-2655, Vol. 9, p. 305-312Article in journal (Refereed)
  • 8. Alkaisee, Rasha
    et al.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Influence of Layer Removal Methods in Residual Stress Profiling of a Shot Peened Steel using X-ray Diffraction2014In: Residual Stresses IX, 2014, Vol. 996, p. 175-180Conference paper (Refereed)
  • 9.
    Almer, J.
    et al.
    Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois.
    Lienert, U
    Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois.
    Peng, Ru
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Schlauer, Christian
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Odén, Magnus
    Engineering Materials Luleå University of Technology.
    Strain and texture analysis of coatings using high-energy x-rays2003In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 94, no 1, p. 697-702Article in journal (Refereed)
    Abstract [en]

    We investigate the internal strain and crystallographic orientation (texture) in physical-vapor deposited metal nitride coatings of TiN and CrN. A high-energy diffraction technique is presented that uses synchrotron x rays and an area detector, and which allows the strain and intensity distributions of multiple crystallographic planes to be measured by a single x-ray exposure. Unique texture states and nonlinear sin2 ψ strain distributions are observed for all coatings investigated. Quantitative analysis indicates that existing micromechanical models can reasonably predict strain and corresponding stress for mixed-hkl reflections but are inadequate for fully describing measured data. Alternative mechanisms involving deposition-induced defects are proposed.

  • 10.
    Borlado, C R
    et al.
    Inst de Ciencia de Materiales de Madrid Madrid.
    Mompean, F J
    Inst de Ciencia de Materiales de Madrid Madrid.
    Peng, Ru
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    Izquierdo, J
    IBERDROLA Madrid.
    de Luis, J
    IBERDROLA Madrid.
    Neutron strain scanning in bimetallic tubes: experimental and Monce Carlo simulation results2000In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 276-278, p. 907-908Article in journal (Refereed)
  • 11.
    Borlado, C R
    et al.
    Inst de Ciencia de Materiales de Madrid Madrid.
    Mompean, F J
    Inst de Ciencia de Materiales de Madrid Madrid.
    Peng, Ru
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    Izquierdo, J
    IBERDROLA Madrid.
    Roman, M A
    Babcock and Wilcox Galindo.
    Lopez Serrano, V
    Centro Nacional de Investigaciones Metalurgicas Madrid.
    Neutron strain scannin gon bimetallic tubes2000In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 288, p. 288-292Article in journal (Refereed)
  • 12.
    Calmunger, Mattias
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Chai, Guocai
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology. Sandvik Materials Technology, Sandviken, Sweden.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Advanced Microstructure Studies of an Austenitic Material Using EBSD in Elevated Temperature In-Situ Tensile Testing in SEM2014Conference paper (Refereed)
    Abstract [en]

    In this study an advanced method for investigation of the microstructure such as electron backscatter diffraction (EBSD) together with in-situ tensile test in a scanning electron microscope (SEM) has been used at room temperature and 300°C. EBSD analyses provide information about crystallographic orientation in the microstructure and dislocation structures caused by deformation. The in-situ tensile tests enabled the same area to be investigated at different strain levels. For the same macroscopic strain values a lower average misorientation in individual grains at elevated temperature indicates that less residual strain at grain level are developed compared to room temperature. For both temperatures, while large scatters in grain average misorientation are observed for grains of similar size, there seems to be a tendency showing that larger grains may accumulate somewhat more strains.

  • 13.
    Chai, G.
    et al.
    R and D Centre, Sandvik Materials Technology, Sandviken, Sweden.
    Lillbacka, R.
    FS Dynamics, Göteborg, Sweden.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Micro heterogeneous deformation and strain localization behavior in austenitic ferritic duplex stainless steels2011In: Advances in heterogeneous material mechanics 2011: proceedings of the Third International Conference on Heterogeneous Material Mechanics, Destech Publications , 2011, p. 186-193Conference paper (Other academic)
    Abstract [en]

    This paper provides a review on the recent work done on the micro heterogeneous deformation and strain localization behavior in austenitic ferritic duplex stainless steels studied using TEM, SEM and in-situ X-ray diffractometer and neutron diffractometer and the simulation using multi-scale material modelling. The results from both studies show that the difference in the elasto-plastic properties of the austenite and ferrite phases has caused different amounts of plastic deformations occurring in these two phases, and consequently different static and cyclic stress strain behaviours and substructures. From the simulations it is found that the coupling effect plays a key role in producing the changes in the cyclic stress-strain behaviour and also on the substructure evolution. TEM investigation also shows that the dislocation slipping behaviour and substructures strongly depend on the elasto-plastic properties of the individual phases and also on the coupling effect. The study indicates that the material damage and crack initiation in a two phase metal start mainly in the weakest phase if the deformation hardening is considered.

  • 14.
    Chai, Guocai
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology. Sandvik Materials Technology, Sandviken, Sweden.
    Kivisäkk, Ulf
    Sandvik Materials Technology, R&D Centre, Sandviken, Sweden.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Hydrogen Induced Stress Cracking Behavior in Duplex Stainless Steels2013Conference paper (Other academic)
  • 15.
    Chai, Guocai
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Lillbacka, Robert
    FS Dynamics, Göteborg.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Micro Heterogeneous Fatigue Behavior of Duplex Stainless Steel During Cyclic Loading2012Conference paper (Other academic)
  • 16.
    Chai, Guocai
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology. Sandvik Materials Technology, Sweden.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Micro Deformation Behavior in Duplex Stainless Steels2015Conference paper (Other academic)
  • 17.
    Chai, Guocai
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology. Sandvik Materials Technology, Sandviken, Sweden.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Fatigue Behaviors in Duplex Stainless Steel Studied Using In-Situ SEM-EBSD Method2014In: Procedia Materials Science, ISSN 2211-8128, Vol. 3, p. 1748-1753Article in journal (Refereed)
    Abstract [en]

    Austenite and ferrite in duplex stainless steels have different physical and mechanical properties. They can behave different during cyclic loading. To understand the fatigue behaviors of these two phases, an in-situ SEM/EBSD fatigue test has been performed. Flat specimens made from the specimens of pre-fatigue tested with three point bending were cyclically loaded in a scanning electron microscope via a compact test rig. By in situ/ex situ SEM/EBSD examination, slip activities and propagation of the fatigue cracks have been studied. Microstructures along the path of the fatigue crack were characterized. The different phase properties seem to lead to certain difference in the slip activity and formation of PSBs. Inhomogeneous slip activities and local strain concentrations were also found, which developed with increasing number of load cycles. Crack propagation behaviors in grain and cross the grain or phase boundaries have been discussed. Crack deflection occurs at the phase boundaries, but crack branching occurs mainly in the grains due to the dislocation slip. In-situ SEM/EBSD fatigue test confirms that crack propagation deflection and formation of crack branches can significantly reduce the crack propagation rate.

  • 18.
    Chai, Guocai
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology. Sandvik Materials Technology, Sandviken, Sweden.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Micro Fatigue Crack Propagation Behavior in a Duplex Stainless Steel Studied Using In Situ SEM/EBSD Method2014In: 11TH INTERNATIONAL FATIGUE CONGRESS, PTS 1 AND 2, Trans Tech Publications Inc., 2014, Vol. 891-892, p. 313-318Conference paper (Refereed)
    Abstract [en]

    Fatigue crack propagation behaviors in a duplex stainless steel have been studied using an in-situ SEM/EBSD fatigue test and a conventional da/dN test. Crack propagation behaviors in grain, effect of Schmid factor, propagation cross the grain or phase boundaries have been discussed. Crack propagation occurs mainly in the grains with a high Schmid factor, but with very small Schmid factor. Crack deflection occurs mainly at the phase boundaries, but crack branching occurs mainly in the grains due to the dislocation slip. In-situ SEM/EBSD fatigue test confirms that crack propagation deflection can lead to a decrease in crack propagation rate. Formation of crack branches can significantly reduce the crack propagation rate, which can cause crack growth retardation in the main crack path in the worst case. The crack branches formed are usually not ideal. They can propagate almost transversely to the main crack direction with a mode II stress intensity factor, SIF, and a rate that is much higher than that of the main crack.

  • 19.
    Chai, Guocai
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Kivisäkk, Ulf
    Sandvik Materials Technology, R&D Centre, Sandviken.
    Hydrogen Induced Stress Cracking in Heterogeneous Materials2012Conference paper (Other academic)
  • 20. Chai, Guocai
    et al.
    Peng, Ru Lin
    Linköping University, Department of Management and Engineering, Engineering Materials . Linköping University, The Institute of Technology.
    Slamecka, Karel
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials . Linköping University, The Institute of Technology.
    Fatigue Crack Branching Behavior in Dual Phase Material2009Conference paper (Other academic)
    Abstract [en]

    Fatigue crack branching behaviour in a dual phase steel has been investigated using an in-situ SEM/EBSD fatigue test and a conventional da/dN test. Crack branching results mainly from the extrusions and intrusions of slip bands developed in the grains. The number of crack branches formed depends strongly on the loading condition and the microstructure of the material. The in-situ observation confirms that the formation of crack branches can significantly reduce the crack propagation rate that leads to crack growth retardation in the main mode I crack path. The crack branches formed are usually not ideal. They can propagate almost transversely to the main crack direction with a mode II stress intensity factor, SIF, and a rate that is much higher than that of the main crack.

  • 21.
    Chai, Guocai
    et al.
    Sandvik Materials Technology, Sandviken.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials . Linköping University, The Institute of Technology.
    Slamecka, Karel
    Brno University of Technology, Czech Republic.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials . Linköping University, The Institute of Technology.
    In Situ SEM(EBSD analysis of fatigue crack propagation behavior of a super duplex stainless steel2008Conference paper (Refereed)
  • 22.
    Chai, Guocai
    et al.
    Sandvik Mat Technology.
    Ronneteg, Sabina
    Sandvik Mat Technology.
    Kivisakk, Ulf
    Sandvik Mat Technology.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials . Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials . Linköping University, The Institute of Technology.
    Mechanisms of Hydrogen Induced Stress Crack Initiation and Propagation in Super Duplex Stainless Steels2009In: STEEL RESEARCH INTERNATIONAL, ISSN 1611-3683, Vol. 80, no 7, p. 482-487Article in journal (Refereed)
    Abstract [en]

    Austenitic and ferritic duplex stainless steels, DSS, have recently suffered from hydrogen stress induced cracking, HISC, in subsea components with a cathodic protection. This paper provides discussions on possible HISC mechanisms. HISC initiation can occur at the ferritic grain boundaries and phase boundaries at a stress lower than the yield strength, but dominantly at phase boundaries at a stress higher than the yield strength. EBSD analysis shows that HISC in DSS results from the interaction between the dynamic plasticity by creep and hydrogen diffusion. A model on the formation of microstresses in these two phases under creep conditions is proposed, which explains why HISC occurs mainly in the ferritic phase. Discontinuous two-dimensional HISC paths were observed. The austenitic phase acts as obstacles for crack propagation. The fracture covers "valleys" and "peaks" with the cleavage ferrite and the austenite with microfacets or striations due to the hydrogen-enhanced localized-plasticity.

  • 23.
    Chai, Guocai
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Zhou, Nian
    Sandvik Materials Technology, Sandviken.
    Ciurea, Sorina
    Sandvik Materials Technology, Sandviken.
    Andersson, Marcus
    Sandvik Materials Technology, Sandviken.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Local Plasticity Exhaustion in a Very High Cycle Fatigue Regime2012In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 66, no 10, p. 769-772Article in journal (Refereed)
    Abstract [en]

    Very high cycle fatigue behaviors of four metal materials with different microstructures have been studied focusing on their damage mechanisms. It was found that the cyclic plastic deformation in the materials was highly localized in the very high cycle regime or the elastic deformation regime. This high strain localization can cause local plasticity exhaustion, which leads to a stress concentration and consequently fatigue crack initation, and finally the formation of a subsurface non-defect fatigue crack origin.

  • 24.
    Chen, Zhe
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Hörnqvist Colliander, Magnus
    Department of Physics, Chalmers University of Technology, Gothenburg, Sweden.
    Sundell, Gustav
    Department of Physics, Chalmers University of Technology, Gothenburg, Sweden.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Zhou, Jinming
    Division of Production and Materials Engineering, Lund University, Sweden.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Nano-scale characterization of white layer in broached Inconel 7182017In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 684, p. 373-384Article in journal (Refereed)
    Abstract [sv]

    The formation mechanism of white layers during broaching and their mechanical properties are not well investigated and understood to date. In the present study, multiple advanced characterization techniques with nano-scale resolution, including transmission electron microscopy (TEM), transmission Kikuchi diffraction (TKD), atom probe tomography (APT) as well as nano-indentation, have been used to systematically examine the microstructural evolution and corresponding mechanical properties of a surface white layer formed when broaching the nickel-based superalloy Inconel 718.

    TEM observations showed that the broached white layer consists of nano-sized grains, mostly in the range of 20–50 nm. The crystallographic texture detected by TKD further revealed that the refined microstructure is primarily caused by strong shear deformation. Co-located Al-rich and Nb-rich fine clusters have been identified by APT, which are most likely to be γ′ and γ′′ clusters in a form of co-precipitates, where the clusters showed elongated and aligned appearance associated with the severe shearing history. The microstructural characteristics and crystallography of the broached white layer suggest that it was essentially formed by adiabatic shear localization in which the dominant metallurgical process is rotational dynamic recrystallization based on mechanically-driven subgrain rotations. The grain refinement within the white layer led to an increase of the surface nano-hardness by 14% and a reduction in elastic modulus by nearly 10% compared to that of the bulk material. This is primarily due to the greatly increased volume fraction of grain boundaries, when the grain size was reduced down to the nanoscale.

  • 25.
    Chen, Zhe
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Surface Integrity and Fatigue Performance of Inconel 718 in Wire Electrical Discharge Machining2016In: 3RD CIRP CONFERENCE ON SURFACE INTEGRITY, 2016, Vol. 45, p. 307-310Conference paper (Refereed)
    Abstract [en]

    This paper presents a study to characterize the surface integrity in wire electrical discharge machining (EDM) of Inconel 718 and investigate its effect on the fatigue performance of the alloy in a four-point bending fatigue mode at room temperature. The EDM process generates a rough recast surface with multi-types of defects. Surface craters, micro-cracks and micro-voids within the recast layer have been found to be most detrimental from the point of view of fatigue as they could provide many preferential initiation sites for fatigue cracks. As a consequence, the specimens with an EDM cut surface show an approximately 30% decrease in fatigue life compared to those with a polished surface, and multiple crack origins were observed on the fracture surface. The high tensile residual stresses generated on the EDM cut surface, on the other hand, are also believed to be partly responsible for the loss in fatigue life of the alloy machined by EDM.

  • 26.
    Chen, Zhe
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Gustafsson, David
    Siemens Industrial Turbomachinery AB, SE-61283 Finspång, Sweden.
    On the Conjoint Influence of Broaching and Heat Treatment on Bending Fatigue Behavior of Inconel 7182016In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 671, p. 158-169Article in journal (Refereed)
    Abstract [en]

    In this study, the conjoint effect of a broaching operation, similar to that used for machining fir-tree slots on turbine discs, and subsequent heat treatments at 550 °C and 650 °C on the fatigue performance and corresponding crack initiation behavior of forged Inconel 718 has been investigated. Four-point bending fatigue tests were conducted under load control on specimens of two groups, i.e. a polished group and a broached group, with totally six different surface conditions. Compared to the as-polished specimens, a beneficial effect of the broaching operation was found on the fatigue life due to the high compressive residual stresses on the broached surface which transfer the fatigue crack initiation from surface to sub-surface regions. Introducing a heat treatment generally deteriorated the fatigue performance of the alloy because of the oxidation assisted crack initiation, while the reduction in fatigue life was found to be more remarkable for the broached specimens, in particular when heat treated at 650 °C, as the thermal impact also led to a great relaxation of the compressive residual stresses; the combined effect, together with the substantial anomalies created by broaching on the surface, such as cracked carbides and machining grooves, caused an increased propensity to surface cracking in fatigue and consequently a loss of the lifetime. Furthermore, it was found that the occurrence of surface recrystallization at elevated temperatures in machined Inconel 718 could lead to intergranular oxidation, creating micro-notches as preferable sites for the fatigue crack initiation.

  • 27.
    Chen, Zhe
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Moverare, Johan
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Peng, Ru Lin
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Damage analysis of a retired gas turbine disc2014In: Proceedings of the 2014 Energy Materials Conference, John Wiley & Sons, 2014, p. 405-410Conference paper (Refereed)
    Abstract [en]

    Gas turbine discs operate mostly at high temperature gradients and are subjected to mechanical loads simultaneously. The high thermal and mechanical loads eventually could result in degradation and damages in disc material, thereby increasing the risk of disc failure. In this study, a damage analysis was performed in a retired gas turbine disc made of Inconel 718. Oxidation attack and microstructural degradation as the consequence of the high service temperature have been found to be the main damages that take place in the non-contact area of the retired disc. In the blade/disc contact area, fretting fatigue occurs, with a result that cracks initiate from the oxide/metal interface and propagate in the disc alloy parallel to the sliding direction of fretting, consequently reducing the stability and safety of the disc. Meantime, oxygen diffuses into the fretting fatigue cracks, thereby exacerbating the oxidation attack. A multi-layered scale with periodic formation of the Fe-oxide/spinel layer and the metallic layer is formed on the contact surface. In both contact and non-contact area, recrystallization and α-Cr precipitation take place in the surface layer of the disc alloy. The locations where α-Cr precipitates are commonly considered to be the natural sites for mechanical weakness.

  • 28.
    Chen, Zhe
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Avdovic, Pajazit
    Siemens Industrial Turbomachinery, Finspång, Sweden.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Karlsson, Fredrik
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Zhou, Jinming
    Division of Production and Materials Engineering, Lund university.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Analysis of Thermal Effect on Residual Stresses of Broached Inconel 7182014Conference paper (Refereed)
    Abstract [en]

    Inconel 718 is a nickel based superalloy that is widely used as a turbine disc material in gas turbine industries. This study details the effect of thermal exposure on the residual stresses produced when broaching Inconel 718. The chosen parameters for broaching in this study are similar to those used when manufacturing turbine discs. The broaching operation produced a high level of tensile residual stresses at the broached surface. A layer with tensile residual stresses was formed in the sub-surface region, followed by a layer several times thicker with compressive residual stresses. Thermal exposure was conducted at 550 °C. The depth distributions of residual stresses after thermal exposure are presented and discussed in this paper. Complete relaxation of the surface tensile residual stresses was observed after 30 h thermal exposure, whereas the 3000 h thermal exposure influenced both the surface and sub-surface residual stress states.

  • 29.
    Chen, Zhe
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Avdovic, Pajazit
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Zhou, Jinming
    Division of Production and Materials Engineering, Lund university, Sweden.
    Moverare, Johan
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Karlsson, Fredrik
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Effect of thermal exposure on microstructure and nano-hardness of broached Inconel 7182014In: MATEC Web of Conferences Vol. 14 (2014) EUROSUPERALLOYS 2014 – 2nd European Symposium on Superalloys and their Applications: Session 8: Recrystallization and Grain Growth / [ed] J.Y. Guédou and J. Choné, Les Ulis, France: E D P Sciences , 2014, p. 08002-p.1-08002-p.6Conference paper (Refereed)
    Abstract [en]

    Inconel 718 is a high strength, heat resistant superalloy that is used extensively for components in hot sections of gas turbine engines. This paper presents an experimental study on the thermal stability of broached Inconel 718 in terms of microstructure and nano-hardness. The broaching process used in this study is similar to that used in gas turbine industries for machining fir-tree root fixings on turbine discs. Severe plastic deformation was found under the broached surface. The plastic deformation induces a work-hardened layer in the subsurface region with a thickness of ∼50 μm. Thermal exposure was conducted at two temperatures, 550 C and 650 C respectively, for 300 h. Recrystallization occurs in the surface layer during thermal exposure at 550 C and α-Cr precipitates as a consequence of the growth of recrystallized δ phases. More recrystallized grains with a larger size form in the surface layer and the α-Cr not only precipitates in the surface layer, but also in the sub-surface region when the thermal exposure temperature goes up to 650 C. The thermal exposure leads to an increase in nano-hardness both in the work-hardened layer and in the bulk material due to the coarsening of the main strengthening phase γ′′.

  • 30.
    Chen, Zhe
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Peng, Ru Lin
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Avdovic, Pajazit
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Zhou, Jinming
    Division of Production and Materials Engineering, Lund university.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Surface Integrity and Structural Stability of Broached Inconel 718 at High Temperatures2016In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 47A, no 7, p. 3664-3676Article in journal (Refereed)
    Abstract [en]

    The current study focused on the surface integrity issues associated with broaching of Inconel 718 and the structural stability of the broached specimen at high temperatures, mainly involving the microstructural changes and residual stress relaxation. The broaching operation was performed using similar cutting conditions as that used in turbo machinery industries for machining fir-tree root fixings on turbine disks. Thermal exposure was conducted at 723 K, 823 K, and 923 K (450 A degrees C, 550 A degrees C, and 650 A degrees C) for 30, 300, and 3000 hours, respectively. Surface cavities and debris dragging, sub-surface cracks, high intensity of plastic deformation, as well as the generation of tensile residual stresses were identified to be the main issues in surface integrity for the broached Inconel 718. When a subsequent heating was applied, surface recrystallization and alpha-Cr precipitation occurred beneath the broached surface depending on the applied temperature and exposure time. The plastic deformation induced by the broaching is responsible for these microstructural changes. The surface tension was completely relaxed in a short time at the temperature where surface recrystallization occurred. The tensile layer on the sub-surface, however, exhibited a much higher resistance to the stress relief annealing. Oxidation is inevitable at high temperatures. The study found that the surface recrystallization could promote the local Cr diffusion on the broached surface.

  • 31.
    Chen, Zhe
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Peng, Ru Lin
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Zhou, Jinming
    Bushlya, Volodymyr
    Saoubi, Rachid M
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Effect of Cutting Conditions on Machinability of AD 730 TM during High Speed Turning with PCBN Tools2017Conference paper (Refereed)
  • 32.
    Chen, Zhe
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Peng, Ru Lin
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Zhou, Jinming
    Division of Production and Materials Engineering, Lund University, Lund, Sweden.
    M'Saoubi, Rachid
    Seco Tools AB, Fagersta, Sweden.
    Gustafsson, David
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Effect of Machining Parameters on Cutting Force and Surface Integrity when High-Speed Turning AD730™ with PCBN Tools2019In: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015, Vol. 100, no 9-12, p. 2601-2615Article in journal (Refereed)
    Abstract [en]

    The novel wrought nickel-based superalloy, AD 730™, is a good candidate material for turbine disc applications at high temperatures beyond 650 °C. The present study focuses on the machining performance of this newly developed alloy under high-speed turning conditions with advanced PCBN tools. Meanwhile, the machined surface integrity as influenced by cutting speed and feed rate was also investigated. The surface integrity was thoroughly characterized in terms of surface roughness and morphology, machining-induced plastic deformation, white layer formation, and residual stresses. It has been found that the cutting speed and feed rate had a strong effect on the cutting forces and resultant surface integrity. The cutting forces required when machining the alloy were gradually reduced with increasing cutting speed, while at 250 m/min and above, the flank tool wear became stronger which led to increased thrust force and feed force. A higher feed rate, on the other hand, always resulted in higher cutting forces. Increasing the cutting speed and feed rate in general deteriorated the surface integrity. High cutting speeds within the range of 200–250 m/min and a low feed rate of 0.1 mm/rev are preferable in order to implement more cost-effective machining without largely reducing the surface quality achieved. The formation of tensile residual stresses on the machined AD 730™, however, could be of a concern where good fatigue resistance is critical.

  • 33.
    Chen, Zhe
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Widman, Olle
    Ytstruktur Arboga AB, Arboga, Sweden.
    Gustafsson, David
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Effect of Cooling and Shot Peening on Residual Stresses and Fatigue Performance of Milled Inconel 7182017In: Residual Stresses 2016 ICRS 10 / [ed] T.M. Holden, O. Muránsky, and L. Edwards, 2017, Vol. 2, p. 13-18Conference paper (Refereed)
    Abstract [en]

    The present study highlights the effect of cooling and post-machining surface treatment of shot peening on the residual stresses and corresponding fatigue life of milled superalloy Inconel 718. It was found that tensile residual stresses were created on the milled surface, regardless of the use of coolant, however, the wet milling operation led to a lower surface tension and a reduced thickness of the tensile layer. The shot peening performed on the dry-milled specimens completely annihilated the surface tensile residual tresses and introduced a high level of surface compression. A comparable fatigue life for the wet-milled specimens was obtained as compared with the specimens prepared by dry milling. This is very likely attributed to that the milling-induced surface damage with respect to cracked non-metallic inclusions is the predominant cause of the fatigue failure. The presence of the compressive layer induced by shot peening resulted in a significant increase of the fatigue life and strength, while the extent to which the lifetime was prolonged was decreased as the applied load was increased.

  • 34.
    Chen, Zhe
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Zhou, Jinming
    Division of Production and Materials Engineering, Lund university.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Bushlya, Volodymyr
    Division of Production and Materials Engineering, Lund university.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    ECCI and EBSD Study of Surbsurface Damages in High Speed Turning of Inconel 718 under Different Tools and Machining Parameters2013Conference paper (Refereed)
  • 35.
    Chen, Zhe
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Zhou, Jinming
    Division of Production and Materials Engineering,Lunds University, Sweden.
    Peng, Ru Lin
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    M'Saoubi, R
    Seco Tools AB, Fagersta, Sweden.
    Gustafsson, David
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Palmert, Frans
    Siemens Industrial Turbomachinery AB, Finspång.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Plastic Deformation and Residual Stress in High Speed Turning of AD730™ Nickel-based Superalloy with PCBN and WC Tools2018In: Procedia CIRP 71 (2018) pp 440-445, Elsevier, 2018, Vol. 71, p. 440-445Conference paper (Refereed)
    Abstract [en]

    A higher gas turbine efficiency can be achieved by increasing the operating temperature in hot sections. AD730™ is a recently-developed wrought/cast nickel-based superalloy which can maintain excellent mechanical properties above 700 ℃. However, machining of AD730™ could be a difficult task like other nickel-based superalloys. Therefore, studies are needed with respect to the machinability of this new alloy.

    In this paper, high-speed turning was performed on AD730™ using polycrystalline cubic boron nitride (PCBN) tools and coated tungsten carbide (WC) tools at varied cutting speeds. The surface integrity was assessed in two important aspects, i.e., surface and sub-surface plastic deformation and residual stresses. The PCBN tools generally showed better performance compared with the WC tools since it led to reduced machining time without largely compromising the surface integrity achieved. The optimal cutting speed was identified in the range of 200-250 m/min when using the PCBN tools, which gives rise to a good combination of machining efficiency and surface integrity. The further increase of the cutting speed to 300 m/min resulted in severe and deep plastic deformation. Meanwhile, a continuous white layer was formed at the machined surface. When turning with the WC tools, the increased cutting speed from 80 m/min to 100 m/min showed very little effect with respect to the plastic deformation on the machined surface. It was found that tensile residual stresses were developed on all machined surfaces no matter when the PCBN or WC tools were used, and the surface tension was generally increased with increasing cutting speed. The tensile layer might need to be modified by e.g., post-machining surface treatments such as shot peening, if taking good fatigue performance into consideration.

  • 36.
    Cong, D Y
    et al.
    School of Materials and Metallurgy, Northeastern University, Shenyang, China.
    Wang, Yandong
    Key Lab for Anisotropy & Texture of Mater., Northeastern Univ., Shenyang, China.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials . Linköping University, The Institute of Technology.
    Zetterström, P
    The Studsvik Neutron Research Laboratory, Uppsala University.
    Zhao, X
    School of Materials and Metallurgy, Northeastern University, Shenyang, China.
    Liaw, P K
    Dept of Materials Science and Eng, The University of Tennessee, Knoxville, USA.
    Zuo, L
    School of Materials and Metallurgy, Northeastern University, Shenyang, China.
    Crystal structures and textures in the hot-forged Ni-Mn-Ga shape memory alloys2006In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 37A, no 5, p. 1397-1403Article in journal (Refereed)
    Abstract [en]

    Three ferromagnetic shape-memory alloys with the chemical compositions of Ni53Mn25Ga22, Ni48Mn30Ga22, and Ni48Mn25Ga22Co5 were prepared by the induction-melting and hot-forging process. The crystal structures were investigated by the neutron powder diffraction technique, showing that Ni53Mn25Ga22 and Ni48Mn25Ga22Co5 have a tetragonal, I4/mmm martensitic structure at room temperature, while Ni48Mn30Ga22 has a cubic, L2(1) austenitic structure at room temperature. The development of textures in the hot-forged samples shows the in-plane plastic flow anisotropy from the measured pole figures by means of the neutron diffraction technique. Significant texture changes were observed for the Ni48Mn25Ga22Co5 alloy after room temperature deformation, which is due to the deformation-induced rearrangements of martensitic variants. An excellent shape-memory effect (SME) with a recovery ratio of 74 pct was reported in this Ni48Mn25Ga22Co5 polycrystalline alloy after annealing above the martensitic transformation temperature, and the "shape-memory" influence also occurs in the distributions of grain orientations.

  • 37.
    Cong, D Y
    et al.
    School of Materials and Metallurgy, Northeastern University, Shenyang, China.
    Wang, Yandong
    Key Lab for Anisotropy & Texture of Mater., Northeastern Univ., Shenyang, China.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials . Linköping University, The Institute of Technology.
    Zetterström, P
    The Studsvik Neutron Research Laboratory, Uppsala University.
    Zhao, X
    School of Materials and Metallurgy, Northeastern University, Shenyang, China.
    Liaw, P K
    Dept of Materials Science and Eng, The University of Tennessee, Knoxville, USA.
    Zuo, L
    School of Materials and Metallurgy, Northeastern University, Shenyang, China.
    Crystal Structures and Textures in the Hot-Froged Ni-Mn-Ga Shape Memory Alloys2006In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 37A, no 5, p. 1397-1403Article in journal (Refereed)
  • 38. Cong, DY
    et al.
    Wang, YD
    Zetterstrom, P
    Peng, Ru
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Engineering Materials .
    Delaplane, R
    Zhao, X
    Zuo, L
    Crystal structures and textures of hot forged Ni48Mn30Ga22 alloy investigated by neutron diffraction technique2005In: Materials Science and Technology, ISSN 0267-0836, E-ISSN 1743-2847, Vol. 21, no 12, p. 1412-1416Article in journal (Refereed)
    Abstract [en]

    A ferromagnetic shape memory alloy of Ni48Mn30Ga22 prepared by induction melting was successfully hot forged. Strong textures and a large anisotropy of in plane plastic flow were developed during the hot forging process. The crystal structures, both in austenitic and martensitic states, were investigated by means of neutron powder diffraction technique. The result suggests that Ni48Mn30Ga22 has a cubic L2(1) Heusler structure at room temperature, the same as that in the stoichiometric Ni2MnGa. When cooled to 243 K, the Ni48Mn30Ga22 alloy changes into a seven layered orthorhombic martensitic structure. No substantial change of the neutron diffraction pattern was observed upon further cooling to 19 K, indicating that there is no intermartensitic transformation in the investigated alloy, which is different from the transformation processes in the Ni-Mn-Ga alloys with higher martensitic transformation temperatures.

  • 39.
    Deng, Dunyong
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Peng, Ru Lin
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Söderberg, Hans
    Microstructural Heterogeneity Along the Building Direction of Inconel 718 Produced by Electron Beam Melting (EBM)2017Conference paper (Refereed)
  • 40.
    Deng, Dunyong
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Peng, Ru Lin
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Söderberg, Hans
    Sandvik Machining Solutions AB, Sandviken, Sweden.
    Microstructure and Anisotropic Mechanical Properties of EBM Manufactued Inconel 718 and Effects of Post Heat Treatment2017In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 693, p. 151-163Article in journal (Refereed)
    Abstract [en]

    Materials manufactured with electron beam melting (EBM) have different microstructures and properties to those manufactured using conventional manufacturing methods. A detailed study of the microstructures and mechanical properties of Inconel 718 manufactured with EBM was performed in both as-manufactured and heat-treated conditions. Different scanning strategies resulted in different microstructures: contour scanning led to heterogeneous grain morphologies and weak texture, while hatch scanning resulted in predominantly columnar grains and strong 〈001〉 building direction texture. Precipitates in the as-manufactured condition included γ′, γ″, δ  , TiN and NbC, among which considerable amounts of γ″ yielded relatively high hardness and strength. Strong texture, directionally aligned pores and columnar grains can lead to anisotropic mechanical properties when loaded in different directions. Heat treatments increased the strength and led to different δ precipitation behaviours depending on the solution temperatures, but did not remove the anisotropy. Ductility seemed to be not significantly affected by heat treatment, but instead by the NbC and defects inherited from manufacturing. The study thereby might provide the potential processing windows to tailor the microstructure and mechanical properties of EBM IN718.

  • 41.
    Deng, Dunyong
    et al.
    Linköping University, Faculty of Science & Engineering. Linköping University, Department of Management and Engineering, Engineering Materials.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Brodin, Håkan
    Siemens Ind Turbomachinery AB, Sweden.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Microstructure and mechanical properties of Inconel 718 produced by selective laser melting: Sample orientation dependence and effects of post heat treatments2018In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 713, p. 294-306Article in journal (Refereed)
    Abstract [en]

    Inconel 718 produced by selective laser melting (SLM) has been characterized with focus on the microstructure, the dependence of sample orientation on the mechanical properties and the effects of post heat treatments. The as-manufactured IN718 has a very fine cellular-dendritic structure with fine Laves phases precipitating in the interdendritic region, and electron backscatter diffraction (EBSD) analysis shows that both the vertically and horizontally built samples have relatively weak texture. The vertically built samples show lower tensile strength but higher ductility than the horizontally built samples, and the mechanism is shown to be partly due to the crystallographic feature but more importantly due to the different amount of residual stress and dislocations accumulated in these two kinds of samples. Applying heat treatments can significantly increase the strength while decrease the ductility correspondingly, and difference in yield strength between the vertically and horizontally built samples decreases with increasing the heat treatment temperatures, mainly due to the removal of residual stress and dislocations.

  • 42.
    Deng, Dunyong
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    On the dwell-fatigue crack propagation behavior of a high strength superalloy manufactured by electron beam melting2019In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 760, p. 448-457Article in journal (Refereed)
    Abstract [en]

    To demonstrate the reliability of additively manufactured superalloys for critical turbine engine components, dynamic tests simulating in-service condition are required. The present study aims to study the dwell-fatigue crack propagation behaviors of IN718 manufactured via electron beam melting (EBM). The textured and columnar-grained microstructure of EBM IN718 shows anisotropic dwell-fatigue cracking resistance when loading axis is aligned parallel and perpendicular to the columnar grains. High and low angle grain boundaries interact differently with the dwell-fatigue cracking path. The effect of different heat treatments on the cracking behavior is also discussed. The dwell-fatigue crack propagation rate of EBM IN718 is compared with forged IN718 under both dwell-fatigue test condition and pure fatigue test condition. The superiority of dwell-fatigue cracking resistance of EBM IN718 to forged IN718 is shown and discussed.

  • 43.
    Deng, Dunyong
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Soderberg, Hans
    Sandvik Machining Solut AB, Sweden.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    On the formation of microstructural gradients in a nickel-base superalloy during electron beam melting2018In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 160, p. 251-261Article in journal (Refereed)
    Abstract [en]

    Electron beam melting (EBM) is one of the most widely used additive manufacturing (AM) methods for metallic components and has demonstrated great potential to fabricate high-end components in the aerospace and energy industries. The thermal condition within a melt pool and the complicated thermal cycles during the EBM process are of interest but not yet well-understood, and will significantly affect the microstructural homogeneity of as-manufactured nickel-base superalloy components. To establish the thermal profile evolution during electron beam melting of nickel-base superalloys, Inconel 718 (IN718) is manufactured and characterized in the as-manufactured condition, on account of its representative segregation and precipitation behaviours. The microstructure gradient within a build, specifically the Laves phase volume fraction evolution, is rationalized with the solidification condition and the following in-situ annealing. Precipitations of carbide/nitride/carbonitride, delta and gamma/gamma are also discussed. Hardness is measured and correlated to the Laves phase volume fraction evolution and the precipitation of gamma/gamma . The results of this study will (i) shed light on microstructure evolution during the EBM process with regard to thermal history; and (ii) deepen the current understandings of solidification metallurgy for additive manufacturing of Ni-base superalloys. (C) 2018 Elsevier Ltd. All rights reserved.

  • 44.
    Deng, Dunyong
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Saarimäki, Jonas
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Söderberg, Hans
    AB Sandvik Coromant, Sandviken.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Brodin, Håkan
    Siemens Industrial Turbomachinery AB, Finspång.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Microstructural Characterization of AS-Manufactured and Heat Treated Electron Beam Melted Inconel 7182016In: Materials Science and Technology 2016 (MS&T16): Proceedings, Warrendale, PA: Materials Science & Technology , 2016, p. 105-112Conference paper (Refereed)
    Abstract [en]

    As manufactured and heat treated electron beam melted Inconel 718 exhibit inhomogeneous grain morphologies, mainly equiaxed close to the surface and more elongated columnar grains in the bulk. Different processing settings i.e., contouring in the surface region and hatching in the bulk region are responsible for differences in grain morphologies and textures, which are characterized using the SEM techniques electron contrast channeling imagine (ECCI) and electron backscattering diffraction (EBSD). Niobium carbides prefer to nucleate at TiN and are found to be in the grain growth direction. Regarding processing conditions, defects, such as porosities and segregations are discussed, as well as differences in microstructure emphasizing on grain morphologies and precipitates with regards to heat treatment and hardness indentation.

  • 45.
    Deng, Jiangning
    et al.
    Northeastern University.
    Yang, Yanling
    Northeastern University.
    Wang, Yandong
    Northeastern University.
    Chen, Jingeng
    Northeastern University.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials . Linköping University, The Institute of Technology.
    Yuan, Chenchen
    Northeastern University.
    Bouzy, Emmanuel
    University of Metz.
    Fundenberger , Jean-Jacques
    University of Metz.
    Texture Evolution in Heavily Cold-Rolled FeCo-2V Alloy during Annealing2009In: JOURNAL OF MATERIALS SCIENCE and TECHNOLOGY, ISSN 1005-0302 , Vol. 25, no 2, p. 219-224Article in journal (Refereed)
    Abstract [en]

    The recrystallization texture evolution in heavily cold-rolled (93%) FeCo-2V alloy with annealing temperature and time was investigated by X-ray diffraction and electron backscatter diffraction. It was found that the orientation density of a-fiber texture component fluctuates with increasing annealing temperature and time. The transmission electron microscopy images show that abundant precipitates appear inside the recrystallized grains and around the grain boundaries. The amount and size of the precipitates also vary with annealing temperature and time. The enhancement of the a-fiber coincides well with the increase of number density of fine precipitates, indicating that the fine precipitates facilitate the development of a-fiber. The annealing texture evolution observed in the FeCo alloy could be attributed to the facilitating effect of the precipitates on the development of a-fiber and the ordering process.

  • 46. Deng, JN
    et al.
    Bouzy, E
    Fundenberger, JJ
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials . Linköping University, The Institute of Technology.
    He, CS
    Zhang, Z F
    Shenyang National Laboratory for Materials Science, Inst of Metal Research, Chinese Academy of Sciences, Shenyang, China.
    Yang, Yanling
    Key Lab for Anisotropy & Texture of Mater., Northeastern Univ., Shenyang, China.
    Textures and local textures in severely cold-rolled and annealed ultra-fine-grained FeCo alloy2005In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 495-497, p. 731-736Article in journal (Refereed)
    Abstract [en]

    We find that a severely rolled FeCo alloy has anomalous enhancement of the rotated-cube {100}< 011 > texture component and a decrease of the {111} components after annealing, which is contrast to the recrystalliization behaviors reported in traditional BCC metals and alloys. The local texture measurements show that two kinds of grains with obviously different orientations, i.e. {100} and {111}, are heterogeneously distributed in the deformed specimen and the migration of high-angle grain boundaries is observed after annealing in the disordering temperature region.

  • 47.
    Ericsson, Torsten
    et al.
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Larsson, Cecilia
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Peng, Ru
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Studies of residual stress, microcracks, hardness and microstructure of cold compacted metallic green bodies2003In: Materials Research Society Symposium Proceedings, ISSN 0272-9172, E-ISSN 1946-4274, Vol. 759, p. 53-64Article in journal (Refereed)
    Abstract [en]

    The residual stresses have been measured by X-ray and neutron diffraction on PM green bodies manufactured by conventional and high speed compaction of iron powder with and without added copper and brass powder. Compressive residual stresses are present in a thin layer in both top and side surfaces. They are largest in the side surfaces due to plastic deformation of the surface material caused by the friction forces during ejection out of the die. In the interior of the green body residual stresses exist with certain region under compression (periferical regions) and other under tension (more central regions). It is unclear whether mixing iron powder with brass or copper powder leads to considerable phase stresses between the two phases.

  • 48.
    Eriksson, Robert
    et al.
    Siemens Industrial Turbomachinery AB, Berlin, Germany.
    Gupta, Mohit
    University West, Trollhättan, Sweden.
    Broitman, Esteban
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Jonnalagadda, Krisha Praveen
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Nylén, Per
    University West, Trollhättan, Sweden.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Stresses and Cracking During Chromia-Spinel- NiO Cluster Formation in TBC Systems2015In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 24, no 6, p. 1002-1014Article in journal (Refereed)
    Abstract [en]

    Thermal barrier coatings (TBC) are used in gas turbines to reduce the temperatures in the underlying substrate. There are several mechanisms that may cause the TBC to fail; one of them is cracking in the coating interface due to extensive oxidation. In the present study, the role of so called chromia-spinel-NiO (CSN) clusters in TBC failure was studied. Such clusters have previously been found to be prone to cracking. Finite element modeling was performed on a CSN cluster to find out at which stage of its formation it cracks and what the driving mechanisms of cracking are. The geometry of a cluster was obtained from micrographs and modeled as close as possible. Nanoindentation was performed on the cluster to get the correct Young’s moduli. The volumetric expansion associated with the formation of NiO was also included. It was found that the cracking of the CSN clusters is likely to occur during its last stage of formation as the last Ni-rich core oxidizes. Furthermore, it was shown that the volumetric expansion associated with the oxidation only plays a minor role and that the main reason for cracking is the high coefficient of thermal expansion of NiO.

  • 49.
    Eriksson, Robert
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology. Siemens AG, Berlin, Germany.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Li, Xin-Hai
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Influence of Cu and Zn Residues from Wire Electro-Discharge machining on TBS Durability2014In: Proceedings of the 2014 Energy Materials Conference  (CD-ROM), Wiley-TMS , 2014, p. 387-392Conference paper (Refereed)
    Abstract [en]

    Thermal barrier coatings (TBC) are deposited on superalloys in gas turbines to prolong component life. Electro-discharge machining (EDM) provides a convenient way of machining superalloys prior to coating deposition. Wire-EDM may leave residues from the wire material on the cut surface. A study was performed to investigate if brass residues from the EDM wire affected TBC oxidation behavior and spallation life. Isothermal oxidation at 1050 ℃ and thermal cycling at 1100 ℃ were performed on plasma sprayed TBCs on two different EDM cut substrates. No decrease in TBC life was detected due to the brass residues on the cut surfaces.

  • 50.
    Eriksson, Robert
    et al.
    Linköping University, Department of Management and Engineering. Linköping University, Faculty of Science & Engineering.
    Yuan, Kang
    Linköping University, Department of Management and Engineering. Linköping University, Faculty of Science & Engineering.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    INTERSPLAT OXIDATION OF ATMOSPHERIC PLASMA SPRAYED MCRALY COATINGS2014In: PROCEEDINGS OF THE ASME TURBO EXPO: TURBINE TECHNICAL CONFERENCE AND EXPOSITION, 2014, VOL 6, AMER SOC MECHANICAL ENGINEERS , 2014, no V006T22A017Conference paper (Refereed)
    Abstract [en]

    MCrAlY coatings and thermal barrier coatings (TBC) are commonly used in gas turbines to prolong the life of structural parts. The atmospheric plasma spray (APS) process yields coatings with a typical splat-on-splat structure which oxidizes at intersplat boundaries during high-temperature exposure. A study was performed to establish the influence of intersplat oxidation on Al depletion. It was found that the P -depletion based life may be overestimated by a factor of 1.8-18 if intersplat oxidation is not considered. Two different mechanisms of intersplat oxidation were observed: At high temperature (1050 degrees C), a fraction of the intersplat boundaries remained in contact with the coating surface and oxidized with the same kinetics as the surface oxides. At lower temperature (900 degrees C), intersplat oxidation occurred by considerable slower growth rates than surface oxidation. The mechanisms behind intersplat oxide growth was further studied by O diffusion calculations.

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