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  • 151.
    Schlauer, Christian
    et al.
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Odén, Magnus
    Div of Enginnering Materials, Luleå University.
    Residual stress evolution and near-surface microstructure after turning of the nickel-based superalloy Inconel 7182005In: Zeitschrift für Metallkunde, ISSN 0044-3093, Vol. 96, no 4, p. 385-392Article in journal (Refereed)
    Abstract [en]

    Turning experiments have been carried out with the cutting speed and feed as variables that were systematically varied between 10 m min−1 and 1200 m min−1, and 0.1 mm and 0.5 mm, respectively, while all other cutting parameters were held constant. The arising residual stress distributions are presented and the influence of the varied machining parameters is investigated. Compressive residual stresses dominate the depth profiles but are often accompanied by a thin tensile residual stress layer at the surface. Microstructural investigations of near-surface cross-sections by means of transmission electron microscopy showed a zone where the grains had undergone plastic deformation, indicated by slip bands. On top of this layer, a surface layer exists where the grain size has radically decreased to only 50 nm to 130 nm. The grain size of the nanocrystalline layer is fairly constant for a certain cutting speed and feed, but depends on these cutting parameters. An increase in cutting speed and feed leads to larger grains in the nanocrystalline layer.

  • 152.
    Schlauer, Christian
    et al.
    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.
    Odén, Magnus
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Residual Stresses in a Nickel-based Superalloy Introduced by Turning2002In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 404-407, p. 173-178Article in journal (Refereed)
    Abstract [en]

    Near-surface residual stress distributions in the nickel-based superalloy Inconel 718 that originate from the machining operation turning are studied. The turning process that is used in the experiments is face grooving which gives quasi-orthogonal cutting conditions. Cutting speed and feed have been varied to investigate their effects on the residual stress state. Tensile residual stresses with a maximum of 1300 MPa were found at the surface that turn rapidly into compressive residual stresses of up to -800 MPa. The depth distributions of the residual stresses are presented and discussed with respect to observations made by optical and transmission electron microscopy.

  • 153.
    Shin, C-S
    et al.
    Material Research Lab University of Illinois.
    Gall, D
    Material Research Lab University of Illinois.
    Desgardins, P
    Material Reseach Lab University of Illinois.
    Vailionis, A
    Materials Research Lab University of Illinois.
    Kim, H
    Materials Reseach Lab University of Illinois.
    Petrov, I
    Materials Reseach Lab University of Illinois.
    Greene, J E
    Materials Research Lab University of Illinois.
    Odén, Magnus
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    Growth and physical properties of epitaxial metastable cubic TaN (001)1999In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 75, no 24, p. 3808-3810Article in journal (Refereed)
  • 154.
    Sjögren, Torsten
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    The influence of graphite morphology on the elastic behaviour of cast irons2005Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The morphology of the graphite phase largely controls the resulting properties of different grades of cast iron. In flake graphite cast irons, the mechanical properties are low while the thermal conductivity is high. In contrast, with spheroidal graphite cast irons, the mechanical properties are high while the thermal conductivity is low. These differences must be accounted for in the design work of diesel engines when choosing the material grade of different components. In this work the influence of graphite morphology on the deformation behaviour of cast irons has been studied with an emphasis on the elastic region.

    The studied material grades originated from castings for marine diesel engine piston rings with different chemical analyses. This gave rise to six material grades with different nodularities and three material grades with different carbon equivalents. For these different material grades the mechanical properties were determined and the deformation behaviour was examined by means of mechanical testing and acoustic emission measurements. These data were correlated to microstructural parameters.

    When studying the modulus of elasticity it was found that the modulus of elasticity of the inherent graphite phase depends on the roundness of the graphite particles and is due to the different elasticity in the two main crystallographic directions of the graphite lattice. The graphite particles are structured in different ways in flake graphite and spheroidal graphite, which gives rise to different stiffness at loading. The modelling and experiments support the observation that the average modulus of elasticity of the graphite phase depends on the morphology. This improves the understanding of the differences in the modulus of elasticity of the different studied material grades. The correlation between the modulus of elasticity of the graphite phase and the bulk nodularity of the cast iron specimen was found to be linear. This linear function was used when modelling the effective modulus of elasticity of the different cast iron grades with very high accuracy between experimental and theoretical values.

    Another factor affecting the elastic response when subjecting a cast iron component to tensile load was found to be the plastic deformation that actually occurs at very low strains for all of the studied cast iron grades. lt was found that the plastic deformation in the low strain, elastic region governs the modulus of elasticity of cast irons. The plastic deformation in the seemingly elastic region was quantified by using acoustic emission measurements. These measurements showed that the amount of plastic deformation in the elastic region was largely controlled by the graphite morphology. It was concluded that, as the roundness of the graphite particles increases, the plastic activity in the elastic region decreases and the energy absorption ability increases.

    List of papers
    1. High Performance Piston Rings for Two-Stroke Marine Diesel Engines
    Open this publication in new window or tab >>High Performance Piston Rings for Two-Stroke Marine Diesel Engines
    2004 (English)In: Proceedings // 24th CIMAC World Congress on Combustion Engine Technology, 2004Conference paper, Published paper (Other academic)
    Abstract [en]

    The piston ring is a key component in a marine combustion engine. High mechanical loads, relatively high temperatures and corrosive gases and liquids influence its performance in terms of sealing capacity, wear of cylinder liner and the ring itself. Base material of the ring, coating technology and ring geometry design are discussed in the article.

    When tailoring cast iron materials suitable as piston ring base material two parameters are of importance; the morphology of the graphite and the constituents of the matrix. To optimize the properties of the cast iron a compromise is needed to achieve a satisfactory performance of the piston rings.

    Daros Piston Rings AB is currently developing a second generation of chromium-ceramic coating the so called Z-chrome. The objective of this project has been to increase the maximum operating temperature of the coating and leave the other characteristics of the coating unaffected. The difference between the commercial Daros coating Tritor® and the Z-chrome is the ceramic component included in the coated layer.

    Insufficient conformability of piston ring and liner geometry may produce a large local cylinder wall pressure which will destroy the oil film leading to uncontrolled wear and scuffing. Lack of conformability can also produce leakage paths for the combustion gases. Therefore a correct ring shape is of utmost importance. A new design philosophy designated OPCORE® has been developed and is presented here.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-14415 (URN)
    Conference
    24th CIMAC World Congress on Combustion Engine Technology, June 7-11, Kyoto, Japan
    Available from: 2007-04-20 Created: 2007-04-20 Last updated: 2013-11-28
    2. Comparison of Mechanical Properties in Flake Graphite and Compacted Graphite Cast Irons for Piston Rings
    Open this publication in new window or tab >>Comparison of Mechanical Properties in Flake Graphite and Compacted Graphite Cast Irons for Piston Rings
    2004 (English)In: International Journal of Cast Metals Research, ISSN 1364-0461, Vol. 17, no 2, p. 65-71Article in journal (Refereed) Published
    Abstract [en]

    Cast iron is often used as the piston ring material in marine diesel engines. The mechanical properties of cast irons are to a great extent governed by the size, distribution and shape of the incorporated graphite particles. In a set of experiments, the mechanical properties of a pearlitic grey cast iron and a pearlitic compacted graphite cast iron are compared. Both cast iron grades have a eutectic composition. The experiments confirm the importance of micro-yielding of the matrix at the tip of the graphite particles on the macroelastic behaviour of the studied cast irons. This applies especially for the flake graphite cast iron where the graphite tip is sharper and the matrix bridges between the graphite particles are shorter than in the case of the compacted graphite cast iron resulting in micro-yielding at the graphite tip at a very low macro-stress and macro-strain. The high local stresses at the graphite tips also result in the opening of the graphite cavities which is much more severe in the flake graphite cast iron than in the compacted graphite cast iron. The mechanical properties of the eutectic flake graphite cast iron are largely affected by the size and amount of the graphite particles. The smaller the graphite particles (faster solidification) in the microstructure, the lower the values of the mechanical properties. In compacted graphite cast iron, the macro-elastic behaviour is influenced by the matrix and the overall coarseness of the microstructure to a greater extent and the effect of the incorporated graphite particle size is much less pronounced.

    Keywords
    Mechanical properties, Eutectic pearlitic cast iron, Graphite shape, compacted graphite, Flake graphite, Micro-yelding
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-14416 (URN)10.1179/136404604225017474 (DOI)
    Available from: 2007-04-20 Created: 2007-04-20 Last updated: 2013-11-28
    3. Modelling the Effect of Graphite Morphology on the Modulus of Elasticity in Cast Irons
    Open this publication in new window or tab >>Modelling the Effect of Graphite Morphology on the Modulus of Elasticity in Cast Irons
    2004 (English)In: International Journal of Cast Metals Research, ISSN 1364-0461, Vol. 17, no 5, p. 271-279Article in journal (Refereed) Published
    Abstract [en]

    Nine grades of pearlitic cast iron containing different graphite morphologies (from flake, compacted and spheroidal) have been studied. The parameters investigated include the graphite aspect ratio, nodularity, graphite size and modulus of elasticity. These parameters have been correlated and compared with different existing bound and model equations. It has been found that the modulus of elasticity of the graphite phase increases as the aspect ratio and nodularity of the graphite increases, i.e.flake graphite gives a lower modulus of elasticity than spheroidal graphite. The experimental values of the modulus of elasticity show good agreement to bound and model equations, although flake graphite cast irons show higher deviation from the modelled values. An equation for the correlation between the graphite modulus of elasticity and the nodularity is presented. Introducing this linear correlation into an existing model for the determination of the effective modulus of elasticity gives a continuous function, including all grades of cast irons, with a very good agreement with experimental values. The modulus of elasticity of cast irons can be accurately predicted from both bound and especially model equations, using the aspect ratio and nodularity of the contained graphite particles. The fit is improved by using a modulus of elasticity of the graphite phase that is based on the graphite morphology, considering that the modulus of elasticity of the graphite is different in the basal and prismatic planes.

    Keywords
    Cast iron, Modulus of elasticity, Graphite morphology, Graphite aspect ratio, Compacted graphite, Flake graphite, Spheroidal graphite, Modelling
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-14417 (URN)10.1179/136404604225022694 (DOI)
    Available from: 2007-04-20 Created: 2007-04-20 Last updated: 2013-11-28
    4. Studying Elastic Deformation Behaviour of Cast Irons by Acoustic Emission
    Open this publication in new window or tab >>Studying Elastic Deformation Behaviour of Cast Irons by Acoustic Emission
    2005 (English)In: International Journal of Cast Metals Research, ISSN 1364-0461, Vol. 18, no 4, p. 249-256Article in journal (Refereed) Published
    Abstract [en]

    The deformation of metallic materials includes both an elastic and a plastic deformation. In the case of cast irons, the elastic region becomes less pronounced as the graphite changes from spheroidal to flake shaped, as observed in nodular and grey cast iron, respectively. The present study aims to correlate the shape of the graphite phase with the deformation behaviour, where the plastic deformation and other strain accommodating events are quantified by measurements of the acoustic emission events occurring in the interior of the material at loading. It also aims to explain how the appearance of cast iron stress–strain curves depends on the graphite morphology where, for instance, spheroidal graphite cast irons exhibit a seemingly linear elastic behaviour in contrast to flake graphite cast irons. The present study includes a series of pearlitic cast iron material grades with differences in nodularity and carbon equivalent, respectively. It is shown that as the roundness of the graphite phase increases, the ability to absorb energy increases. The measured acoustic emission indicates that plastic deformation occurs in the seemingly linear elastic region regardless of the cast iron grade, i.e. no cast iron grade exhibits perfect linear elasticity. The plastic deformation rate in the elastic region increases as the roundness of the graphite decreases and as the carbon equivalent increases. It is shown that the plastic deformation governs the resulting modulus of elasticity in all kind of cast irons, i.e. the modulus of elasticity decreases as the yielding of the material increases. The present study improves the understanding of the deformation behaviour in the elastic region of different cast irons. The survey shows that acoustic emission testing is a useful method when studying the deformation behaviour of cast irons.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-14418 (URN)10.1179/136404605225023117 (DOI)
    Available from: 2007-04-20 Created: 2007-04-20 Last updated: 2013-11-28
  • 155.
    Sjöström, Per
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    Fatigue of clinched joints in stainless steel2004In: French-Swedish seminar,2004, 2004Conference paper (Other academic)
  • 156.
    Sjöström, Per
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Mechanical properties of stainless steel clinched joints2006Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Clinching is a joining method for sheet material where the joint is created without need of heat or additional material. The material is joined by local plastic deformation creating a geometrical locking. Since the materi al is not heated during joining, problems caused by HAZ or phase transformation during heating or cooling can be avoided.

    Clinching has mainly been used for joints where other properties than the load carrying ability are the main point, for example in the white goods industry where rectangular clinches can make necessary flanges smaller since they can be placed very close to other geometries and the use of round clinches when joining coated sheets keeping the coating intact. In recent years the focus have moved more and more towards using clinching in load carrying details.

    Clinching can be divided in two main groups, round and rectangular. The main difference is, as the names suggest, the geometry of the joints. To make a rectangular clinch the sheets have to be cut which is not needed when making a round joint.

    In this work it has been investigated if clinching is a suitable joining method for austenitic stainless steels or not. Overlap joints in three different steels; AISI 301, AISI 304 and AISI 316 in thicknesses ranging from 0,8 mm to 1,5 mm have been used. The high load required to produce a clinch (95 kN for round clinch in 1.0 mm AISI 304) might be a problem since only a few tools are designed for such high loads. It is very important to keep good position accuracy when clinching, otherwise cracks in the neck area might appear.

    During clinching the material is highly plastically deformed, the hardness in a round clinch in AISI 304 reaches values of up to 500 HV as compared to the unclinched material with a hardness of around 200 HV. If this hardening effect is removed, in this case by heat treatment, the tensile strength of the joint is lowered somewhat, but the main part of the strength remains and can thus be assigned to the geometrical locking.

    Strength of rectangular clinches is direction dependent, shear tests show that when loaded along the cuts made during production a rectangular clinch loses 20-30 % of its strength. When round and rectangular clinches are compared the strength of the round clinches reach higher values but they also show a higher variation in strength.

    In fatigue the difference in life between round and rectangular clinches is high. Staircase testing was used to find the fatigue limit, for 2 million cycles it is more than twice as high for round joints compared to rectangular ones. The explanation for the lower fatigue limit in rectangular clinches is in that the sheets are cut during forming of the clinch and thus already contain macro cracks when loading begins.

    In rectangular clinches fatigue cracks grow from the ends of the cuts already present in the material. In round clinches fatigue cracks initiate in fretting damages on the surface between the sheets. Measurements of residual stresses in the area where cracks initiate suggest that residual stresses do not play a major role in fatigue failure.

    List of papers
    1. Strength and fatigue properties of stainless steel clinched joints
    Open this publication in new window or tab >>Strength and fatigue properties of stainless steel clinched joints
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    Tensile strength and fatigue life of clinched overlap joints in austenitic stainless steels have been investigated. Tensile tests show that round clinches have higher strength than rectangular and that rectangular clinches have different strength depending on the loading angle. Tensile tests on rectangular clinches in different sheet thicknesses and different steels showed that clinches made in thicker sheets had higher strength and that the strength differed only slightly between clinches in the three different tested steels. Staircase fatigue testing was performed to find the fatigue limit for 2 million cycles. Round clinches were found to have more than twice the fatigue limit compared to rectangular ones. In fatigue the material seemed to be more important, the most stable grade exhibits the highest fatigue life and the least stable the lowest.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-102007 (URN)
    Available from: 2013-11-26 Created: 2013-11-26 Last updated: 2013-11-26
    2. Fatigue mechanisms and residual stresses of stainless steel clinched joints
    Open this publication in new window or tab >>Fatigue mechanisms and residual stresses of stainless steel clinched joints
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    The fatigue crack initiation of clinched joints has been investigated. In rectangular clinches, fatigue cracks grow from the cuts made during clinching. Those cuts, in this case perpendicular to the load, act as cracks and stress raisers and are already present before fatigue loading begins. Residual stresses measured in the area where the cracks grow are tensile and could therefore be detrimental to the fatigue life, but since the magnitude of the stress is low the influence on the fatigue life should be small. In round clinches, fatigue cracks initiate outside the clinch on the die side surface of the punch side sheet. Fractography with SEM shows that the fatigue cracks are initiated in a region with fretting damage on the surface of the punch side sheet. Residual stresses measured in the region where fatigue cracks initiate are compressive but the influence on the fatigue life is probably small since the value of the stress is low.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-102008 (URN)
    Available from: 2013-11-26 Created: 2013-11-26 Last updated: 2013-11-26
  • 157.
    Sjöström, Per
    et al.
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Fatigue mechanisms and residual stresses of stainless steel clinched jointsManuscript (preprint) (Other academic)
    Abstract [en]

    The fatigue crack initiation of clinched joints has been investigated. In rectangular clinches, fatigue cracks grow from the cuts made during clinching. Those cuts, in this case perpendicular to the load, act as cracks and stress raisers and are already present before fatigue loading begins. Residual stresses measured in the area where the cracks grow are tensile and could therefore be detrimental to the fatigue life, but since the magnitude of the stress is low the influence on the fatigue life should be small. In round clinches, fatigue cracks initiate outside the clinch on the die side surface of the punch side sheet. Fractography with SEM shows that the fatigue cracks are initiated in a region with fretting damage on the surface of the punch side sheet. Residual stresses measured in the region where fatigue cracks initiate are compressive but the influence on the fatigue life is probably small since the value of the stress is low.

  • 158.
    Sjöström, Per
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    Johansson, Sten
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    Residual Stress Relaxation During Fatigue of Clinched joints in Stainless Steels2004In: ICRS7,2004, 2004Conference paper (Refereed)
  • 159.
    Sjöström, Per
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    Johansson, Sten
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    Residual Stress Relaxation During Fatigue of Clinched Joints in Stainless Steels2005In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 490-491, p. 404-408Article in journal (Refereed)
  • 160.
    Sjöström, Per
    et al.
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Strength and fatigue properties of stainless steel clinched jointsManuscript (preprint) (Other academic)
    Abstract [en]

    Tensile strength and fatigue life of clinched overlap joints in austenitic stainless steels have been investigated. Tensile tests show that round clinches have higher strength than rectangular and that rectangular clinches have different strength depending on the loading angle. Tensile tests on rectangular clinches in different sheet thicknesses and different steels showed that clinches made in thicker sheets had higher strength and that the strength differed only slightly between clinches in the three different tested steels. Staircase fatigue testing was performed to find the fatigue limit for 2 million cycles. Round clinches were found to have more than twice the fatigue limit compared to rectangular ones. In fatigue the material seemed to be more important, the most stable grade exhibits the highest fatigue life and the least stable the lowest.

  • 161.
    Stekovic, Svjetlana
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    Comparison of low cycle fatigue properties of two uncoated and coated single crystal nickel-base superalloys2005In: 9th International Fatigue Congress,2006, 2005Conference paper (Other academic)
  • 162.
    Stekovic, Svjetlana
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    Damage Occurring During Low Cycle Fatigue of a Coated Single Crystal Nickel-Base Superalloy SCB2005In: 2005 ASME International Mechanical Engineering Congress and Exposition,2005, 2005Conference paper (Other academic)
  • 163.
    Stekovic, Svjetlana
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Influence of long term aging on microstructure, LCF properties and deformation behaviour of coated nickel-base superalloys at elevated temperaturesManuscript (preprint) (Other academic)
    Abstract [en]

    The objective of this study is to examine and establish the influence of long-term aging on microstructure, low-cycle fatigue life properties and the fracture behaviour of coated polycrystalline and single-crystal nickel-base superalloys. Long-term aging in metallic coating results in the changes of mechanical properties due to the significant interdiffusion of the main alloying elements between substrate and coatings. For this purpose, a polycrystalline nickel-base superalloy IN792 and two single crystal nickel-base superalloys CMSX-4 and SCB coated with three different coatings were used. The coatings were an overlay coating AMDRY997, a platinum-aluminide diffusion coating RT22 and an innovative coating with interdiffusion barrier of NiW called IC1. Cylindrical solid specimens were first aged at 1050oC under 2000 h to simulate long-term exposure of aircraft engine service environment and then cyclically deformed with fully reversed tension-compression loading total strain amplitude control at two elevated temperatures of 500oC and 900oC and a constant strain rate of 10-4s-1 (6%/ min) in air atmosphere without any dwell time. This tests indicate that long-term aging influences the fatigue behaviour and fracture of coated superalloys by oxidation and diffusion mechanisms when compared to non-aged and uncoated samples. Fatigue life of aged samples exhibit longer life in some cases and shorter life during other test conditions. Fatigue cracks in most cases were initiated at the surface of the coating, growing intergranularly perpendicular to the load axis. Major degradation mechanism in AMDRY997 coating deposited on CMSX-4 tested at 900oC is surface oxidation and interdiffusion with the substrate. Cracks in this aged coated system propagated transgranularly through the coating changing the path behaviour when passing the interdiffusion zone.

  • 164.
    Stekovic, Svjetlana
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Isothermal low cycle fatigue of uncoated and coated nickel-base superalloys2004Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    High strength nickel-base superalloys have been used in turbine blades for many years because of their superior performance at high temperatures. However, the superalloys have limited oxidation and corrosion resistance and to solve this problem, protective coatings are deposited on the surface of the superalloys.

    The positive effect of coatings is based on protecting the surface zone in contact with hot gas atmosphere with elements like aluminium, chromium, which form a thermodynamically stable oxide layer that acts as a diffusion barrier to slow down the react ion between the substrate material and the aggressive environment. There are also other degradation mechanisms that affect nickel-base superalloys such as aging of microstructure, fatigue and creep. Long-term aging in metallic coating results in the changes of mechanical properties due to the significant interdiffusion of the main alloying elements between substrate and coatings. However, application of the coatings has mechanical side effects, the significance of which is not yet fully investigated.

    This work covers a study on the fatigue behaviour of a polycrystalline, IN792, and two single crystal nickel-base superalloys, CMSX-4 and SCB, coated with three different coatings, an overlay coating AMDRY997, a platinum aluminide modified diffusion coating RT22 and an innovative coating with an interdiffusion barrier of NiW called ICl , under low cycle fatigue loading conditions. Both low cycle fatigue properties, cyclic strain and stress response and fracture behaviour of the uncoated, coated and long-term aged coated specimens are presented.

    The main conclusions are that at 500oC the presence of the coatings have, in most cases, reduced the fatigue lives of the nickel-base substrates while at 900oC the coatings do improve the fatigue lives of the superalloys except RT22 coated on some superalloys and under certain test conditions. The reduction of the fatigue life at 500oC can be related to early cracking of the coatings below their ductile to brittle transition temperature (DBTT), where their surface roughness can act as notches affecting fatigue crack initiation. The beneficial effect of the coating at 900oC may be due to slower crack propagation caused by oxidation at the front of the crack tip. The tests also indicate that long-term aging influences the fatigue and fracture behaviour of coated superalloys by oxidation and diffusion mechanisms when compared to non-aged and uncoated samples. The aged samples exhibit longer life in some cases and shorter life during other test conditions. Fatigue cracks were in most cases initiated at the surface of the coatings, growing intergranularly perpendicular to the load axis.

    List of papers
    1. Strain controlled fatigue and fracture behaviour of uncoated and coated polycrystalline and single crystal nickel-base superalloys at elevated temperature
    Open this publication in new window or tab >>Strain controlled fatigue and fracture behaviour of uncoated and coated polycrystalline and single crystal nickel-base superalloys at elevated temperature
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    In this paper, the low-cycle fatigue life and mechanisms governing the fracture behaviour of coated nickel-base superalloys are presented and discussed. Cylindrical solid specimens were cyclically deformed with fully reversed tension-compression loading total strain amplitude control at two elevated temperatures and a constant strain rate of 10-4 s-1 (6%/ min) in air atmosphere without any dwell time. Three nickel-base superalloys, IN792, CMSX-4 and SCB, were coated with three different coatings: an overlay coating AMDRY997, a diffusion coating RT22 and an innovative coating ICl. The cyclic stress response, low-cycle fatigue (LCF) life and final fracture behaviour at the two temperatures are observed and compared.

    At 500oC the coatings reduced fatigue life relative to the uncoated specimens while at 900oC the coated specimens showed longer life at all strain ranges than the uncoated specimens except RT22 under certain test conditions. The decrease in the fatigue life was caused by brittle coating cracking under their ductile to brittle transition temperature (DBTT). Over DBTT, lower yield strength of the coated superalloys with subsequent increase in ductility could cause the improvement of the fatigue life. These cracks could be also slowed by oxidation on front of the crack tip.

    All uncoated and coated superalloys exhibit hardening and higher stress levels at higher applied strain amplitudes and at 500°C. At 900oC softening occurred together with lower stress response level. The coatings lowered the stress level response of the superalloys from about 12% to 31 %. Higher hardening was observed for polycrystalline IN792 caused by dislocation pileups at the the grain boundaries.

    Most of the observed cracks initiated at the coating surface and majority was arrested in the transition zone except for IN792 where internal pores served as initiation sites for most cracks. Some improvement in the fatigue life have also been seen in coated IN792. No cracks found initiated from TCP phases were found. Cracks initially grew more or less perpendicular to the load axis in Stage II manner. Crack propagation path in IN792 is governed by grain or dendrite boundaries while in single crystals crack growth path is determined by concentration of deformation and damage in γ and γ' phases. Surface roughness or rumpling was found in the overlay coating AMDRY997 with some cracks initiated from the rumples maybe due to cyclic straining and not thermal cycling.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-100230 (URN)
    Available from: 2013-10-31 Created: 2013-10-31 Last updated: 2013-10-31
    2. Influence of long term aging on microstructure, LCF properties and deformation behaviour of coated nickel-base superalloys at elevated temperatures
    Open this publication in new window or tab >>Influence of long term aging on microstructure, LCF properties and deformation behaviour of coated nickel-base superalloys at elevated temperatures
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    The objective of this study is to examine and establish the influence of long-term aging on microstructure, low-cycle fatigue life properties and the fracture behaviour of coated polycrystalline and single-crystal nickel-base superalloys. Long-term aging in metallic coating results in the changes of mechanical properties due to the significant interdiffusion of the main alloying elements between substrate and coatings. For this purpose, a polycrystalline nickel-base superalloy IN792 and two single crystal nickel-base superalloys CMSX-4 and SCB coated with three different coatings were used. The coatings were an overlay coating AMDRY997, a platinum-aluminide diffusion coating RT22 and an innovative coating with interdiffusion barrier of NiW called IC1. Cylindrical solid specimens were first aged at 1050oC under 2000 h to simulate long-term exposure of aircraft engine service environment and then cyclically deformed with fully reversed tension-compression loading total strain amplitude control at two elevated temperatures of 500oC and 900oC and a constant strain rate of 10-4s-1 (6%/ min) in air atmosphere without any dwell time. This tests indicate that long-term aging influences the fatigue behaviour and fracture of coated superalloys by oxidation and diffusion mechanisms when compared to non-aged and uncoated samples. Fatigue life of aged samples exhibit longer life in some cases and shorter life during other test conditions. Fatigue cracks in most cases were initiated at the surface of the coating, growing intergranularly perpendicular to the load axis. Major degradation mechanism in AMDRY997 coating deposited on CMSX-4 tested at 900oC is surface oxidation and interdiffusion with the substrate. Cracks in this aged coated system propagated transgranularly through the coating changing the path behaviour when passing the interdiffusion zone.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-100231 (URN)
    Available from: 2013-10-31 Created: 2013-10-31 Last updated: 2013-10-31
    3. ALLBATROS advanced long life blade turbine coating systems
    Open this publication in new window or tab >>ALLBATROS advanced long life blade turbine coating systems
    Show others...
    2004 (English)In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 24, no 11-12, p. 1745-1753Article in journal (Refereed) Published
    Abstract [en]

    The scientific and technological objectives of this program are to increase the efficiency, reliability and maintainability of industrial gas turbine blades and vanes by

    • developing coatings that can warrant a 50 000 h life, i.e. twice that of the usual life, of the hot components (800–1100 °C) even with the use of renewable fuels such as biomass gas or recovery incinerator gas i.e. low-grade fuels with high pollutant levels,

    • characterising advanced existing coatings to assess lifetime and performance of coatings and coated materials,

    • providing material coating data and design criteria to use coating as a design element,

    • increasing the fundamental understanding of the behaviour of coated materials, their degradation, fracture mechanisms and engineering because of the strong need for a mechanism-based modelling of durability.

    These programmes permitted the selection of two reference coatings and the development of two innovative coatings. Concurrently work has been done in order to develop corrosion, oxidation and thermo-mechanical property models. Correlations between coatings development, experimental results and calculations will be discussed.

    Keywords
    MCrAlY, Aluminium, Oxidation, Corrosion, Thermo-mechanics, Turbine
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-22775 (URN)10.1016/j.applthermaleng.2003.11.018 (DOI)000222717900018 ()2106 (Local ID)2106 (Archive number)2106 (OAI)
    Available from: 2009-10-07 Created: 2009-10-07 Last updated: 2017-12-13
  • 165.
    Stekovic, Svjetlana
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    Low Cycle Fatigue of an Uncoated and Coated Single Crystal Nickel-Base Superalloy SCB2005In: AeroMat 2005,2005, 2005Conference paper (Other academic)
  • 166.
    Stekovic, Svjetlana
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    Low Cycle Fatigue of Single Crystal Nickel-Base Superalloy CMSX-4 Coated with a New Coating IC12005In: AeroMat 2005,2005, 2005Conference paper (Other academic)
  • 167.
    Stekovic, Svjetlana
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    Low cycle fatigue of single crystal nickel-base superalloy cmsx-4 coated wsith a new coating IC12005In: IMECE 2005 ASME Intgernational Mechanical Engineering Congress and Exposition,2005, Orlando: American Society of Mechanical Engineers , 2005, p. 235-Conference paper (Refereed)
  • 168.
    Stekovic, Svjetlana
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Strain controlled fatigue and fracture behaviour of uncoated and coated polycrystalline and single crystal nickel-base superalloys at elevated temperatureManuscript (preprint) (Other academic)
    Abstract [en]

    In this paper, the low-cycle fatigue life and mechanisms governing the fracture behaviour of coated nickel-base superalloys are presented and discussed. Cylindrical solid specimens were cyclically deformed with fully reversed tension-compression loading total strain amplitude control at two elevated temperatures and a constant strain rate of 10-4 s-1 (6%/ min) in air atmosphere without any dwell time. Three nickel-base superalloys, IN792, CMSX-4 and SCB, were coated with three different coatings: an overlay coating AMDRY997, a diffusion coating RT22 and an innovative coating ICl. The cyclic stress response, low-cycle fatigue (LCF) life and final fracture behaviour at the two temperatures are observed and compared.

    At 500oC the coatings reduced fatigue life relative to the uncoated specimens while at 900oC the coated specimens showed longer life at all strain ranges than the uncoated specimens except RT22 under certain test conditions. The decrease in the fatigue life was caused by brittle coating cracking under their ductile to brittle transition temperature (DBTT). Over DBTT, lower yield strength of the coated superalloys with subsequent increase in ductility could cause the improvement of the fatigue life. These cracks could be also slowed by oxidation on front of the crack tip.

    All uncoated and coated superalloys exhibit hardening and higher stress levels at higher applied strain amplitudes and at 500°C. At 900oC softening occurred together with lower stress response level. The coatings lowered the stress level response of the superalloys from about 12% to 31 %. Higher hardening was observed for polycrystalline IN792 caused by dislocation pileups at the the grain boundaries.

    Most of the observed cracks initiated at the coating surface and majority was arrested in the transition zone except for IN792 where internal pores served as initiation sites for most cracks. Some improvement in the fatigue life have also been seen in coated IN792. No cracks found initiated from TCP phases were found. Cracks initially grew more or less perpendicular to the load axis in Stage II manner. Crack propagation path in IN792 is governed by grain or dendrite boundaries while in single crystals crack growth path is determined by concentration of deformation and damage in γ and γ' phases. Surface roughness or rumpling was found in the overlay coating AMDRY997 with some cracks initiated from the rumples maybe due to cyclic straining and not thermal cycling.

  • 169.
    Stekovic, Svjetlana
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    Ericsson, Torsten
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    Thermo-Mechanical and Low Cycle Fatigue of Two Uncoated and Coated Single Crystal Nickel-Base Superalloys, CMSX-4 and SCB2007In: Fatigue 2007 - The 6th Engineering Integrity Society International Conference on Durability and Fatigue,2007, 2007Conference paper (Other academic)
  • 170.
    Talyzin, A V
    et al.
    Dept of Inorganic Chemistry , Ångström Lab Uppsala university.
    Dubrovinsky, L S
    Theoretical Geochemistry Program; Inst of Eart Sciences Uppsala university.
    Odén, Magnus
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    Jansson, U
    Dept of Inorganic Chemistry, Ångström Lab Uppsala University.
    Superhard and superelastic films of polymeric C602001In: Diamond and related materials, ISSN 0925-9635, E-ISSN 1879-0062, Vol. 10, no 11, p. 2044-2048Article in journal (Refereed)
    Abstract [en]

    The C60 thin film deposited on steel substrate was transformed by high pressure-high temperature treatment to a superhard and superclastic material. The films were studied by Raman spectroscopy in situ at 20 GPa after heating at 300░C and ex situ after the quenching. The hardness and elastic properties of the high-pressure phases have been characterized with nanoindentation. The hardness of the films were determined to be 0.5 ▒ 0.1 GPa and 61.9 ▒ 9 GPa for unmodified C60 and HPHT treated films, respectively. The hardness of the pressurized film is higher than for cubic BN but lower than hardness values reported for ultrahard fullerite samples prepared from powders. An interesting observation was that the HPHT treated film showed an extreme elastic response with an elastic recovery of approximately 90%. ⌐ 2001 Elsevier Science B.V. All rights reserved.

  • 171.
    Wang, Duxiang
    et al.
    Linköping University, Department of Science and Technology.
    Peng, Ru
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    McGreevy, R.
    High Anisotropy of Orientation Dependent Residual Stress in Austenite of Cold Rolled Stainless Steel1999Other (Other (popular science, discussion, etc.))
  • 172.
    Wang, Y D
    et al.
    Studsvik Neutron Researh Lab Uppsala university.
    Peng, Ru
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    McGreevy, R
    Studsvik Neutron Research Lab Uppsala university.
    Analysis of Orientation-Dependent Stress Heterogeneity1999In: ICOTOM-12,1999, 1999Conference paper (Refereed)
  • 173.
    Wang, Y D
    et al.
    Studsvik Neutron Research Lab Uppsala University.
    Peng, Ru
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    McGreevy, R
    Studsvik Neutron Research Lab Uppsala University.
    High Anisotropy of Orentation Dependent Residual Stress in Austenite of Cold Rolled Stainless Steel1999In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, ISSN 1359-6462, Vol. 41, no No 9, p. 995-1000Article in journal (Refereed)
  • 174.
    Wang, Y D
    et al.
    Studsvik Neutron Research lab Uppsala university.
    Peng, Ru
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    McGreevy, R
    Studsvik Neutron Research lab Uppsala unïversity.
    Bolle, B
    LETAM Universite de Metz.
    Vadon, A
    LETAM Universite de Metz.
    Heizmann, J J
    LETAM Universite de Metz.
    The Orientation Distribution of Interface Determined According to the Maximum-Entropy Principle1999In: ICOTO-12,1999, 1999Conference paper (Refereed)
  • 175.
    Wang, Y D
    et al.
    Studsvik Neutron Research Lab Uppsala university.
    Peng, Ru
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    McGreevy, R L
    Studsvik Neutron Research Lab Uppsala university.
    A novel method for constructing the mean field of grain-orentation-dependent residual stress2001In: Philosophical magazine letters : physics of condensed matter, Vol. 81, no 3, p. 153-163Article in journal (Refereed)
  • 176.
    Wang, Y D
    et al.
    Studsvik Neutron Research Lab Uppsala University.
    Peng, Ru
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    Wang, X-L
    Oak Ridge National Lab Oak Ridge.
    McGreevy, R L
    Studsvik Neutron Research Lab Uppsala University.
    Grain-orientation-dependent residual stress and the effect of annealing in cold-rolled stainless steel2002In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 50, no 7, p. 1717-1734Article in journal (Refereed)
    Abstract [en]

    Cold rolling leads to a residual stress that is dependent not only on the specimen directions but also on the orientation of the grain. Neutron diffraction was used to investigate residual stresses and the effect of annealing in cold-rolled stainless steel, a two-phase material consisting of 62 vol% austenite and the rest deformation-induced martensite. The specimens were prepared by cold rolling of AISI 301 stainless steel with 48% reduction. The grain-orientation-dependent residual stress, or inter-granular stress, was determined by constructing the stress orientation distribution function, a recently developed concept, from the residual strains measured along various crystallographic directions. For the cold-rolled sample, a strong grain orientation anisotropy was observed for residual stresses in both phases. Detailed analysis of the experimental stress and texture data indicates that the observed orientation anisotropy was caused by the selective phase transformation that occurred during cold rolling. Annealing at 500░C leads to recovery, which significantly reduces the orientation anisotropy of the residual stress. The experimental data show that the recovery dynamics in the austenite and martensite phases are quite different. It appears that the overall recovery behavior in this two-phase material is driven by the martensite phase. ⌐ 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.

  • 177.
    Wang, Y D
    et al.
    Studsvik Neutron Reseach Lab Uppsala University.
    Peng, Ru
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    Zeng, Xiaohu
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    McGreevy, R
    Studsvik Neutron Research Lab Uppsala University.
    Stress-Orientation Distribution Function (SODF) - Description, Symmetry and Determination1999In: ECRS5,1999, 1999Conference paper (Refereed)
  • 178.
    Wang, Y D
    et al.
    Spallation Neutron Soruces Oak Ridge National Lab, Oak Ridge.
    Wang, X-L
    Metal and Ceramic Div Oak Ridge National Lab, Oak Ridge.
    Stoica, A D
    Sapllation Neutron Source Oak Ridge National Lab, Oak Ridge.
    Richardson, J W
    Intense Pulsed Neutron Source Argonne National Lab, Argonne.
    Peng, Ru
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    Determination of the stress orientation distribution function using pulsed neutron sources2003In: Journal of applied crystallography, ISSN 0021-8898, E-ISSN 1600-5767, Vol. 36, no 1, p. 14-22Article in journal (Refereed)
    Abstract [en]

    The stress orientation distribution function (SODF) was recently introduced as a mean-field representation to describe the grain- orientation dependence of intergranular stress. Pulsed neutron sources are ideally suited for the determination of the SODF since multiple reflections can be measured simultaneously with comparable precision. A method is developed for constructing the SODF from strain pole figures measured with a pulsed neutron source and demonstrated with cold-rolled interstitial-free steel. The experimental results are compared with those measured with a reactor-based constant-wavelength diffractometer. It is shown that access to a large number of reflections on a pulsed neutron source improves the precision of the experimental SODF and facilitates in situ studies of the evolution of the intergranular stress during deformation and annealing.

1234 151 - 178 of 178
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