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Characterization of Hastelloy X Produced by Laser Powder Bed Additive Manufacturing
Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.ORCID iD: 0000-0002-8304-0221
Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering. Siemens Industrial Turbomachinery AB, Finspång, Sweden.
2016 (English)In: World PM2016 Proceedings, European Powder Metallurgy Association (EPMA) , 2016, p. 1-6Conference paper, Published paper (Refereed)
Abstract [en]

The grain structure of the selective laser melting (SLM) material is complicated and cannot easily be resolved by etching of the as-manufactured surface. One method to reveal the true morphology is by performing an electron backscatter diffraction (EBSD) analysis of the material. An analysis of the SLM material is reported. The analysis reveals that the grain structure is very complicated and the grain size is non-uniform. The microstructure contains large grains with multiple low angle grain boundaries together with small grains that approach nanometre size in the smallest size range. Grains are to a large extent, not equiaxed, but rather elongated.

Varying degrees of texture in different regions of the material have been observed. The degree of texture coincides with material volumes manufactured with different process parameter settings. Also areas with and without indications of texture have shown to exhibit different hardness. This is an indication of variation in mechanical properties in the different material volumes. Thin-walled areas, surface regions of solid material and lattices constitutes one group with similar microstructure indicating one class of material and secondly the bulk material with another microstructure would constitute the other material class

Place, publisher, year, edition, pages
European Powder Metallurgy Association (EPMA) , 2016. p. 1-6
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:liu:diva-132934ISBN: 978-1-899072-48-4 (electronic)OAI: oai:DiVA.org:liu-132934DiVA, id: diva2:1051502
Conference
World PM2016 - Powder Metallurgy World Congress & exhibition, Hamburg, Germany, October 9-13, 2016
Available from: 2016-12-02 Created: 2016-12-02 Last updated: 2021-08-21Bibliographically approved
In thesis
1. Residual stresses, fatigue and deformation in cast iron
Open this publication in new window or tab >>Residual stresses, fatigue and deformation in cast iron
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The complex geometry of cylinder heads in heavy-duty diesel engines makes grey iron or compact graphite iron a preferred material choice due to its price, castability, thermal conductivity and damping capacity. Today’s strict emission laws have increased the demands on engine performance and engine efficiency. This means that material properties such as fatigue resistance need to be improved. Shot peening is often used to improve the fatigue resistance of components and the benefits of shot peening are associated with the induced compressive surface stresses and surface hardening. How different shot peening parameters can affect fatigue strength of grey and compact graphite iron has been investigated within the project underlying this thesis. To do this, X-ray diffraction (XRD) was utilized for residual stress measurements, scanning electron microscopy (SEM) for microstructural characterizations and mechanical fatigue testing for mechanical quantifications. The ultimate aim of this work has been to increase the fatigue resistance of cast iron by residual stress optimization.

XRD measurements and SEM examinations revealed that the shot peening parameters shot size and peening intensity significantly influence residual stresses and surface deformation. Residual stress profiles, similar to the one general considered to improve the fatigue strength in steels, were obtained for both grey and compact graphite iron. Uniaxial push-pull fatigue testing on grey iron with these shot peening parameters reduced the fatigue strength with 15–20 %. The negative effect is likely related to surface damage associated with over peening and relatively high subsurface tensile residual stresses. With very gentle shot peening parameters, the uniaxial fatigue strength were unaltered from the base material but when subjected to bending fatigue an increase in fatigue strength were observed. An alternative way to increase the fatigue strength was to conduct a 30 min annealing heat treatment at 285 XC which increased the fatigue strength by almost 10 % in uniaxial loading. The improvement could be an effect of favourable precipitates forming during the annealing, which could hinder dislocation movement during fatigue.

Measuring residual stresses using XRD and the sin2 -method demands accurate X-ray elastic constants (XEC) for meticulous stress analysis. The XEC referred to as 1~2s2 should therefore always be calibrated for the specific material used. The experiments conducted revealed that the XEC value is independent of the testing method used in this work. A small correction from the theoretical value should be applied when the material contains small amounts of residual stresses. The amount of residual stresses has a great impact on the XEC and thus on the stress analysis. Concluding that proper analysis of residual stresses in cast iron is not straight forward.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2018. p. 44
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1908
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:liu:diva-150783 (URN)10.3384/diss.diva-150783 (DOI)9789176853580 (ISBN)
Public defence
2018-09-28, ACAS, Campus Valla, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2018-08-30 Created: 2018-08-30 Last updated: 2019-09-30Bibliographically approved

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