Abstract
In this work, the effect of surface mechanical attrition treatment (SMAT) on the cyclic behaviour of a 316L stainless steel under low cycle fatigue (LCF) is investigated. The LCF results are presented in the form of cyclic stress amplitude evolution for both untreated and SMATed samples. In order to better understand the microstructure change due to cyclic loading, electron backscatter diffraction (EBSD) is used to characterize the microstructure of the SMATed samples before and after fatigue tests. A microstructure gradient is highlighted for samples after SMAT from the top surface layer in nanocrystalline grains to the interior region non-affected by impacts. Under LCF loading, new slip systems are activated in the work hardened region, whereas no plastic slip is activated in the nanostructured layer. The residual stresses generated by SMAT are measured using X-ray diffraction (XRD), and their relaxations under cyclic loading are studied by taking into account the microstructure change. The cyclic behaviour of the samples in different material states is interpreted based on these investigations.
Highlights
Fatigue properties of metallic materials are important for design and life prediction of mechanical components subjected to cyclic loading in service
The results show that no obvious difference in grain size distribution can be noticed in the interior region for the samples before and after fatigue tests
The effect of Surface mechanical attrition treatment (SMAT) on low cycle fatigue behaviour of a 316L austenitic stainless steel was investigated, and the following conclusions can be drawn: (1) After SMAT, a microstructure gradient is generated in the SMAT affected region, from the nanostructured layer to the non-affected bulk of the sample, through the transition region where many plastic slips are present
Summary
Fatigue properties of metallic materials are important for design and life prediction of mechanical components subjected to cyclic loading in service. The presence of compressive residual stress is beneficial for fatigue life improvement through increasing the resistance to both crack initiation and propagation. SMAT is based on mechanical impacts on the surface of a structure by metallic balls with high kinetic energy This technique is able to generate a large quantity of crystallographic defects such as dislocations, deformation twins, which can lead to the formation of refined grains down to the nanometer scale at the surface. The obtained nanostructured layer coupled with compressive residual stresses generated by SMAT can effectively improve the fatigue strength of materials [7]. The near surface compressive residual stresses can improve fatigue life by increasing the resistance to crack initiation and propagation. In the case of SMAT, the presence of a superficial nanostructured layer can effectively increase the yield strength and enhance the materials’ fatigue crack initiation resistance [8]. Microstructure change and residual stress relaxation due to cyclic loading
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