Improving the fatigue strength of superelastic NiTi by using constrained groove pressing severe plastic deformation deform 3D modeling and microstructural analysis

Abstract

NiTi has wide ranges of applications in the aerospace, biomedical, automotive, and other sectors due to its superelasticity and shape memory effect smart properties. Numerical modeling is an efficient and cost-effective approach to investigate the effects of applied loads and plastic deformation processes on the mechanical properties of NiTi. The aim of this work is to apply Deform 3D modeling of constrained groove pressingsevere plastic deformation to improve the fatigue strength of superelasticNiTi by considering cantilever beam structure subjected tobending load. After applying the constrained groove pressing severeplastic deformation, the effects of deformation parameterson the fatigue strength were evaluated by comparing with theproperties of the undeformedbeam. First, to increase the resilience of NiTito fatigueloadings, the stress relief groove geometry wasdesigned by using Deform 3D software. Theeffects of deformation temperature, groove depth, and groove radius were investigated and the optimum values were selected for further analysis. The grain size of the deformed NiTispecimen was significantly reduced and the fatigue resistance was increased corresponding to the groove depth and groove radius increment. Due to constrained groove pressing severe plastic deformation, the grain refinement (15.8 nm-2.5277 μm)of NiTiwas observed at the maximum groove depth (5–6 mm). By using the Hall-Petch relations, the yield strength of NiTi was determined. As a result, the yield strength is improved by 239 % in comparison with the initial value. Furthermore, in comparison with the undeformedNiTi specimen, the fatigue strength is improved by 54.6%.