Fatigue-Resistant Heterogeneous Gradient Nanocrystalline NiTi Shape Memory Alloy Fabricated by Pre-Strain Laser Shock Peening

Abstract

NiTi shape memory alloy (SMA) has been widely used in many fields for its superelastic and shape memory behaviors. The compressive fatigue life of NiTi is very high, but the tensile and bending fatigue life is relatively low. In this study, pre-strain laser shock peening (LSP) is introduced to solve these challenges. Different heterogeneous nanostructured (containing B2, B19′ phases, and precipitates including Ni3Ti and Ni4Ti3) gradient residual stress layers were created by controlling the pre-strain during LSP treatment. The highest bending fatigue life under the maximum tensile strain of 2.4% reached over 34,000 cycles, 33 times that of the untreated sample. The proposed pre-strain LSP method provides a new avenue to fabricate fatigue-resistant superelastic NiTi SMA.