Enhancement of the three-point bending behavior of a coarse-grained NiTi shape memory alloy with surface heterogeneous gradient microstructure and compressive residual stress

Abstract

NiTi shape memory alloys offen subject to bending deformation as common functional materials. Laser shock peening (LSP) was utilized to fabricate a gradient layer to improve the bending mechanical behavior of a coarse-grained NiTi plate. A surface gradient layer with a thickness of approximately 100 µm was created in a 1.38 mm thick coarse-grained NiTi plate. The LSPed surface contained nanocrystals, dislocations, and amorphous, while the interior layer contained a substantial number of deformation twins, dislocations, and precipitates. The nanohardness of the surface treated with LSP can reach 10 GPa. The results of a three-point bending experiment indicate that LSP treatment increases the bending resistance of the NiTi plate. This study demonstrated that laser shock peening is an effective method for increasing the deformation resistance of a coarse-grained NiTi by means of surface gradient structures, residual stress, and precipitates.