激光冲击强化对NiTi形状记忆合金力学性质的影响

Mechanical Properties of NiTi Shape Memory Alloy Processed by Laser Shock Peening

采用激光冲击强化技术对初始相为奥氏体的NiTi形状记忆合金进行强化处理,研究了NiTi形状记忆合金力学性质的变化。实验发现激光冲击强化后NiTi合金的影响层深度在300μm左右,表面硬度提高了约10%。通过数字图像相关技术从拉伸过程拍摄的照片中得到材料的应变,从而获得NiTi合金的应力-应变关系的变化。激光冲击强化后NiTi样品的超弹性应力应变曲线表明相变应力几乎没有变化,马氏体的屈服应力下降了约100MPa,最大相变应变减少了13%。激光冲击强化产生的超高应变率的塑性变形导致材料硬度提高,超弹性应变减少。

An austenite NiTi shape memory alloy is processed by laser shock peening （LSP）, and the mechanical properties is investigated. It is found that the thickness of shock affected layer is about 300 μm. The surface hardness of the specimen is increased by approximately 10% after LSP. The strain of the specimen is extracted from the images recorded in the tension by the digital image correlation technique in order to obtain the stress-strain curves. The superelastic stress-strain curves of the fully LSP processed NiTi material show no change in phase transition stress, the martensite yield stress decreases to about 100 MPa, and a loss of maximum transition strain about 13 % after LSP. The ultrahigh-strain-rate plastic deformation by LSP results in dense dislocation underneath the surface which is responsible for the hardness increase and superelastic strain loss.