超音波ショットピーニングによる傾斜機能TiNi形状記憶合金の機能特性の改善

Abstract

In this study, the authors proposed a functionally-graded TiNi shape memory alloy to expand the application range of TiNi shape memory alloys. The manufacturing process of the functionally-graded TiNi shape memory alloy consists of powder metallurgy, hot rolling, and ultrasonic shot peening. The effects of the hot rolling and the ultrasonic shot peening on various properties were clarified. The main results obtained in this study are as follows: (1) Vickers hardness is increased by the hot rolling and the ultrasonic shot peening. The main causes of this phenomenon are consolidation of hot rolling and work hardening effect in the ultrasonic shot peening. (2) The ultrasonic shot peening introduces compressive residual stress of up to 300 MPa in the surface layer of the sintered material. (3) Each peak obtained by differential scanning calorimetry shifts to lower temperatures side with increasing Ni composition. This is consistent with the well-known trend in a general TiNi shape memory alloy. Furthermore, the ultrasonic shot peening hardly changes this trend. In other words, the ultrasonic shot peening has almost no effect on the transformation properties of the TiNi shape memory alloy. (4) The ultrasonic shot peening work-hardens the hot-rolled sintered TiNi shape memory alloy. The effect is higher especially in the Ni-rich region, and as a result, the functionally-graded property of the deformation resistance becomes clearly visible.