Alloying effects of Ga on the Co-V-Si high-temperature shape memory alloys

Abstract

Co64V15Si21−xGax (x=4, 6, 8, 10) alloys have been prepared to investigate the alloying effects of Ga on various properties of Co-V-Si high-temperature shape memory alloys, including crystal structure, transformation behavior, thermal cycle stability, microstructure evolution, mechanical property and shape memory behavior. Results show that the D022-type martensite single-phase is transformed from the L21-type parent phase in Co64V15Si17Ga4 alloys. With the increase of Ga content, R phase appears along grain boundaries of martensite and martensitic transformation temperatures decrease rapidly. Furthermore, the Co64V15Si17Ga4 alloy exhibits excellent thermal cycle stability and stable microstructure even after heated to high temperatures of ~800°C repeatedly. On the other hand, for the (martensite+R) dual-phase alloys (i.e., Co64V15Si15Ga6, Co64V15Si13Ga8 and Co64V15Si11Ga10), (εCo) phase precipitates during thermal cycle process, with respective thermal cycle stabilities enhanced at different temperatures simultaneously. In addition, although excess Ga addition deteriorates the mechanical property significantly, it is still concluded that the doping of Ga has a positive effect on the development of shape memory effect of Co-V-Si high-temperature shape memory alloys.