Effects Of Microstructure, Aging and Chemical Composition On The Shape Memory Properties Of Nitihfpd Alloys

Thermo-mechanical treatments have been one of the most powerful tools to improve or control the mechanical properties of NiTi-based shape memory alloys. Precipitation formation and microstructure are effective in altering the crucial shape memory properties such as matrix strength and transformation strain, temperatures (TTs) and critical stress for stress induced martensite. Beside the thermo-mechanical treatments, alloying has been known to be an effective way to engineer SMA properties. NiTiHfPd alloys have been developed as a reaction to weak properties (e.g. TTs<100 ^oC and low strength) of NiTi alloys. These alloys can be utilized in high temperature and high strength applications in oil-gas, automotive and aerospace industries as connectors, couplings, flow control devices, actuation tubes, linear actuators and moving or morphing configurations in aerospace/aeronautics fields. In this work, microstructure and chemical composition have been investigated in order to reveal their effects on the crucial shape memory properties such as TTs, shape memory effect, superelasticity, and transformation strain. It was observed that shape memory effect and superelasticity are affected by initial microstructures and aging. On the other hand, TTs and transformation strain are strong functions of Hf content in NiTiHfPd alloys.