Microstructures and Mechanical Properties of Shape Memory Alloy Using Pre-Mixed TiNi Powders with TiO2 Particles

In this study, microstructural and mechanical properties of the extruded and heat-treated TiNi alloys by sintering the mixture of TiNi pre-mixed powder with titanium dioxide (TiO2) particles were investigated. Pure Ti and pure Ni powder with TiO2 particles were mixed and consolidated by spark plasma sintering (SPS). SPSed TiNi alloy compacts were extruded and heat-treated subsequently. SPSed TiNi alloy compacts had TiNi matrix and Ti4Ni2O phase. Ti4Ni2O phase was formed during SPS by reaction between TiNi matrix and oxygen atoms originated from additive TiO2 particles. Consequently, the heat-treated Ti-50.5 at% Ni alloy using pre-mixed powder with 1.0 vol% TiO2 particles showed a high plateau stress of 630 MPa and a good shape recovery of 79.7% in 8% strain applied. The heat-treated TiNi alloy with 1.0 vol% TiO2 particles revealed the high strength and good shape memory properties. The high strengthening mechanism of the TiNi alloy using pre-mixed powder with TiO2 particles was mainly due to a decrease martensitic transformation temperature by an increase solute Ni content in TiNi matrix after reaction between TiNi and TiO2.