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

Abstract

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 soluted Ni content in TiNi matrix after reaction between TiNi and TiO₂.