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 (TiO 2) particles were investigated. Pure Ti and pure Ni powder with TiO 2 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 Ti 4 Ni 2 O phase. Ti 4 Ni 2 O phase was formed during SPS by reaction between TiNi matrix and oxygen atoms originated from additive TiO 2 particles. Consequently, the heat-treated Ti-50.5 at%Ni alloy using pre-mixed powder with 1.0 vol% TiO 2 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% TiO 2 particles revealed the high strength and good shape memory properties. The high strengthening mechanism of the TiNi alloy using pre-mixed powder with TiO 2 particles was mainly due to a decrease martensitic transformation temperature by an increase solute Ni content in TiNi matrix after reaction between TiNi and TiO 2 .

Microstructure evolution and mechanical property of powder metallurgy Ti6Al4V alloy with high oxygen concentrations

“…Recently, several researches have indicated that PM titanium with oxygen concentration above the critical oxygen content threshold fabricated by spark plasma sintering (SPS) and hot extrusion exhibits both high strength and elongation, which breaks the strengthductility trade-off dilemma [14,15]. Compared with other traditional sintering technologies, SPS can achieve rapid sintering at a lower temperature to obtain samples with smaller grain size and reduce materials loss during sintering [16][17][18].…”