2012 年 1 巻 6 号 p. 288-292
Titanium-nickel (TiNi) alloys of near-equiatomic composition are the most popularly commercialized shape memory alloys (SMAs) with excellent characteristics, such as shape memory effect, superelasticity, a high strength, good corrosion resistance and good biocompatibility. Recently, TiNi SMAs with superelastic behavior are used in advanced medical devices, such as guide wire, catheter and stent to restore a damaged blood vessel. Improvement of mechanical and shape memory properties of TiNi SMAs cause a remarkable reduction of wire diameter, and results in a reduction of surgical invasion and an improvement of quality of life (QOL). In this study, microstructural, mechanical and shape memory properties of the extruded and heat-treated TiNi alloys by sintering the mixture of TiNi pre-alloyed powder with titanium dioxide (TiO2) particles were investigated. Ti-51.19 at.% Ni pre-alloyed powder with TiO2 particles were consolidated by spark plasma sintering (SPS) at 1173 K in vacuum. SPSed TiNi alloy powder compacts were extruded at 1373 K and shape memory heat-treated at 773 K. Ti4Ni2O phase was formed during SPS by reaction between TiNi matrix and oxygen atoms originated from additive TiO2 particles. As a result, the soluted Ni content in TiNi matrix of the TiNi alloy with 1.0 vol.% TiO2 particles was increased by 0.78 at.% compared to the original TiNi alloy with no TiO2 particle. The tensile and shape memory properties of the heat-treated TiNi alloy with 1.0 vol.% TiO2 particles were obtained as follows; an average value of plateau stress: 524 MPa, ultimate tensile strength (UTS): 1298 MPa, and shape recovery rate when 8% strain: 89.3%. 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 alloys 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.