MICROSTRUCTURES AND MECHANICAL PROPERTIES OF SINTERED AND EXTRUDED TiNi SHAPE-MEMORY ALLOYS USING PREALLOYED POWDER WITH ADDITIONS OF TiO_2 POWDER

摘要

Microstructures and mechanical properties, in particular the plateau-tensile stress and shape-recovery performance, of sintered and extruded TiNi shape-memory alloys (SMAs) were investigated. Powder blends of TiNi and TiO_2 were consolidated by spark plasma sintering (SPS) and then extruded and heat treated. Ti-rich Ti4Ni_2O formed in the SPS-consolidated compacts via reactions between the TiNi matrix and oxygen from the TiO_2 additives. This resulted in an increase in the solute content of nickel in the matrix and a decrease in the martensitic transformation temperature (M_S). Consequently, the heat-treated TiNi alloy with an addition of 1.0 v/o TiO_2 particles showed a high plateau stress of 524 MPa at ambient temperature and excellent shape-recovery performance (89.3%) for 8% strain in tension.