Abstract
The Ti–Ni–Fe elemental mixture powder was consolidated by spark plasma sintering and hot extrusion process. The homogenization and aging heat treatment was applied to the Ti–Ni–Fe sintered alloys for uniform precipitation of ultra-fine Ti3Ni4 needle-like intermetallics with 50 − 100 nm length in TiNi matrix. ALCHEMI analysis clarified the additive Fe elements were completely solid-soluted into Ni atom sites of the TiNi alloy after aging heat treatment. The plateau stress gradually increased with increase in Fe content because the Martensite transformation temperature drastically decreased. The measured plateau stress corresponded well with the calculation result by using Clausius-Clapeyron equation. The shape recovery rate under 8 % strain was 89～95 % when Fe content was over 0.3at.%. This is also due to solid-soluted Fe atoms causing the decrease of Austenite transformation temperature. PM Ti–50.5at.%Ni alloy with 1.0at.%Fe after aging heat treatment showed an excellent balance of mechanical properties; 906 MPa plateau stress, 1260 MPa UTS and 95.4 % shape recovery rate.
