Application of shape memory alloy TiNi in low thermal expansion copper composites

The thermal expansion behavior of compressive stress aged Ti–50.7% Ni (atom fraction) alloy was investigated. The feasibility for preparing a Cu/TiNi composite with low coefficient of thermal expansion (CTE) through TiNi alloy was explored. Detached TiNi alloy strips were placed between two Cu plates, the assembly body was rolled at 800 °C, then the Cu/TiNi composite was solution-treated followed by compressive stress aging. Due to the obvious mechanic joggle of the mating surfaces during hot rolling process and diffusion in the interface of Cu and TiNi alloy during solution treatment, the solution-treated and compressive stress aged Cu/TiNi composite exhibits a good interface bonding. It is found that compressive stress causes the parallel alignment of precipitate Ti3Ni4 during aging process, resulting in all-round shape memory effect and negative thermal expansion behavior of TiNi alloy in the temperature range approximately between −50 and 75 °C. Therefore, the average CTE of the Cu/TiNi composite is greatly lowered by the negative CTE of its TiNi strips. Due to the connectivity of Cu and its excellent thermal conductivity, the Cu/TiNi composite possesses high thermal conductivity.