Effect of solution and aging treatments on the microstructure and mechanical properties of a Ni₅₀Ti₄₄Al₆ alloy

Scanning electron microscopy (SEM), X-ray diffraction (XRD) and compressive tests at room temperature and elevated temperatures were used to investigate the effect of solution and aging treatments on the microstructure and mechanical properties of a Ni₅₀Ti₄₄Al₆ alloy. The microstructure of the alloy includes NiTi matrix phase and a reticular structure which precipitates on grain boundaries. With the rising of solution treatment temperature, parts of the reticular structure vanish, and the second phase dissolves into the matrix and distributes more homogeneously. With the prolonging of aging time, the strength of the alloy firstly increases and then decreases. Heat treatment can obviously improve the mechanical properties of the alloy. The optimal heat treatment regime was obtained as follows:solution treatment at 1 150℃ for 6 h, water-cooling and then aging at 700℃ for 6 h.