Dynamic observation of the phase transformation in Cu–Al–Ni alloys using an optical reflectivity technique

The colour change of Cu-13.8 mass% Al-4.0 mass% Ni and Cu-14.2 mass% Al-3.1 mass % Ni alloys was measured after annealing at 500 and 620°C, and quenching from 900°C by means of a recording spectrophotometer equipped with an integrating sphere. A large colour change of these alloys occurred on heat treatment, depending on the different phases of γ′, β1, (γ2+β1) and (α+γ2). The phase transformation between β1 phase with the DO3 structure, and γ′ martensite with the Cu3Ti-type structure, occurred in the alloys. The phase transformation was dynamically observed by the change in the spectral reflectivity on the surface of these alloys during heating and cooling. A great hysteresis in the phase transformation was noticed in the spectral reflectivity-temperature curves and the premonitory phenomenon of the martensitic transformation was observed in the curves.