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% A l-3.1 mass% Ni alloys was measured after annealing at 500 and 620 degr ees C, and quenching from 900 degrees C by means of a recording spectr ophotometer equipped with an integrating sphere. A large colour change of these alloys occurred on heat treatment, depending on the differen t phases of gamma', beta(1), (gamma(2)+beta(1)) and (alpha+gamma(2)). The phase transformation between beta(1) phase with the DO3 structure, and gamma' martensite with the Cu3Ti-type structure, occurred in the alloys. The phase transformation was dynamically observed by the chang e in the spectral reflectivity on the surface of these alloys during h eating and cooling. A great hysteresis in the phase transformation was noticed in the spectral reflectivity-temperature curves and the premo nitory phenomenon of the martensitic transformation was observed in th e curves.