ATOMIC ORDERING AND MARTENSITIC-TRANSFORMATION IN CU-ZN-AL AND CU-AL-NI INDUSTRIAL ALLOYS

The isothermal relaxation process near room temperature in b Cu-Zn-Al and Cu-Zn-Al-Ni industrial alloys which follows a step quenching or an up quenching thermal treatment has been studied by isothermal calorim etric technique. The transition temperature Ms and its evolution have been obtained by differential scanning calorimetry and by detecting th e acoustic emission. The dissipated energy of the sample measured duri ng the relaxation process present a complex behaviour, characterized b y a continuous slowing down. On the other hand, the evolution of MS at the beginning of the phenomenon obeys a. different law. We show that all measured evolutions are much more slow in the case of Cu-Zn-Al-Ni alloy, comparing to Cu-Zn-Al alloy. The presence of nickel, which slow s diffusion processes can explain this behaviour, influenced by quench ing rate and annealing time. We interpret the relaxation processes and the evolutions of Ms in term of atomic reordering (B2 and L21). These phenomena are so slow in Cu-Zn-Al-Ni alloys near room temperature tha t the equilibrium state of order cannot be reached.