MARTENSITIC TRANSFORMATIONS IN SINGLE-CRYSTALS OF CU-AL-NI INDUCED BY TENSILE-STRESS

The martensitic transformations beta(1)(DO3) <---->gamma(1)'(2H), beta(1) <----> beta(1)'(18R(1)) and gamma(1)' <----> beta(1)' were investigated in the middle oriented single crystals of Cu-14.3Al-4.1Ni (wt.%) alloy. Thermal cycling and tensile deformation were performed to induce the transformation process. in addition to complete thermal cycling and complete stress cycling, partial cycles also were performed in order to eliminate the nucleation effects. Moreover, sophisticated combinations of temperature and stress changes were used to follow the stability of individual phases. The experimental results were summarized in a non-equilibrium sigma-T phase diagram (sigma-T map), which exhibits five regions: two one-phase regions, two two-phase regions, and one three-phase region. The equilibrium phase diagram constructed from the non-equilibrium diagram consists of three regions with the energy minimum for phases beta(1), beta(1)' and gamma(1)' respectively.