Structural and mechanical spectroscopy study of the β1′ martensite decomposition in Cu-12%Al-3%Ni(wt%) alloy

In this work, the effect of annealing on the martensitic structure of a water quenched Cu-12%Al-3%Ni alloy is studied, Elastic moduli, electrical resistivity, X-ray diffraction and internal friction experiments have been performed for temperatures and/or after annealings between 300 K and 790 K. Several stages of structural evolution have been evidenced. First, for annealing below 573 K, the beta(1)' martensitic structure is not changed but a reorientation effect in the (110) plane is evidenced while the freezing of the martensitic interface motion has been observed by internal friction. Further annealings lead to the beginning of the gamma(2), precipitation immediately followed by the irreversible decomposition of the beta(1)' martensite in two stable phases gamma(2)+alpha(2). Moreover, internal friction experiments have evidenced a thermally activated peak. This peak is amplified when the martensite is decomposed so it cannot be linked to the presence of martensite but rather, referring previous works, to reversible dislocation segment motions. (C) 1998 Elsevier Science S.A.