A large number of stress-strain (S-S) curves obtained for Cu–Zn–Al alloy single crystals with the electron atom ratio of 1.40 are quantitatively analysed, and values of the critical resolved shear stress (CRSS) for the two successive transformations, β
1\
ightleftarrowsβ
1′\
ightleftarrowsα
1′, are evaluated. As reported previously, two types of S-S curves, two-stage type and stress-drop type, are recorded depending upon the tensile direction and testing temperature. These curves are analysed by a systematic procedure of calculating the shape deformation of the transformation, referring to the morphological change due to the interaction of β
1′ variant crystals as well as the formation of α
1′ martensite. The obtained value of CRSS in the first transformation, β
1→β
1′, i.e., τ
β, shows a linear positive temperature dependence, whereas, the CRSS, τ
α, in the second transformation, β
1′→α
1′, indicates a slightly negative temperature dependence. It is reported that the obtained values of τ
β or τ
α are on a linear line with respect to the temperature independent of the type of S-S curves. The difference in the temperature dependence between τ
β and τ
α is attributed to the difference in the mechanism of the successive transformations. Very small values of τ
α, 25–40 MPa, and negative values of τ
α′, (−10)–(−20)MPa, are obtained for the forward and reverse transformations, respectively. Brief discussion has been made on the inducibility and stability of α
1′ martensite which are associated with the character of fatigue fracture and the appearance of reversible shape memory in this alloy system.
View full abstract