Analysis of Stress-Strain Curves in the Tensile Test of Cu–Zn–Al Alloy Single Crystals

抄録

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, β₁\ ightleftarrowsβ₁′\ ightleftarrowsα₁′, 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 β₁′ variant crystals as well as the formation of α₁′ martensite. The obtained value of CRSS in the first transformation, β₁→β₁′, i.e., τ_β, shows a linear positive temperature dependence, whereas, the CRSS, τ_α, in the second transformation, β₁′→α₁′, 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 α₁′ martensite which are associated with the character of fatigue fracture and the appearance of reversible shape memory in this alloy system.