THERMODYNAMICAL ANALYSIS OF THE STRESS-INDUCED MARTENSITIC-TRANSFORMATION IN CU-15.0 AT-PERCENT SN ALLOY SINGLE-CRYSTALS

The stress-strain behavior associated with the martensitic transformation in the Cu-15.0 at.% Sn alloy has been examined thermodynamically. Tensile tests using single crystals showed that the successive martensite-to-martensite transformation can be induced under the applied tensile stress and is observed as a multi-stage stress-strain curve. The entropy change and the latent heat of stress-induced martensitic transformation were estimated from the calculation taking the dissipative energy of transformation into account. It will be shown that the dissipative energy contributes the decrease in the heat of the forward martensitic transformation and the increase in that of the reverse transformation. The calculated value is in good agreement with that measured by the differential scanning calorimeter. The dependence of the critical stress to induce martensite on the orientation of tensile axis has been examined, and it can be successfully explained by the orientation dependence of the mechanical driving force by the applied stress.