2004 Volume 45 Issue 5 Pages 1679-1683
Compression tests were performed at different temperatures in an 82.5%Cu-13.5%Al-4.0%Ni (mass %) single crystal, a composition giving the β′ (18R) thermally induced martensitic phase. In all cases, the non-twinned γ′ (2H) martensite was obtained after compression, so, the β′ → γ′ or β → γ′ martensitic transformations were induced, depending of the test temperature. The critical stress vs. temperature, σc−T, relationship was established for both types of transformations, obtaining a negative slope dσc/dT (considering compressive stresses as negative) for the austenite-martensite transformation and a small positive slope for the martensite-martensite. The experimental dσc/dT values were compared with those calculated from the Clausius-Clapeyron type equation and reasonable good agreement between them was obtained. For these calculations, the entropy changes ΔSβ′−γ′ and ΔSβ−γ′ were directly obtained from the calorimetric runs performed after each mechanical test.
