THE MARTENSITIC TRANSITION-TEMPERATURE IN TERNARY CU-ZN-AL ALLOYS INFLUENCE OF THE L21 STRUCTURE

We study the contribution of the L21 long range ordered structure on the Ms temperature of Cu-Zn-Al alloys. Measuring the resolved shear stress required to induced the transformation in alloys with sufficiently low TL21 ordering temperature shows that it is possible to supperss the B2-L21 ordering transition by a rapid quench from temperatures Tq above but close to TL21. An analysis of the experimental results in terms of a simple model shows that the contribution of the L21 structure on the Ms temperature behaves linearly with (2xCu - 1)2 for the alloys considered. Finally we propose an emperical expression giving the Ms temperature of CuZnAl alloys as a function of composition. The expression is an extension of one proposed recently for CuZn binary alloys. We show that for ternary alloys with only B2 ordering. 1 at.% A1 has the effect of (96/64) at.% of Zn, while this effect reduces to (90.64) at.% when the alloy develops the L21 superlattice. © 1990.