THE STABILIZATION OF 18R AND 2H MARTENSITES IN CU-ZN-AL ALLOYS WITH AN ELECTRON-CONCENTRATION E/A = 1.534

Stabilization has been studied in Cu-Zn-Al alloys with an electron concentration e/a = 1.534. In addition to the usual 18R and 6R martensites in which stabilization has been already investigated quite extensively, these alloys exhibit at low temperature a transformation to a 2H structure. Our results show that aging of the 18R phase leads to a stabilization of the 18R phase with respect to the parent L2(1) phase which is very reduced compared to the one observed in alloys with e/a = 1.48. In addition, stabilization of the 18R phase with respect to the 2H phase results in the suppression of the 18R --> 2H transformation which occurs normally upon unloading at low temperature. In contrast, no change is observed for the 18R --> 6R transformation. First results of the stabilization of the 2H phase with respect to the parent L21 phase are presented.