Structural study and phase transformation of Cu-Al-Ni shape memory alloy produced by severe plastic deformation

Abstract

Martensitic transformation and mechanical behavior are investigated on extremely brittle Cu-13Al-4Ni shape memory alloy subjected to severe plastic deformation (SPD) by high speed high pressure torsion (HSHPT). The HSHPT process involves high pressure coupled with torsional deformation of the alloy, at which large rotation speed (1795 rpm) of the upper punch generates heat by friction. The experiments are carried out in a Bridgman cell right from room temperature. The disc-shaped Cu-Al-Ni samples produced by this technique have diameter between 20 and 29 mm and thickness until 0.16 mm, depending on the extent of deformation. Microstructural analyses are performed on the alloy that had undergone processing by optical, scanning electron as well as transmission electron microscopy. The microstructural investigations show that increasing the degree of deformation leads to gradual grain refinement. The microstructural changes are correlated with the Vickers hardness of the alloy. The alloy processed by HSHPT shows reversible martensitic transformation without the necessity for post-deformation annealing and phase transformation stability after 10 thermal cycles, too.