The machining characteristics and shape recovery ability of Ti-Ni-X (X = Zr, Cr) ternary shape memory alloys using the wire electro-discharge machining

The wire electro-discharge machining (WEDM) characteristics of TiNiX ternary shape memory alloys (SMAs) have been investigated in this study. Experimental results show that the maximum feeding rate without breakage of wire electrode of Ti35.5Ni49.5Zr15 and Ti50Ni49.5Cr0.5 alloys in the WEDM process exhibits a reverse relationship with the product of the alloy's melting temperature and thermal conductivity. The surface roughness (Ra) of the machined TiNiX alloys increases with growing pulse duration. Having a larger lambda K-circle dot(T) value, Ti35.5Ni49.5Zr15 alloy has a lesser Ra value and feeding rate of wire electrode than those of Ti50Ni49.5Cr0.5 alloy after WEDM. Electro-discharge craters and recast materials are observed on the wire electro-discharge machined (WEDMed) surface of TiNiX alloys. The thickness of the recast layer varies with pulse duration. The hardening effect near the outer surface for WEDMed TiNiX alloys arises from the recast layer. The WEDMed TiNiX alloys still exhibit a good shape recovery, but a slight degradation of shape recovery occurs due to the depression of the recast layer. (C) 2009 Elsevier Ltd. All rights reserved.