Understanding the Micro-Mechanical Behaviour of Recast Layer Formed during WEDM of Titanium Alloy

Abstract

In the course of wire electro-discharge machining (WEDM), the unavoidable and undesirable formation of a recast layer on titanium (Ti) alloy was observed to have taken place. As a result, subsequent processing steps are required to remove this recast layer. In order to facilitate its removal, this study investigates the micro-mechanical properties of the said recast layer to better understand them. To that end, micro-pillars were fabricated on a recast layer after which in situ micro-pillar compression and nanoindentation were carried out. The in situ compression technique helps visualize deformation of materials in real time with corresponding features in stress–strain curves. The recast layer exhibits relatively brittle behaviour associated with the heat-affected zone (HAZ) and base alloy. Whereas the base alloy experienced substantial work hardening as evidenced by the formation of slip/shear bands, the recast layer was found to break down under external loading without any visible strain accommodation. This understanding of the recast layers could facilitate the design of effective removal operations, saving time and money. In addition, the recast layer might be useful in some applications.