Effect of wire electro discharge machining process parameters on surface integrity of TiNi shape memory alloy for orthopedic implant application.

TiNi (atomic %) shape memory alloy (SMA) is a unique class of smart materials because of its unbeatable property. It plays a very important role in the construction of novel orthopedic implants, because of its lower Young's modulus compared to other biomedical implant materials, Conventional machining of Ti-Ni yields poor surface finish and low dimensional accuracy of the machined components. Wire electro-discharge machining (WEDM) can achieve high dimensional accuracy, but its thermal nature causes great concern regarding surface integrity for biocompatibility application of Ti-Ni material. Therefore, it is necessary to investigate the surface morphology and non-toxic, non-hazardous surface conductive to the human body. Hence, WEDM of Ti-Ni can be used. Shape memory effect (SME) of SMA was achieved by subsequent heat treatment processes which include annealing followed by ageing. For manufacturing the Ti-Ni implants, a WEDM optimized process has been used and various performance attributes such as material removal rate (MRR), surface roughness (SR), surface topography, metallurgical changes, recast layer, micro-hardness, residual stresses and shape recovery ability of the machined components have been evaluated, so as to obtain high biocompatibility of machined surface. The minimum surface roughness with consistency, suitable surface integrity parameters like less deposition of material, minimum recast layers thickness, consentaneous amount of surface hardness and less affecting subsurface residual stresses have been determined for validated experiment with an increase in wire feed. MRR increases with increase in wire feed. SR decreases with increase in wire feed due to enhanced splashing of molten material. Shape recovery ability near wire electro-discharge machined surface has been investigated from the biocompatible point of view. Heat treatment like annealing is found to be the most suitable process to recover shape memory effect of WEDMed samples.