Contents lists available at ScienceDirect Materials Science & Engineering C journal homepage: www.elsevier.com/locate/msec Efect of wire electro discharge machining process parameters on surface integrity of Ti 49.4 Ni 50.6 shape memory alloy for orthopedic implant application A.M. Takale a, ⁎ , N.K. Chougule b a Department of Mechanical Engineering, J.S.P.M.'S Rajarshi Shahu College of Engineering, Savitribai Phule Pune University, Pune, Maharashtra, India b Department of Mechanical Engineering, College of Engineering, Savitribai Phule Pune University, Pune, Maharashtra, India ARTICLE INFO Keywords: Ti-Ni shape memory alloy Wire electro-discharge machining Topography Finite element analysis Shape recovery Dynamic compression plate ABSTRACT Ti 49.4 Ni 50.6 (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 fnish 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 efect (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 to- pography, 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 ma- terial, minimum recast layers thickness, consentaneous amount of surface hardness and less afecting 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 bio- compatible point of view. Heat treatment like annealing is found to be the most suitable process to recover shape memory efect of WEDMed samples. 1. Introduction Nickel-Titanium (Ti 49.4 Ni 50.6 ) based binary SMA is a unique class of smart materials with the ability to change its shape with applied heat, stress or magnetic feld. SMAs exhibit superior properties like shape memory efect, superelasticity (pseudoelasticity), biocompatibility, high specifc strength and reversible martensitic transformation phase and thus fnd wider applications such as sealing and coupling, sensors, micro electro mechanical systems (MEMS), fuid injectors and medical applications like surgical stents, active catheters, eyeglass frames etc. [1–4]. However hindrances to their development were caused by dif- fculties found in their manufacturing because of the severe strain hardening, high toughness, serious tool wear. The peerless pseudo- elastic behavior caused machining characteristic is quite complicated (less dimensional accuracy and time consuming). The machining of these difcult to cut alloys by conventional machining processes poses various difculties and brings about changes in the properties of ma- terial [5]. Whenever a conventional machining process gets drossy then inevitable option is of non-conventional machining processes such as abrasive water jet machining (AJWM), laser beam machining (LBM), electrochemical machining (ECM), electrical-discharge machining (EDM) and wire-electro discharge machining (WEDM). These processes could be successfully implemented to machine these smart materials. Among these processes, WEDM which is not dependent on the me- chanical assets of the workpiece, is the best suited procedure for ma- chining of “difcult to machine” materials which are problematic to process by conventional machining processes [6]. WEDM provides higher fexibility in cutting the complex shapes with high precision and https://doi.org/10.1016/j.msec.2018.12.029 Received 31 July 2018; Received in revised form 14 November 2018; Accepted 10 December 2018 ⁎ Corresponding author. E-mail address: adik1617@redifmail.com (A.M. Takale). Materials Science & Engineering C 97 (2019) 264–274 Available online 11 December 2018 0928-4931/ © 2018 Elsevier B.V. All rights reserved. T