Surface integrity aspects for NiTi shape memory alloys during wire electric discharge machining: A review
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Surface integrity aspects for NiTi shape memory alloys during wire electric discharge machining: A review Himanshu Bisaria1,a) Pragya Shandilya1 1
Mechanical Engineering Department, MNNIT Allahabad, Prayagraj 211004, India Address all correspondence to this author. e-mail: [email protected]
a)
Received: 1 October 2019; accepted: 15 January 2020
NiTi shape memory alloys (SMAs) are extensively used in various significant areas such as aerospace industries, biomedical sector, automobile industries, and robotics field because of their inherent properties, namely, shape memory effect and superelasticity. Nevertheless, the machining of these alloys is a problematic task by conventional machining practices because of various difficulties such as strain hardening, tool failure, high machining time, and poor surface quality. In recent years, researchers have explored various advanced/ unconventional machining processes to surmount these challenges and improve the performance characteristics of NiTi SMAs. Wire electrical discharge machining (WEDM) is an effective and reasonable alternative to machine these hard-to-machine alloys among the other available advanced machining processes. A brief overview, characteristics, applications, and conventional machining of NiTi SMAs have been incorporated in this study. This review article provides substantial insight into the various aspects of surface integrity (SI) for NiTi SMAs using WEDM. The current study highlights literature review on the research work accomplished so far in the domain of SI aspects for NiTi-based SMAs, namely, surface characteristics, react layer, phase analysis, elemental composition, micro-hardness, shape recovery ability, and residual stress in WEDM.
Introduction Shape memory alloys (SMAs) can be categorized under the class of a wide range of smart materials [1]. NiTi SMAs may be defined as multifunctional materials [2] which have the talent to memorize the predetermined shape under the use of heat [3]. The exceptional properties of NiTi SMAs such as biocompatibility [4], high electrical resistivity [5], high corrosion resistance [6], and fatigue resistance [7, 8, 9] make them a suitable choice in the applications of aerospace [10], biomedical [11], and other important industries [12, 13, 14]. The machining of these alloys is a vital criterion for their successful applications [15]. Many researchers have attempted the conventional machining (cutting, milling, turning, and drilling) of NiTi SMAs. During the conventional cutting of Ni50.4Ti49.6 SMAs, many severe problems such as the high machining time, high tool wear, and fatigue hardening were faced by Wu et al. [16]. During cutting and drilling of Ti50Ni50 and Ti49Ni51 SMAs, high surface roughness, the formation of burrs, lower dimensional accuracy, strain hardening, and the existence of intermetallic compounds on the surface after WEDM were
ª Materials Research Society 2020
observed by Lin et al. [17]. Similar problems were faced by Weinert and Petzoldt [18] during the conventional machining of Ni50.3
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