Multi-objective particle swarm optimization of EDM parameters to deposit HA-coating on biodegradable Mg-alloy

The present research work is aimed to discuss a novel method of depositing hydroxyapatite coats, with interconnected pores, on the surface of bio-degradable MgZnMn alloy by using hydxroxyapatite (HA) powder mixed electric discharge machining (HAM-EDM) process. The parameters of HAM-EDM process has been optimized using multi-objective particle swarm optimization (MO-PSO) technique to determine the optimal levels of concentration of hydroxyapatite powder (CHA), peak-current (Ip), pulse-on (Ton), and pulse-off (Toff). The surface roughness (SR), thickness of recast layer (RLT), and micro-hardness (MH) were chosen as output response characteristics. The experiments were performed according to L27 orthogonal array and an empirical model has been developed to interpret the co-relation amongst input and output parameters. A number of optimal solutions (∼100) were obtained by MO-PSO technique, where all responses were optimized. Among them, best optimal condition is to deposit biomimetic HA-containing layer with low SR (0.70 μm), low RLT (11.85 μm) and high MH (246 HV) was CHA = 5.28 g/l, Ip = 3.48 A, Ton = 40.33 μs, and Toff = 109.29 μs? Further, the specimens produced were characterized, morphologically and topologically, and revealed the existence of hydroxyapatite (HA) layer with interconnected pores of 5-10 μm size. The EDS spectrum showed that presence of Ca, P, and O on the modified surface, which conferred the deposition of HA-layer on the surface. The XRD pattern investigations of modified surface confirmed the formation of various biocompatible phases, which enhanced the mechanical properties, corrosion and osseintegration characteristics.