Cobalt free refractory high entropy alloys for total joint arthroplasty: In-vitro wear, corrosion and cytocompatibility evaluation

CoCrMo alloys are extensively used for bearing surfaces in total joint arthroplasty (TJA); however, Co poisoning remains a concern. Therefore, we propose a Co free refractory metal based high entropy alloys (RHEAs) for use in TJA. In this work, TiMoNbTaW based RHEA was prepared by arc melting. The alloy was further modified by Cr addition for improvement in wear, corrosion and cytocompatibility. X-ray diffraction revealed single bcc crystal structure where lattice constant decreased upon Cr addition. The improved hardness, yield strength and a ten-fold enhancement in wear resistance with Cr addition is ascribed to its severely distorted bcc lattice. In-vitro corrosion in Hank's salt solution (HBSS) suggests superior thermodynamic stability and passivation of both RHEAs. Enhanced pitting resistance was seen upon Cr addition. Further, electrochemical impedance spectroscopy (EIS) analysis of the surface film showed an increase in film resistance by an order of magnitude attributed to the presence of Cr2O3 on the TiMoNbTaWCr surface as confirmed by X-Ray photoelectron spectroscopy (XPS) analysis after anodic passivation. Meanwhile, the live/dead imaging and MTT assay indicated good cell viability and proliferation of RHEAs. However, an enhanced cell adhesion and growth on TiMoNbTaWCr RHEA proves its potential applicability as a bearing surface in TJA.