Synergistic effects of Cr addition on surface characteristics and its implications on wear and in vitro biocompatibility of TiMoNbTaW alloys

Abstract

Refractory metal based high entropy alloys (RHEAs) presents promising anti-wear and cytocompatibility to meet the articulating demands in artificial hip/knee prosthesis. In this study, TiMoNbTaW RHEAs were fabricated through arc melting, and modified with Cr to enhance their bulk, and surface characteristics. The Cr addition resulted in a gradual increase in bulk hardness from ⁓4.9 GPa to ⁓7.1 GPa, and yield strength from ⁓1.3 GPa to ⁓1.9 GPa, attributed to lattice distortion induced misfit strain. X-ray photoelectron spectroscopy (XPS) confirmed the formation of a native passive film on alloys surface, consisting of oxides TiO2, MoO2, MoO3, WO3, Nb2O5, Cr2O3 and Ta2O5. The wear resistance improved in accordance with Archard's law, while friction responses were influenced by Cr2O3 content. Higher Cr2O3 content imparted lubricating effect, reducing friction coefficient ⁓0.18–0.23, and wear rate in the order 10−5 mm3/Nm. Moreover, higher Cr2O3 in the native film contributed to the excellent cytocompatibility against MC3T3-E1 cells. Cell proliferation increased with increase in Cr content in the RHEA and showed higher alkaline phosphatase activity (ALP) activity when Cr content was 10% or more. This study evaluates the effect of Cr increment on the microstructural and mechanical properties in TiMoNbTaW RHEAs, and highlights the synergistic effects of the passivation-mediated native film, influencing tribological, and in-vitro cellular response.