Functional medium entropy alloys for joint replacement: An atomistic perspective of material deformation and a correlation to wear, corrosion, and biocompatibility

The present study adopts a multi-facet approach to design bio inspired concentrated alloys for potential application as articulating surfaces in joint replacements. A series of equiatomic, Nb rich and Ti rich TiMoNbZr based medium entropy alloys (MEAs) were processed via arc melting and their mechanical, in-vitro corrosion, wear, and in vitro and in vivo biocompatibility were investigated. Equiatomic MEA had primarily bcc with minor hcp phases where the single bcc was achieved with the addition of Nb. The single bcc Nb rich alloy resulted in 13 % elongation, much higher than equiatomic or Ti rich alloy. All the MEAs showed comparatively higher yield strength due to the climb of edge dislocations which is the main rate limiting mechanism at 300 K, as evident molecular dynamics (MD) simulation. The locally fluctuating energy landscape promotes kinks on edge dislocation, and at local minima nanoscale segments gets pinned. Upon yielding the entangled kink leaves a trail of vacancies/interstitials and escapes via climb motion to render high yield strength. The higher corrosion and pitting resistance of Nb enriched alloys can be attributed to the stable ZrO₂, Nb₂O₅, TiO₂, and MoO₃ oxides, high polarization resistance (10⁶–10⁵ Ωcm⁻²), and low defect densities (10¹⁶–10¹⁸). In vitro cell-materials interaction using MC3T3-E1 showed bioinert but cytocompatible nature of the MEAs. The wear rate of the MEAs was in the range of 7–9 × 10⁻⁵ mm³N⁻¹m⁻¹. The wear debris did not show any tissue necrosis when implanted in rabbit femur rather new bone regeneration can be seen around the particles.

Statement of significance

In the present work, a noble Nb enriched MEAs with superior mechanical, in vitro wear, corrosion and cytocompatibility properties was designed for articulating surfaces in joint replacement.

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  Single bcc in Nb enriched MEAs resulted in 13 % elongation with high hardness and yield strength.
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  Climb of entangled edge segment is the rate limiting mechanism in controlling high yield strength of MEAs at 300 K.
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  High polarization resistance (10⁶–10⁵ Ωcm⁻²), and low defect densities (10¹⁶–10¹⁸) attributes to ZrO₂, Nb₂O₅, TiO₂, and MoO₃ oxides enriched passive film.
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  Wet sliding wear rate ranged in order 7–9 × 10⁻⁵ mm³N⁻¹m⁻¹. In-situ generated wear debris when implanted in rabbit femur did not show any tissue necrosis rather new bone regeneration was observed around debris.