Boosting biocompatibility and mechanical property evolution in a high-entropy alloy via nanostructure engineering and phase transformations

TL;DR

This study enhances a biocompatible high-entropy alloy's strength, reduces its elastic modulus, and improves biocompatibility through nanostructure engineering and phase transformations induced by high-pressure torsion.

Contribution

It demonstrates a novel approach combining nanograin generation and phase transformation to tailor mechanical and biocompatible properties of HEAs for biomedical applications.

Findings

Tensile strength up to 2130 MPa achieved

Elastic modulus reduced to 69 GPa

Enhanced biocompatibility and surface oxide nanotube formation

Abstract

High-entropy alloys (HEAs), as multi-component materials with high configurational entropy, have garnered significant attention as new biomaterials; still, their low yield stress and high elastic modulus need to be overcome for future biomedical applications. In this study, nanograin generation is used to enhance the strength and phase transformation is employed to reduce the elastic modulus of a biocompatible Ti-Zr-Hf-Nb-Ta-based HEA. The alloy is treated via the high-pressure torsion (HPT) process, leading to (i) a BCC (body-centered cubic) to omega phase transformation with [101]{\omega}//[011]BCC and [211]omega//[121]BCC through a twining mechanism, (ii) nanograin formation with a mean grain size of 20 nm, and (iii) dislocation generation particularly close to BCC-omega interphase boundaries. These structural and microstructural features enhance hardness, increase tensile strength up to 2130 MPa, achieve tensile elongation exceeding 13%, reduce elastic modulus down to 69 GPa and improve biocompatibility. Additionally, the HEA exhibits improved anodization, resulting in a homogenous distribution of oxide nanotubes on the surface with a smaller tube diameter and a higher tube length compared to pure titanium. These remarkable properties, which are engineered by the generation of defective nanograins and the co-existence of BCC and metastable omega phases, highlight the potential of HEAs treated using severe plastic deformation for future biomedical usage, particularly in the orthopedic sector.