TiCoCr-Based Multi-Principal Element Alloys for Biomedical Applications

Next-generation biomedical implants require materials with excellent wear resistance, corrosion resistance, and biocompatibility. This study developed two novel multi-principal element alloys (MPEAs) based on the TiCoCr composition (equiatomic and non-equiatomic) with ultra-high hardness, excellent wear resistance, corrosion stability, and biocompatibility. The as-cast microstructures revealed a multiphase combination of Ti-rich hexagonal closed packing (HCP), C₁₄ Laves, and face-centered cubic (FCC) phases. Upon heat treatment, equiatomic (Ti₃₃Co₃₃Cr₃₃) MPEA developed two major body-centered (BCC) phases and a minor HCP phase, whereas heat treatment of non-equiatomic (Ti₅₀Co₂₅Cr₂₅) MPEA revealed one BCC and C₁₄ Laves phase. The hardness of both MPEAs was slightly reduced after heat treatment. Wear and corrosion tests conducted in Hanks' balanced salt solution (HBSS) at 37°C on heat-treated MPEAs demonstrated improved tribological and corrosion behavior, with reduced wear and a lower coefficient of friction (COF). Electrochemical analysis indicated superior corrosion resistance, particularly for Ti₃₃Co₃₃Cr₃₃ MPEA. With respect to biocompatibility, both MPEAs demonstrated excellent cell adhesion and proliferation properties. Cell viability improved significantly, increasing from the control (100%) to ∼105% and 115% after 3 and 5 days, respectively. The combined results highlight the strong potential of these MPEAs for biomedical applications, offering a unique balance of high "density-normalized" hardness, excellent corrosion resistance, and biological compatibility for future implant solutions.