Bidirectional improvement of strength and ductility of CoCrFeNiTi (Co40Cr16Fe35Ni8Ti1) high-entropy alloys suitable for coronary stents

Abstract

A new type of non-equivalent atomic ratio Co40Fe35Cr16Ni8Ti1 HEA that can be used as an alternative material for coronary stents was successfully designed and synthesized, and one of its main features was the low Ni and containing Ti, which made it have good biocompatibility while also achieving the bidirectional improvement of strength-ductility. XRD tests showed that Co40Fe35Cr16Ni8Ti1 HEA had precipitation of R and Laves phases. SEM tests equipped with EDS showed that Co40Fe35Cr16Ni8Ti1 HEA with grains and grain boundaries corroded by aqua regia appeared rich Ni & Ti elements and rich Co & Ti elements at different locations, which matched the R and Laves phases shown in XRD respectively. EBSD test showed that Co40Fe35Cr16Ni8Ti1 HEA had a smaller proportion of deformed grains and a higher proportion of small-angle grain boundaries, and the grain size of Co40Fe35Cr16Ni8Ti1 had a more typical bimodal structure, which indicates that it was a perfect combination of both high strength and high ductility. Tensile experiments showed that the yield strength and ductility of Co40Fe35Cr16Ni8Ti1 HEA had reached the upper limit of ASTM F90. The Tafel test showed that Co40Fe35Cr16Ni8Ti1 HEA also had excellent corrosion resistance.

Keywords

• HEA
• Strength
• Ductility
• Hank's simulated body fluid