Effects of Cold Rolling or Precipitation Hardening Treatment on the Microstructure, Mechanical Properties, and Corrosion Resistance of Ti-Rich Metastable Medium-Entropy Alloys

Abstract

Titanium-rich metastable medium-entropy alloys, designed for low elastic moduli, sacrifice strength. However, enhancing their mechanical strength is crucial for bio-implant applications. This study aims to enhance the mechanical properties and corrosion resistance of a metastable Ti80–Nb10–Mo5–Sn5 medium-entropy alloy using various treatments, including cold rolling (at 50% and 75% reduction) and precipitation hardening (at room temperature, 150 °C, 350 °C, 550 °C, and 750 °C). The results showed that the alloy underwent a stress-induced martensitic transformation during the rolling process. Notably, the α phase was precipitated in the β grain boundaries after 30 days of precipitation hardening at room temperature. The yield strengths of the alloy increased by 51% and 281.9% after room-temperature precipitation and 75% cold rolling, respectively. In potentiodynamic corrosion tests conducted in phosphate-buffered saline solution, the pitting potentials of the alloy treated using various conditions were higher than 1.8 V, and no pitting holes were observed on the surface of the alloys. The surface oxide layer of the alloy was primarily composed of TiO2, Nb2O5, MoO3, and SnO2, contributing to the alloy’s exceptional corrosion and pitting resistance. The 75% rolled Ti80–Nb10–Mo5–Sn5 demonstrates exceptional mechanical properties and high corrosion resistance, positioning it as a promising bio-implant candidate.