Designing TiAlNbZr multi-principal element (MPE) alloys for high-temperature strength enhancement

In this study, five different compositions of Multi-Principal Element (MPE) alloys with Al, Nb, and Zr, were designed to achieve a two-phase structure of α-HCP and β-BCC. Phase stabilities and yield strengths at various temperatures were investigated through heat treatment and high-temperature compression testing. Due to MPE alloying, the β-transus temperature varied significantly, and the alloys formed an α phase on a β-matrix phase after homogenization and aging treatments. This α phase formation contributed to the increased yield strength, combined with the strong solid-solution strengthening effect achieved through MPE alloying. Among the alloys, the α phase formation observed in Alloy D (Ti₆₅Al₁₅Nb₁₀Zr₁₀) and Alloy E (Ti₅₅Al₁₅Nb₁₀Zr₂₀) was maintained up to 1273 K, resulting in high-temperature strengths of 690 MPa for Alloy D and 860 MPa for Alloy E. This result is noteworthy, as conventional alloys experienced a severe drop in strength even at 873 K.