Al_12.5Hf₃₅Ti₃₅Zr_17.5 Alloy with Hexagonal Close-Packed Structure Designed from Al₄₀Ti₆₀ Alloy

Abstract

An Al_12.5Hf₃₅Ti₃₅Zr_17.5 alloy was experimentally examined to determine whether it can form a single hexagonal close-packed (hcp) structure. The Al_12.5Hf₃₅Ti₃₅Zr_17.5 alloy was computationally selected through an Al_12.5Hf₄₀Ti_47.5 alloy from a prototypical Al₄₀Ti₆₀ alloy. A characteristic of the Al₄₀Ti₆₀ alloy was utilized in the alloy design; it exhibits a single hcp structure in the temperature range of approximately 200 K, which is below the stable body-centered cubic structure. The Al_12.5Hf₄₀Ti_47.5 and Al_12.5Hf₃₅Ti₃₅Zr_17.5 alloys were prepared experimentally using conventional arc melting. Furthermore, the Al_12.5Hf₃₅Ti₃₅Zr_17.5 alloy was annealed at 1600 K for 1 h, followed by water quenching. X-ray diffraction profiles revealed that the as-prepared Al_12.5Hf₄₀Ti_47.5 alloy and both the as-prepared and annealed samples of the Al_12.5Hf₃₅Ti₃₅Zr_17.5 alloy formed an hcp structure. A single hcp structure was confirmed using scanning electron microscopy combined with elemental mapping via energy-dispersive X-ray spectroscopy for an annealed sample of the Al_12.5Hf₃₅Ti₃₅Zr_17.5 alloy. The calculated results for the Al_12.5Hf₃₅Ti₃₅Zr_17.5 alloy disagreed with the experimental results because of the incomplete reproducibility of the calculated phase diagram for the constituent Al–Hf system. The present results provide a method to derive a multi-component alloy with an hcp structure by compensating for the deficiencies in thermodynamic predictions.

Formation of a hexagonal close-packed structure in Al_12.5Hf₃₅Ti₃₅Zr_17.5 alloy annealed at 1600 K for 1 h followed by water quenching. (a) Predictions, (b) experiments, and (c) analysis of constituent binary phase diagrams to clarify the differences between calculations and experiments.