Al<sub>12.5</sub>Hf<sub>35</sub>Ti<sub>35</sub>Zr<sub>17.5</sub> Alloy with Hexagonal Close-Packed Structure Designed from Al<sub>40</sub>Ti<sub>60</sub> Alloy

An Al12.5Hf35Ti35Zr17.5 alloy was experimentally examined to determine whether it can form a single hexagonal close-packed (hcp) structure. The Al12.5Hf35Ti35Zr17.5 alloy was computationally selected through an Al12.5Hf40Ti47.5 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 Al12.5Hf40Ti47.5 and Al12.5Hf35Ti35Zr17.5 alloys were prepared experimentally using conventional arc melting. Furthermore, the Al12.5Hf35Ti35Zr17.5 alloy was annealed at 1600 K for 1 h, followed by water quenching. X-ray diffraction profiles revealed that the as-prepared Al12.5Hf40Ti47.5 alloy and both the as-prepared and annealed samples of the Al12.5Hf35Ti35Zr17.5 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 Al12.5Hf35Ti35Zr17.5 alloy. The calculated results for the Al12.5Hf35Ti35Zr17.5 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.