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This study explores Ti-containing complex concentrated alloys (CCAs) within the AlMoNbTiZr system, focusing on compositions located in regions of the Bo–Md diagram characterized by low bond order (Bo) and d-orbital energy level (Md). Four alloys were designed near the line predicting stress-induced martensite formation in conventional Ti alloys, then cast, annealed at 1200 °C, and water quenched. Their microstructures and phases were analyzed and compared against phase prediction tools commonly applied to high-entropy alloys (HEAs), namely empirical parameters and CALPHAD simulations. Results highlight the strong influence of chemical affinity, particularly the roles of Al, Mo, and Zr concentrations, on solid-solution stability. A maximum Al content of ∼10 at.% was identified as the threshold for achieving a “single-phase” microstructure, observed in the 10Al15Mo10Nb35Ti30Zr alloy. This alloy exhibited a bcc/b2 structure with high compressive strength (>1300 MPa), low Young’s modulus (∼28 GPa), and limited strain (<6%), but lacked the transformation-induced strengthening mechanisms expected for Ti alloys with comparable Bo–Md values.
Casas-Luna et al. (Wed,) studied this question.