Differential effects of Ti addition on microstructure and corresponding mechanical and tribological properties of AlCr3Fe3NiTix high-entropy alloys

High-entropy alloys (HEAs), particularly those with an A2+B2 dual-phase structure, offer balanced strength and toughness, leading to superior and well-adjustable wear resistance. The effect of titanium, known to promote the formation of hard intermetallic phases and enhance mechanical properties, on A2+B2 dual-phase HEAs remains less understood. In this work, selecting a representative AlCr 3 Fe 3 Ni alloy with A2+B2 phases as the base alloy, we systematically investigated the phase evolution induced by various amounts of Ti addition and their differential effects on the sliding wear and solid-particle erosion of AlCr 3 Fe 3 NiTi x HEAs (x = 0–1.5, molar ratio). Microstructural analysis reveals that Ti addition promotes the formation of AlNi 2 Ti-type L2 1 and (Fe,Cr) 2 Ti-type C14 Laves phases, both of which strengthen the alloys at the expense of plasticity. However, a low Ti content (i.e., x = 0.2) helps improve both yield strength and plasticity, due to the solid-solution strengthening effect and refinement of grain size. Micro-indentation and scratching tests demonstrate that the C14 Laves phase exhibits the highest hardness but the lowest toughness, whereas the A2+B2 dual-phase structure possesses the highest toughness but the lowest hardness. The L2 1 phase displays intermediate properties between the two. Sliding wear and dry-sand erosion tests reveal that moderate Ti additions enhance wear resistance through solid-solution strengthening, hard-phase reinforcement, and oxidation-induced surface protection. However, erosion resistance deteriorates with increasing Ti content, primarily due to lowered toughness under impact conditions. This study elucidates the dual roles of Ti-induced hard yet brittle phases, i.e., beneficial for sliding wear resistance but detrimental to erosion performance in impact-involving environments requiring higher toughness. The findings provide valuable insights into structure-property relationships for the design of advanced structural and tribo-materials.