Enhancing mechanical performance and wear resistance of Co-free B2/A2 CrFeNiAl alloy via Cr and Ti adjustment

The adjusted mixture of ordered body-centered cubic (bcc) structure, referred to as B2, and disordered bcc structure, referred to as A2, in high-entropy alloys (HEAs) leads to a substantial enhancement in their strength. Via selecting elements in B2/A2 HEAs, their microstructure could be optimized for desirable properties (e.g., strength, ductility, and wear resistance) to meet requirements for specific applications. In this study, we delved into the effect of interplay between Cr and Ti in shaping the microstructure, mechanical properties, and wear resistance of Co-free B2/A2 CrFeNiAl alloy. CrxFeNiAl and CrxFeNiAlTi0.5 (x = 0, 0.5, 1, and 1.5) alloys were synthesized. For Ti-free FeNiAl alloy, the introduction of Cr led to a transition from a single B2 phase to a mixture of B2 and A2 phases, along with a morphological change from A2 nanoparticles embedded in B2 phase to an alternating lamellar eutectic structure or cellular structure. While in the Ti-containing FeNiAlTi0.5 alloy, Cr induced a shift from a microstructure of B2 + Fe2Ti Laves phase to one consisting of B2 + A2 phases. Ti increased the B2 lattice parameter. Notably, the strength, hardness, and ductility of the HEA increase with increasing Cr content, attributed to the precipitation and augmentation of A2 phase, Cr-facilitated solution hardening, and elimination of the Laves phase. The incorporation of Ti enhances strength at the expense of ductility. For the FeNiAl alloy, the developed oxide film caused by frictional heating during wear test enhanced its wear resistance, surpassing that of harder Cr0.5FeNiAl alloy. The wear resistance was improved with added Cr. Ti also contributes positively to wear resistance due to increased mechanical strength and the formation of a protective oxide scale.