Enhancing mechanical properties of AlCrFeNiTi_x high-entropy alloy coatings via Ti-induced sunflower microstructure

Laser cladding was employed to fabricate AlCrFeNiTi_x (x = 0, 0.25, 0.5, 0.75, and 1) high-entropy alloy (HEA) coatings on Q235 steel substrates. The study systematically investigated the influence of Ti content on the phase composition, microstructure, and mechanical properties of the coatings. With increasing Ti content, the phase composition of the coatings transitioned from a BCC + B2 dual-phase structure to a BCC + B2 + L2₁ multiphase system. Ti addition promoted the formation of the L2₁ phase and induced a unique sunflower-like microstructure, characterized by L2₁ phase embedding within the sunflower structure. This microstructural evolution significantly enhanced the hardness and wear resistance of the coatings. The AlCrFeNiTi coating (x = 1) exhibited the highest microhardness of 750 HV, while the AlCrFeNiTi_0.5 coating showed the highest wear resistance with a wear volume of only 0.004 mm³, which is an order of magnitude lower than that of the Ti-free coating (0.034 mm³) However, excessive Ti content led to increased brittleness due to the growth of the L2₁ phase, resulting in a gradual decline in wear performance.