Oxidation resistant FeCoNiCrAl high entropy alloy/AlSi12 composite coatings with excellent adhesion on Ti-6Al-4 V alloy substrate via mechanical alloying and subsequent laser cladding

In this study, FeCoNiCrAl high entropy alloy/AlSi12 composite coatings were prepared on Ti-6Al-4V substrate using a newly developed mechanical alloying (MA) and subsequent laser cladding (LC). The effects of milling duration and laser specific energy on the coatings were investigated. The mechanical alloying coating before and after laser cladding were comparatively studied in terms of phase composition, microstructure, mechanical properties and oxidation resistance. The results revealed that after laser cladding processing, the coating possessed a more refined and homogenous structure with high densification, consisting of dendrite (DR) phase, interdendrite (IR) phase and white particle phase. The microhardness has been greatly improved and the nano-hardness increased from 2.42 GPa to 12.63 GPa. Owing to metallurgical bonding of the substrate/coating interface, the higher bonding strength was obtained and it is hard for the coating to fail during the scratch test. The oxidation behaviors of the coatings at 850 °C for 100 h were systematically studied. With subsequent laser cladding, the coating shows considerable oxidation resistance. On the one hand, the formed Al2O3 film and high entropy alloy with sluggish diffusion effect could effectively prevent the diffusion of oxygen. On the other hand, the composite structure layer of the coating presents high densification, thereby inhibiting further diffusion of oxygen.