Microstructures and corrosion resistance enhancement of ultrasonic vibration-assisted medium entropy alloy base laser multi-phase coating

The CoCrNi medium entropy alloy base coating (MEABC) was fabricated on the TC4 titanium alloy by the laser cladding (LC) technology, the effects of the ultrasonic vibration (UV) on the microstructures and the corrosion resistance of the coatings were studied. The MEABC was consisted primarily of BCC and (Ni,Co)Ti2, Cu could be precipitated at the grain boundary, producing the AlCu2Ti nanocrystals. The micro-forming quality of the coating was enhanced due to the UV effect. The temperature gradient/heat flux density of the UV assisted laser induced pool (LIP) were varied under an action of the high frequency vibration, refining the microstructure. The corrosion resistance and micro-hardness of the coating were enhanced due to the UV effects and the slow diffusion effect of the medium entropy alloy system, producing the multi-phase, such as the amorphous phases (APs) and the nanocrystalline phases (NPs), etc. This study provides the theoretical/experimental basis for the multi principal component coating by UV assisted LC process. •The medium entropy alloy base coatings with BCC and (Ni,Co)Ti2 were fabricated.•The UV effect broke the precipitating dendrites, retarding the grain growth.•NPs/APs were formed due to the rapid cooling of LIP, forming multi-phase.•Atomic diffusion was promoted by UV, forming LAGBs to enhance corrosion resistance.