Microstructure and properties of Cr–AlSi12 composite coatings pre-coated on Ti–6Al–4V alloy substrate via mechanical alloying and subsequent laser cladding treatment

Abstract

Cr–AlSi12 composite coating on Ti–6Al–4V alloy substrate was fabricated by mechanical alloying (MA) and subsequent laser cladding (LC). The weight ratio of the mixed powders was Cr: AlSi12 = 60:40. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were applied to investigate the evolution of surface morphologies, cross-section microstructures and phase composition of the coatings before and after laser treatment. The results showed that Al8Cr5, AlCr2, (Si, Al)2Cr and Cr5Si3 were generated in the MA-LC coating through in-situ alloying reaction. The formation of Al3Ti and Ti5Si4 intermetallic compounds was caused by interdiffusion. Metallurgical bonding was achieved at the coating/substrate interface. Results of the scratch test indicated that laser treatment could significantly improve the bonding quality of the interface. Meanwhile, the microhardness of the MA-LC coating was about 3–4 times higher than that of the MA coating. The high-temperature oxidation resistance of the MA-LC Cr–AlSi12 coating was also studied. It was found that after 100 h of oxidation, the MA-LC coating could effectively enhance the oxidation resistance of the substrate. The oxide films and intermetallic phases formed during oxidation process could play a role of intense hindrance to the diffusion of oxygen into the internal Ti–6Al–4V substrate. The oxidation mechanism of the coating is discussed in detail.