Microstructure and High-Temperature Oxidation Resistance of In-Situ Ti-Al-B Functional Coatings by Laser Cladding
In order to improve the inherent poor high-temperature oxidation resistance and extend the service life of titanium alloy in extreme environments,Ti-Al-B functional coating was prepared on TC4 titanium alloy surface by in-situ laser cladding technology.The phase composition,metallographic structure,microstructure,microhardness,and high-temperature oxidation resistance of the coating after 120 hours at 800℃ cyclic oxida-tion condition were characterized by XRD,OM,SEM,XPS,microhardness tester,and tubular resistance furnace,respectively.The results showed that the coating formed a good metallurgical bond with the substrate,and the coating was composed of α-Ti,Ti3Al,TiB,Al2O3,and a small amount of Ti oxide.Ti in the coating mainly exists in the forms of Ti and Ti3Al,while Al mainly exists in the forms of Ti3Al and Al2O3.The maximum microhardness of the coating reaches 1 177.5 HV0.2,which is 3.27 times that of the substrate.The oxidation resistance of the coating after 120 hours at 800℃ cyclic oxidation condition is 10-15 times higher than that of TC4 titanium alloy substrate.The main reason for the improvement of the high-temperature oxidation resistance of the coating is at-tributed to the grain refinement of B and the hindering effect of the continuous dense oxide film on the surface of the coating on the diffusion of oxygen from the air into the coating.Laser cladding in-situ Ti-Al-B functional coatings can significantly improve the high-temperature oxidation resistance of titanium alloys.
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