Study on the Effect of Carburizing on the Microstructure and High-Temperature Oxidation Properties of Hot-Dip Aluminum Coating on Titanium Alloy

A Ti–Al alloy phase layer/Ti–Al carburizing composite coating was prepared on the surface of titanium alloy by the stepwise coating method of hot-dip aluminizing and then carburizing. The weight gain results of the composite coating showed that the titanium alloy coated with the composite coating had long-term stability (≥16 days) at 800 °C. The microstructure, phase structure, and composition of the composite coating were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The composite coating is composed of an alloy phase layer and a carburized layer. The natural transition of four phases (Ti3Al/TiAl/TiAl2/TiAl3) in the alloy phase layer significantly improves the interfacial bonding between the coating and the substrate and slows down the propagation of microcracks through the coating. Al2O3, TiC, and C in the carburizing layer improve the surface hardness of the coating, and TiAl2 and Al2O3 also have excellent oxidation resistance at high temperature.