Enhanced High Temperature Oxidation Resistance of the Conventional Ti-48Al-2Nb-2Cr Alloy through Carbon Pack Cementation and Analysis of the Carbon Diffusion Path

Abstract

γ-TiAl alloys have attracted interest as lightweight materials for structural applications at temperatures below 800 o C. With recent improvements in microstrutural control of the γ-TiAl alloys, resulting in excellent creep properties and high temperature strength, their use can be extended to temperatures higher than 800 o C. To increase their application temperature range, the oxidation resistance of γ-TiAl alloys must be improved through alloy design or coating techniques. To improve the high temperature oxidation resistance of γ-TiAl alloys, it is important to suppress the growth of TiO2 oxide by forming a dense coating layer to block oxygen atoms. In this study, we tried to improve the high temperature oxidation resistance of a conventional γ-TiAl alloy, Ti-48Al-2Nb-2Cr (Ti 4822) using a pack cementation process, with carbon sources and activating materials, XRD and EDS analysis results for the surface products indicated the formation of coating layers comprising oxides and carbides including TiC, Al4C3, Ti2AlC, and Ti3AlC. Based upon the sequential formation of coating layers and phase diagrams, the diffusion path of the carbon during the pack cementation process is proposed. Also, detailed carburization and oxidation behaviors of the γ-TiAl alloys in the temperature range of 800-1000 o C are discussed in terms of microstructural observations. Enhanced high temperature oxidation resistance was obtained in Ti-48Al2Nb-2Cr (Ti 4822) through a proper carbon pack cementation process.