Plasma spraying Ti-Al-C based composite coatings from Ti/Al/graphite agglomerates: Synthesis, characterization and reaction mechanism

This study explored the feasibility of fabricating Ti-Al-C based composite coatings using 2T(i/xAl/)0.5C (x = 0.2-1.5) agglomerated powders by plasma spraying technique. The effect of Al content on microstructure and mechanical properties of spray coatings was studied, and the reaction mechanism was revealed. Results showed that the typical structure of agglomerates developed from C@Ti to C@Ti-Al and isolated Al as increasing Al additions. All the as-sprayed coatings consist of TiC, (Ti,Al)Cx (metastable solid solution formed by Al replacing Ti site in TiC), Ti2AlC and some TixAly phases. Ti2AlC phase grew tightly surrounded by TiC and (Ti,Al)C-x nanoparticles embedded in the TixAly regions. With elevated Al additions, the Ti2AlC phase content increases first and then decreases at x = 1.0. Correspondingly, the hardness of the composite coatings first increased and then decreased. The study proved the possibility of reaction synthesis of Ti2AlC phase by plasma spraying element powder mixtures and its formation mechanism was proposed.