Carbide/nitride ternary materials of M_n+1–A–X_n formula, known as MAX phase, have a great industrial potential due to their intermediate metal-ceramic properties resulting from their covalent/ionic bonds and their complex atomic nanolayer structure. These characteristics generally give MAX phases good electrical/thermal conductivity, thermal shock resistance, damage tolerance, and machinability (as metallic properties), as well as low density, high melting point, and excellent resistance to oxidation/corrosion at high temperature (as ceramic properties). Among the available compositions, the Al-based MAX phases show the best resistance to oxidation/corrosion at high temperature (800–1300°C) owing to the in-situ formation of a protective Al₂O₃ layer resulting from Al ion diffusion at high temperature. However, Al₂O₃ formation kinetics and thus oxidation mechanisms are negatively affected by the impurities, secondary phases, and microstructure (notably grain size) of the material. Hence, the interest in synthesizing them with high purity by simple and less energy-intensive methods is the key driver.

The attractive properties of the MAX phases are particularly interesting for their use as high-performance coatings. Different physical and chemical methods have been used to develop them. However, these processes, mostly energy-intensive, tend to deteriorate the MAX phase properties and even those of the substrate. The Aerosol Deposition (AD) method, meanwhile, has in recent years become an innovative, efficient, low-cost, and non-energy-intensive alternative for the coating production at room temperature. This coating process (still maturing) requires an appropriate control of the starting powders and an understanding of the coating formation mechanisms.

Hence, TAC-type (Ti–Al–C) MAX phase powders were synthesized by solid state reaction to evaluate the effect of the nature/stoichiometry of the precursor mixture (TiC, Ti, Al, Al₄C₃) without sintering additives, the nature of the atmosphere (vacuum or argon) and the sintering temperature (1350 to 1450°C) on the phase purity. The particle size of high purity lab-made MAX phase powders, as well as commercial ones; was then suitable for forming AD coatings on TiAl substrates. Several AD method conditions (mainly the nature/volumetric flow rate of the carrier gas) on formed coating characteristics were evaluated. The adhesion and high temperature oxidation resistance of the coatings were performed by scratch and thermal cycling tests. Characterization techniques were carried out to evaluate the phase content and particle size of the synthesized and starting powders to be atomized, as well as the morphology, roughness, thickness, crystalline evolution, and elementary chemical composition of the coatings before and after scratch and oxidation tests. The presentation will first focus on the synthesis conditions suitable for obtaining TAC-type MAX phase with a high purity. The talk will then present the best AD operating conditions for growing coatings, and the resulting properties, namely the oxidation resistance as a function of the purity of the starting powder.