WEB High-temperature oxidation resistance of Ti2AlC MAX phase based systems
“MAX” phases have attracted a lot of attention over the last three decades. These ternary carbides and nitrides are so called due to their chemical formula, with M being an early transition metal, A being an A-group element and X being carbon and/or nitrogen. By combining both metallic and ceramic properties such as high electrical and thermal conductivities, thermal shock resistance, damage tolerance, stiffness, they bridge the gap between ceramics and metals. Additionally, Al-containing MAX phases show excellent oxidation resistance, due to the formation of an outer α-Al2O3 scale. Ti2AlC demonstrates the best performance among all MAX phases.
Pure and fine-grained Ti2AlC MAX phase was produced by a molten salt based synthesis method. Spark Plasma Sintering (SPS) of as-synthesized Ti2AlC rapidly yielded dense samples without any degradation. In parallel, Ti2AlC was mixed with chopped Nextel 610™ alumina fibers, and subsequently densified by SPS. Fiber dispersion, fiber/matrix adhesion and interfacial reaction were investigated.
Additionally, oxidation resistance of monolithic Ti2AlC and fiber reinforced Ti2AlC composites was studied at 1200 °C for 50 h in static air. An 8 µm thin protective Al2O3 scale formed, covered with clusters of TiO2 crystals. In addition, the effect of initial surface finish on oxide growth was investigated. In parallel, thermal cycling experiments were also performed at 1200 °C on a Ti2AlC substrate coated with an atmospheric plasma sprayed YSZ coating. Cross-sectional analysis of cycled samples was carried out in order to identify the features of the Thermally Grown Oxide (TGO). The thickness of the Al2O3 scale was 20 µm after 500 h and samples survived more than 1000 h without any indication of YSZ coating spallation.