On the interactions of Ti2AlC, Ti3AlC2, Ti3SiC2 and Cr2AlC with silicon carbide and pyrolytic carbon at 1300 °C

Herein we report on the reactivity between silicon carbide, SiC, and pyrolytic carbon, PG, with the MAX phases, Ti2AlC, Ti3AlC2, Ti3SiC2 and Cr2AlC. Diffusion couples were assembled and heated to 1300 °C under a load corresponding to a uniaxial stress of ∼30 MPa for 4, 10, and 30 h in a vacuum hot press, at a vacuum level of less than 1 Pa. The couples were then examined using optical and scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, and orientation image microscopy. Based on the totality of the results - after 30 h at 1300 °C - it is concluded that neither Ti3SiC2 nor Cr2AlC appear to react with SiC. The former also appears not to react with PG. When heated in the vacuum of the hot press, both Ti2AlC and Ti3AlC2 dissociated to form TiC surface layers that were ≈15-20 μm thick. After reaction of Ti2AlC with SiC and PG, the TiC layer was only ≈10 μm thick, indirectly confirming that the dissociation of these phases in vacuum was due to the Al evaporation from the surfaces. The Ti3AlC2/SiC and Ti3AlC2/PG diffusion couples resulted in TiC layers that were ≈50 μm and ≈100 μm thick, respectively. The Cr2AlC/PG diffusion couple resulted in the formation of ≈10 μm interfacial layer comprised of Cr3C2 and Cr7C3 at the interface between the two materials.