Effects of PTFE activation and carbon sources on combustion synthesis of Cr2AlC/Al2O3 composites

Formation of Cr2AlC/Al2O3 in situ composites was investigated by self-propagating high-temperature synthesis (SHS) involving both PTFE activation and aluminothermic reduction. In addition to Al and Cr2O3 as the starting materials, carbon black, graphite, and Al4C3 were used as the carbon sources. PTFE was employed not only as a reaction promoter, but also as a carburizing agent. Depending on different sources of carbon, the threshold amounts of PTFE for inducing self-sustaining combustion were 1.5, 4.0, and 3.0 wt% for the samples adopting carbon black, graphite, and Al4C3, respectively. The combustion front velocity and temperature increased with increasing PTFE content. Moreover, the sample using carbon black was the most exothermic, while the Al4C3-based sample was the least. For the powder compacts adopting carbon black or graphite, Cr2AlC/Al2O3 composites were produced with no impurities. Due to relatively weak reaction exothermicity, however, the synthesized composites containing small amounts of Cr7C3 and Al4C3 were obtained from the Al4C3-based reaction scheme.