Sintering Behavior: Al–SiC Compacts in Different Atmospheres

The effect of sintering atmosphere on densification of Al–SiC compacts was investigated. Dimensional changes were monitored in situ in a dilatometer in flowing nitrogen, nitrogen/hydrogen mixture (95/5 by volume), and argon. Two grades of SiC powder were used—F240 characterized by large particles and FCN13 with very fine particles. Mixtures containing 10 and 30 vol.% of SiC reinforcement were prepared in a Turbula mixer. Green compacts of about 80% of theoretical density were made of each mixture. For comparison, compacts made of pure aluminum powder were also investigated. It was shown that nitrogen is the only sintering atmosphere producing shrinkage. This ceramic constituent lowers the sintering densification. Metallographic examinations of sintered composites revealed that sintering of compacts occurs in the presence of a liquid phase exclusively in nitrogen. The melt appearing in Al–SiC compacts is capable to wet the solid phases, which makes shrinkage possible and is beneficial for metal/ceramic bond formation.