Influence of powder properties on in-situ platelet reinforcement of LPS-SiC

摘要

Starting from fine, submicron α-SiC powders with different polytype compositions (SiC-Green, SiC-Dark, SiC-Extra), which were doped with 7 vol. % sintering additives on the basis of AIN-YAG-(SiO{sub}2), test specimens were prepared and sintered in a gas pressure furnace (1950℃, 5/95 bar argon). By subsequent annealing (2050℃, 20 bar Ar, ≥4 h) of the sintered specimens, it was possible to transform their globular microstructure into a platelet microstructure with elongated plate crystals, i.e. platelets, and thereby achieve in-situ microstructural reinforcement. The platelets only began to develop after completion of a 6 H -> 4 H polytype transformation. The lower the 4H content in the starting powder is, the greater is the aspect ratio of the platelets. The evolution of the platelet microstructure was attended by an increase in fracture toughness by 60 to 80 % compared to the non-annealed, globular LPS-SiC.