✍ Scribed by Y.S. Song; D. O'Sullivan; S. Hampshire
No coin nor oath required. For personal study only.
Studies of pressureless sintering of Si3N 4 based matrices and Si3N4-SiC composites in the Y-Si-A1-O-N and Hf-Y-Si-A1-O-N additive systems have been carried out. Mechanical testing indicated that matrices had higher hardness and higher flexural strength than composites. Composites had higher fracture toughness than mauices. The main toughening mechanisms are thought to be crack deflection and microcracking. Effective improvements in fracture toughness can be achieved by coarser SiC particles due to the fact that coarser dispersions enhance the amplitude of crack deflection and produce a greater number of microcracks.
Using HfO 2 as a sintering aid had little effect on densification but was found to give improved flexural strength especially for composites. It is proposed that this may be due to the formation of HfO2-Y203 solid solution which had a beneficial influence on microstructural development in the composites.
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