Abstract
Yttria-stabilised tetragonal polycrystalline ZrO 2-based composites with 40 vol.% TiN were hot pressed at 1450 °C for 1 h using a jet-milled thermally synthesized and a self-propagating high-temperature synthesis (SHS) TiN powder. The ZrO 2 phase of the SHS-TiN powder-based composites was found to be substantially coarser than for the jet-milled TiN powder-based ceramics and prone to spontaneous transformation to m-ZrO 2 and microcracking, due to the CaTiO 3 impurity in the SHS-TiN starting powder. In order to prove this, a set of experiments was performed to investigate the effect of the addition of CaO and TiO 2 on an yttria-stabilised tetragonal ZrO 2 polycrystalline (Y-TZP). The addition of 0.2 mol% of CaO to a Y-TZP ceramic was found to destabilise the t-ZrO 2 phase, whereas the addition of 1 mol% TiO 2 results in significant grain growth and the formation of less transformable t-ZrO 2. The CaTiO 3 impurity could be removed from the SHS-TiN powder by hot hydrochloric acid leaching, allowing to obtain a similar microstructure and mechanical properties as with conventional TiN powder.
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