Ceramics-Silikáty 59, (4) 261 - 269 (2015)

Spark Plasma sintering (SPS) was applied for the densification of Calcia stabilized ZrO₂ based composites obtained from mixtures of pure zirconia (m-ZrO₂) and calcium aluminate cement (HAC). Two commercial powders of pure zirconia were employed as reactants. One of these powders had a coarse mean particle size (d₅₀ = 8 μm) and the other was a submicrometer sized power (d₅₀ = 0.44 μm). Several compositions containing different proportions of HAC (5 to 30 mol. % CaO in ZrO₂) were sintered by SPS at temperatures between 1200 and 1400°C under a pressure of 100 MPa during 10 min. The effect of processing conditions on phase composition, densification, microstructure and Vickers hardness of the obtained composites was examined. SPS significantly enhanced the densification in both type of composites (relative density > 93 %) as compared to those previously produced by conventional sintering. Composites with low CaO content consisted of mixtures of c-ZrO₂, (Ca_0.15Zr_0.85O_1.85), unreacted m-ZrO₂ and calcium dialuminate (CaAl₄O₇ or CA₂). The highest hardness was determined for composites sintered at 1400ºC being related to the maximum relative density (~ 99 %). High densification of composites with 30 mol. % CaO composed by similar proportions of CaAl₄O₇ and c-ZrO₂ were obtained even at 1200ºC but led to a slightly lower hardness. In general, the use of the finer m-ZrO₂ powder contributed to increase both the c-ZrO₂ content and densification of composite sintered at a relatively lower temperature. For these composites, best hardness (H_v near to 10 GPa) resulted when the microstructure consisted of a fine grained ZrO₂ matrix surrounding the dispersed CaAl₄O₇ grains instead of large interconnection between grains of both phases existed.