The influence of in-situ formation of hibonite on the properties of zirconia toughened alumina (ZTA) composites

This paper reports an investigation on the impact of in-situ formation of CaAl12O19 (hibonite) on the microstructure and mechanical properties of zirconia-toughened-alumina (ZTA). Various amounts of CaCO3 (0–13 wt%) were added to ZTA to form CaAl12O19. Samples were sintered at 800 °C for 4 h to obtain CaO from decomposition of CaCO3, and then at 1600 °C for 4 h to produce elongated CaAl12O19 grains. Analyses of samples were done using XRD and FESEM. The higher the amount of CaCO3 added, the higher the amounts of CaAl12O19 and pores observed. The toughness value increased with the increase of CaAl12O19 for a critical range, and subsequently decreased; the reverse trend was observed for the hardness and density results. The sample with 0.5 wt% CaCO3 addition produced the highest toughness (6.3 MPa m1/2), reasonable hardness (1568.6 HV), density (4.11 g/cm3), and porosity (1.29%) values.