چكيده به لاتين
The weak toughness and reliability of ceramic cannot meet the engineering demands. The combination of transformation reinforcement of zirconia and metal particles has shown a significant improvement in toughness caused by the synergistic toughening. In the present work, the effect of Ni content, heating schedules and MgO doping on densification, microstructure and mechanical properties of Al2O3/(ZrO2+Ni) composites was investigated. The content of ZrO2 was adopted at 15 vol.% in the final composites. Powder mixtures of Al2O3, 3YSZ and nickel nitrate as a source of Ni metal were prepared by precipitated Ni on ceramic powders. The powder mixtures were calcined at 450 °C and then reduced within a carbon powder bed at 750 °C. The effect of 0, 2.5, 5, 7.5 vol.% Ni addition to composites was studied, at which they were pressureless sintered at 1600 °C for 3 h within a carbon powder bed. The results shown that the addition of 5 vol.% Ni results in the highest relative density of 93 % and the maximum fracture strength and toughness values of 348 MPa and 2.22 MPa.m½, respectively. To ensure full density, the Al2O3/(15 vol.% ZrO2+5 vol.% Ni) composites were conducted by one-step sintering (OSS) at temperatures T for 3 h (T/3 h), and two-step sintering (TSS) at preheating temperatures T1 for 0.5 h and followed by a lower temperature T2 at 1600 °C for 3 h (T1/0.5 h, 1600 °C/3 h). TSS technique produced more homogeneity and controllable microstructure than that for OSS. By comparison, the hardness of composites increased with sintering temperature and attained its highest value of 14.51 GPa at T1 = 1720 °C for TSS, as well as the strength was enhanced and had an equal value of 417 MPa at all T1. However, the toughness for TSS was decreased with increasing T1. The influence of MgO doping Al2O3/(15 vol.% ZrO2+5 vol.% Ni) composites was explored using PLS and SPS. By PLS, the samples bloated because of higher volatility of Mg gas with the presence of carbon. Nevertheless, applying external pressure with SPS overcame that and made possible full dense bodies. In addition, the mechanical properties of the MgO doping composite were greatly enhanced due to the combination of pinning effect and transformation toughening progress. In this case, the hardness, strength and toughness reached values of 17 GPa, 801 MPa and 6 MPa.m½, respectively.
