DEVELOPMENT OF ZIRCONIA TOUGHENED ALUMINA MATRIX CERAMIC NANO-COMPOSITES REINFORCED WITH MgO AND CNTs

Abstract

Composites are a class of materials developed by reinforcing one or more materials to the matrix. The properties of a composite mainly depend on factors like reinforcement material, processing method, etc. The main objective of the present work here was to investigate of reinforcement of ZrO2, MgO and MWCNTs on properties such as density, microhardness, fracture toughness and microstructure in alumina matrix composites through powder metallurgy route and processed using microwave sintering and spark plasma sintering process. In the first phase, investigations with reinforcement of ZrO2 and MgO to the alumina matrix were conducted using microwave sintering process in which the powders were compacted at a pressure 100 MPa and sintered at 1300 °C, 1450 °C, 1500 °C, and 1550 °C and held for 20 minutes under pressure-less condition. Similarly, the reinforcement of ZrO2 and MgO to the alumina matrix was investigated using the spark plasma sintering process, in which heat and pressure were applied simultaneously at a pressure of 60 MPa and sintered at 1250 °C, 1300 °C, and 1350 °C, and held for 5 minutes. In both the MWS and SPS processes, the volumetric proportion of MgO reinforcement was varied at 0.5 vol. %, 1 vol. %, and 2 vol. % and the volumetric proportion of 3 mol %yttria-stabilized zirconia were varied at 5 vol.%, 10 vol. %, and 15 vol.%in the alumina matrix. The highest density, highest microhardness and minimum average grain size were obtained with reinforcement of 1 vol. % of MgO and 10 vol. % of ZrO2 to the alumina matrix using microwave sintering. The highest fracture toughness was also found with reinforcements of 1 vol. % of MgO and 15 vol. % of ZrO2 to the alumina matrix, at a sintering temperature of 1500 °C for holding time of 20 minutes. Similarly, the optimum properties were found with reinforcements of 1 vol. % of MgO and 10 vol. % of ZrO2 to the Al2O3 matrix using spark plasma sintering process. The coefficient of friction and wear rate were performed varying the normal load and sliding speed with the reinforcement of 1 vol. % of MgO and 10 vol. % of ZrO2 to the alumina matrix using the MWS and SPS process. In the second phase, investigations with reinforcement of ZrO2 and functionalized MWCNTs in the alumina matrix were conducted using microwave sintering process in which the powders were compacted at a pressure of 100 MPa and sintered at 1450 °C, 1500 °C, and 1550 °C and held for 20 minutes under pressure-less condition. Similarly, investigations with reinforcement of ZrO2 and MWCNTs in the alumina matrix were conducted using the spark plasma sintering process in which heat and pressure were applied simultaneously at pressure 60 MPa and sintered at 1250 °C, 1300 °C, and 1350 °C, and held for 5 minutes. Both in the MWS and SPS process, the reinforcement of functionalized MWCNTs was varied at 0.5 vol. %, 1 vol. % and 2 vol. % and 3 mol % yttria-stabilized zirconia was varied at 5 vol. %, 10 vol. % and 15 vol. % in the alumina matrix. The highest density, highest microhardness, and minimum average grain size were obtained with the reinforcement of 1 vol. % of functionalized MWCNTs and 10 vol. % of ZrO2 to the alumina matrix using microwave sintering. The highest fracture toughness was also found with reinforcement of 1 vol. % of MWCNTs and 15 vol. % of ZrO2 to the alumina matrix, at a sintering temperature of 1500 °C for holding time 20 minutes. Similarly, the optimum properties were found with reinforcements of 1 vol. % of functionalized MWCNTs and 10 vol. % of ZrO2 reinforced to the Al2O3 matrix using the spark plasma sintering process. The optimum tribological properties were observed with reduced coefficient of friction and wear rate and increased normal loads at sliding velocities 0.79 m/s, 1.4 m/s, and 1.8 m/s. The values of the coefficient of friction and wear rate decreased with an increase in the sliding velocity, while the values of COF decreased and wear rate increased with an increase in the normal load. The tribological tests were repeated with higher sliding velocity (2.4 m/s), and a higher normal load range (65-95 N) and COF and wear rate rapidly increased beyond 65 N. The mechanical properties and microstructure of SPS sintered samples were observed to be superior compared to the MWS sintered samples. Among all the samples, the highest density, highest microhardness, and minimum average grain size were observed with the MgO-ZTA reinforced composite processed through SPS, while the highest fracture toughness was observed with the MWCNTs-ZTA reinforced composite processed through SPS. The minimum value of COF and wear rate were observed with the MgO-ZTA reinforced composite processed through SPS.