Optimization of sintering profile to achieve highly toughened alumina based ceramic

Abstract

Alumina (Al2O3) based ceramics are widely used for making machine parts, high-temperature components, wear-resistant material and biological ceramic due to their high hardness, strength, wear-resistance, and chemical and thermal stability. However, low fracture toughness (KIC∼3.0 MPa.m1/2) inhibit its usage in other potential applications where high toughness is a pre-requisite (e.g. ceramic engine). In an attempt to improve the strength, particularly the fracture toughness, two step sintering process was used. Sintering temperature was optimized based on the results obtained from dilatometer and DSC-TG analysis. X-ray fluorescence (XRF) was used to make compositional analysis of as received raw powders and X-ray Diffraction (XRD) was used to analysis the phase purity and crystallinity for both powder and sintered samples. Microstructure was investigated by using SEM. Hardness and fracture toughness was measured and its correlation with microstructure was investigated. Density was measured by Archimedes method and crystalline density from XRD. Microhardness diamond indenter was used and the diagonal length of indent and the crack lengths were measured by SEM to calculate the Vickers hardness values and fracture toughness, respectively. The maximum fracture toughness was obtained 4.03 MPa.m1/2 for Al2O3 ceramic and the hardness value was 15.97 GPa. Density was found 99.6% of the relative density of Alumina at optimum sintering cycle and the grain size was found 0.38 µm. Thermal expansion coefficient was measured by dilatometer and the calculated value was 7.9×10-6 K-1. The physical properties of the Alumina were good enough and comparable to withstand high temperature applications.