Toughness enhancement of zirconia-toughened alumina ceramic composite using multi-phasic additives and microwave heat treatment

Abstract

Aluminium oxide is a chemical compound, also known as alumina (Al2O3), is being widely used as a material in a cutting tool due to its superior mechanical properties. Nevertheless, alumina is not a straightforward solution for practical application due to its brittle nature. One of the solutions was to integrate other components into the base material of alumina. For an example, adding zirconia (ZrO2) in alumina (Al2O3) matrix produced a ceramic that improved the toughness of the material, though the toughness can be further improved. As a solution, the present work aims to enhance the ZTA ceramic composite’s fracture toughness by introducing a combination of microwave heat treatment and multi-phasic additives. Part 1 and Part 2 of this study utilised a conventional sintering process operating at a temperature of 1600°C for a total of 1 hour dwelling time. In the case of Part 3, 2.45 GHz microwave is used for sintering process at a temperature range of 1200°C - 1400°C in a 10-minutes dwelling time. The first phase of this work reported an enhanced ZTA properties with an addition of 3.0 wt.% TiO2. Moreover, the hardness is improved from 1516.13 HV/14.87 GPa (0 wt.% TiO2) to 1615.8 HV/15.85 GPa (3.0 wt.% TiO2), while the fracture toughness is improved from 5.93 MPa.m1/2 (0 wt.% TiO2) to 6.56 MPa.m1/2 (3.0 wt.% TiO2). Additionally, the enhanced mechanical properties can also be attributed to the presence of TiO2 as a vital sintering aid, which impeded Al2O3 grain growth, and consequently led to the formation of a denser and finer microstructure. In the second part, Cr2O3 is introduced as a new additive material that can be used with ZTA-3.0 wt.% TiO2. The outcome revealed that the properties associated with ZTA–3.0 wt.% TiO2 ceramic composite improved after the addition of 0.6 wt.% Cr2O3. Subsequently, the fracture toughness (7.15 MPa.m1/2) improved due to the formation of an isovalent solid solution between Al2O3 and Cr2O3. On the other hand, the enhanced hardness (1681 HV/16.5 GPa) is associated with the grain growth inhibition of Al2O3. Lastly, the microwave sintering process is used to produce ZTA-3.0 wt.% TiO2-0.6 wt.% Cr2O3 to enhance the microstructure and its properties. The outcome of the process exhibited that increased hardness (1803.4 HV/17.7 GPa) and excellent fracture toughness (9.61 MPa.m1/2) are obtained when the sample was sintered at a temperature of 1350°C within a 10-minutes dwelling time. The finding can be attributed to the process of volumetric heating, which led to shorter sintering time and lower sintering temperature. Thus, it produced tool material that has better densification, finer grain size, and excellent mechanical properties.