The effects of MgO addition on microstructure, mechanical properties and wear performance of zirconia-toughened alumina cutting inserts

The microstructure, mechanical properties and wear performance of ceramic cutting inserts produced from Al2O3, yttria stabilized zirconia and magnesium oxide system were investigated. The MgO weight percent was varied from 0 wt% to 3.5 wt%. Each batch of composition was mixed, uniaxially pressed into rhombic 80° cutting inserts with an average 0.6 mm tip radius and sintered at 1600 °C for 4 h in pressureless conditions. Studies on the effects of the inserts’ microstructures on their mechanical and physical properties such as nose wear, Vickers hardness and fracture toughness were carried out. Mild steel (AISI 1018) was used as the workpiece in the machining test. Results show that an addition of 0.7 wt% of MgO produces the minimum wear area. When the amount of MgO was increased to more than 0.7 wt%, the wear area increased from 0.019 mm2 to 0.065 mm2. Thus, ZTA cutting inserts fabricated with MgO additives show 50% improvement of wear compared to ZTA cutting inserts without MgO addition. Furthermore, microstructural observations show that the Al2O3 grain size is significantly dependent on the amount of MgO additives. Results of the Vickers hardness test is directly related to the result of wear area, where the cutting insert with the minimum wear area also showed the highest hardness. The increase of hardness of the cutting insert is mainly contributed by small sized Al2O3 grains.