Correlation between Microstructure and Mechanical Properties of YSZ/Al2O3 Ceramics and Its Effect on High Speed Machining of Steel

An attempt has been made to correlate the mechanical properties with microstructure and machining performance of zirconia toughened alumina composite fabricated from different ratios of Al2O3 with yttria stabilized zirconia (YSZ) powder. The developed 3 mol% YSZ powder has been mixed with Al2O3 in the ratios of 10:90, 15:85 and 20:80 for fabrication of cutting inserts. Study reveals the relation between microstructure of the composites with the mechanical properties, i.e. hardness, fracture toughness, flexural strength. Conventional lathe NH-26 is used to evaluate the machining performance, i.e. flank wear, surface roughness and cutting force of all three types of developed inserts by machining of AISI 4340 steel bar. The maximum hardness, 15.55 GPa, has been obtained for 90% Al2O3 with 10% YSZ. The maximum values of fracture toughness (5.96 MPa.m(1/2)) and flexural strength (510 MPa) are noticed for 80% Al2O3 with 20% YSZ. The analysis also shows that when the YSZ percentage increases, the smaller grain size of YSZ particle and crack bridging phenomena enhances the mechanical properties like fracture toughness and flexural strength of the composites. The composition comprising of YSZ:Al2O3::10:90 shows less flank wear, best surface finish and lowest cutting force.