Role of fabrication route and sintering on wear and mechanical properties of liquid-phase-sintered alumina

Liquid-phase-sintered Al2O3 (LPS) fabricated by slip casting, tape casting, isopressing, uniaxial pressing, piston and auger extrusion showed substantial differences in wear due to differences in morphology as observed in image analyses of SEM micrographs. The abrasive wear was low in the case of uniaxial pressing and high in the case of tape casting in the ‘dry sand and rubber wheel’ test. The wear surface of the tape cast specimen exhibited extensive microcracking possibly due to orientation of Al2O3 platelet (major face) parallel to the abraded surface whereas some degree of perpendicular orientation in extruded surface resulted in lower wear loss. In wet-milling wear test, the isopressed balls of a 95–97 wt% LPS derived from reactive powder (<1 μm) showed 25% lower wear loss than that of the extruded balls of a 91–94 wt% LPS derived from coarse powder (70–100 μm). Sintering at a lower temperature with longer duration and batch milling of the composition in between 12 and 16 h resulted in low wear loss. Flexural strength also improved by longer sintering time but did not show any improvement by increasing milling time. However, the variation in flexural strength was minimized by isopressing the extruded specimen. A high indentation fracture toughness at 49.03 N test load was associated with (i) large elongated reinforcement grains in a fine-grained microstructure with overall elongated morphology and (ii) with an intergranular fracture.