Hot-Pressing of Alumina-Iron Composite Ceramics and Their Properties

Abstract

Alumina-iron composite ceramics were fabricated by hot-pressing from well mixed alumina and iron powders at 1550°C and 300kgf/cm2 for 30min. Sintered bodies with nearly theoretical density were obtained for addition of less than 20wt% Fe, but the relative density decreased gradually with increasing Fe content more than that. The alumina-iron composites showed more extensive grain growth than pure alumina, and there were many open spaces around iron grains generated by the thermal expansion mismatch. The fracture toughness increased with increasing Fe content, reaching 4MN/m3/2 at 50wt% Fe. The Vickers hardness, on the other hand, decreased rapidly around 10wt% Fe addition. The specific wear rate measured on a sintered alumina disk increased with increasing Fe content, but was lower than 10-7mm2/kgf at 40wt% Fe, which is comparable to that of dense silicon nitride ceramics. The cutting resistance was reduced significantly by Fe addition. Especially, the tangential resistance of Al2O3-30wt% Fe composite was lower than that of pure alumina by the factor of 10. The iron which existed near the surface of composite was removed in the first few minutes when treated in boiling H2SO4, but no subsequent weight loss was observed. The fracture strength of the composite decreased gradually up to 600°C, and then rapidly at higher temperature.