Load Dependence of Hardness in Sintered Submicrometer Al2O3 and ZrO2

Monolithic alumina bodies with a grain size of 0.5 micrometer and submicron tetragonal ZrO2(3 mol-percent Y2O3) polycrystals were produced and investigated. With decreasing indentation load, the hardness increases but may again decrease below about 5 N; relevant measurements require the application of fairly high loads. Decreasing grain sizes increase the hardness of alumina and zirconia ceramics even for very small grain sizes in the submicron range .