Microstructure and tribological properties of pulsed electric current sintered alumina–zirconia nanocomposites with different solid lubricants

Dense Al2O3-15 wt% (ZrO2-3 mol%Y2O3) nanocomposites modified with 3 wt% of self-lubricating component (CaF2, BaF2, MoS2, WS2, h-BN, or graphite) were consolidated by pulsed electric current sintering. Their microstructure as well as mechanical and tribological properties were evaluated. During consolidation composition of the self-lubricating components was conserved except for BaF2, which partially melted. The Al2O3/ZrO2(3 mol%Y2O3) matrix showed hardness of 20.35 GPa and Young’s modulus of 320 GPa determined by Vickers indentation. All solid lubricant additives led to a decrease in hardness of the composite. Solid lubricant additives lowered the coefficient of friction (CoF) against alumina at room temperature. In pin-on-disc tests CoF of 0.38–0.42 was measured for all the materials against alumina ball. The lowest CoF of 0.043 was measured for Al2O3/ZrO2(3 mol%Y2O3)/CaF2 in the scratch test against diamond stylus while the matrix material showed lower friction than other materials. The measured wear rates were in the order of 10−12 for Al2O3/ZrO2(3 mol%Y2O3)/CaF2, Al2O3/ZrO2(3 mol%Y2O3)/MoS2, and Al2O3/ZrO2(3 mol%Y2O3)/WS2.