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.