Abstract: In order to improve the wear resistance of aluminum alloy frictional parts, the nanostructured Al2O3-40%TiO2 (NAT40) multiphase ceramic coatings are prepared on the surfaces of 7005 aluminum alloy by plasma spray technology. The microstructure of the coating is analyzed and its main mechanical properties are tested. The tribological behavior and wear mechanisms of the coatings are investigated in dry and 3.5%NaCl solution frictional conditions respectively. The results show that the microhardness of the NAT40 coating is 638.6 HV0.5, and its fracture toughness is 13.3 MPa•m1/2, moreover, the critical adhesion strength between the coating and the substrate reaches 80.35 N, which are all higher than those of the micron Al2O3-40%TiO2 (MAT40) coating. In dry friction condition, the friction coefficients of the NAT40 coatings increase from 0.20 to 0.32 and the wear losses rise from 1.3 mg to 2.2 mg with the loads increasing from 3 N to 12 N. At the light load of 3 N, the NAT40 coating mainly suffers from micro-cutting wear. At the heavy load of 12 N, the calculated value of flash temperature on the worn surface is 541.65 ℃, which decreases the strength and hardness of the NAT40 coating, so the wear mechanisms turn into multi-plastic deformation wear, adhesive wear and oxidative wear. In 3.5%NaCl solution, the friction coefficients of the NAT40 coatings are obvious lower than which in dry friction, however, the wear loss at 12 N increases by 22.7% compared with that in dry friction condition. The wear mechanisms of the NAT40 coating change from fatigue wear to stress corrosion wear as loads increase.

Key words: Critical adhesion strength, Fracture toughness, Nanostructured Al2O3-40%TiO2 coating, Plasma spray, Tribology