Mechanical and tribological properties of nano/micro composite alumina coatings fabricated by atmospheric plasma spraying

Abstract Adding nano particles can significantly improve the mechanical properties and wear resistance of thermal sprayed Al2O3 coating. However, it still remains a challenge to uniformly incorporate nano particles into traditional coatings due to their bad dispersibility. In the present work, nanometer Al2O3 (n-Al2O3) powders modified by KH-560 silane coupling agent were introduced into micrometer Al2O3 (m-Al2O3) powders by ultrasonic dispersion to afford nano/micro composite feedstock, and then four resultant coatings (weight fraction of n-Al2O3: 0%, 3%, 5% and 10%) were fabricated by atmospheric plasma spraying. The features and constitutes of feedstock and as-sprayed coatings, as well as their porosity, bonding strength, microhardness and frictional behaviors were investigated in detail. Results show that the nano/micro composite feedstock with uniform microstructure can be better melted in the spraying process, thereby obtaining coatings with denser microstructure, higher hardness and bonding strength. Added n-Al2O3 has no obvious effect on the friction coefficient of composite coatings, whereas can improve their wear-resistant and reduce the worn degree of counterpart. The wear mechanism of traditional coating is brittle fracture and lamellar peeling, while that of composite coating with weight fraction of n-Al2O3 of 10% is adhesive wear.