Sliding wear performance of high-velocity oxy-fuel spray Al2O3/TiO2 and Cr2O3 coatings

High-velocity oxy-fuel (HVOF) spray ceramic oxide coatings have immense potential in industrial applications. However, they are not widely used yet due to the lack of an adequate scientific database created after testing these coatings for specific industrial applications. Two such ceramic coating powders, Al2O3 + (40%)TiO2 and Cr2O3, were deposited on AISI 309 SS stainless steel by the HVOF spray technique, in order to enhance its wear resistance. This stainless steel is used in many components of thermal power plants in India, where it suffers one or more types of wear. The as-sprayed coatings were characterized by XRD and SEM analyses. Subsequently, the sliding wear behaviours of the uncoated, HVOF spray Al2O3 + (40%)TiO2 and Cr2O3 coated AISI 309 SS were investigated according to ASTM standard G99-03 on a pin-on-disc wear test rig. Cumulative wear rate and coefficient of friction (P) were calculated for the coated as well as the uncoated specimens for 30, 50, and 70 N normal loads at a constant sliding velocity of 1 m/s. Some of the worn-out surfaces were characterized by SEM analysis. Both the as-sprayed coatings exhibited typical splat morphology of a thermal spray process. The XRD analysis indicated the formation of Al2O3 and TiO2 phases for the Al2O3 + (40%)TiO2 coating, and Cr2O3 phase for the Cr2O3 coating. It has been concluded that HVOF spray Al2O3 + (40%)TiO2 and Cr2O3 coatings can be useful in minimizing the wear problem of AISI 309 SS. These coatings were found to be successful in retaining their surface contact with the substrate after the wear tests. The HVOF spray Cr2O3 coating can be recommended as a slightly better choice to reduce the wear of AISI 309 SS in comparison with the Al2O3 + (40%)TiO2 coating.