Tribological properties of Al2O3 hard coatings modified by mechanical blasting and polishing post-treatment

The tribological behaviour of post-treated CVD α- and κ-Al2O3 hard coatings is investigated in this study between room temperature and 900 °C. Friction and wear are correlated to the different coating surface topographies in the as-deposited state and generated by metal-blasting with AlSi granulate or polishing. As a result of its higher surface roughness, the quantity of AlSi transfer material is considerably higher for α- compared to κ-Al2O3. The coefficient of friction is comparable for both Al2O3 modifications and for all testing temperatures. Increased wear is observed for metal-blasted surfaces, especially for α-Al2O3 at high temperatures, which can be attributed to generation of abrasive wear debris by oxidation of the transfer material. Polishing reduces wear due to a decrease in surface roughness.