Improved Mechanical Properties of Al2O3 Ceramics by Sputtered TiN Coatings

In this study, TiN thin films have been prepared as the coating layers on Al2O3 ceramic substrates to enhance the mechanical properties of Al2O3 ceramics. TiN films with various thicknesses of 0.5 and 1 mu m were deposited by DC sputtering at room temperature. The TiN film prepared on the Al2O3 substrate has a columnar structure without large bumps or steps formed on the films surface. Without the TiN coating, the average friction coefficient of the Al2O3 substrate was 0.51. As 0.5-and 1-mu m-thick TiN films were coated on Al2O3 substrates, the average friction coefficients of these two samples reduced to 0.36 and 0.32, respectively, revealing the tribological characteristics of Al2O3 ceramic was enhanced with the TiN coating. Additionally, the 1-mu m-thick TiN/Al2O3 sample possesses a slightly higher attrition resistance than that of the 0.5-mu m-thick TiN/Al2O3 sample, and this can be also con firmed by performing the elemental mapping method on the wear-treated samples. From the adhesion performances, we observed no critical load of L-C2 appeared in these two samples during the scratch test, while the critical load of L-C1 values were 11 and 9 N for 0.5-mu m-thick TiN/Al2O3 and 1-mu m-thick TiN/Al2O3, respectively. Due to the increment of TiN thickness, the internal stress formed in the film would increase. This is the reason why the 1-mu m-thick TiN/Al2O3 sample has a lower critical load of L-C1. Obviously, the 0.5-mu m-thick TiN film coated on the Al2O3 substrate has a better adhesion characteristic. According to these results, the sputtered TiN coating is indeed useful for improving the mechanical properties of Al2O3 ceramics, in particular for the 0.5-mu m-thick TiN coating.