Structure, mechanical and tribological properties of sputtered TiAlBN thin films

Abstract

TiAlBN films were produced by simultaneously sputtering from TiAl and TiB2 targets in Ar/N2 mixtures at a substrate temperature of 150 °C. The goal of this investigation was to study the influence of the nitrogen content (0-40 at.%) on two sets of four coatings with B/Al ratios of approximately 1 and 5. All coatings showed very dense structures and were mainly found to be only partially crystalline. Evidence of Al, AlN, Ti, TiB2, TiN and BN bonding was observed in the XPS spectra, and correlation of the compositional and mechanical data showed that film hardness and elastic modulus decreased with the presence of a 'soft' phase (Al, Ti or amorphous BN). Hardness and elastic modulus values of up to 25 and 250 GPa, respectively, were found for TiAl0.3B1.7 coatings. Coatings with a similar elastic modulus to that of the steel substrate showed the best adhesion. Friction coefficient values between approximately 0.5 and 0.7 were recorded in sliding wear experiments against SAE52100 and WC/6%Co balls. Although friction coefficients could not be correlated to the amorphous BN contents, it was noted that low combined ball and disc wear rates were found for coatings containing large amounts of BN. Coatings with B/Al 5 and elastic moduli of ≤290 GPa showed two orders of magnitude better sliding wear resistance against WC/6%Co balls compared to commercially available TiN. TiAlBN films were produced by simultaneously sputtering from TiAl and TiB2 targets in Ar/N2 mixtures at a substrate temperature of 150 °C. The goal of this investigation was to study the influence of the nitrogen content (0-40 at.%) on two sets of four coatings with B/Al ratios of approximately 1 and 5. All coatings showed very dense structures and were mainly found to be only partially crystalline. Evidence of Al, AlN, Ti, TiB2, TiN and BN bonding was observed in the XPS spectra, and correlation of the compositional and mechanical data showed that film hardness and elastic modulus decreased with the presence of a `soft' phase (Al, Ti or amorphous BN). Hardness and elastic modulus values of up to 25 and 250 GPa, respectively, were found for TiAl0.3B1.7 coatings. Coatings with a similar elastic modulus to that of the steel substrate showed the best adhesion. Friction coefficient values between approximately 0.5 and 0.7 were recorded in sliding wear experiments against SAE52100 and WC/6%Co balls. Although friction coefficients could not be correlated to the amorphous BN contents, it was noted that low combined ball and disc wear rates were found for coatings containing large amounts of BN. Coatings with B/Al approximately 5 and elastic moduli of ≤290 GPa showed two orders of magnitude better sliding wear resistance against WC/6%Co balls compared to commercially available TiN.