Microstructure, mechanical and thermo-physical properties of CVD TiCxN1-x coatings on cemented carbide substrates grown with C2H6 as C feeding precursor

Abstract

The established industrial processes used for the growth of TiCxN1-x coatings by chemical vapor deposition (CVD) suffer from substantial limitations, either in regard of brittle phase formation or restriction in the C/(C + N) ratio. Using the alternative C precursor C2H6 allows to overcome these issues. Thus, within this work, the microstructure, phase composition, micro-mechanical and thermo-physical properties of CVD TiCxN1-x coatings grown with C2H6 were investigated. Through adjustment of the C2H6 and N2 flow in the feed gas, the C/(C + N) ratio in the coatings was varied between pure TiN and TiC0.80N0.20. All coatings are characterized by a single-phase face centered cubic structure. The 〈110〉 fiber texture present in all coatings becomes more pronounced with increasing C content. None of the investigated coatings showed thermal cracks on the surface. The thermal conductivity decreases with addition of C from 45 ± 5 W/mK in TiN to 32 ± 3 W/mK in all ternary TiCxN1-x coatings. TiC0.47N0.53 exhibits the highest hardness (30.0 ± 1.4 GPa), while TiC0.63N0.36 turned out as the stiffest coating with a Young's modulus of 576 ± 23 GPa. The fracture stress σF and toughness KIC are superior in coatings with moderate C and N content, with TiC0.63N0.37 being the strongest (σF = 7.7 ± 0.4 GPa) and TiC0.47N0.53 (KIC = 4.4 ± 0.3 MPa m1/2) the toughest within this series. Coatings with moderate to high C content were found to exhibit a microstructure provoking a lower thermal conductivity and improved mechanical properties compared to those with a low C/(C + N) ratio.