Effects of deposition parameters on the microstructure and mechanical properties of Ti(C,N) produced by moderate temperature chemical vapor deposition (MT-CVD) on cemented carbides

Abstract

Using an industrial-scale chemical vapor deposition (CVD) system, a series of Ti(C,N) films were deposited from a TiCl4–CH3CN–H2–N2 gas mixture at 850–950 °C and 70–700 mbar with N2/H2 molar ratio varying from 0.27 to 3.77. Within the investigated temperature range, it is found that the growth rate of Ti(C,N) films is strongly dependent on the total pressure. Such behavior agrees with a diffusional limitation step. The lowest growth rate is measured at the N2/H2 molar ratio of 3.77, because of the low reduction rate of TiCl4 in a H2 deficient atmosphere. No significant influence of processing conditions on the carbon content of Ti(C,N) films could be found, as determined by X-ray diffraction and EPMA. The microstructure and mechanical properties were investigated and chiefly influenced by deposition conditions. In this work, the Ti(C,N) films deposited at 850 °C and 70 mbar with N2/H2 molar ratio of 0.27 exhibit a mixed texture with laminated facetted grains, the superior hardness reaching 30 GPa and the Young's modulus of 394 ± 32 GPa were measured. Furthermore, experimental results reveal that residual stresses could be thickness-dependent, due to the evolutionary film microstructure during film growth, and the stress relaxation is particularly attributed to cooling cracks.