Influence of the substrate treatment on the microstructure and properties of chemical vapour deposited Ti(C,N) coatings

Abstract

The effect of the mechanical treatment on the surface morphology of cemented carbide substrates and on the microstructure and properties of chemical vapour deposited (CVD) Ti(C,N) coatings is described in terms of the functional relationships between the substrate surface roughness, and the grain size, preferred orientation of crystallites, residual stress, indentation hardness and adhesion of the coatings. The substrates were flat fine-grained and coarse-grained cemented carbides inserts that underwent different treatments – wet blasting, grinding or polishing. Although the Ti(C,N) coatings were produced in the same moderate-temperature deposition process, their microstructure characteristics and mechanical properties differed significantly. Microscopic steps and edges present on ‘rough’ substrates facilitated the growth of large V-shaped Ti(C,N) grains with a weak {211} texture. In these samples, the tensile residual stress that is typically produced during the cooling of the CVD samples was reduced. The Ti(C,N) coatings deposited on ‘smooth’ substrates were fine-grained, and possessed a pronounced {211} texture and a better adhesion to the substrate. In these samples, the thermal tensile stress was less reduced than in the samples deposited on ‘rough’ substrates. The indentation hardness of the Ti(C,N) coatings was not affected by the substrate treatment. The physical background of these relationships is explained.