Coating with controlled grain size and morphology for enhanced wear resistance and toughness

摘要

Wear resistance of the prior-art Ti(C,N) layers can be considerably enhanced by optimising the grain size and microstructure. This invention describes a method to obtain controlled, fine, equiaxed grain morphology in Ti(C,N) layers produced using moderate temperature CVD (MTCVD). The control of the grain size and shape can be obtained by doping using CO, CO2, ZrCl4 and AlCl3 or combinations of these. Doping has to be controlled carefully in order to avoid nanograined structures and oxidisation. This kind of coatings shows new enhanced wear properties. The fine grain size together with equiaxed grain morphology enhances the toughness of the coating with at least maintained wear resistance, which can be seen especially in sticky steels like stainless steels. The optimum grain size is from 50 to 300 nm, preferably from 50 to 150. The coatings according to this invention are characterised by the lack of any strong preferred growth orientation, the length-to-width ratio (L/W) around 1 and only with a slight to moderate XRD line broadening.