INTERFACIAL CHARACTERIZATION OF CHEMICALLY VAPOR-DEPOSITED TITANIUM CARBIDE ON CEMENTED CARBIDE

Titanium carbide coatings were obtained on cemented carbide substrates by chemical vapour deposition under non-decarburizing and decarburizi ng conditions, i.e. without and with interfacial eta-carbide respectiv ely. The interfacial structures were studied by transmission electron microscopy. In the absence of eta-carbide, it was confirmed that TiC n ucleated and grew epitaxially on both {0001}WC and {1010BAR}WC surface s. The epitaxy on the {0001}WC surface was that of close-packed planes on close-packed planes, i.e. {111}TiC on {0001}WC, and the epitaxial orientation relationship between TiC and WC was (111)TiC\\(0001)WC;[11 0BAR]TiC\\[1120BAR]WC. On the {1010BAR}WC surface two orientation rela tionships (001)Tic\\(1010BAR)WC; [110}\\[1120BAR] and (112BAR)TiC\\(10 10BAR)WC; [111]\\[0001]WC were observed. Interfacial misfit of the bou ndaries defined by the obtained orientation relationships is discussed , with misfit dislocation structures being estimated using the 0-latti ce theory. As a result of a decarburizing deposition process, eta-carb ide was formed and it substituted WC at the original TiC-WC interface. This can be explained by the relatively long incubation time encounte red in the formation of eta-carbide. The eta phase which was typically formed as a result of chemical vapour deposition was Co6W6C, and it e xhibited relatively large grain size and few defects. The dissolution of WC associated with the formation of eta-carbide was found to occur preferentially along the {1010BAR}WC planes.