SPALLING RESISTANCE OF CEMENTED CARBIDE WITH PHYSICALLY AND CHEMICALLY VAPOR-DEPOSITED COATINGS

As a previous study had indicated that cemented carbide inserts coated with TiN by physical vapor deposition (PVC) methods have lower spalling resistance than those coated by chemical vapor deposition (CVD), in the present work the mode of loss caused by the milling of nodular cast iron was studied. It is found that CVD coatings may begin to fail cohesively but failure always causes damage well into the substrate. In contrast, PVD coatings always begin to fail cohesively and the areas expand and reach down to the substrate; adhesive loss causes less substrate damage. Scratch tests performed at loads well above the critical load appear to show the same characteristics of crack propagation as found during the coating loss in the milling studies.