A cutting insert with a titanium oxycarbonitride coating and its method of manufacture

A method for making a coated cutting insert includes a step of providing a substrate 24 which has a surface 26, and depositing a CVD coating layer of titanium oxycarbonitride 44. The gaseous mixture from which the coating layer of titanium oxycarbonitride is deposited has a composition of nitrogen (5-40 mol%), methane (0.5-8.0 mol%), titanium tetrachloride (0.2-3.0 mol%), acetonitrile (0.02-0.15 mol%), carbon monoxide ((0.4-2.0 mol%), and hydrogen (41.85-93.88 mol%). Optionally, hydrogen chloride (up to 5.0 mol%) may also be present in the mixture. Further layers including, for example, titanium nitride 38, titanium carbonitride 40 and alpha-alumina 46 may also be present. In a further aspect, the coated cutting insert comprises a layer of titanium oxycarbonitride in the form of whiskers having, as measured in a two-dimensional plane view, an average length greater than 1.0 µm, an average width greater than 0.2 µm, and an average aspect ratio greater than 2.0.