DIAMOND-COATED HARD MATERIAL, THROWAWAY INSERT AND A PROCESS FOR THE PRODUCTION THEREOF

摘要

An object of the present invention is to provide a diamond-coated hard material having a high bonding strength to a substrate and a diamond-coated throwaway insert capable of cutting various light alloys such as Al-Si alloys at a high cutting rate for a long time. This object can effectively be attained by a diamond-coated hard material comprising a sintered body consisting of Si3N4 as a predominant component, at least a part of the sintered body having a sintered surface at least a part of which is coated with diamond and a diamond-coated throwaway insert having a diamond- or diamond-like carbonoated layer with a thickness of 0.1 to 200 .mu. m, deposited from gaseous phase,on the surface of a substrate consisting of Si3N4 as a predominant component, in which the surface state of the substrate is maintained as sintered and a part or whole of the sintered surface is coated with the diamond- or diamondlike carbon-coated layer.