Patent GB-1394108-A (GB)
Title: Coated hard metal body
IPC: B32B7/00
Filed: 1972-11-10
Abstract: 1394108 Alumina and zirconia coatings SANDCO Ltd 10 Nov 1972 [12 Nov 1971] 52084/72 Heading C1A [Also in Divisions B2 and C7] A coated body comprises a core of sintered hard metal containing at least one carbide and a binder metal, one or more intermediate coatings deposited on the core and made of one or more carbides and/or nitrides of one or more of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Si and B and one or more wear-resistant ceramic coatings deposited from a gaseous phase on to the one or more intermediate coatings. The coated body may be a cutting insert. The ceramic coating may be aluminium oxide or zirconium oxide. The ceramic material may be deposited by chemical vapour deposition process or by sputtering. Several oxide layers, e.g. a first layer of aluminium oxide and then a second layer of zirconium oxide can be applied upon mixed layers or successive layers of carbide and/or nitride. The hard metal core may be oxidized or nitrated before forming the carbide or nitride coatings and the surface of the carbide or nitride coatings may be oxidized prior to deposition of the ceramic layer. As shown in Fig. 1, apparatus for coating a hard metal core with a carbide or nitride includes gas containers 1, 2 for supplying hydrogen and methane respectively, pipes 3 and 4 leading to a single pipe 5 through which the gas mixture is brought to a vessel 6 in which a metal halide, e.g. TiCl 4  is heated to evaporation, a heat exchanger 7 controlled by a thermostat 8 to adjust the content of TiCl 4  in the gas, a valved pipe 9 for passing the mixture of gases to a reaction vessel 11 heated by a furnace 10 and containing the metal core. From the reaction vessel 11 the gas is sucked out by valved pipe 12 and cooling trap 13 and gas is exhausted from the system through a valved pipe 14 by means of a vacuum pump 15 having an outlet pipe 16. As shown in Fig. 2 apparatus for depositing the ceramic oxide coating includes a chlorination reactor 25 for the production of AlCl 3  or ZrCl 4  in vapour form and means for the application of a surface layer of aluminium or zirconium oxide using this chloride to a metal core. The reactor contains aluminium or zirconium in the form of grains or chips 26. Hydrogen from gas container 1 is mixed via taps 19, 20 with chlorine or hydrochloric acid gas from container 17 and the mixture is passed through the chlorination reactor 25 through pipe 21. The gas mixture from the chlorination reactor 25 is then mixed with hydrogen from the container 1, carbon dioxide from container 18 and optionally with carbon monoxide from container 28 and the mixture conveyed to coating reaction vessel 11 via a valved pipe 27. In a typical example sintered cemented carbide inserts containing 40% WC, 15% Co and 45% cubic carbides in the form TiC, Tac and NbC were placed on strainer-like plates in a reaction vessel and heated to 1000‹C. A gas mixture containing 10% TiCl, 8% CH 4  and 82% H was passed into the reaction vessel, the pressure in the vessel being maintained at 15 torr (mmHg) to produce TiC-layers on the inserts. The gas supply system was then modified so that a gas of the composition 70% H, 5% CO 2 , 20% CO and 5% AlCl is supplied, the temperature of the cores being 1100‹ C. and the pressure 15 torr to form a layer of aluminium oxide on the TiC-coated inserts.