Process for producing boron carbide coatings of controlled hardness

摘要

PCT No. PCT/FR85/00136 Sec. 371 Date Apr. 28, 1986 Sec. 102(e) Date Apr. 28, 1986 PCT Filed Jun. 3, 1985 PCT Pub. No. WO86/00345 PCT Pub. Date Jan. 16, 1986.A process for producing a coating of boron carbide of predetermined, controlled hardness on a substrate comprising heating the surface of the substrate to a temperature of between 800 DEG C. and 1200 DEG C., reducing a gaseous mixture containing at least one boron compound and at least one carbon compound in the presence of the heated substrate while causing the gas mixture to flow over the heated surface of the substrate at a total pressure of less than or equal to 100 millibars and at an average flow rate of between 10-4 and 10-3 g.cm2.5-1 so as to deposit a coating comprising tetragonal boron carbide B50C2 or rhombohedral boron carbide B13C2 or a mixture thereof, establishing a curve of the variation of the hardness of the coating as a function of the composition of the gas mixture for the conditions of temperature, pressure and flow rate selected, determining the value of the composition corresponding to the hardness of the coating obtained and adjusting the composition of the gas mixture for obtaining a predetermined hardness.