Procédé de fabrication d'un corps métallique

In the production of a metallic body consisting of an alloy hardened by a dispersion of fine particles of a non-metallic phase, particularly an oxide, and in which a minor proportion of the matrix alloy is a metal or metals which form oxides having at 18 DEG C. a heat of formation in excess of 80 K.cal./gm.atom of oxygen, small porous agglomerates of a powder mixture of the non-metallic phase and the major component of the matrix alloy are heated in the presence of vapour of the minor component or a compound thereof and in the absence of oxygen whereby the minor component is caused to deposit on and diffuse into the major component. The mass is then consolidated. Metals used in the initial powder mixture may be nickel, cobalt, molybdenum, iron, copper or tungsten and elements deposited thereon may be chromium (which may be deposited from the fluoride), aluminium, silicon, beryllium, magnesium, cerium and carbon. The dispersed phase is generally an oxide such as that of thorium, aluminium, magnesium or rare-earth metals, but other materials inert to the matrix such as sulphides of cerium, thorium, calcium, and molybdenum disilicide. The initial powder mixture is preferably made mechanically as by ball-milling, but may be obtained by partial reduction of mixed oxides, as by reduction in hydrogen of mixed oxides resulting from the ignition of mixed calcium and nickel formates. The agglomerates may be produced by compacting the powder mixture by pressure or by light sintering at 400-1000 DEG C., followed by crushing to a particle size preferably of 500-800 microns. A further treatment at 400-1000 DEG C. in a reducing gas preferably follows to eliminate oxygen. The rate of deposition of the minor matrix component should not be greater than the rate of its diffusion into the major component; the former rate may be controlled by the admission of inert gas into the vaporization zone. As exemplified, nickel powder and thoria were ball milled together, compacted at 35 tons/sq.inch, and crushed. The agglomerates were then mixed with chromium granules of substantially greater size, and heated in a rotary cylindrical furnace for 16 hours at 400 DEG C. in dry hydrogen. The furnace was then evacuated, argon admitted to a pressure of 50 mm. mercury and the temperature raised to 1200 DEG C. for 60 hours. The mixture was then sieved to remove the chromium granules, consolidated at 35 tons/sq. inch, sintered at 1200 DEG C. in hydrogen for 16 hours, sheathed in nickel and ext