GB732618A - A method for the manufacture of metal articles by sintering at low temperatures - Google Patents

Abstract

732,618. Powder metallurgy. AGTE, C. July 13, 1953 [July 25, 1952], No. 19353/53. Class 83 (4). For producing articles by powder metallurgy at comparatively low sintering temperatures, the initial metal powder comprises 60-90 per cent of grains of size 0.2-1.0 micron and 40- 10 per cent of a size 2-5 microns and is compacted at 2-10 tons per square cm. and sintered in dry hydrogen at a temperature which, measured in degrees absolute, is between 0.2 and 0.55 of the melting-point of the metal. The powder is preferably obtained by the reduction of a salt or oxide of a metal in hydrogen and after a second reduction treatment at a higher temperature is ground for at least 40 hours in an organic liquid such as carbon tetrachloride, trichlorethylene, benzene, acetone &c. to which is added 0.5-3 per cent of an aliphatic acid or its ester. In an example, molybdenum oxide is reduced in dry hydrogen at a final temperature of 820-850‹ C. and cooled in carbon dioxide. The resulting molybdenum powder is sifted through a screen of 0.06 mm. mesh, given a further reducing treatment in dry hydrogen at about 800‹C. and ground for 72 hours in tetrachlormethane to which 0.5-3 per cent stearine is added. The powder is then compacted at 2-10 tons per square cm. and the compacts packed in a protective material such as powdered aluminium oxide or beryllium oxide on which a thin layer of fine-grained ferrotitanium is poured to act as a getter and so prevent access of oxygen. The sintering temperature is 900-1250‹ C. For other metals the sintering temperatures would be tungsten 1000‹- 1400‹ C., iron 550-850‹ C., cobalt 650- 800‹ C., nickel 600-850‹ C. and copper 400- 580‹ C.