GB507341A - Process for the surface improvement of metals and alloys - Google Patents

Abstract

507,341. Coating metals; alloys. INSTITUT FUR PHYSlKALISCHE CHEMIE DER METALLE AM KAISER-WILHELMINSTITUT FUR METALLFORSCHUNG Dec. 14, 1937, No. 34633. Convention date, Dec. 14, 1936. [Classes 72, 82 (i), and 82 (ii)] In order to avoid the formation of brittle intermetallic compounds when introducing a metal B into the surface of a metal A by cementation, there is used instead of the metal B itself an alloy of the metal A with the metal B which corresponds approximately, and preferably exactly, with the composition of that intermetallic compound which in accordance with the phase diagram of the system A-B is coexistent as a separate phase with the metal A or with the solid solution of A with B, if any, rich in A. Instead of the alloy a mixture of the components in the same proportions may be used. If it is desired to introduce into A two or more metals B, B1, B2, &c., the composition of the cementation powder will depend on whether the metals B1, B2, &c. do or do not form compounds with A. If the metal A contains alloying constituents A1, A2, &c, the cementation material may or may not contain these metals according to whether it is or is not desired to prevent outward diffusion of these constituents. To diffuse magnesium into aluminium the aluminium may be heated at 445‹C. in a pulverized alloy corresponding to the composition Al3Mg2, i.e. an alloy containing about 38 per cent of magnesium ; if a thicker layer is desired an alloy with a slightly greater magnesium content, e.g. 42 per cent, may be used, or if a particularly gradual transition is desired the percentage of magnesium may be reduced slightly below 38 per cent. To diffuse aluminium into magnesium, the latter is embedded in a powdered magnesium-aluminium alloy containing about 58 per cent of magnesium and heated at a temperature just below the eutectic temperature of 436‹ C. Beryllium may be introduced into copper by heating the copper in vacuo at 830‹ C. in a finely ground alloy of 90 per cent of copper and 10 per cent of beryllium, and bismuth may be introduced into magnesium by embedding the magnesium in a powder consisting of a mixture of about 85 per cent of magnesium and 15 per cent of bismuth (corresponding to the compound Mg3Bi2) and heating at 526‹ C. The Specification as open to inspection under Sect. 91 describes also the impregnation of copper with silicon by heating in vacuo at 770‹ C. in a powder consisting of 87À2 parts by weight of copper and 12À8 parts of silicon (corresponding to the compound Cu3Si). This subject-matter does not appear in the Specification as accepted.