Process for the diffusion of one metal into another metal

933,200. Coating with metals. ROLLSROYCE Ltd. March 30, 1962, No. 12458/62. Class 82. A process for diffusing a metal, such as A1, Cd, Sn, Pb or Zn, into the surface of another, such as nickel base alloys or brass, comprises placing the article to be coated in a sealed enclosure with at least part of its surface in contact with a powder mixture of 0.5-30% of the first metal and 99.5-70% of calcined alumina, heating the enclosure to a temperature above the melting point of the first metal, e.g. > 1150‹ or 980-1050‹ C., for a period of 1-24 hours, preferably 8-12 hours, the enclosure being provided with means which allow gases and vapours to escape during heating but prevent their ingress. The enclosure may be sealed by welding on a cover 14 (Fig. 1) or by bolting a cover 21 on to flanges 24, the projection 27 projecting into the recess 26 which is filled with chromous oxide 28, providing the seal in the case of Fig. 2. The preferred means for allowing gas and vapours to escape during heating but to prevent their ingress is the non-return valve shown in the Figures. The valve 17 may be set by means of screw 19 to open at a pressure within the range 5-20 lbs./sq. inch.