Improvements in process for Titaniding Base Metals

摘要

1,199,027. Electrolytically titaniding metals. GENERAL ELECTRIC CO. Oct. 25, 1967 [Nov. 10, 1966], No.48514/67. Heading C7B. A method of forming a titanide coating on a metal composition, the metal composition having a melting point of at least 600‹ C., at least 50 mole per cent of said metal composition being at least one of the metals selected from the class consisting of metals whose atomic numbers are 13, 23-29, 41-47, and 73-79 inclusive, which method comprises (1) forming an electric cell containing said metal composition as the cathode, joined through an external electrical circuit to titanium serving as anode and a fused salt electrolyte comprising (a) one or more alkali metal fluorides, or a mixture of one alkali metal fluoride with one or more of the fluorides of strontium, barium, calcium and magnesium, and (b) from 0À01-5 mole per cent of titanium fluoride, said electrolyte being maintained at a temperature of at least 500‹ C. but below the melting point of said metal composition in the substantial absence of oxygen and (when said metal composition includes a metal of atomic number 23, 24, 41, 42, 73 or 74 in the substantial absence of carbonaceous material; and (2) controlling the current flowing in said electric cell so that the current density of the cathode is in the range from 0‹01 (preferably 0À05) to 10 amperes/dm2 during the formation of the titanide coating; said cell being operated under a vacuum or inert atmosphere. The term titanide designates any solid solution or alloy or intermetallic compound of Ti and the base metal. The cell generates electric current. The deposition rate of the Ti may be increased by impressing a voltage, e.g. to obtain constant current densities during the reaction. Specified fluorides, that may be used are those of Li, Na, K, Rb and Cs. e.g. a eutectic mixture of (i) NaF and LiF, (ii) LiF, NaF and KF or (iii) LiF and KF. An inert atmosphere of Ar, He, Ne, Kr, or Xe may be used. Impurities such as oxygen and carbon can be removed from the fused electrolyte by an initial electrolysis. Oxygen can also be removed by contacting the fused electrolyte with Ti. Carbon can also be removed by filtering the fused salt through a finely woven wire cloth especially of materials which will react with the carbon to make metal carbides. The titanide has a hard, wearresistant surface.