Electrodeposition of Cermets

Abstract

Modern engineering requirements are frequently near the useful limits of application of conventional materials. This has led to much, mainly empirical, work on the preparation of composites in which more than one conventional material is present. An example, known as a “cermet”, consists of a ceramic in powder or fibre form imbedded in a metal matrix. Satisfactory improvements in properties can often be obtained by the application of a cermet coating onto a common metal and such coatings have been applied by electrodeposition techniques. Some of the factors underlying the cermet electrodeposition process have been investigated. A ceramic particle in contact with an electrolyte solution will carry a charge. Under plating conditions such a charged particle may be transported by electrophoresis; the rate of transport for a given applied potential gradient would be determined by the charge carried by the particle. Measurements of this charge on particles of alumina, silicon carbide and chromium diboride have been made, in terms of the electrokinetic (zeta) potential, by a streaming potential method, Silicon carbide was chosen for a detailed study and the zeta potential on it was determined for various combinations and concentrations of copper sulphate and sulphuric acid and also of nickel sulphate and potassium sulphate. Cermet materials, silicon carbide in copper and chromium diboride in copper, have been produced by electrodeposition and the distribution of ceramic particles through the cermet determined, The ceramic particle density in the cermet was related to the surface roughness, being highest where the surface was most rough and irregular. It is suggested that the mechanism of deposition is a combination of electrophoretic transport of the particle through the double-layer at the cathode surface and of mechanical entrapment of the particle followed by keying into place by electrodeposited metal.