SUMMARY The first part of this review dealt with single metal electrodeposition†. Part II discusses alloy systems especially Pd-Ni, Pd-Ag and Pd-Co. Pd-Fe alloys are considered in detail discussing possible complexants and solution stability as the basis for an experimental study and development programme.

The development of solutions for palladium alloy electrodeposition is described outlining the problems of solution chemistry involved. The discussion is focused on the solution formulation for Pd-Fe alloy, as an alternative to Pd-Ni, and the option of considering Co and Ag as further alternatives to Ni is included. In Part 1 of this review the electrodeposition of the single metals is discussed.

A number of cleanliness assessment techniques related to quality surface preparation prior to electroplating, are in use but in general are comparative or subjective and not very sensitive. Electrochemical techniques are especially applicable to wet surfaces at intermediate stages of processing. One such technique, based on both two and three electrode polarisation, has been evaluated for silver, gold, copper, copper alloys, aluminium and iron alloy substrates and found to be easy to use without specialist competence reliable enough to give reproducible results and at the same time rapid and cost effective. Results are presented justifying this claim and demonstrating how it may be used as a quality measuring instrument.

A systematic study of the relation of the deposition conditions of Ti-N films prepared by d.c. magnetron sputtering to their microstructure and macrostress has been performed using two sets of alpha-Ti(N) and delta-TiN films. The variable parameter in the deposition was the combined parameter S(E) representing the energy delivered to the growing film.The threshold energy S(Etr) necessary for the transition from zone I to zone T of Thornton's structural zone model was investigated for both alpha-Ti(N) and delta-TiN films. S(Etr) for delta-TiN films is about one order of magnitude higher (S(E) = 0.9 MJ cm-3) than for alpha-Ti(N) films (S(E) = 0.15 MJ cm-3) according to X-ray diffraction. This finding can be explained by a difference in the melting temperature T(m) of TiN (T(m) = 3200 K) and that of Ti (T(m) = 1930 K). Values of the macrostress of Ti-N films as a function of S(E) are also given.

The composition of Ni-Mo layers (metallic and non-metallic elements) electrodeposited at temperatures up to 160 °C and pressures up to 5 bars has been determined. The effect of molybdate concentration has been investigated. All the non-metallic elements (C, O, H, N and S) exhibit a maximum content for deposition temperatures between 60 and 80 °C. A correlation between deposit composition and properties is attempted. The deposit growth mode, crystallinity and the corrosion resistance markedly depend on the plating conditions.

After reviewing the fundamentals of corrosion, the various electrochemical and technical corrosion tests will be discussed with special emphasis on their problems and evidence. In addition to the corrosion behavior of the coating material, the effect of the substrate is also important. The experimental potential-current density curves reflect the electrochemical properties of the coating and the influence of the underlying substrate when micropores, pinholes and other defects are present. Examples are given for nitride hard coating-substrate and hard coating-interlayer-substrate systems. The interlayers can act as barrier layers improving corrosion resistance. The nitride hard coatings are deposited by various physical vapor deposition methods and the interlayers by electrochemical or physical vapor deposition.

Stress in nickel electrodeposits charged with hydrogen is found to be extremely sensitive to small amounts of Pd2+ in the electrolyte. Measurement of mechanical stress in the nickel layer provides a calibration for Pd2+ content of the bath in the 0.5-500 ppm range.