Conversion coating

Abstract: Concentrates containing (a) an hydroxylamine sulfate accelerator, and (b) zinc, nickel, manganese, and phosphate ions are formulated into aqueous coating solutions for treating metal surfaces, such as ferrous, zinc, and aluminum surfaces. In the process of using this solution, hydroxylamine ions become depleted or reduced in concentration in the applied solution. A replenishing solution is added for reusing the solution until the replenished coating solution reaches a sulfate level of no more than 14 g/l.

Abstract: The sUlface properties of structural components have a strong influence on their behaviour. In many cases such components are stressed in the surface region by a combination of mechanical, tribological, corrosive, and thermal factors. Under these circumstances, deposition of composite coatings can provide effective surface protection. Deposits can be coated on steel, light metals, ceramics, plastics, and other materials. Composite coatings consist of a metal matrix with, in general, non-metal solid particles or short fibres. The most important coating processes are electrochemical or electro less plating and thermal spraying. This paper reviews the manufacture, properties, and applications of composite coatings and summarises new developments in this field. Fine particles with diameters less than 100 nm are available and are investigated in connection with electroplating experiments. Thermal sprayed aluminium composite coatings on light metals have been manufactured and evaluated. Finally, thermal...

Abstract: In single layer coatings, pores and other coating defects are likely to grow all through the coating. In multilayer coatings, however, the repetitive renucleation reduces the possibility that pores and defects grow that large. It is conceivable that this would, in turn, obstruct diffusion through the coating, thus reducing, e.g., oxidation and hydriding of the underlying substrate. The protective function of five different coatings consisting of ordered stackings of Ti and TiN and one TiN single layer coating (reference), deposited on Zircaloy-4 (Zr-4), were evaluated by means of an autoclave test in pure water at 360°C and 220 bars for 200 days. The oxidation of coated samples was much lower than for uncoated Zr-4. Two different oxidation phenomena were observed. One corresponding to formation of surface oxides and, secondly, a far more serious oxidation in the coating—substrate interface. It is shown that coatings containing many sublayers are more capable in avoiding both of these oxidation phenomena. The uptake of hydrogen was shown to be much lower for coated Zr-4 than for uncoated Zr-4.