Composites and companion coatings

What this section covers

Autocatalytic nickel can carry a second phase. Suspend a powder in the bath and the growing metal layer closes around the particles, giving a deposit that is part nickel-phosphorus and part something else: a fluoropolymer for low friction, a hard ceramic for abrasion resistance. The first two notes cover these two families, what each particle actually contributes, and why some powders codeposit far more easily than others.

The other two notes cover the neighbours. Chromate conversion coating, called chem film in the aluminium industry, is a different chemistry entirely: no metal is deposited, the surface itself is converted into a thin protective film. Abrasive blasting comes earlier still, and decides whether anything downstream adheres.

How to read these notes

Composite deposits are the part of this field where supplier literature is least reliable, because a friction coefficient or a wear figure only means something with its test method, its load and its counterface. The notes give the properties of the particle itself from public sources and are explicit about what cannot be stated as a general number.

Conversion coatings carry a regulatory dimension that plating does not: the classical baths use hexavalent chromium, and that is what the standards and the substitution work are about. The note covers the chemistry and names the standards without pretending to give legal advice.