ASTM B733-22

Annotation of standard text ASTM B733-22 :

This specification establishes the requirements for autocatalytic (electroless) nickel-phosphorus coatings applied from acidic aqueous solutions to metallic products for use in engineering functions operating at elevated temperatures. The coatings covered here are alloys of nickel and phosphorus produced by self-sustaining autocatalytic chemical reduction with hypophosphite. The coatings are grouped into the following classification systems: types, which are based on the general composition with respect to phosphorus; service condition numbers, which are based on the severity of exposure to which the coating is intended to perform and the corresponding minimum thickness that will provide satisfactory performance; and post heat treatment class, which are based on post-plating heat treatment temperature and time to produce the desired adhesion and hardness improvements. Prior to plating, substrates should be pretreated by stress relief for reducing risks of hydrogen embrittlement, peening, and racking. The coatings shall be sampled and tested accordingly to evaluate both acceptance (appearance, thickness, adhesion, and porosity) and qualification requirements (composition, microhardness, and hydrogen embrittlement). Thickness shall be assessed either by microscopical method, a magnetic induction instrument, beta backscatter method, a micrometer, weigh-plate-weigh method, coulometric method, or X-ray spectrometry. Adhesion shall be examined either by bend, impact, or thermal shock tests. And porosity shall be inspected either by ferroxyl test, boiling water test, aerated water test, or alizarin test.


Keywords:
autocatalytic, chemical nickel, coatings, conductive, corrosion resistance, electroless, functional, nickel, nickel phosphorus, wear resistance,, ICS Number Code 25.220.40 (Metallic coatings)