ASTM B733-04 (R2009) pdf free download.Standard Specification for Autocatalytic (Electroless) Nickel-Phosphorus Coatings on Metal.
1.1 This specification covers requirements for autocatalytic (electroless) nickel-phosphorus coatings applied from aqueous solutions to metallic products for engineering (functional) uses.
1.2 The coatings are alloys of nickel and phosphorus produced by autocatalytic chemical reduction with hypophosphite. Because the deposited nickel alloy is a catalyst for the reaction, the process is self-sustaining. The chemical and physical properties of the deposit vary primarily with its phosphorus content and subsequent heat treatment. The chemical makeup of the plating solution and the use of the solution can affect the porosity and Corrosion resistance of the deposit. For more details, see ASTM STP 265 (1)2 and Refs (2) (3) (4) and (5).
1.3 The coatings are generally deposited from acidic solutions operating at elevated temperatures.
1.4 The process produces coatings of uniform thickness on irregularly shaped parts, provided the plating solution circulates freely over their surfaces.
1.5 The coatings have multifunctional properties. such as hardness, heat hardenability, abrasion, wear and corrosion resistance, magnetics. electrical conductivity provide diffusion harrier, and solderahility. They are also used for the salvage of worn or mismachined parts.
1 .6 The low phosphorus (2 to 4 % P) coatings are microcrystalline and possess high as-plated hardness (620 to 750 HK 100). These coatings are used in applications requiring abrasion and wear resistance.
1.7 Lower phosphorus deposits in the range between 1 and 3 % phosphorus are also microcrystalline. These coatings are used in electronic applications providing solderability. bondability, increased electrical conductivity, and resistance to strong alkali solutions.
3. Terminology
3. 1 Definition.
3. 1. 1 significant surfaces—those substrate surfaces which the coating must protect from corrosion or wear, or both, and that are essential to the performance.
3.2 Other Definitions—Terminology B374 defines most of the technical terms used in this specification.
4. Coating Classification
4.1 The coating classification system provides for a scheme to select an electroless nickel coating to meet specific performance requirements based on alloy composition, thickness and hard ness.
4.1. 1 TYPE describes the general composition of the deposit with respect to the phosphorus content and is divided into five categories which establish deposit properties (see Table 1).
NOTE 1—Due to the precision of some phosphorus analysis methods a deviation of 0.5 % has been designed into this classification scheme. Rounding of the test results due to the precision of the limits provides for an effective limit of 4.5 and 9.5 % respectively. For example. coating with a Lest result for phosphorus of 9.7 % would have a classification of TYPE V. see Appendix X5, Alloy TYPEs.
4.2 Service condition Based on Thickness:
4.2.1 Service condition numbers are based on the severity of the exposure in which the coating is intended to perform and minimum coating thickness to provide satisfactory performance (see Table 2).
4.2.2 SCO Minimum Service, 0.1 pm—This is defined by a minimum coating thickness to provide specific material properties and extend the life of a part or its function. Applications include requirements for diffusion harrier, undercoat, electrical conductivity and wear and corrosion protection in specialized environments.ASTM B733 pdf download.