ASTM B733-04
(Specification)Standard Specification for Autocatalytic (Electroless) Nickel-Phosphorus Coatings on Metal
Standard Specification for Autocatalytic (Electroless) Nickel-Phosphorus Coatings on Metal
ABSTRACT
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.
SCOPE
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) and Refs (2) (3) (4)and ().
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 barrier, and solderability. 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.
1.8 The medium phosphorous coatings (5 to 9 % P) are most widely used to meet the general purpose requirements of wear and corrosion resistance.
1.9 The high phosphorous (more than 10 % P) coatings have superior salt-spray and acid resistance in a wide range of applications. They are used on beryllium and titanium parts for low stress properties. Coatings with phosphorus contents greater than 11.2 % P are not considered to be ferromagnetic.
1.10 The values stated in SI units are to be regarded as standard.
1.11 The following precautionary statement pertains only to the test method portion, Sec...
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Designation: B733 – 04
Standard Specification for
Autocatalytic (Electroless) Nickel-Phosphorus Coatings on
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Metal
This standard is issued under the fixed designation B733; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope 1.8 Themediumphosphorouscoatings(5to9 %P)aremost
widely used to meet the general purpose requirements of wear
1.1 This specification covers requirements for autocatalytic
and corrosion resistance.
(electroless) nickel-phosphorus coatings applied from aqueous
1.9 The high phosphorous (more than 10 % P) coatings
solutionstometallicproductsforengineering(functional)uses.
have superior salt-spray and acid resistance in a wide range of
1.2 The coatings are alloys of nickel and phosphorus pro-
applications.They are used on beryllium and titanium parts for
ducedbyautocatalyticchemicalreductionwithhypophosphite.
low stress properties. Coatings with phosphorus contents
Becausethedepositednickelalloyisacatalystforthereaction,
greater than 11.2 % P are not considered to be ferromagnetic.
the process is self-sustaining. The chemical and physical
1.10 The values stated in SI units are to be regarded as
properties of the deposit vary primarily with its phosphorus
standard.
content and subsequent heat treatment. The chemical makeup
1.11 The following precautionary statement pertains only to
of the plating solution and the use of the solution can affect the
the test method portion, Section 9, of this specification. This
porosity and corrosion resistance of the deposit. For more
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standard does not purport to address all of the safety concerns,
details, see ASTM STP 265 (1) and Refs (2)(3)(4) and (5).
if any, associated with its use. It is the responsibility of the user
1.3 The coatings are generally deposited from acidic solu-
of this standard to establish appropriate safety and health
tions operating at elevated temperatures.
practices and determine the applicability of regulatory limita-
1.4 The process produces coatings of uniform thickness on
tions prior to use.
irregularly shaped parts, provided the plating solution circu-
lates freely over their surfaces.
2. Referenced Documents
1.5 The coatings have multifunctional properties, such as
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2.1 ASTM Standards:
hardness, heat hardenability, abrasion, wear and corrosion
B368 Test Method for Copper-AcceleratedAceticAcid-Salt
resistance, magnetics, electrical conductivity provide diffusion
Spray (Fog) Testing (CASS Test)
barrier, and solderability. They are also used for the salvage of
B374 Terminology Relating to Electroplating
worn or mismachined parts.
B380 Test Method for Corrosion Testing of Decorative
1.6 The low phosphorus (2 to 4 % P) coatings are microc-
Electrodeposited Coatings by the Corrodkote Procedure
rystalline and possess high as-plated hardness (620 to 750 HK
B487 Test Method for Measurement of Metal and Oxide
100). These coatings are used in applications requiring abra-
CoatingThicknessbyMicroscopicalExaminationofCross
sion and wear resistance.
Section
1.7 Lower phosphorus deposits in the range between 1 and
B499 Test Method for Measurement of Coating Thick-
3 % phosphorus are also microcrystalline. These coatings are
nessesbytheMagneticMethod:NonmagneticCoatingson
used in electronic applications providing solderability, bond-
Magnetic Basis Metals
ability, increased electrical conductivity, and resistance to
B504 Test Method for Measurement of Thickness of Me-
strong alkali solutions.
tallic Coatings by the Coulometric Method
B537 Practice for Rating of Electroplated Panels Subjected
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to Atmospheric Exposure
This specification is under the jurisdiction of ASTM Committee B08 on
Metallic and Inorganic Coatings and is the direct responsibility of Subcommittee
B08.08.01 on Engineering Coatings.
Current edition approved Aug. 1, 2004. Published August 2004. Originally
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approved in 1984. Last previous edition approved in 1997 as B733 – 97. DOI: For referenced ASTM standards, visit the ASTM website, www.astm.org, or
10.1520/B0733-04. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
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The boldface numbers given in parentheses refer to a list of references at the Standards volume information, refer to the standard’s Document Summary page on
end of the text. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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B733 – 04
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B567 Test Method for Measurement of Coating Thickness MIL-R-8184
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