ASTM B733-04(2009)
(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 (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 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...
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Designation:B733 −04(Reapproved 2009)
Standard Specification for
Autocatalytic (Electroless) Nickel-Phosphorus Coatings on
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.Anumber 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 U.S. Department of Defense.
1. Scope bondability, increased electrical conductivity, and resistance to
strong alkali solutions.
1.1 This specification covers requirements for autocatalytic
(electroless) nickel-phosphorus coatings applied from aqueous 1.8 Themediumphosphorouscoatings(5to9%P)aremost
widely used to meet the general purpose requirements of wear
solutionstometallicproductsforengineering(functional)uses.
and corrosion resistance.
1.2 The coatings are alloys of nickel and phosphorus pro-
1.9 The high phosphorous (more than 10% P) coatings
ducedbyautocatalyticchemicalreductionwithhypophosphite.
have superior salt-spray and acid resistance in a wide range of
Becausethedepositednickelalloyisacatalystforthereaction,
applications.Theyareusedonberylliumandtitaniumpartsfor
the process is self-sustaining. The chemical and physical
low stress properties. Coatings with phosphorus contents
properties of the deposit vary primarily with its phosphorus
greater than 11.2% P are not considered to be ferromagnetic.
content and subsequent heat treatment. The chemical makeup
oftheplatingsolutionandtheuseofthesolutioncanaffectthe
1.10 The values stated in SI units are to be regarded as
porosity and corrosion resistance of the deposit. For more
standard.
details, see ASTM STP 265 (1) and Refs (2)(3)(4) and (5).
1.11 Thefollowingprecautionarystatementpertainsonlyto
1.3 The coatings are generally deposited from acidic solu-
the test method portion, Section 9, of this specification.This
tions operating at elevated temperatures.
standard does not purport to address all of the safety concerns,
if any, associated with its use. It is the responsibility of the user
1.4 The process produces coatings of uniform thickness on
of this standard to establish appropriate safety and health
irregularly shaped parts, provided the plating solution circu-
practices and determine the applicability of regulatory limita-
lates freely over their surfaces.
tions prior to use.
1.5 The coatings have multifunctional properties, such as
hardness, heat hardenability, abrasion, wear and corrosion
2. Referenced Documents
resistance, magnetics, electrical conductivity provide diffusion
2.1 ASTM Standards:
barrier, and solderability.They are also used for the salvage of
B368Test Method for Copper-AcceleratedAceticAcid-Salt
worn or mismachined parts.
Spray (Fog) Testing (CASS Test)
1.6 The low phosphorus (2 to 4% P) coatings are microc-
B374Terminology Relating to Electroplating
rystalline and possess high as-plated hardness (620 to 750 HK
B380Test Method for Corrosion Testing of Decorative
100). These coatings are used in applications requiring abra-
Electrodeposited Coatings by the Corrodkote Procedure
sion and wear resistance.
B487Test Method for Measurement of Metal and Oxide
Coating Thickness by Microscopical Examination of
1.7 Lower phosphorus deposits in the range between 1 and
Cross Section
3% phosphorus are also microcrystalline. These coatings are
B499Test Method for Measurement of CoatingThicknesses
used in electronic applications providing solderability,
by the Magnetic Method: Nonmagnetic Coatings on
Magnetic Basis Metals
B504Test Method for Measurement of Thickness of Metal-
This specification is under the jurisdiction of ASTM Committee B08 on
lic Coatings by the Coulometric Method
Metallic and Inorganic Coatings and is the direct responsibility of Subcommittee
B08.03 on Engineering Coatings.
Current edition approved Sept. 1, 2009. Published December 2009. Originally
approved in 1984. Last previous edition approved in 2004 as B733–04. DOI: For referenced ASTM standards, visit the ASTM website, www.astm.org, or
10.1520/B0733-04R09. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
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
B733−04 (2009)
B537Practice for Rating of Electroplated Panels Subjected G85Practice for Modified Salt Spray (Fog) Testing
to Atmospheric Exposure
2.2 Military Standards:
B567Test Method for Measurement of Coating Thickness
MIL-R-81841Rotary Flap Peening of Metal Parts
by the Beta Backscatter Method
MIL-S-13165Shot Peening of Metal Parts
B568Test Method for Measurement of Coating Thickness
MIL-STD-105Sampling Procedures and Tables for Inspec-
by X-Ray Spectrometry
tion by Attribute
B571Practice for Qualitative Adhesion Testing of Metallic
2.3 ISO Standards:
Coatings
ISO 4527 Autocatalytic Nickel-Phosphorus Coatings—
B578TestMethodforMicrohardnessofElectroplatedCoat-
Specification and Test Methods
ings
B602Test Method for Attribute Sampling of Metallic and
3. Terminology
Inorganic Coatings
3.1 Definitions:
B667Practice for Construction and Use of a Probe for
3.1.1 significant surfaces—those substrate surfaces which
Measuring Electrical Contact Resistance
the coating must protect from corrosion or wear, or both, and
B678Test Method for Solderability of Metallic-Coated
that are essential to the performance.
Products
B697Guide for Selection of Sampling Plans for Inspection
3.2 Other Definitions—Terminology B374 defines most of
of Electrodeposited Metallic and Inorganic Coatings
the technical terms used in this specification.
B762Test Method of Variables Sampling of Metallic and
Inorganic Coatings 4. Coating Classification
B849Specification for Pre-Treatments of Iron or Steel for
4.1 The coating classification system provides for a scheme
Reducing Risk of Hydrogen Embrittlement
to select an electroless nickel coating to meet specific perfor-
B850GuideforPost-CoatingTreatmentsofSteelforReduc-
mancerequirementsbasedonalloycomposition,thicknessand
ing the Risk of Hydrogen Embrittlement
hardness.
B851Specification for Automated Controlled Shot Peening
4.1.1 TYPE describes the general composition of the de-
of MetallicArticles Prior to Nickel,Autocatalytic Nickel,
positwithrespecttothephosphoruscontentandisdividedinto
or Chromium Plating, or as Final Finish
fivecategorieswhichestablishdepositproperties(seeTable1).
D1193Specification for Reagent Water
NOTE 1—Due to the precision of some phosphorus analysis methods a
D2670Test Method for Measuring Wear Properties of Fluid
deviation of 0.5% has been designed into this classification scheme.
Lubricants (Falex Pin and Vee Block Method)
Rounding of the test results due to the precision of the limits provides for
D2714Test Method for Calibration and Operation of the
aneffectivelimitof4.5and9.5%respectively.Forexample,coatingwith
Falex Block-on-Ring Friction and Wear Testing Machine
a test result for phosphorus of 9.7% would have a classification ofTYPE
V, see Appendix X5, Alloy TYPEs.
D3951Practice for Commercial Packaging
D4060Test Method for Abrasion Resistance of Organic
4.2 Service Condition Based on Thickness:
Coatings by the Taber Abraser
4.2.1 Serviceconditionnumbersarebasedontheseverityof
E60Practice for Analysis of Metals, Ores, and Related
the exposure in which the coating is intended to perform and
Materials by Spectrophotometry
minimum coating thickness to provide satisfactory perfor-
E140Hardness Conversion Tables for Metals Relationship
mance (see Table 2).
Among Brinell Hardness, Vickers Hardness, Rockwell
4.2.2 SC0 Minimum Service, 0.1 µm—This is defined by a
Hardness, Superficial Hardness, Knoop Hardness, Sclero-
minimum coating thickness to provide specific material prop-
scope Hardness, and Leeb Hardness
erties and extend the life of a part or its function.Applications
E156Test Method for Determination of Phosphorus in
include requirements for diffusion barrier, undercoat, electrical
High-Phosphorus Brazing Alloys (Photometric Method)
conductivity and wear and corrosion protection in specialized
(Withdrawn 1993)
environments.
E352TestMethodsforChemicalAnalysisofToolSteelsand
Other Similar Medium- and High-Alloy Steels
F519Test Method for Mechanical Hydrogen Embrittlement
Evaluation of Plating/Coating Processes and Service En-
AvailablefromStandardizationDocumentsOrderDesk,Bldg.4SectionD,700
vironments
Robbins Ave., Philadelphia, PA 19111-5094, Attn: NPODS.
G5Reference Test Method for Making Potentiodynamic
Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
4th Floor, New York, NY 10036, http://www.ansi.org.
Anodic Polarization Measurements
G31Guide for Laboratory Immersion Corrosion Testing of
Metals TABLE 1 Deposit Alloy Types
G59TestMethodforConductingPotentiodynamicPolariza-
Type Phosphorus % wt
tion Resistance Measurements
I No Requirement for Phosphorus
II 1to3
III 2to4
IV 5to9
The last approved version of this historical standard is referenced on V 10 and above
www.astm.org.
B733−04 (2009)
TABLE 2 Service Conditions
4.3.4 Class 4—Heat treatment at 120 to 130°C for at least 1
Coating Thickness Requirements
h to increase adhesion of heat-treatable (age-hardened) alumi-
Minimum Coating
num alloys and carburized steel (see Note 3).
Service Condition Thickness µm in.
4.3.5 Class 5—Heat treatment at 140 to 150°C for at least 1
Specification
h to improve coating adhesion for aluminum, non age-
SC0 Minimum Thickness 0.1 0.000004
SC1 Light Service 5 0.0002 hardened aluminum alloys, copper, copper alloys and beryl-
SC2 Mild Service 13 0.0005
lium.
SC3 Moderate Service 25 0.001
4.3.6 Class 6—Heat treatment at 300 to 320°C for at least 1
SC4 Severe Service 75 0.003
h to improve coating adhesion for titanium alloys.
NOTE 3—Heat-treatable aluminum alloys such as Type 7075 can
undergo microstructural changes and lose strength when heated to over
4.2.3 SC1 Light Service,5µm—This is defined by a
130°C.
minimum coating thickness of 5 µm for extending the life of
the part. Typical environments include light-load lubricated
5. Ordering Information
wear, indoor corrosion protection to prevent rusting, and for
5.1 The following information shall be supplied by the
soldering and mild abrasive wear.
purchaser in either the purchase order or on the engineering
4.2.4 SC2 Mild Service,13µm—This is defined by mild
drawing of the part to be plated:
corrosion and wear environments. It is characterized by indus-
5.1.1 Title,ASTM designation number, and year of issue of
trial atmosphere exposure on steel substrates in dry or oiled
this specification.
environments.
5.1.2 Classification of the deposit by type, service
4.2.5 SC3 Moderate Service,25µm—This is defined by
condition, class, (see 4.1, 4.2 and 4.3).
moderate environments such as non marine outdoor exposure,
5.1.3 Specify maximum dimension and tolerance
alkali salts at elevated temperature, and moderate wear.
requirements, if any.
4.2.6 SC4 Severe Service,75µm—This is defined by a very
5.1.4 Peening, if required (see 6.5).
aggressive environment. Typical environments would include
5.1.5 The tensile strength of the material in MPa (see 6.3.1
acid solutions, elevated temperature and pressure, hydrogen
and 6.6).
sulfide and carbon dioxide oil service, high-temperature chlo-
5.1.6 Stress relief heat treatment before plating, (see 6.3).
ride systems, very severe wear, and marine immersion.
5.1.7 Hydrogen Embrittlement Relief after plating, (see
NOTE 2—The performance of the autocatalytic nickel coating depends
6.6).
to a large extent on the surface finish of the article to be plated and how
5.1.8 Significantsurfacesandsurfacesnottobeplatedmust
it was pretreated. Rough, non uniform surfaces require thicker coatings
be indicated on drawings or sample.
than smooth surfaces to achieve maximum corrosion resistance and
minimum porosity.
5.1.9 Supplemental or Special Government Requirements
such as, specific phosphorus content, abrasion wear or corro-
4.3 Post Heat Treatment Class—The nickel-phosphorus
sion resistance of the coating, solderability, contact resistance
coatings shall be classified by heat treatment after plating to
and packaging selected from Supplemental Requirements.
increase coating adhesion and or hardness (see Table 3).
5.1.10 Requirement for a vacuum, inert or reducing atmo-
4.3.1 Class 1—As-deposited, no heat treatment.
sphere for heat treatment above 260°C to prevent surface
4.3.2 Class 2—Heat treatment at 260 to 400°C to produce a
oxidation of the coating (see S3).
minimum hardness of 850 HK100.
5.1.11 Test methods for coating adhesion, composition,
4.3.3 Class 3—Heat treatment at 180 to 200°C for 2 to 4 h
thickness, porosity, wear and corrosion resistance, if required,
to improve coating adhesion on steel and to provide for
selected from those found in Section 9 and Supplemental
hydrogen embrittlement relief (see section 6.6).
Requirements.
5.1.12 Requirements for sampling (see Section 8).
TABLE 3 Classification of Post Heat Treatment
NOTE 4—The purchaser should furnish separate test specimens or
Temperature
CLASS Description Time (h)
couponsofthebasismetalfortestpurposestobeplatedconcurrentlywith
(°C)
the articles to be plated (see 8.4).
1 No Heat Treatment, As Plated
2 Heat Treatment for Maximum Hardness
TYPE I 260 20
6. Materials and Manufacture
285 16
320 8 6.1 Substrate—Defectsinthesurfaceofthebasismetalsuch
400 1
as scratches, porosity, pits, inclusions, roll and die marks, laps,
TYPE II 350 to 380 1
cracks, burrs, cold shuts, and roughness may adversely affect
TYPE III 360 to 390 1
the appearance and performance of the deposit, despite the
TYPE IV 365 to 400 1
TYPE V 375 to 400 1
observance of the best plating practice. Any such defects on
3 Adhesion on Steel 180 to 200 2 to 4
significant surfaces shall be brought to the attention of the
4 Adhesion, Carburized Steel and 120 to 130 1 to 6
Age Hardened Aluminum purchaserbeforeplating.Theproducershallnotberesponsible
5 Adhesion on Beryllium and 140 to 150 1 to 2
for coatings defects resulting from surface conditions of the
Aluminum
metal, if these conditions have been brought to the attention of
6 Adhesion on Titanium 300–320 1–4
the purchaser.
B733−04 (2009)
6.2 Pretreatment—Asuitable method shall activate the sur- purchaser. Guide B850 contains a list of post treatments,
faceandremoveoxideandforeignmat
...
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