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1.1 Nickel boron coatings are produced by autocatalytic (electroless) deposition from aqueous solutions. These solutions contain either an alkylamineborane or sodium borohydride as a reducing agent, a source of nickel ions, a buffer, complexant, and control chemicals.
1.2 This specificationdescribes the requirements for coatings of autocatalytic nickel boron deposited from aqueous solutions onto substrates for engineering use. The specification classifies these coatings into two types:
1.2.1 Type 1 coatings have a boron content of 0.1 to less than 3.5 mass percent with the balance nickel.
1.2.2 Type 2 coatings have a boron content of 3.5 to 6 mass percent and a minimum of 90 mass percent nickel.
1.3 The coatings are hard and uniform in thickness, even on irregular shaped parts, and used in a wide range of applications.
1.4 Process solutions formulated with an alkylamineborane usually produce coatings that contain 0.1 to 3.5 % boron. Thin coatings of this type provide bondability and solderability on electronic components such as lead frames, electrical contacts, and headers. To maintain solderability, these coatings are generally not heat treated.
1.5 Process solutions formulated with sodium borohydride are strongly alkaline and are frequently used to plate steel and titanium parts to impart surface hardness and wear resistance properties. Deposits produced from these processes can contain 3 to 5 % boron and thallium or other metals which are used to stabilize the plating solution and modify the coating properties.
1.6 The physical and mechanical properties of these deposits such as density, hardness, stress, and melting point will vary with the boron content. The variation of boron content also affects the quantity and structure of nickel boride precipitated during heat treatment. In the as-plated condition the deposit consists of a predominantly amorphous mixture of nickel and boron with a hardness of about 700 HKN. When the deposit is heated above 300°C the nickel crystallizes, forming nickel clusters of Ni (111) and boron precipitates as nickel boride, Ni3B (211) and (311), increasing the hardness to greater than 1000 HK100 for Type 2 coatings.
1.7 The nickel boron coatings are microporous and offer limited corrosion protection. Their columnar structure, however, is beneficial in reducing wear because it provides a means of trapping lubricants within the surface of the coated part.
1.8 This document describes only autocatalytic nickel boron coatings that have been produced without use of external electric sources.
1.9 The following hazards caveat pertains only to the Test Methods section of this specification: This standard does not purport to address the safety problems associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Note 1—The following AMS standards are not requirements. They are referenced for information only: AMS 2399 and AMS 2433. X2.1.1 This test method will evaluate the resistance of the coating to abrasive wear. The test is performed on a rotating plated panel that is abraded by two rotating rubber wheels. The panel is weighed before and after each 1000 cycles for weight loss determination. Duration of the test is 5000 cycles and it can be extended to 25 000 cycles. Note X2.1—Variations in results have been attributed to the humidity in the laboratory and the storage conditions of the CS-10 wheels. Care should be taken to control the humidity between tests as recommended by the equipment manufacturer.
Note 1—The following AMS standards are not requirements. They are referenced for information only: AMS 2399 and AMS 2433.
X2.1.1 This test method will evaluate the resistance of the coating to abrasive wear. The test is performed on a rotating plated panel that is abraded by two rotating rubber wheels. The panel is weighed before and after each 1000 cycles for weight loss determination. Duration of the test is 5000 cycles and it can be extended to 25 000 cycles.
Note X2.1—Variations in results have been attributed to the humidity in the laboratory and the storage conditions of the CS-10 wheels. Care should be taken to control the humidity between tests as recommended by the equipment manufacturer.
X2.1.2 The results are variable between tests and therefore three plated test specimens should be tested to 6000 cycles each. The results should be averaged without the first 1000 cycles and the abrasion wear resistance reported.
2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.
B374 Terminology Relating to Electroplating
B487 Test Method for Measurement of Metal and Oxide Coating Thickness by Microscopical Examination of Cross Section
B567 Test Method for Measurement of Coating Thickness by the Beta Backscatter Method
B568 Test Method for Measurement of Coating Thickness by X-Ray Spectrometry
B571 Practice for Qualitative Adhesion Testing of Metallic Coatings
B578 Test Method for Microhardness of Electroplated Coatings
B602 Test Method for Attribute Sampling of Metallic and Inorganic Coatings
B656 Guide for Autocatalytic (Electroless) Nickel-Phosphorus Deposition on Metals for Engineering Use (Discontinued 2000)
B667 Practice for Construction and Use of a Probe for Measuring Electrical Contact Resistance
B678 Test Method for Solderability of Metallic-Coated Products
B697 Guide for Selection of Sampling Plans for Inspection of Electrodeposited Metallic and Inorganic Coatings
B762 Test Method of Variables Sampling of Metallic and Inorganic Coatings
D2670 Test Method for Measuring Wear Properties of Fluid Lubricants (Falex Pin and Vee Block Method)
D2714 Test Method for Calibration and Operation of the Falex Block-on-Ring Friction and Wear Testing Machine
E39 Methods for Chemical Analysis of Nickel
F519 Test Method for Mechanical Hydrogen Embrittlement Evaluation of Plating/Coating Processes and Service Environments
Aerospace Materials SpecificationsAMS2433 Electroless Nickel-Thallium-Boron Plating
U.S. Government StandardsMIL-STD-13165 Shot Peening of Metal Parts
ICS Number Code 25.220.40 (Metallic coatings)