ASTM B994 Nickel Cobalt Plated Fasteners
ASTM B994 specification describes the requirements for corrosion-resistant coatings of electrodeposited nickel-cobalt on metallic substrates and electrodeposited nickel-cobalt used for electroforming. The nickel-cobalt alloy is principally deposited as a coating on Fasteners. It can also be electrodeposited on iron, stainless steel, aluminum, titanium and other Fasteners. The nickel-cobalt alloy coating has a low coefficient of friction of 0.08 that provides a dry lubricant on Bolt & Nut threads that are in contact with each other and are subject to galling. The coating thickness ranges from 5 to < 30 μm, and it can be applied to machined threaded parts, fasteners, etc. The deposit can also be used to electroform parts requiring high strength with the alloy being maintained at 50% nickel-cobalt.
The coatings of nickel-cobalt have been classified as follows: service condition by thickness, class by test methods required, and type by secondary treatments.
(SC)-This number signifies the thickness requirement based on the type of environment and desired mechanical properties.
NOTE 3-The 50% NiCo alloy produces a high strength alloy that is used in electroforming to manufacture parts. These deposits can be used at various thicknesses ranging from 1 µm to hundreds of microns.
- SC5 signifies that the application is slightly corrosive and that a minimum 5 µm of coating is sufficient for protection and to provide the mechanical properties.
- SC12 signifies that the application is mildly corrosive and that a minimum 12 µm of coating is sufficient to protect against corrosion and provide the mechanical properties.
- SC18 signifies that the application is corrosive and that a minimum of 18 µm of coating is sufficient to protect against corrosion and provide the mechanical properties.
- SC25 signifies that the application is corrosive and that a minimum 25 µm of coating is sufficient to protect against corrosion and provide the mechanical properties.
- ASTM B994 Class - This number signifies the type and frequency of testing and monitoring programs that are used to control the process.
- ASTM B994 Class 1 - Incorporates these standard tests: Galling , Composition , Test Methods F519 and B368, and Practices B117 and G85.
- ASTM B994 Class 2 - Incorporates these standard tests: Composition , Test Methods F519 and B368, and Practices B117 and G85.
- ASTM B994 Class 3 - Incorporates these standard tests: Composition and Practice B117.
- Class 4-Incorporates the standard test of composition.
ASTM B994 Type - This number signifies the type of secondary treatment applied after the coating to modify the surface properties.
- ASTM B994 Type - This number signifies the type of secondary treatment applied after the coating to modify the surface properties.
- ASTM B994 Type 0 coatings are not treated with any supplemental coatings.
- ASTM B994 Type 1 coatings are treated with a material to secure the coating to itself.
- ASTM B994 Type 2 coatings are treated with a material to reduce the friction between coated surfaces
The coatings shall be nickel-cobalt alloy produced by electrodeposition. The nickel shall be in the range of 43 to 61% and the cobalt shall be in the range of 39 to 57%.
This coating shall be applied to the significant surface to the desired minimum thickness of the service condition.
The coating shall meet all applicable requirements as established in the purchase order in accordance with Section.
These tests are performed on the process to ensure the system is capable of meeting the coating requirements by class. These tests shall be performed on SC25, Type 0 coupons at a frequency established in subsection based on the class.
- Galling Test
- The producer shall perform the galling test in accordance with the procedures established in Appendix X1. The producer shall prepare the finishing lot galling report and shall demonstrate that loaded specimens will pass 608 days of evaluation with the torque ration of less than 2.5.
- Chemical Composition
- The nickel-cobalt alloy composition shall be measured quarterly or more frequently as specified using Test Method E2465 or other elemental analysis methods that can be demonstrated to meet precision and bias requirements of better than 1% mass weight.
- Hydrogen Embrittlement Test
- The producer shall perform quarterly, or more frequently, the procedure outlined in Test Method F519 by processing a set of four standard 1a specimens. They shall pass Test Method F519 criteria of no failure after 200 hours at 75% UTS.
- Corrosion Testing
- Electrochemical Corrosion Rate - The nickel-cobalt alloy coated article shall have a corrosion rate of less than 0.8636 µm/y when tested under Test Method G59. Corrosion rate shall be calculated in accordance with Practice G102. The test solution shall be prepared by dissolving 5 6 1 parts by mass of sodium chloride in 95 parts of water conforming to Type IV water in Specification D1193 (except that for this practice, limits for chlorides and sodium may be ignored). Careful attention should be given to the chemical content of the salt.
The salt used shall be sodium chloride with not more than 0.3 % by mass of total impurities. Halides (bromide, fluoride, and iodide) other than chloride shall constitute less than 0.1 % by mass of the salt content. Copper content shall be less than 0.3 ppm by mass. Sodium chloride that has had anti-caking agents added shall not be used because such agents may act as corrosion inhibitors. The level of pH shall be equal to 6.5 to 7.2, temperature 25 6 3° C, with atmospheric pressure and static conditions. The frequency of this shall be quarterly unless the purchaser specifies an increased frequency.
- Environmental Testing
- The producer shall evaluate the process corrosion protection by performing Test Method B368 on test coupons quarterly or more frequently as required. Panels processed to SC25 shall not show any red rust before 120 hours of exposure
- Salt Spray (Fog) Test
- The producer shall evaluate the process corrosion protection of the nickel-cobalt alloy by Practice B117 quarterly or more frequently as specified. Panels processed to SC25 shall pass with no red rust before 500 hours of exposure to salt spray (fog) as outlined in Practice B117.
- Modified Salt Spray (Fog) Test
- The producer shall evaluate the process corrosion protection of the nickel-cobalt alloy by Test Method G85 (A2 cyclic acidified salt fog testing) quarterly or more frequently as specified. Coupons processed to SC25 shall pass with no red rust before 200 hours of exposure to the Test Method G85 testing.
- Third Party Reports
- If a third party is used to perform these qualification tests, the test report shall include: Testing laboratory name, name and signature of person responsible for the test, location, list of equipment, current calibration certificates, and required permits for operating equipment (x-ray).
- Frequency of Qualification Tests
- The maintenance of a process requires frequent testing to ensure the quality is maintained and to instruct the operators in good practice to ensure good workmanship at all times. Table 1 shall be used to establish the maximum frequency for qualification testing of the process by class.