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Specs for Electroless Nickel
Here are the applicable specifications:
MIL-C-26074E
Use when hard and smooth surfaces are required on coated parts. Excellent uniform deposits are produced on irregular parts, such as used in air compressors, missile fuel injector plates, pumps, reciprocating surfaces, etc., are protected from oxidation, corrosion and wear. With aluminum electronic devices, not only is product contamination prevented, but the coated parts of stainless steel similarly facilitate brazing.
Hydrogen embrittlement relief bake. Within 4 hours after coating, coated Class 1 and 2 steel parts which have a hardness of RC 40 or above shall require a bake at 375°C ±25°F for not less than 3 hours.
Heat treatments. Class 2 hardness coatings. Shall have a minimum hardness of 800 Knoop or equivalently. The hardness can be achieved by heating the part per schedule given in the specification.
Class 3 hardness coatings. Coated nonheat-treatable aluminum parts shall be heated for 1 to 1-1/2 hours at 375°F±15°F (191°C±8°C) to improve adhesion of nickel.
Class 4 coatings. Coated heat-treatable aluminum alloys shall be heated between 240°C to 260°F (116°C to 127°C) for 1 to 1-1/2 hours to improve adhesion of nickel.
Stress relief heat treatment. Coating all parts of RC 40 or above, which have been machined, ground or surface hardened (includes cold worked but not shot peened surfaces), shall be given a stress-relief heat treatments at a temperature that will produce maximum stress relief without reducing hardness to less than specified minimum.
Shot peening. All steel parts of RC40 or above used in fatigue applications and/or subject to stress or corrosion shall be shot peened in accordance with ML-S-13165.
| Type Class | Thickness | Comments |
| Class 1 | As plated, no subsequent heat treatment. A bake for hydrogen embrittlement relief is not considered a heat treatment. | |
| Class 2 | Heat treated to obtain required hardness. May be used on all metals not affected by heating to 500°F and above. | |
| Class 3 | Aluminum alloy, nonheat-treatable, and beryllium alloys processed to improve adhesion of the nickel deposit. | |
| Class 4 | Aluminum alloy, heat-treatable, processed to improve the adhesion of the nickel deposit. | |
| Grade A | 0.0010" min | Aluminum alloys. |
| Grade B | 0.0005" min | Copper, nickel, cobalt, titanium and beryllium alloys. |
| Grade C | 0.0015" min | Iron based alloys. |
Coatings used typically to provide uniform buildup on complex shapes, to improve wear and/or corrosion resistance, or to improve solderability on or for selected materials. Can be used to service up to 1000°F (540°C) although wear and/or corrosion resistance may degrade as service temperature increases.
Preparation. Unless otherwise specified, fabrication operations, such as forming, perforating, heat treating, welding and brazing, shall be completed before parts are plated, unless surfaces are plated to aid in joining by brazing. Steel parts having a hardness of 40 HRC or higher and which have been ground after heat treatment shall be cleaned to remove surface contamination and stress relieved before preparation for plating. Unless otherwise specified, the stress relief temperature shall be not lees than 275°F ±25 (135°C ±14) for not less than 4 hours for parts with hardness of 55HRD or greater and not less than 375°F ±25 (191°C ±14) for not less than 4 hours for other parts.
Post Treatment Hydrogen Embrittlement Relief. Class 1 and Class 2 plated steel parts 33 HRC and over bake at 375°F ±15° for 3 hours min. Parts, including carburized parts, deleteriously affected by this temperature shall be heated to 275°F ±25 for 5 hours min. Adhesion shall meet requirements of ASTM B571. Carbon and low alloy steel parts having 0.001" min. coating shall pass 48 hours continuous salt spray corrosion test (per ASTM B117).
| Type Class | Thickness | Comments | |||||||||||||
| Class 1 | as specified on drawing | Except for hydrogen embrittlement relief, no post plating thermal treatment. | |||||||||||||
| Class 2 | Thermal treatment at 450°F (232°C) or above to hardened deposit. Hardness shall not be lower than 800 HK 100 or equivalent.
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| Class 3 | Thermal treatment at 375°F (191°C) to verify adhesion for non-heat-treatable aluminum and beryllium alloys (1 to 1.5 hours). | ||||||||||||||
| Class 4 | Thermal treatment at 250°F (121°C) to verify adhesion for heat-treatable aluminum alloys. | ||||||||||||||
