Mil-Spec: MIL-C-26074E

Similar to stainless steel in color. Plates uniformly in recesses and cavities (without extra build up on edges and high current density areas). Corrosion resistance is good for coatings over .001” thickness. Electroless nickel is used extensively in salvage of mis-machined parts. Also, for inside dimensions and irregular shapes.

Class Comments
1 As plated, no subsequent heat treatment: A bake for hydrogen embrittlement relief is not considered a heat treatment.
2 Heat treated to obtain required hardness: Ma be used on all metals not affected by heating to 500 ° F and above
3 Aluminum alloys nonheat-treatable, and beryllium alloys processed to improve adhesion of the nickel deposit.
4 Aluminum alloys heat-treatable, processed to improve adhesion of the nickel deposit.
Grade Thickness
A 0.0010 – inch minimum thickness
B 0.0005 – inch minimum thickness
C 0.0015 – inch minimum thickness

ASTM Designation: B 733

(Electroless) Nickel-Phosphorus Coatings

The performance of the autocatalytic nickel coating depends to a large extent on the surface finish of the article to be plated and how it was pretreated. Rough, non uniform surfaces require thicker coatings than smooth surfaces to achieve maximum corrosion resistance and minimum porosity

Table 1 Deposit Alloy Types

Type Phosphorus % wt.
I No Requirement for Phosphorus
II 1 to 3
III 2 to 4
IV 5 to 9
V 10 and above

Service Conditions

Coating Thickness Requirements

Service Condition Minimum Coating Thickness SpecificationµMIn.
SC0 Minimum Thickness 0.1 0.000004
SC1 Light Service 5 0.0002
SC2 Mild Service 13 0.0005
SC3 Moderate Service 25 0.001
SC4 Severe Service 75 0.003


4.3 Post Heat Treatment Class – The nickel-phosphorus coatings shall be classified by heat treatment after plating to increase coating adhesion and or hardness.4.3.1 Class I – As deposited, no heat treatment.

4.3.2 Class 2 – Heat treatment at 260 to 400°C to produce a minimum hardness of 850 HK100.

4.3.3 Class 3 – Heat treatment at 280 to 200°C for 2 to 4 h to improve coating adhesion on steel and to provide for hydrogen embrittlement relief.

4.3.4 Class 4 – Heat treatment at 140 to 150°C for at least 1 h to improve coating adhesion for aluminum, non age-hardened aluminum alloys, copper, copper alloys and beryllium

Stress relief heat treatment:
Prior to cleaning and coating, all steel parts having a hardness of Rockwell c40 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 treatment.

Shot peening:
Prior to coating, all steel parts having a hardness of Rockwell C40 or above used in fatigue applications and/or subject to stress corrosion shall be shot peened in accordance with MIL-S-13165.

Unless otherwise specified, minimum thickness of the nickel coating shall be 0.0010 inch (0.026 mm) (grade A) for aluminum based alloys, 0.0005 inch (0.013 mm) (grade B) for copper, nickel, cobalt, titanium and beryllium alloys, and 0.0015 inch (0.039 mm) (grade C) for iron-based alloys.

Hydrogen embrittlement relief back:
Within 4 hours after coating, coasted class 1 and class 2 steel parts that have a hardness of Rockwell C40 or above shall require a hydrogen embrittlement relief bake.