ISSUE 3

Electroless Nickel: An Engineering Delight

 



Electro-what nickel?”  The name may be confusing, but once you see Electroless Nickel in action, you’ll be impressed.  The more common “electrolytic” nickel plating utilizes an electric charge, known as “electroplating”.  However, Electroless Nickel (EN), is plated without  the use of electricity. 

Formally known as “Hypophosphite Reduced Nickel-Phosphorous Electroless Nickel”, due to its unusual method of application, and unique properties, and is an important finish for many engineering applications.  EN is a metallic glass, and depending on the formulation of the plating solution, commercial coatings may contain 6-12% phosphorus dissolved in nickel, and as much as 0.25% of other elements. 

Many properties of EN make it an excellent choice for many engineering applications:

·   Uniform coating thickness.  Unlike electroplating, EN coating thicknesses are the same on any section of the part exposed to fresh plating solution. 

·   Text Box: Significant “EN” Properties:
•	Uniform Coating
•	Excellent Adhesion
•	High Corrosion Resistance
•	High Lubricity 
•	High Surface Hardness
•	Decorative appearance
Excellent Adhesion to most metals.  The initial replacement reaction with catalytic metals, and the plating bath’s removal of submicroscopic soils, allows the deposit to establish metallic as well as mechanical bonds with the metal substrate yielding bond strengths  of at least 40-60 ksi. 

·   Excellent Corrosion Resistance. EN works as a barrier coating, sealing from attack by the environment, or chemicals, is often a better choice than pure nickel or chromium.  Steel parts plated with EN will exceed 1000 hours of salt spray testing. 

·   Excellent lubricity.  EN deposits, provide excellent frictional properties, making EN useful in applications involving plastic molding tooling and wear applications. 

·   Excellent Surface Hardness, yielding excellent abrasion & wear resistance.  The microhardness of EN is approximately 48-52 HRC and equivalent to many hardened alloy steels.  Heat treatment causes these alloys to age harden and can produce hardness values as high as 100 HV100, equal to most commercial hard chromium coatings.  As EN plated parts are heated above 430-500°F, crystalline structural changes begin to occur, and distinct, particles of nickel phosphite (Ni3P) form within the alloy.  Then, above 610°F the deposit begins to crystallize and lose its amorphous character.  With continued heating, nickel phosphite particles conglomerate and a two-phase alloy forms.  These changes cause a rapid increase in the hardness and wear resistance of the coating, but cause its corrosion resistance and ductility to be reduced. 

Hydrogen Embrittlement Relief:  In cleaning and plating hardened ferrous and other substrates sensitive to embrittlement, careful attention must be given to post-plate H2 embrittlement relief.  Using standard commercial plating standards, the risks caused by H2 embrittlement can be eliminated, which include a waiting period of 24-48 hours after plating before the parts are put under stress.  However, with a low-temperature (less than 400°F) baking procedure, the waiting period can be eliminated. 

 

Phosphorous Content in EN:  Higher phosphorous content increases corrosion resistance.  Lower phosphorous content increased hardness.  The “mid-phos” solution used by InfiniTech gives a good overall blend of properties, plus a decorative finish, and is preferred for most applications.


“You guys did EN samples for us a year ago, and it worked great and to this day the parts look like new.  The EN added lubricity to the threads, and there is no sign of wear, or plating coming off!  - InfiniTech Customer, Star Fiberglass’, Duane Hemphill