GPS3117-1 (Honeywell), HP4-90 (Boeing), M7019883 (Honeywell), EMS52545 (Allied Engines)

The plating of components with electroless or autocatalytic nickel is one of the most rapidly developing metal finishing processes. The advantages of coating uniformity, corrosion resistance and hardness are providing designers with opportunities to protect and improve base materials in ways that were not previously possible.

Plating by autocatalyctic method gives allover, uniform-thickness plating.	Electrolytic method gives uneven deposit with build-up on shoulders and very little thickness inside bore.

Simply, autocatalytic nickel plating is a process for depositing a nickel alloy relying on chemical rather than electrical energy. This enables a totally uniform deposit to be applied to a component without the "throwing power" problems usually encountered during conventional electroless nickel plating. A by-product of the chemical reduction process is phosphorous which is found in the deposit at concentrations of between 2-14 weight percent. This nickel-phosphorous alloy is in a microcrystalline or amorphous state when deposited, with hardness of about 550 VPN. Heat treatment of the coating allows re-crystallization of the nickel, together with precipitation of the phosphorous as Nip, increasing the hardness up to 1000 VPN, i.e. equivalent to hard chromium plate.

In addition to the benefits mentioned above, the autocatalytic nickel coating confers a degree of lubricity on the component, enhancing the coating’s suitability for pumps, compressors, pistons, brake cylinders and hydraulic components. The precise uniformity of the deposit enables the coating to be utilized as a true finishing process, with no post plate grinding or polishing required after plating.

Further advantages in performance can be accrued by plating a composite coating consisting of an autocatalytic nickel matrix containing second phase particles that impart additional advantageous properties. Of the second phase particles available, the most interesting is Polytetrafluoroethylene - or PTFE. This is a very slippery polymer, chemically inert and capable of continuous operation at temperatures up to 290 degrees C or under cryogenic conditions. The autocatalytic nickel matrix provides an ideal supporting medium for the approximately 25 volume per cent of rather soft submicron particles of PTFE. As the composite surface is slowly worn away during operation, so more PTFE rich coating is exposed to the wearing surface, providing a continuous supply of solid lubricant to the critical areas.

AUTOCATALYTIC
NICKEL/PTFE PLATING PROCESS FOR LOW FRICTION SURFACES

Heat treatment is possible to either sinter the PTFE in the coating, or additionally to increase the matrix nickel-phosphorous hardness to the values mentioned above.

Substantial improvements in performance have been noted in components coated with the composite, in some cases the introduction of the composite has made previously impossible processes, viable.

COMPOSITE COATINGS-ELECTROLESS NICKEL/PTFE PIN AND RING WEAR TESTS
Pin Material: Ni/PTFE 250 Hv Bulk Hardness
Heat Treatment at 300 degrees C., 4 hours gives bulk hardness of 400 Hv.
Ring Material: Chromium Steel
non-heat treated wear rate
=4 x 10-5 mm 3/minute Coeff.of friction 0.2-0.3 Heat Treated wear rate.
=2 x 10-5 mm 3/minute Coeff.of friction 0.2-.05
Ring Material: Ni/PTFE Composite
Non-heat treated wear rate
=1 x 10-6 mm 3/minute Coeff.of friction 0.1-.0.2
Heat Treated wear rate
=2 x 10-6 mm 3/minute Coeff.of friction 0.1-0.7

DATA SHOWN ARE AVERAGE VALUES OR AVERAGE RANGES AND SHOULD NOT BE USED FOR SPECIFICATIONS.