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Electroless Nickel |
[AMS-2404C,
AMS-2405B, AMS-2433B]
Previously
Mil-C-26074. Coatings typically
used to provide a hard-ductile, wear-resistant and corrosion-resistant
surface for operation in service temperatures up to 1000°F
(538°C).
Electroless nickel plating provides uniform build-up on complex
shapes.
Electroless nickel
plating, also known
as chemical or autocatalytic nickel plating. In contrast to the
electroplating
technique, electroless (chemical)
nickel plating
baths work without
an external current source. The plating operation is based upon the
catalytic
reduction of nickel ions on the surface being plated.
There are 3 main
types of electroless
nickel coatings:
1.
nickel-phosphorus
2.
nickel-boron
3. poly
alloys
Nickel-phosphorus
is generally used
for engineering applications. The most widely used electroless nickel
is
deposited by the catalytic reduction of nickel ions with sodium hypo-
phosphite
in acid baths at pH 4,5ñ5,0, and at a temperature of
85ñ95°C.
The deposits contains typically 3 to 13% phosphorus by weight. The
alloy
obtained is dependent upon the chemical
composition of the
solution and the
operating conditions. The phosphorus content significantly influences
its
chemical and physical properties in both the as-plated condition and
after
heat treatment. A distinction is made between three variants:
1.
Phosphorus content between
3 and 7%. These coatings have excellent high wear resistance. Excellent
corrosion resistance in concentrated caustic soda.
2.
Phosphorus content between
9 and 12%. Corrosion protection and abrasion resistance are good enough
for most applications. The plating
bath works
particularly economically.
3.
Phosphorus content between
10 and 13%. The coatings are very ductile and corrosion resistant. They
fulfil the highest demands for corrosion
resistance against
chlorides and simultaneous
mechanical stress.
Nickel-boron is
very often used in
industrial wear applications for its as-plated hardness which is higher
than that of nickel-phosphorus. The boron content can be varied from
0.1
to 10%. The re- ducing agent used is dimethylamine boron or sodium
borohydride
depending on the desired alloy composition.
More
extensive reading.
Technical
Data Table. |
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