Electro and electroless plates
Because they are very
similar to hard chrome plating, alternative plating
materials are often adopted as hard chrome alternatives.
The most common are electroless Ni coatings – either
electroless Ni-P (the most common electroless Ni coating) or
Ni-B (which is a little harder and less widely available).
These coatings are commonly used in aircraft engines
(primarily Ni-B) and some landing gear and actuators
(primarily Ni-P).
-
As-deposited these coatings are somewhat
softer and less wear-resistant than hard chrome.
-
They can be hardened considerably by heat
treating, but the temperature required is well above the
375°F (190°C) allowed for high strength steels.
However, heat treating reduces their corrosion
resistance.
-
They are excellent for complex shapes and
internals since they do not require electric fields as
electroplates do.
-
They work well for small components but
often have adhesion problems on large components.
-
Older formulations were self-limiting in
thickness but some modern formulations can now be built
to high thickness (several mils or tens of microns)
-
Electroless Ni plating solutions require
more care than chrome plating solutions since they
require a delicate balance between holding the Ni in
solution and allowing to plate out on anything placed
into the plating bath
RoHS compliance: Note
that electroless Ni-B usually has either lead or thallium in
the solution, and they tend to plate out with the Ni. Both
Pb and Tl are heavy metal poisons and any electroless Ni-B
containing Pb is likely not to be RoHS compliant.
Integran Technologies of
Toronto has developed a new nanophase Co-based coating using
pulse electroplating. Developed for DoD under SERDP
funding, it is now being validated under ESTCP funding at
NADEP Jacksonville.
[ref to materialoptions]
Hard chrome alternatives
summary – electroplates and electroless coatings (primary
alternatives in blue, technologies under validation in
yellow)
|
Alternative |
Compliance |
Usage |
Notes |
|
Electroless Ni-P* |
RoHS, WEEE, ELV, OSHA Cr |
Hydraulic cylinder IDs, gun parts, especially
complex shapes, internals |
Must be heat treated for max hardness. |
|
Electroless Ni-B* |
OSHA Cr |
Aircraft engine components |
Harder than Ni-P. Usually contains lead or thallium.
|
|
Ni electroplates* |
RoHS, WEEE, ELV, OSHA Cr |
Aircraft parts, automotive, build up |
Often used for build-up (sulfamate Ni). Hard Ni used
for wear resistance |
|
W-B-Si |
RoHS, WEEE, ELV, OSHA Cr |
Under evaluation for aircraft industry, especially
internals |
Alloy electroplates always difficult to maintain
chemistry on complex shapes |
|
Hard particle filled electro- and electroless
plates* |
RoHS, WEEE, ELV, OSHA Cr |
Small usage on wear components |
Usually Ni-based. Uniformity and handling hard
particles can be difficult |
|
Electroplated Co filled with SiC (Tribomet) |
RoHS, WEEE, ELV, OSHA Cr |
Aircraft engines |
Not widely used, limited availability |
|
Pulse electroplated nanophase Co-P
|
RoHS, WEEE, ELV, OSHA Cr |
Currently being validated – no commercial use |
Developed as an alternative to chrome on internals,
and thin dense chrome |
|
*Note: Ni is
RoHS-compliant but is under increasing ESOH scrutiny
and regulation. |
|
