Canadian Finishing & Coatings Manufacturing Magazine - May/June 2023 - 23

PLATING AND ANODIZING: CHROME ALTERNATIVES
or the aerospace industry, hard chrome plating
has been the go-to solution for manufacturers
for more than six decades. But with the health
and environmental concerns of this commonlyused
deposit well known-and with legislation in Europe
bringing the reign of hard chrome plating to an end-now
is the time to seek a viable alternative.
F
To manufacturers operating within the aerospace
industry, the benefits of hard chrome plating are
clear to see. It has been-and, particularly for military
applications, continues to be-a critical process both
in terms of manufacturing and maintenance, providing
surfaces which are wear and corrosion-resistant for
essential equipment, from hydraulic piston rods and
propeller hubs to landing gear, gear shafts and gun
barrels.
plating
However, despite its many advantages, hard chrome
of
has one major
drawback:
the
hazards
hexavalent chrome. One of the notorious four Cs-along
with cadmium, cyanide, and chlorinated solvents-
hexavalent chrome is a known carcinogen which causes
damage to key organs, including the heart, lungs, and
kidneys. Exposure to hexavalent chrome can occur at
any stage of the plating process and demands lengthy
preparation and clean-up afterwards. This fact, coupled
with the production of toxic waste during the plating
process, has led to a major reconsideration of its use.
Legislation is driving this agenda, not least REACH, a
European directive which aims to protect human health
and the environment from hazardous chemicals. Despite
applying only to chemicals which are manufactured
or imported into the EU, the directive is slowly having
wider ramifications. As the aerospace industry begins to
shift in-line with global trends towards more sustainable
products, replacing hard chrome plating is creeping
steadily up the list of priorities for many manufacturers.
Challenging the dominance of hard chromium
plating
In finding an alternative, the problem lies in the
dominant suitability of hard chromium plating for
the aerospace sector. It performs at extremely high
temperatures, has excellent corrosion and wear
resistance and, together with hardness levels of 7001,000
HV, delivers an excellent surface finish across a
wide range of applications. With all these attributes,
finding an alternative solution which covers all bases is
challenging. Moreover, the dominance of hard chrome
plating leads many people to ignore its limitations,
including the fact it's a relatively slow process, while the
nature of the coating can lead to internal and residual
stresses that may result in poor adhesion or the formation
ADHESION TESTING
of microcracks. However, chromium plating is a universal 'one
stop shop' and has become the default option for the aerospace
industry. But that doesn't mean others aren't available.
A wide range of new technologies
Manufacturers can choose from a wide range of technologies,
none of which use hexavalent chrome. These include various
spraying techniques such as thermal spray, PVD and CVD,
however, these methods require a high temperature, high
vacuum, or high melting point for the substrate. There is also a
new breed of super steels. Yet while each has advantages, they
also have drawbacks including-in the case of new alloys-the
fact they are costly and still unproven over time.
As a result, deciding which to choose can be challenging.
Added to this, the aerospace industry is typically cautious. Any
change-particularly one of this scale-is perceived to have
a high level of risk involved. With particular attention to the
components manufactured for the aerospace industry, many are
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May/June 2023
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Canadian Finishing & Coatings Manufacturing Magazine - May/June 2023

Table of Contents for the Digital Edition of Canadian Finishing & Coatings Manufacturing Magazine - May/June 2023
