Canadian Finishing & Coatings Manufacturing September/October Issue - 32

PLATING AND ANODIZING: PHYSICAL VAPOUR DEPOSITION
BRINGING FINISHING
CAPABILITIES IN-HOUSE
Physical Vapour Deposition (PVD)
Coating: the coatings, the process,
industries and applications, and costs
BY DAVID WAYNE
A
lthough the term PVD (physical vapour deposition)
isn't a household name, products coated using the
PVD process are found in most households and in
the automotive, sporting goods, medical device, and
tooling industries. Go into a home goods big box store and look
at faucets, door hardware, lighting fixtures-products offering a
" lifetime finish " are often PVD-coated. This finish is ubiquitous
in industries globally.
What is PVD coating?
PVD coatings enhance metal, plastic, and ceramic parts, but
PVD is not paint, powder coating or electroplating. PVD is a
metallurgical coating process that applies at least one metal on
a part's surface via a vacuum deposition process. The process
creates a very thin " film " on parts (from less than a micron to five
microns for specialty coatings). Commonly used metals include:
* Zirconium (Zr)
* Titanium (Ti)
* Chromium (Cr)
Often, the metal is deposited as a nitride, carbide, or oxide,
meaning the metal is combined with nitrogen, carbon, or oxygen
to form a metal ceramic compound with increased durability and/
or a desirable colour. These elements are added to the process in
trace amounts as a gas.
Why use PVD coatings?
As manufacturers know, it's difficult to find materials with all the
properties your product requires. The base material may not be
hard or durable enough or be an undesirable colour. PVD coatings
can improve the durability, appearance, or functional properties
of many products. And it can be divided into two basic (and often
overlapping) categories.
Colour PVD coatings for durable/decorative
applications
PVD coatings can improve both the appearance and durability
of your product. These finishes are scratch- and wear-resistant,
improve corrosion resistance, and are so thin-less than one
micron-they are suitable for high-tolerance parts. Products that
benefit from durable coatings in many colours include jewelry,
door hardware, plumbing fixtures, sporting goods, consumer
electronics, and automotive trim. These coatings include
metallic colours such as copper, stainless steel, gold, nickel, brass,
and chrome. Specialty colours such as grey, blue, or black include
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semi-transparent optical layers that can refract light to darken or
change the product's colour.
Performance coatings
Performance coatings add hardness, toughness, corrosion
protection, wear resistance, and lubricity to cutting tools,
injection moulds, metal forming tools, engine components,
surgical instruments and implants, and sporting goods. These
performance coatings are only microns thick and are suitable for
even the highest tolerance parts. They're designed to make your
product last longer, operate more efficiently due to lower friction,
withstand high temperatures, and resist corrosion. And they can
also offer both decorative and performance characteristics when
a product must meet functional as well as aesthetic specifications.
The Process
PVD coating machines use several processes to apply finishes.
The processes take place in a vacuum chamber where the coating
is evaporated and condenses onto the surface of the part, atom by
atom or ion by ion.
The vacuum chamber removes unwanted molecules from the
deposition environment (i.e.: water and oxygen) for increased
control over the reactions that take place, by using a series of
pumps to remove the air and water vapour from the chamber
and continuously pump to the desired vacuum throughout the
process.
The Material
The vacuum chamber contains a solid coating material,
commonly referred to as the source or the " target. " Depending
on the machine, the target may be shaped as a plate, a disk, or
a cylinder. Parts to be coated are loaded into to the vacuum
chamber, and once the chamber has been pumped down to a high
vacuum setting, energy applied to the target evaporates it. As
the evaporated material travels to the substrates, the material
reacts with gases in the chamber and condenses on part surfaces,
covering them with the coating.
All coating processes use a non-reactive (inert) gas such
as argon to generate a high energy plasma that helps drive the
deposition process. To alter the metal coating material for a
specific purpose such as increased durability or colour, reactive
gases such as nitrogen (N2), oxygen (O2), methane (CH4), or
acetylene (C2H2) are added to the process. These gases react with
the source material to create coatings. For example, the popular
bright gold coating used on cutting tools is made of titanium
nitride (TiN), in which a titanium target metal combines with
nitrogen gas in the chamber before condensing on the part.
And for an energy source, the PVD process typically uses
sputtering or cathodic arc.
The Cost
A common misperception is that PVD coating adds substantial
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