Gas that has been heated to a temperature that permits ionisation and is able to conduct electricity is called plasma.
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Many people favour plasma spray over other thermal spray processes as it
permits a coat of most other substances to be placed on to a wide range of
substrates.
It does this using a mix of high temperatures, high energy heat sources, a
fairly inert spraying medium compared to other methods and high particle
velocity. Utilising plasma spraying techniques creates unbeatable bond strength
whilst ensuring that any distortion of the substrate material is as small as
possible.
Key benefits of thermal plasma
spray
are:
– Thickness is usually between 0.2mm and 2mm.
– The bond strength you can expect is in excess of 80 MPa, subject to the type
of coating you decide to use.
– It accepts a wide powder particle size, usually between 5µm to 100µm, which
compares very favourably with HVOF spraying.
– As a long established process for coating, its availability is vast.
– It can spray coat a wide range of small and large components.
– Plasma provides exceptional wear resistance.
There are endless possibilities when investigating the range of materials that
benefit from thermal plasma spray. You could consider almost any material that
presents in a powder format.
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The types of material it can lay a foundation for thermal plasma spray include
extreme usage matter such as tungsten carbide, electrical conductors, metal
alloys for coatings resistant to corrosion. It will also protect against wear
caused by sliding or friction control. It provides an excellent base for oxide
ceramics for thermal barriers.
In terms of porosity, you’re looking at a potential 5% to 10% volume, and an
oxide point of circa 1 wt% to 3 wt% if your coating is metallic.
Thermal plasma spraying is used broadly when depositing a zirconia based system
for gas turbines, which require the application of a thermal barrier. It can
also help with fretting wear on gas turbines. Some of the most used materials
when laying a coating include, ceramics, plastics, composite materials, metals,
abradables and alloys.
Plasma spraying is an indisputable improvement over many other traditional
processes using thermal spraying. A plasma jet operates at extremely high
temperature, ensuring that it can cope with substrate materials such as glass,
ceramic and refractory metals including ZrO2, B4C and tungsten.
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