Plasma Group Science

Thermal Spray Coating

 

Plasma Coating Process


Introduction

The plasma process has evolved over the years in to a highly flexible coatings system capable of applying a wide range of materials. These include most metals/alloys, ceramics, cermets, composites and other materials such as plastics.

Main Applications

Diverse uses include

    • aerospace
    • petrochemicals
    • mining
    • textiles
    • biomedical

and other industrial environments.

Process Description

An inert gas such as Argon, when excited by an electric arc, becomes partially ionised and in this state is able to carry an electric current for the generation of a hot gas stream having temperatures approaching 12000°C. Powder material is injected in to the flame at optimum conditions and projected in a semi-molten (plastic) state on to a suitably prepared workpiece to form high integrity coatings of typically 0.05mm. to 3mm.thickness. The gun is manipulated by hand or by using a robot, enabling a wide range of component configurations to be coated.

General Coating Characteristics

    • high bond strength (55 Mpa / 8000 p.s.i. or higher).
    • high density, low porosity.
    • able to be ground or lapped to a fine finish(O.1-0.2 microns).

Due to the range of materials that can be sprayed it is difficult to generalise on coating characteristics, but with the correct choice of material plasma coatings can:-

    • perform better than chrome plating.
    • be more cost effective than solid sintered carbide.
    • resist wear better than the same material in cast or wrought form.

Available Coatings

The table below gives typical coating properties and applications for a variety of materials. It is by no means an exhaustive list, rather, it is a guide to the diversity of coatings that can be offered.

Coating Characteristics Typical Applications
Tungsten Carbide / Cobalt (83/17) Macrohardness - Rc 50-55
Microhardness - DPH300 750-950
Tensile Bond Strength - 62MPa(9000psi)
Surface Texture 
- as sprayed - 6 - 9 microns
- as ground - 0.25 - 0.5 microns		 Used in low temperature environments below 500°C on parts subject to fretting and abrasive wear. Many aero engine applications including brackets and mounts. Industrial applications include pump shafts, piston and wire drawing capstans.
Chrome Oxide Macrohardness - Rc 70-72
Microhardness - DPH300 900-1300
Tensile Bond Strength - 41MPa(6000psi)
Surface Texture 
- as sprayed - 6 - 7.5 microns
- as ground - 0.4 - 0.5 microns		 Used extensively in high wear areas on pump seals, impellers and sleeves where resistance to corrosion by acids, alkalis and alcohols is important. Also used in the textile and paper industries on parts subject to wear by thread or paper products.
Yttria stabilised Zirconia Macrohardness - Rc 30-35
Surface Texture 
- as sprayed - 9 - 12 microns		 Used as a thermal barrier coating where resistance to high temperature corrosion and thermal shock is important. Components coated with this material include gas turbine parts, cylinder liners, exhaust ports and other engine parts subject to temperatures above 850°C.
Nickel/Chromium (80/20) + 6% Aluminium Macrohardness - RB 90
Microhardness - 215(Knoop50)
Tensile Bond Strength - 28MPa(4000psi)
Surface Texture 
- as sprayed - 7 - 11 microns
- as ground - 0.25 - 0.5 microns		 Used to produce heat resistant coatings to minimise oxidation and corrosion of carbon steels up to 980°C. Applications include turbine engine components and heat treating fixtures.
Cobalt / Chromium / Nickel / Tungsten Macrohardness - Rc 59
Surface Texture 
- as sprayed - 9 - 11 microns
- as ground - 0.25 - 0.5 microns		 Able to be used at temperatures between 540 - 840°C, this material resists wear by particle erosion or fretting. Typical applications include exhaust valves, seats, and seals and hot crushing rolls.
Aluminium / Polyester Macrohardness - R15Y 60 - 80
Surface Texture 
- as sprayed - 15 - 18 microns
- as ground - 1.75 - 2.5 microns		 Used as an abradable coating below 345°C as an air or oil seal in both high and low pressure compressors

 

Plasma Coatings Limited

Unit 3, Whitecross Road Industrial Park

Tideswell, North Derbyshire

SK17 8PY, England

e-mail : info@plasma-group.co.uk

Tel : +44 (0) 1298 873700, Fax : +44 (0) 1298 873708

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