Plasma & Thermal Coatings HomePlasma & Thermal Coatings Home
spacer

COATINGS

With each application often having unique coating requirements due to the environment in which it operates or specific surface characteristics, coatings are frequently application engineered. Most thermally sprayed coatings do however fall into one of the following categories.

Click on any TOPIC below for further detail.

arrow Thermal Barrier
arrow Corrosion & Chemical Resistant
arrow Erosion Resistant
arrow Abrasion Resistant
arrow Cavitation Resistant
arrow Abradable
arrow Electrically Conductive/Insulating

Abradable

Derived from aero engine gas turbine compressors, these abradable and rub tolerant coatings are now applied to automotive engine turbochargers, pumps and compressors to provide clearance control. A turbocharger rotor spins at high speed within its housing. As its rotational speed increases, and to some extent the operating temperature, the outside diameter of the rotor also increases. If the clearances between the rotor blade tips and its housing were designed for optimal aerodynamic performance, this growth would cause the rotor blade trips to touch the bore of the housing. These clearances are therefore larger than desirable due to mechanical considerations.

turbocharger

Abradable clearance control coating applied to rotor path of turbocharger

The thermal spray coating solution for this problem is to apply a soft abradable coating to the housing bore that can be rubbed away by the rotor blades without causing material loss from the rotor. These coatings reduce the risk of blade damage and at the same time improve the efficiency and performance of the turbocharger by managing the rotor path tip clearance

Abradable Coating Features/Benefits

  • Raise Levels of Reliability
  • Lower Cost of Overhaul
  • Increase fuel Efficiency
  • Increase Performance
  • Low Material Transfer
  • Coating Wear without Surface Deformation
  • Low Adhesive Transfer
  • Low Turbine/Rotor Wear

Typical Applications

  • Turbochargers
  • Land Based Turbines
  • Aerospace Power Units<
  • Compressors
  • Pumps

Processes

  • Plasma
  • Combustion

Typical Materials

  • Aluminium-Polymer
  • Nickel Graphite
  • CoNiCrAlY-BN-Polymer

to the top

Cavitation Resistant

pump impeller

Pump Impeller - Plasma sprayed Alumina Titania to protect against cavitation

This is the term used to describe the phenomenon of liquid to gas, and gas to liquid phase changes that occur when the local fluid dynamic pressure in areas of accelerated flow drop below the vapor pressure of the local fluid. The gas to liquid phase change is akin to the boiling of water, except that it occurs at ambient temperatures.

triple vane

Coated Industrial gas turbine nozzle guide vanes

Typical Applications

Cavitation often occurs in hydro-electric turbines and is often a major consideration within the Marine industry.

  • Turbines
  • Guide Vanes
  • Wicket gates
  • Turbine runner
  • Draft tube
  • Pumps
  • Impellers
  • Propellers

Typical Processes

  • HVOF
  • Plasma

Typical Materials

  • Tribaloy T-800
  • WC - 17 Co
  • Cr3C2 - 25NiCr
  • Cr2O3
  • Alumina/Titania

to the top

Corrosion & Chemical Resistant

Corrosion and chemical resistant coatings have traditionally been deposited by either welding or electroplating. Welding applications are limited due to the problem associated with the heat affected zone (HAZ) and the dilution of weld material with the substrate. Electroplating is becoming an environmental concern due the nature of its' effluent. Thermally applied coatings are rapidly becoming the preferred choice. Non-porous HVOF coatings can be applied with hardnesses in excess of 1,200 Hv which can also be superfinished. Other materials deposited by Plasma or Arc Wire can be 'sealed' to enhance their corrosion resistance.

The coatings enable the utilisation of low cost or lightweight materials without suffering poor performance or short life due to corrosive action on the surface.

wear

Pelton Wheel After Special WC coatings lasts 200+ days

Typical Applications:

  • Off Shore structures - Zinc
  • Petrochemical - process vessels
  • Pumps

Typical Processes

  • HVOF
  • Plasma
  • Arc Wire

Typical Materials

  • Zinc
  • Ni/Cr
  • Stainless Steels
  • Tantalum
  • Nickel
  • WC/Ni

to the top

Electrically Conductive/Insulating

As most thermal spray processors utilise powders as ‘feedstock’ materials, and almost every material is now accessible in powder form, there is a near infinite number of coatings and coating composites available. The benefits of thermal spraying, to the electronic and electrical industries are now becoming exploited. Components can be coated to provide the exact level of electrical conductivity required.

Applications can be broken down into two areas.

  • Conductive workings. Typically these may be copper, aluminium and zinc etc. Precise conductive paths can be created using masking techniques. These conductive coatings can be deposited onto a wide variety of substrates such as carbon fibre, glass reinforced plastics and numerous other polymeric materials.
  • Insulative Coatings. Typically these may be pure ceramics, such as Alumina or Titania. As with the conductive coatings, deposits can be laid down accurately to customer specifications. Conductive and Insulative coatings can also be used together to produce a composite insulated component with an integral electrical path.

to the top

Erosion Resistant

Erosion is a result of the impact of sharp particles on to a surface. Solid particles transported in a gas or liquid flow can cause severe damage to industrial components, leading to expensive repair or replacement. Thermally applied coatings offer excellent resistance to erosion at high and low service temperatures, due to the way they are formed. Large particles of Carbide (typically tungsten carbide) are sprayed with a matrix bonding material (typically cobalt). The cobalt is melted and bonds the solid carbides to the substrate and to each other, producing a dense carbide protective surface.

Erosive Wear Test

Materials

  • Mild Steel
  • Welded Hardface
  • HVOF Applied WC/Co

Wear : Life ratio   1 : 4 : 12

Gas turbine vane

Industrial Gas Turbine Row 1 Vane - High temperature erosion-resistant coating on all gas washed surfaces.

Typical Applications

  • Fans - pulverised coal and cement etc.
  • Centrifugal Compressors
  • Centrifugal Pumps

Typical Materials

  • Carbide/Nickel Chrome(High Temp.)
  • High Carbon Steels
  • Nr, Cr, Si, B
  • Aluminium Titania

Processes

  • Plasma
  • HVOF
  • Arc

to the top

Thermal Barrier

A range of coatings designed to enable components to work within elevated or reduced temperatures. Thermal Barriers are often used on materials that work in temperatures above their melting point. The coatings also protect against oxidation, spalling and other associated heat induced effects.

Gas turbine

Application of Thermal Barrier Coating to the inside surface of land based gas turbine combustor. (Process - Plasma Spray  Coating system - CoNiCrAlY. Zirconia)

Thermal barrier Coatings (TBC's) are used to reduce the operating temperature of a metallic component which in turn leads to extended working life. High energy, reliability and longer maintenance intervals are demanded from today's TBC's to reduce surface temperatures in environments of over 14,000°C. Components suffering from oxidation at high temperatures can be protected by using MCrAlY materials. The 'M' factor (Ni,Co,Fe or a combination thereof) will depend on the requirements of the application. TBC's are then applied to the surface of this material providing excellent reliability and long life.

Thermal Barrier Features

  • Oxidation & Corrosion Resistance
  • Low Thermal Conductivity
  • Enhanced Erosion Resistance
  • Longer Duty Cycle & Increased Part Life
  • Reduction of substrate operating temperature - lower thermal & creep stresses
  • Protection against 'hot spots'
  • Enhanced operation temperature resulting in increased thermal efficiency
  • Reduction of Nox emissions
  • Reduction in cooling requirement
  • Improved efficiency and fuel economy

Typical Applications

  • Diesel Engines -
    Piston Crowns, Valves etc.
  • Land Based Turbines -
    Transistion Ducts, Vanes, Combustors etc.
  • Aero Engines -
    Discharge nozzle, combustors etc.

Processes

  • Plasma Spray
  • HVOF

Typical Materials

Top Coat

  • Yttria Stabilised Zirconia
  • Ceria Stabilised Zirconia (CeSZ)
  • Magnesia stabilised Zirconia

Bond Coat

  • CoNiCrAlY
  • NiCrAlY

to the top

Abrasion Resistant

The abrasive wear mechanism similar to machining, grinding, polishing or lapping used for shaping materials. Two body abrasive wear occurs when one surface (usually harder than the second) cuts material away from the second.. This mechanism very often changes to three body abrasion as the wear debris then acts as an abrasive between the two surfaces. Abrasives can act as in grinding where the abrasive is fixed relative to one surface; or as in lapping where the abrasive tumbles, producing a series of indentations as apposed to a scratch. There is a large range of thermally sprayed coatings designed to protect against abrasion. These can be grouped as Metallics, Ceramics, Carbides and self-fused, self-fluxing Alloys. Coatings are designed to operate at high temperatures or within aggressive environments.

Typical Applications

  • Ball valve
  • Gate valves
  • Bearing Journals

Processes

  • HVOF
  • PLASMA
  • ARC

Materials

  • Tungsten Carbide
  • Chrome Carbide

to the top

chandos media