Copy of `Poeton - Glossary of Surface Engineering Terms`

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Poeton - Glossary of Surface Engineering Terms Category: General technical and industrial > Coating Date & country: 15/12/2007, UK Words: 133

Zinc Plating
The electro-deposition of zinc or zinc alloys (eg Zn/Ni, Zn/Sn) to provide galvanic corrosion protection.

Wear
Loss of material from a surface by means of relative motion between it and another body. Third bodies i.e. grit

Wire spraying
A thermal spray process whereby the supply for the coating material is fed into the gun in the form of a continuous wire.

Ultrasonic
An NDE technique which relies on an ultrasonic beam passing through a coating and substrate and providing a signal from the back wall which is then detected. The height of this backwall echo depends on the discontinuity in impedance from the sprayed coating to the substrate. Bonding flaws can be easily seen by the weakening of the back wall echo.

Transferred arc
In a plasma torch the plasma jet is emitted from the torch and the current flows from the internal cathode to the internal anode represented by the nozzle of the torch. When the jet is carried to another anode with it being electrically favourable to do so the current will then transfer to the second anode, usually the workpiece and the arc is said to be transferred.

Thermography
An NDE technique in which the coating is flash heated and then viewed with an infra red camera. 'Hot spots' indicate areas of poor bonding or greater coating thickness.

Thermochemically formed coatings
A painted, dipped or sprayed chromium oxide based coating consolidated by repeated deposition and curing cycles (about 500oC).

Thermal spraying
A process in which coating material is heated and accelerated from a spray torch towards the workpiece. The deposited material forms a coating on the surface.

Thermal barrier coating
A coating produced to present an insulating barrier to a heat source and to protect the substrate.

Tensile stress
Axial forces per unit area applied to a body that tend to extend it.

Surfacing
The application of a coating or cladding to a surface to impart a change in its surface behaviour.

Tensile strength
A measure of the resistance that a material offers to tensile stress. It is defined as the stress, expressed as the force per unit cross sectional area, required to break it.

Surface preparation
Cleaning and roughening the surface to be sprayed, usually by grit or bead blasting. This is to increase the adhesion of the coating to the substrate.

Substrate
The parent or base material to which the coating is applied.

Stress
The force per unit area on body that tends to cause it to deform. It is a measure of the internal forces in a body between particles of the material of which it consists as they resist separation, compression, or sliding.

Steam tempering
The production of a stable oxide on steel parts by treatment in steam at about 300oC. Improves corrosion performance and reduces friction.

Strain
A measure of the extent to which a body is deformed when it is subjected to a stress.

Sputtering
This is a glow discharge process whereby bombardment of a cathode releases atoms from the surface which then deposit onto a nearby target surface to form a coating.

Spray-fused coatings
A process in which the coating material is deposited by flame spraying and then fused into the substrate by the addition of further heat. This can be applied by flame induction heating or by laser.

Spray dried powder
Powder formed by the spray drying process.

Spray chamber
A chamber in which the spraying process is carried out. It may merely be an acoustic chamber for plasma spraying or a vacuum chamber for vacuum plasma spraying.

Spalling
The lifting or detachment of a coating from the substrate.

Size distribution
The distribution of sizes within a size analysis. The distribution may be normal or skewed in some way due to the powder manufacturing process.

Size analysis
Analysis of the size of the particles being deposited by spraying processes.

Silver plating
The electro-deposition of silver for electrical, decorative or anti-fretting properties.

Shot peening
The bombardment of a component surface with steel or ceramic shot. Produces a residual compressive stress in the surface and improves fatigue and stress corrosion performance.

Shroud
A gaseous and/or mechanical or physical barrier placed around the spraying process designed to reduce the ingress of air into the system and so reduce oxidation of the of the particles being sprayed.

Salt Bath Nitriding
See Nitriding

Salt Bath Nitrocarburising
See Nitrocarburising

Rhodium plating
The electro-deposition of rhodium for oxidation resistance combined with surface hardness.

Salt Bath Carburising
See Carburising

Resin
A synthetic or naturally occurring polymer

Quality Control
All aspects of the control of the spraying process including the surface preparation, spraying, control of thickness deposited and the oxide and porosity levels, surface finish and NDE checks as specified.

PVD
See Physical Vapour Deposition

Pull-out
Pull-out occurs when particles are removed from the coating cross-section by the action of polishing. It is sometimes confused with porosity.

Powder injection angle
The angle from which the powder is injected into the plasma jet in plasma spraying.

Powder gas flow rate
The flow rate of the gas propelling the powder into the plasma jet in plasma spraying.

Powder coating (PTA)
A polymeric coating deposited via electrostatic attraction

Porosity
The presence of pores or voids in a coating whether connected or not. Porosity is not the same as pull-out.

Polymer
A substance having large molecules consisting of repeated units. There are a number of natural polymers, such as polysaccharides synthetic polymer are extensively used in plastics.

Plasma Transferred Arc
See Transferred Arc

Polyester
A condensation polymer formed by the interaction of polyhydric alcohols and polybasic acids. They are used in the manufacture of glass-fibres products. See Alkyd resin.

Plasma Spraying
A thermal spraying process in which the heat source is a plasma jet.

Plasma Nitriding
Also called Ion Nitriding. See Nitriding

Plasma jet
A jet of highly ionised gas usually produced from a plasma torch. An electric arc is struck between a cathode and anode and is then blown through a nozzle to form the jet.

Plasma Carburising
See Carburising

Physical Vapour Deposition
A term covering all the vapour deposition processes including Ion plating, It does not include CVD as this is chemical not physical.

Phosphating
A conversion treatment to produce a thin phosphate-based layer on a steel surface, providing improved corrosion protection.

Photo-thermal NDE
An NDE technique for spayed coatings. A repeated pulse of heat, from a laser source, flows through the coating and substrate. The thermal signature is detected and related to the input signal thereby indicating coating thickness.

Peening
A stream of sharp material particles which break superficial fibres, reducing internal stress fields.

Passivating
The post treatment (usually by chromating) of nickel, cadmium or zinc coatings to reduce their corrosion rates.

Particle chemistry
The elements contained within the particles of a spray powder.

Pack carburising
See Carburising

Painting
The application of organic based layers (acrylics, etc) for corrosion protection and decorative purposes.

Oxidation
Chemical reaction between the surface elements and oxygen causing oxides of the elements to be formed.

Oxidising
The production of a stable oxide layer on a steel component by heating in a controlled atmosphere. Provides corrosion protection and reduced friction.

Nitrocarburising
The diffusion of nitrogen and carbon into alloy steel or mild steel to form hard nitrides in the surface layer (typically 250µ). Performed at between 500 and 750oC from a gas, salt bath or plasma glow discharge.

Nitriding
The diffusion of nitrogen into alloy steel to form hard nitrides in the surface layer (typically 250µ). Performed at between 500 and 750oC from a gas, salt bath or plasma glow discharge.

Microtrack
A device for measuring powder particle size distributions.

Nickel plating
The electrolytic deposition of nickel to forma corrosion barrier or to reclaim a worn part. Can also include hard ceramic particles to from a wear resistant composite coating.

Micro-hardness
The hardness of a coating as measured on a microscopic scale.

Micrograph
A micrograph is produced when a section of the coating is taken, polished to show the particulate layers and then photographed through a microscope.

Metallurgical bonding
Produced by chemical bonding between areas of the coating and substrate in intimate contact or even by diffusion interaction between the coating and substrate. Metallurgical bonding can be enhanced by post spraying diffusion heat treatments.

Mechanical bonding
Usually represented by mechanical interlocking of the deposited particles with the rough heights on the substrate surface produced during grit blasting.

Magnetron sputtering
See Sputtering. In this PVD process, the sputtering action is enhanced by intense magnetic fields.

LPPS
See 'Vacuum or Low Pressure Plasma Spraying.'

Laser hardening
The localised surface heating of a medium carbon steel by an incident laser so that the temperature is raised above 900oC. The part is quenched (or self-quenches by virtue of the remaining cool bulk of the component) and tempered to produce a hard martensitic structure at the surface.

Laser glazing
The melting and quenching of a surface to form a fine grained structure or 'glaze'.

Laser alloying
The application of a powder to a surface followed by fusing and alloying into the surface via the heat from an impinging laser.

Ion-Implantation
A process in which a beam of positive ions is projected towards and into the surface. It is carried out in partial vacuum and the ions diffuse into the surface layer of the substrate. Typically this is carried out with nitrogen giving a nitrided effect.

Ion nitriding
Also called plasma nitriding. A vacuum glow discharge technique of nitriding. See Nitriding.

Induction hardening
The localised surface heating of a medium carbon steel by an induction coil so that the temperature is raised above 900oC. The part is quenched (or self-quenches by virtue of the remaining cool bulk of the component) and tempered to produce a hard martensitic structure at the surface.

HVOF
See High Velocity Oxy-fuel spraying

HIPPING
The high temperature/high pressure consolidation of a powder metallurgy component or thermally sprayed coating. Density is greatly increased and metallurgical changes provide enhanced corrosion and wear properties.

Hardness test
A test designed to assess the resistance to penetration from a load. The surface is indented under a defined load and the depth of penetration is observed.

Hardfacing
The application of a cladding or coating of material designed to resist wear.

Hard Chrome plating
The electrolytic deposition of chromium to form a very hard (1000Hv), tough coating with good wear resistance. The structure is micro-cracked.

Gold plating
The electrolytic deposition of gold for decorative or electrical applications.

Grit blasting
A pressurised stream of hard metal or oxide grit material used to clean and/or roughen surfaces prior to coating.

Gas nitriding
see Nitriding

Gas nitrocarburising
See Nitrocarburising

Gas carburising
See Carburising

Gas flow rate
The flow rate of gas (eg litres per minute) through the spraying torch.

Galvanising
A hot dip process for deposition of zinc for galvanic corrosion protection of steel.

Galling
Damage to the surfaces of materials sliding in contact with each other, usually caused by the localised welding together of high spots. Common for materials like stainless steel, aluminium alloys and titanium.

Fused and crushed powder
Powder formed from a fused solid mass which is then crushed to the appropriate size for spraying.

Fretting
Surface damage caused by very small relative movement between two surfaces usually under heavy load.

Flame spraying
A thermal spraying process in which the particles are heated and accelerated in a flame produced from the combustion of oxygen and fuel.

Flame hardening
The localised surface heating of a medium carbon steel by an impinging gas flame so that the temperature is raised above 900oC. The part is quenched (or self-quenches by virtue of the remaining cool bulk of the component) and tempered to produce a hard martensitic structure at the surface.

Filler
A solid inert material added to a synthetic resin or rubber, either to change its physical properties or simply to dilute it for economy.

Fatigue
A cumulative effect causing a metal to fail after repeated applications of stress none of which exceeds the ultimate tensile strength. The fatigue strength (or fatigue limits) is the stress that will cause failure after specified number cycles.

Erosion
Removal of material from a surface caused by the flow of particles within a liquid or gas.

Exothermic reaction or material
Certain materials undergo chemical reactions when heated in a arc or plasma and produce extra heating. This can be useful in improving adhesion of the coating to the substrate. There is also a potential explosive or fire hazard when handling powders which are exothermic.

Electroplating
The application of a layer of metal onto a substrate in a conducting solution of metal slats.

Electroless Nickel
The autocatalytic deposition of nickel/phosphorous and nickel/boron have many useful corrosion and tribo/corrosion applications. Unlike the electrolytic processes, they produce a deposit with completely uniform coverage. In the case of Ni P, deposits around 25 to 50 microns thick with a hardness of about 500Hv is obtained, but thermal ageing at temperatures around 400°C can develop hardness values in excess of 1000Hv.

Elasticity
The property of certain materials that enables them to return to their original dimensions after an applied stress.

Diamond-like Carbon
A thin carbon-based coating applied by either PVD or PACVD. It has high hardness and low friction.

CVD
See Chemical Vapour Deposition

Detonation Gun
A thermal spraying process in which the coating material is heated and accelerated to the workpiece by shock waves from a series of detonations or explosions from gas mixtures. Also known as D-Gun (Praxair).

Crushed powder
Powder formed from a solid which is then crushed to the appropriate size for spraying.