SurfaceWeb Glossary

Surface Engineering - A-Z Glossary

Abradable coatings: Coatings which are designed to rub down against the action of a mating surface to form a tight gas or air seal.
Abrasive blasting: A pressurised stream of hard metal or oxide grit material used to clean and/or roughen surfaces prior to coating.
Abrasive Wear: Wear caused by hard, sharp particles.
Acoustic emission: Acoustic emissions are sound or ultrasound pulses generated during crack initiation or propagation in materials and coatings as a result of being subjected to stress. Acoustic emissions can be detected by transducers.
Adhesion measurements: The simplest qualitative test to measure the adhesion of a film to its substrate consists in determining whether or not the film peels off along with a strip of sticky tape pressed onto it and then pulled off. A more quantitative test is performed by gluing to the film a metal stud of cross section A, and then applying a force ramp (F) until either the substrate or the glue or the film/substrate interface breaks. When the film/substrate interface breaks first, the interfacial tensile strength is given by F/A.
Adhesion scratch test: Currently the most commonly used method of assessing coating adhesion.
Adhesive Wear: Wear caused by sliding surfaces, where surface asperities interact and adhere.
Agglomerated powder: A mechanically mixed combination of fine particles of different materials held together with an organic binder and formed into power particles.
Air Cap: A component of thermal spray guns used for shaping the air flow for atomazing the wire or rod feedstock.
Alkyd resin: A type of polyester resin used in paints and other surface cotating. The original alkyd resins were made by copolimerizing phathalic anhydride with glycerol, to give a brittle cross. Linked polymer.
Alumina: Aluminium Oxide compound used in both abrasive blasting as an abrasive and in thermal spraying as a consumable feedstock (powder and rod) for the production of coatings. Alumina is a hard wear resistance ceramic and can be alloyed with various amounts of titania (titanium dioxide) to improve certain properties.
Aluminising (gas): High temperature (approx 900^oC) pack or gaseous diffusion of aluminium into the surface of a component to enhance high temperature corrosion and oxidation resistance.
Aluminising (hot dip)
Aluminising (Hot Dip): A liquid aluminium submersion technique at temperatures above 600 oC depositing layer of aluminium (usually on steel sheet) for enhance corrosion protection
Aluminium Ion Plating: The deposition of aluminium by a vacuum evaporative process. Provides galvanic corrosion resistance. Normally given a passivation treatment.
Anode: The positive electrode in a plasma spray torch (gun). Generally made from copper but can be lined with tungsten to increase life. (See also cathode).
Anodising: The production of an oxide layer on aluminium alloys. The process is electrolytic, a typical electrolyte being sulphuric acid. Treatment at room temperture produces thin, decorative layers with some corrosion protection. Treatment at 0^oC produces hard, thicker layers (up to 100?) with wear resistance. They can be post sealed to give improved corrosion resistance.
Antireflection coating (AR coating): A coating whose reflection is zero, used for lenses. They are usually fabricated by the technique of interference oscillations with a He-Ne laser.
Apticote: A coating trade name of A T Poeton and Son Ltd, Gloucester, UK.
Arc Blow (Plasma): Arc blow is the deflection of an electric arc under the influence of the magnetic field associated to the flow of electrons (electric charge), which results in arc instability. Arc blow can be reduced and minimized in plasma welding by an appropriate design of shape and sizes of the electrodes (namely cathode tip and anodic nozzle plenum).
Arc welding: The production of a stable, protective oxide on steel parts by treatment in a pressurised, high temperture steam containing atmosphere.
Arc Wire Spraying: A thermal spray process in which two electrically conducting wires are brought together to form an electric arc. The consequent molten metal is then projected by a air stream towards the workpiece to form a coating.
Auger Electron Spectroscopy AES: An electron beam technique applied for near-surface elements identification. well used in thin film science.
Blackadising: A presurised stream of some materials (Glass, plastic, metal, ahs, etc) applied on a surface to clean and/or roughen. It can be, depending on the media, abrasive an non-abrasive.
Bond: This represents the state of adhesion between the coating and the substrate. It's strength will depend on the details of the spraying process and the materials used. Bonding mechanisms may be mechanical, physical or metallurgical or a combination of these.
Bond coat: A coating applied as an intermediary between the main or top coating and the substrate in order to improve the bond strength.
Bond strength: The strength of the adhesion between the coating and the substrate. A number of test methods are in use to measure the bond strength of coatings.
Boronising: The diffusion of boron into the surface of a component (usually steel) by a high temperture (approx 900^oC) gas or pack process. Produces hard phases within the surface (Typically 100? deep).
boundary condition: The loads, displacements, temperatures, densities etc. at the periphery of the domain or mesh in a numerical simulation.
Cadmium ion plating: The deposition of cadmium by a vacuum process to provide galvanic corrosion protection.
Cadmium plating: The electrolytic deposition of cadmium to provide galvanic corrosion protection. Restricted by environmental considerations.
Carbide diffusion: A salt bath treatament at about 900^oC for high carbon tool steels. Produces a very hard layer of vanadium carbide, typically 10? thick.
Carbonitriding: Similar to Carburising (see below). Diffusion of carbon and nitrogen at about 900^oC (by pack, gas, salt bath or plasma process) into low carbon steel, followed by quenching and tempering to produce martensitic case (typically 1mm thick).
Carburising (also called Case Hardening): Diffusion of carbon at about 900^oC (by pack, gas, salt bath or plasma process) into low carbon steel, followed by quenching and tempering to produce martensitic case (typically 1mm thick).
Case-Depth: The hardened depth on Carburised or Nitrided parts, often defined as the depth to which the hardness exceeds 500 Hv
Case-hardening: See Carburising
Cathode: The negative electrode in a plasma torch (gun). Generally made from thoriated tungsten (thorium is added to reduce the metal work function aiding electron release). (See also anode).
Cavitation Erosion: A form of erosion causing material to be removed by the action of vapour bubbles in a very turbulent liquid.
Cermet powders: A composite powder of metal and ceramic constituents produced by methods such as agglomeration, sintering and spray drying. Examples include WC-Co, TiC-Ni.
CFD: An acronym for Computational Fluid Dynamics
Chemical Vapour Deposition (CVD): The deposition of a coating by means of a chemical reaction in gases in a chamber producing components which deposit on and adhere to the substrate.
Chromating: See 'Chromate Conversion Coating'
Chromic Acid Anodising: A grey/brown anodic coating (1-2 micron) produced on Aluminium Alloys in Chromic acid at room temperature. It will act as an effective undercoat for paint.
Chromising: High temperature (approx 900^oC) pack or gaseous diffusion of chromium into the surface of a component to enhance high temperature corrosion and oxidation resistance.
Chromium Nitride: Metallic coloured ceramic, often applied as a thin coating (1 to 55) by PVD. Very hard (3500Hv). Used on cutting tools and other surfaces needing wear resistance
Cladding: The application of a thick (generally above 1mm) coating which melts or diffuses into the substrate. Processes include weld cladding and plasma transferred arc (PTA).
Coating: The application of a thin (generally less than 1mm) layer of material onto the surface of a substrate.
Composite: Mixture of two or more materials. Nearly all have a reinforcing material(wood, glass, etc), called filler, and a natural or artificial resin, called matrix to achieve specific characteristics and required properties.
Compound Layer: A non-etching layer of iron nitrides formed at the surface of ferrous materials during nitriding or nitrocarburising. It is usually about 55 thick and it is normal to remove it by grinding prior to component installation
compressible: A flow where the density changes due to the nature of the flow. Usually associated with high speed or high temperature.
Computational Fluid Dynamics (CFD): A method of simulating a flow field on a computer, by replacing the governing nonlinear partial differential equations (Navier-Stokes Equations) with numbers, and advancing these numbers in space/time to obtain a final numerical description of the flow.
Constricted Arc (Plasma): Column of plasma arc obtained by a constricted nozzle (usually in Copper and water cooled)connected to positive polarity (anode), while the negative polarity is connected to the cathodic electrode (usually Tungsten added with Thorium Oxides).
convergence: A description of the decrease in the relative error between successive iterations in a numerical solution. When a certain predefined limited has been reached, the solution is considered to have converged, and therefore the solution is stable and correct.
Copper plating: The electrolytic deposition of copper to provide either a corrosion barrier (often as an undercaot for hard chrome plate) or for reclamation of worn parts.
Corrosion: Chemical or electrochemical reaction between a metal and the local environment whether wet or dry which results in deterioration in the properties of the metal.
Cr-Ni coatings: Anticorrosion coatings resistant to high temperatures.
Crushed powder: Powder formed from a solid which is then crushed to the appropriate size for spraying.
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).
Diamond Like Carbon: A thin film coating (1 or 25) applied by a PVD or CVD process. It posesses some of the hardness of diamond, but with the low friction properties of graphite (Friction Coefficient = about 0.1). Used on cutting and forming tools, on medical implants and for low friction surfaces.
Elastic modulus: (also called Young's modulus). A parameter which measures the stiffness of a material. It is indicated usually as Y (Pa).
Elasticity: The property of certain materials that enables them to return to their original dimensions after an applied stress.
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.
Electroplating: The application of a layer of metal onto a substrate in a conducting solution of metal slats.
element: The domain is divided up into small areas/volumes, called elements. A node is placed at each corner and/or at the Gaussian integration points.
Energy Dispersive X-ray (SEM-EDX): An electron beam microprobe for X-ray-fluorescence analysis. Commonly associated with electronic microscopy, it permits measuring the elementary composition of materials.
entrainment: The sucking in of fluid from outside the shroud or nozzle of a plasma spray gun. To conserve momentum, the total momentum of the entrained flow must balance the total momentum of the expelled fluid.
Epitaxy: A film is called epitaxial when its crystallographic order is being significantly influenced by that of the substrate as a result of some degreee of matching between the two along the interface.
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.
Explosive cladding
Explosive Cladding: See 'Cladding' - Coatings applied by explosive gas mixture.
Fatigue: A cumulative effect causing a metal to fail after repeated aplications of stress none of which exceeds the ultimate tensile strength. The fatigue strenght (or fatigue limits) is the stress that will cause failure after specified number cycles.
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.
finite difference: A numerical method of solving the Navier-Stokes equations, where the domain is divided up into small areas/volumes, with nodes (or grid points) placed at each corner. The fluid is then considered to exist only at these nodes. The difference between the nodes describes the property gradients in the fluid.
finite element: A numerical method of solving the Navier-Stokes equations, where the domain is divided up into small areas/volumes. A shape function is then placed over the volume, it should be representative of the shape of the variation over the volume.
finite volume: A numerical method of solving the Navier-Stokes equations, where the domain is divided up into small areas/volumes, and the flow properties are considered to be constant across the volume.
Flame hardening: The localised surface heating of a medium carbon steel by an impinging gas flame so that the temperture is raised above 900^pC. 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.
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.
Fretting: Surface damage caused by very small relative movement between two surfaces usually under heavy load.
Fused and crushed powder: Powder formed from a fused solid mass which is then crushed to the appropriate size for spraying.
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.
Galvanising: A hot dip process for deposition of zinc for galvanic corrosion protection of steel.
Gas carburising: See Carburising
Gas flow rate: The flow rate of gas (eg litres per minute) through the spraying torch.
Gas nitriding: see Nitriding
Gas nitrocarbursing: See Nitrocarburising
Gold plating: The electrolytic deposition of gold for decorative or electrical applications.
Graphite: A black lamella solid with low friction, anti wear properties. The low friction is not sustained in vacuum. In air it can be used up to 400 oC.
Grit blasting: A pressurised stream of hard metal or oxide grit material used to clean and/or roughen surfaces prior to coating.
Hafnium Nitride (HN): Gold coloured ceramic, typically applied as a thin coating (1 to 55) by. Very hard (3500Hv). Used on cutting tools and forming tools and other surfaces needing wear resistance
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.
Hardfacing: The application of a cladding or coating of material designed to resist wear.
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.
HCD: See Hollow Cathode Discharge
High Velocity Oxy-fuel Spraying (HVOF): A Thermal spray process. The spray powder particles are injected into a jet formed by the combustion of oxy-fuel, heated and accelerated to the workpiece.
HIPPING: The high temperture/high pressure consolidation of a powder metallurgy component or thermally sprayed caoting. Density is greatly increased and metallugical changes provide enhanced corrosion and wear properties.
Hollow Cathode Discharge: A technique to deposit high quality TiN, CrN, TiCN, and TiCrN thin films on cutting tools, machine parts, moulds, etc
HVOF: See High Velocity Oxy-fuel spraying
Hydroxyapatite: Hydroxyapatite is a biocomaptible ceramic. It may be deposited by plasma spray onto orthopaedic implants in order to increase the bone-implant contact. It may also be sprayed over a porous titanium coating where it is used to promote bone ingrowth.
Indium-tin oxide (ITO): Transparent semiconducting material used as an electrode on flat-panel displays and other electro-opto devices.
Induction hardening: The localised surface heating of a medium carbon steel by an induction coil so that the temperture is raised above 900^pC. 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.
Ion nitriding: Also called plasma nitriding. A vacuum glow discharge technique fo nitriding. See Nitriding.
Ion plating: A process in which positive ions produced in a glow discharge are attracted to the substrate which is connected as the cathode. The ions are typically made by evaporation.
Ion Scattering Spectroscopy: Surface sensitive technique where the depht of analysis can be limited to the outermost atomic layer. In ISS a low-energy monoenergetic beam of ions is focused onto a solid surface and the energy of the scattered ions is measured at a fixed angle. A primary beam of an inert gas (He+, Ne+, Ar+) is usually employed, and since the collision with the atoms on the surface can be considered as elastic, the energy loss identifies the element on the surface.
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.
laminar flow: The flow regime which exists when Reynolds Number is below 2000. The path lines of the particles are smooth and regular, and there is little interchange of fluid mass between adjacent layers.
Laser Ablation: A deposition techique which uses a pulsed UV laser beam for vaporizing solid source materials. Much of the material ablates as macroparticles rather than vaporizing as atoms or molecules. A key advantage is that it can achieve congruent evaporation of complex materials, such as mixed oxides.
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.
Laser glazing: The melting and quenching of a surface to form a fine grained structure or 'glaze'.
Laser hardening: The localised surface heating of a medium carbon steel by an incident laser so that the temperture is raised above 900^oC. 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.
LPPS: See 'Vacuum or Low Pressure Plasma Spraying.'
Magnetron sputtering: See Sputtering. In this PVD process, the sputtering action is enhanced by intense magnetic fields.
MCrAlY: MCrAlY's (where M = Ni, Co or Fe) are a group of high temperature, corrosion resistant alloys used to combat sulphidation and oxidation.
Mechanical bonding: Usually represented by mechanical interlocking of the deposited particles with the rough heights on the substrate surface produced during grit blasting.
mesh: The area made up of elements and nodes (or grid points) in a numerical simulation.
Metallurgical bonding: Produced by chemical bonding between areas of the coating and substrate in intimate contact or even by diffusional interaction between the coating and substrate. Metallurgical bonding can be enhanced by post spraying diffusion heat treatments.
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.
Microhardness: The hardness of a coating as measured on a microscopic scale.
Microtrack: A device for measuring powder particle size distributions.
Molybdenum Disuplhide (MoS2): A black, lamella structured solid with low sliding friction. Often applied as a powder filler to lubricants or dispersed in a polymer coating.
Multiport Nozzle (Plasma): Constricted nozzle with two or more internal bores, in order to achieve a better control of the shape and stability of plasma arc.
Navier-Stokes Equations: Probably the most pivotal equations in all of theoretical fluid dynamics, these equations relate all the flow field variables together into nonlinear partial differential equations. The NS equations are basically a reformulation of Newtons 2nd Law of a Motion, F=ma.
NCA: See Notched Coating Adhesion
Nickel plating: The electrolytic depostion 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.
Nitriding: The diffusion of nitrogen into alloy steel to form hard nitrides in the surface layer (typically 250?). Performed at between 500 and 750^oC from a gas, salt bath or plasma glow discharge.
Nitrocarburising: The diffusion of nitrogen and carbon into alloy steel or mild steel to form hard nitrides in the surface layer (typically 250?). Performed at between 500 and 750^oC from a gas, salt bath or plasma glow discharge.
node: Used in a numerical simulation to attach the adjacent elements.
Non Transferred Arc (Plasma): The plasma arc which transferes heat energy to plasmagenic gas (Argon, Helium, Hydrogen, Nitrogen) in order to promote the plasma state according to the Saha's law. This arc strikes between the tungsten electrode (cathode) and the constricting nozzle (anode). The term Pilot Arc is also used in Plasma Transferred Arc process (P.T.A. welding).
Notched Coating Adhesion: NCA: A recent characterization technique (test) used to analyze adhesive bond durability.
Nuclear Reaction Analysis NRA: An ion beam technique which allows light mass elements profiling into materials. Analysis depth up to one micrometer.
OMCVD: See Organic Metal Chemical Vapor Deposition
Organic Metal Chemical Vapor Deposition: This process uses metal organic reactants having a low cracking temperature.It allows deposition of metallic carbides such as CrC with a moderated process temperature (~400:C).
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.
Pack carburising: See Carburising
PACVD: See Plasma Assisted Chemical Vapor Deposition
Painting: The application of organic based layers (acrylics, etc) for corrosion protection and decorative purposes.
Particle: The metal powder which is introduced into a plasma spray gun. One of two phases after the fluid that are modelled in a two-phase flow plasma spray gun simulation.
Particle chemistry: The elements contained within the particles of a spray powder.
Particles Induced Gamma-ray Emission or PIGE: An ion beam technique particulary well suited for the determination of light mass element concentrations into materials. Anaylsis depth up to a few micrometers.
Particles Induced X-ray Emission or PIXE: An ion beam technique used in surface science for stoichiometry analysis and trace elements quantification. Ideal for coating impurities analysis.
Passivating: The post treatement (usually by chromating) of nickel, cadmium or zinc coatings to reduce their corrosion rates.
Peening: A stream of charp material particles which break superficial fiber, reducing internal stress fields.
Perfluro Alkyle Ether (PFA): Relatively hard long chain polymer with inert, orientated structure. Applied by spraying and then melt flowing at tempertures above 250^oC. Combines non-stick with wear resistance.
Perfuoroether (FEP): A soft long chain polymer with an inert, orientated structure. Applied by spraying and then melt flowing at 400^oC. Excellent non-stick properties.
Phosphating
Phosphating: A conversion process fro steel surfaces to enhance corrosion protection. It is often zinc based and is rarely more than 25 thick
Photothermal 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.
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.
Plasma: Plasma is a gas (usually Argon, Helium, Nitrogen, Hydrogen) that has been heated to a sufficiently high temperature to become partially ionized and therefore electrically conductive. The term was introduced by Irving LANGMUIR in 1930.
Plasma Assisted Chemical Vapor Deposition: This process enables to reduce the high process temperature of CVD (commonly 800-1000 :C) to the 150-250 :C range. It allows to larger panel of basic materials.
Plasma Carburising: See Carburising
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 Nitriding: Also called Ion Nitriding. See Nitriding
Plasma Spraying: A thermal spraying process in which the heat source is a plasma jet.
Plasma Transferred Arc
Plasma Transferred Arc: See 'Transferred Arc'
Plasma-Based Ultra-fine Particle Synthesis: A liquid precursor is atomized and injected into the plasma flame; the plasma synthesized particles are collected either as a deposit on a substrate or as a powder on an electrostatic precipitator.
Plenum (Plasma): Space or chamber confined by the inner wall of the constricting nozzle and the cathodic electrode. The shape and size of this annular chamber play the highest role in Plasma Arc torches (welding, spraying).
Polyester: A condensation polymer formed by the interaction of polyhydric alcohols and polybasic acids. They are used in the manufacture of glass-fiber products. See Alkyd resin.
Polymer: A substance having large molecules consisting of repeated units. There are a number of natural polymers, such as polisacharides synthetic polymer are extensively used in plastics.
Polytetrafluorethylene (PTFE): A long chain polymer with orientated structure providing low friction. Applied as a coating (by spraying or dipping and curing) or as powder additions to other coatings (for instance electroless nickel).
Porosity: The presence of pores or voids in a coating whether connected or not. Porosity is not the same as pull-out.
Powder Coating: Polymeric coatings applied for corrosion protection on low friction. Applied dry with electrostatic attraction to the part
Powder coating (PTA)
Powder gas flow rate: The flow rate of the gas propelling the powder into the plasma jet in plasma spraying.
Powder injection angle: The angle from which the powder is injected into the plasma jet in plasma spraying.
properties: Fluid or particle properties as used in a CFD simulation. Fluid properties would be; density, viscosity, volume of expansion,. Particle properties would be; density, specific heat of evaporisation.
PSP: See Plasma-Based Ultra-fine Particle Synthesis
PTA welding: See Plasma Transferred Arc Welding
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.
PVD: See Physical Vapour Deposition
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.
Resin: A synthetic or naturally occurring polymer
Rhodium plating: The electrodeposition of rhodium for oxidation resitance combined with surface hardness.
Rutherford Backscattering Spectrometry or RBS: A relevant ion beam technique for surface composition analysis (analysed depth: up to 1 micrometer). It is widely used in thin film science.
Salt Bath Carburising: See Carburising
Salt Bath Nitriding: See Nitriding
Salt Bath Nitrocarburising: See Nitrocarburising
Salt spray test: Accelerated testing of corrosion properties of metallic coatings
Scanning Tunneling Microscopy: Technique to directly observe individual atoms on surfaces. In STM a solid specimen in air, liquid or vacuum is scanned by a sharp tip located within a few Å from the surface. A quantum -mechanical tunneling current flows between atoms on the surface and those on the tip. The magnitude of the current depends upon the separation between the surface and tip atoms, so that it is possible to obtain surface topography with atomic resolution.
Shot peening: The bombardment of a component surface with steel or cermamic 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.
Silver plating: The electrodeposition of silver for electrical, decorative or anti-fretting properties.
simulation: A procedure which describes, numerically, a given flow regime. The solution of the numerical method should replicate the real life flow characteristics.
Single Port Nozzle (Plasma): Constricted nozzle with only one internal bore, concentric with the longitudinal axis of the tungsten electrode. The shape and design accuracy of this single orifice is decisive for arc stability in plasma welding.
Size analysis: Analysis of the size of the particles being deposited by spraying processes.
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.
Spalling: The lifting or detachment of a coating from the substrate.
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.
Spray dried powder: Powder formed by the spray drying process.
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.
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.
Steam tempering: The production of a stable oxide on steel parts by treatement in steam at about 300^oC. Improves corrosion performaance and reduces friction.
Strain: A measure of the extent to which a body is deformed when it is subjected to a stress.
streamlines: A streamline is a line of fluid particles, the velocity of each particle is tangential to the line, the particle can not cross the streamline.
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.
Substrate: The parent or base material to which the coating is applied.
Surface energy: Surface energy exists because the molecules of a condensed phase are atttracted to each other, which is what causes the condensation. The force required for the removal of molecular contact from above a surface, i.e. for the bond-breaking, is the surface energy.
Surface Finish (or Surface Texture): A measure of the roughness of a surface by expressing the average deviation of the peaks and valleys from the mean line (denoted Ra).
Surface parameter Ra: Arithmetical mean roughness: is the arithmetical average value of all departures of the surface profile from the mean line throughout the sampling length.
Surface parameter Rmax: It is the largest single peak-to-valley height within five adjoining sampling lengths 'le'.
Surface parameter Rt: Maximum roughness depth: is the distance between the highest and the lowest points of the surface profile within the evaluation length Lm.
Surface parameter Rz: Mean peak-to-valley height: is the average of the single peak-to-valley of five adjoining sampling lengths 'le'.
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.
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.
Tensile stress: Axial forces per unit area applied to a body that tend to extend it.
Thermal barrier coating: A coating produced to present an insulating barrier to a heat source and to protect the substrate.
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.
Thermochemically formed coatings: A painted, dipped or sprayed chromium oxide based caoting consolidated by repeated depostion and curing cycles (about 500^oC).
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.
Titanium Nitride: Gold coloured ceramic, typically applied as a thin coating (1 to 55) by either PVD or CVD. Ver hard (3500Hv). Used on cutting tools and forming tools and other surfaces needin wear resistance
trajectory: The path a particle takes when its injected into a stream of moving gas (or fluid). It is used in CFD to predict the path of the metal powder used in the plasma spray gun analysis.
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.
Transferred Arc (Plasma): The plasma arc which transferes heat energy to the workpiece (base material). This arc strikes between the tungsten electrode (cathode) and the base material (anode). The term Main Arc is also used in Plasma Transferred Arc process (P.T.A. welding).
Transmission Electron Microscopy TEM: Applied to thin and thick film analysis, it permits observation of smaller features such as microcolumnar voids and patterns of dislocations in the bulk.
trap: This condition applies to a wall entity during a CFD analysis of a particulate two-phase flow. A particle touches the wall entity, its momentum and energy are assumed to be completely lost to the wall entity, while the mass is assumed lost to the fluid.
Tungsten Carbide: Metallic coloured ceramic, often applied as a coating by thermal spraying. Typically 50 to 2505 thick with a Co or Ni binder. Used for high load applications requiring extreme wear resistance.
Tungsten Disulphide: Dry lubricant coating - applied at ambient temperature. Coating is 0.5 micron thick works at temperatures -273deg k to 650deg C. For use at high vacuum, cryogenic or high temperatures. Extends bearing life. Prevents galling, fretting & seizing. Can be applied to miniture ball races in assembled condition. Developed by NASA for use in deep space. Used in plastics industry as permanent release coating.
turbulent flow: Technical terminology for the type of flow which occurs when the Reynolds Number exceeds 2000. In contrast to laminar flow, turbulent flow can be described as an irregular and random-looking motion.
two-phase: Particular type of analysis where two of the three phases (gas,liquid and solid) are modelled together. The numerical equations are modified to produce an interaction between the two phases
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.
Vacuum or Low Pressure Plasma Spraying: Plasma spraying carried out in a chamber which has been evacuated to a low partial pressure of oxygen. It is then usually partially backfilled with argon to avoid the possibility of forming a glow discharge.
vector plot: A way of displaying results from a CFD analysis, where the velocity of each particle is visualised with an arrow. Since the arrow represents "velocity" it has a direction and magnitude (the length of the arrow indicates the relative magnitude)
Wear: Loss of material from a surface by means of relative motion between it and another body. Third bodies i.e. grit
White Layer: See 'Compound layer'
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.
X-Ray Diffraction XRD: A surface science technique for cristalline structure analysis of materials. Widely used both in the research and industrial area. analysed depth up to 10 micrometers.
X-ray Photoelectron Spectroscopy XPS: An electron beam technique applied for near-surface elements identification and chemical state analysis. Widely used in thin film science. Analysis depth: a few Angstroms.
Zinc Plating: The electrodeposition of zinc or zinc alloys (eg Zn/Ni, Zn/Sn) to provide galvanic corrosion protection.

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