Wear due to hard particles or hard protuberances forced
against and moving along a solid surface.
Acetylene C2H2 (ethyne)
Unsaturated aliphatic hydrocarbon gas. Used as a fuel gas
in combustion thermal spray processes, welding and cutting. Acetylene
has the highest flame temperature and requires the smallest
amount of oxygen to form a neutral flame.
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.
Wear due to localised bonding between contacting solid
surfaces leading to material transfer between the two surfaces or the
loss from either surface.
Agglomerate
Several particles adhering together.
Agglomerated powder
A powder made up of agglomerates
Air classification
The separation of powder into particle size fractions by
means of an air stream of controlled velocity.
Aluminising (gas)
High temperature (approx. 900oC) pack or
gaseous diffusion of aluminium into the surface of a component to
enhance high temperature corrosion and oxidation resistance.
Alkyd resin
A type of polyester resin used in paints and other surface
coatings. The original alkyd resins were made by co-polymerising
phathalic anhydride with glycerol, to give a brittle cross. Linked
polymer.
Aluminising (hot dip)
An aluminium coating process based on submersion in liquid
metal, usually with a strip steel product being continuously fed
through the bath. Provide galvanic corrosion protection.
Aluminising (Thermal Spray Method)
Thermal sprayed coatings of aluminium usually on
substrates of steel or nickel chromium alloys which are subsequently
heat treated to aluminise the surface.
Aluminium Ion Plating
The deposition of aluminium by a vacuum evaporative
process. Provides galvanic corrosion resistance. Normally given a
passivation treatment.
Amorphous
non-crystalline, or devoid of regular structure.
Anion
A negatively charged ion
Anode
Positively charged electrode (nozzle in plasma gun) - the
electrode of an electrolytic cell at which oxidation is the principle
reaction. (Electrons flow away from the anode in the external circuit.
Its usually the anode where corrosion occurs and metal ions enter
solution.) Anodic coating
A coating that becomes the anode in an electrochemical
cell with the substrate (cathode). The only metals in common use for
thermal spraying which are anodic to iron and steel are zinc and
aluminium.
Anodising
The production of an oxide layer on aluminium alloys. The
process is electrolytic, a typical electrolyte being sulphuric acid.
Treatment at room temperature produces thin, decorative layers with
some corrosion protection. Treatment at 0oC produces hard,
thicker layers (up to 100µ) with wear resistance. They can be
post sealed to give improved corrosion resistance.
Apparent density
The weight of a unit volume of powder or coating
Apparent hardness
The value obtained by testing a coating or sintered
material with standard indentation hardness equipment. (See
macrohardness) Since the reading reflects a composite of pores and
solid material, (which may be particles relatively poorly bonded
together) it is usually lower than that of an equivalent solid wrought
or cast material. Not to be confused with particle hardness (See
microhardness).
A thermal spray process where two electrically conducting
wires are brought together to form an electric arc. Molten material
formed in the arc is projected by a compressed gas stream towards the
work piece to form a coating.
Monatomic noble gas, atomic number 18, one of the most
inert elements. Commonly used as a plasma gas
for plasma spraying and providing inert
environments for many processes.
Atomisation
The dispersion of a molten material into particles by a
rapidly moving gas or liquid stream or by mechanical dispersion.
Atomised powder
A powder produced by the dispersion of a molten material
into particles by a rapidly moving gas or liquid stream or by
mechanical dispersion.
Autoclaving
The production of a stable, protective oxide on steel
parts by treatment in a pressurised, high temperature steam containing
atmosphere.
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, chemical 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
and/or to provide a corrosion or oxidation barrier.
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 temperature (approx. 900oC) gas or
pack process. Produces hard phases within the surface (Typically
100µm deep).
The electrolytic deposition of cadmium to provide galvanic
corrosion protection. Restricted by environmental considerations.
Cadmium ion plating
The deposition of cadmium by a vacuum process to provide
galvanic corrosion protection.
Carbonitriding
Similar to Carburising. Diffusion of carbon and nitrogen
at about 900oC (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 900oC (by pack, gas, salt
bath or plasma process) into low carbon steel, followed by quenching
and tempering to produce martensitic case (typically 1mm thick).
Carrier gas
Usually nitrogen or argon gas that carries powder into the
thermal spray process.
Case-hardening
See Carburising
Cathode
Negatively charge electrode. Electrode of an electrolytic
cell at which reduction is the principle reaction. (Electrons flow
towards the cathode in the external circuit.) Cathodic coating
Coatings which become the cathode in an electrochemical
cell with the substrate (anode). This type of coating protects the
substrate from corrosion only by being a complete barrier. If the
coating allows the environment to reach the substrate, accelerated
corrosion of the substrate will occur.
Cathodic protection
A technique to reduce the corrosion rate of a metal by
making it the cathode of an electrochemical cell. Thermal spray zinc
and aluminium coatings provide this protection to steel substrates, the
coating being the anode and the steel being the cathode.
A form of erosion causing material to be removed by the
action of vapour bubbles in a very turbulent liquid.
Cermet powders
A blended or composite powder of metal and ceramic
constituents.
Chemical conversion coating
A protective or decorative non-metallic coating produced in situ
by chemical reaction of a metal with a chosen environment. (It is often
used to prepare the surface prior to the application of an organic
coating.)
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
Chromate conversion is a process which completely
degreases and removes all traces of the oxide film, replacing it by
immersion with a chromate coating which can then be painted. It is used
as a post-treatment for cadmium, zinc and aluminium coatings
Chromising
High temperature (approx. 900oC) pack or
gaseous diffusion of chromium into the surface of a component to
enhance high temperature corrosion and oxidation 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 layer of material onto the surface of
a substrate.
Cold welding
Cohesion between two surfaces of a metal, generally under
the influence of externally applied pressure at room temperature.
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.
Composite Coating
Mixture of two or more materials. Many thermal spray
coatings could be considered as composites.
Composite Powder
A powder in which each particle consists of two or more
distinct materials joined together.( Not the same as a powder blend.)
Chemical or electrochemical reaction between a material
and it's environment which results in deterioration in the properties
of the material.
Corrosion fatigue
The process in which a metal fractures prematurely under
conditions of simultaneous corrosion and repeated cyclic loading at
lower stress levels or fewer cycles than would be required in the
absence of the corrosive environment.
Corrosion potential
The potential of a corroding surface in an electrolyte
relative to a reference electrode measured under open circuit
conditions.
Localised corrosion of a metal surface at, or immediately
adjacent to, an area that is shielded from the full exposure to the
environment because of close proximity between the metal and the
surface of another material.
Crushed powder
Powder formed from a solid which is then crushed to the
appropriate size for spraying.
Copper plating
The electrolytic deposition of copper to provide either a
corrosion barrier (often as an undercoat for hard chrome plate) or for
reclamation of worn parts.
The removal of grease and oil from a surface. Degreasing
by immersion in liquid organic solvents or by solvent vapours
condensing on the parts to be cleaned.
Deposit corrosion
Localised corrosion under or around a deposit or
collection of material on a metal surface. (See also crevice
corrosion.)
A thermal spray process in which the coating material is heated
and accelerated to the work piece by a series of detonations or
explosions from oxy-fuel gas mixtures.
Diamond-like Carbon
A thin carbon-based coating applied by either PVD or
PACVD. It has high hardness and low friction.
Diffusion Coating
An alloy coating produced by applying heat to one or more
coatings deposited on a basis metal.
Ductility
The ability of a material to deform plastically without
fracturing.
An electrochemical system consisting of an anode and a
cathode in metallic contact and immersed in an electrolyte. (The anode
and cathode may be different metals or dissimilar areas on the same
metal surface.
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.
Electrolyte
A conducting medium in which the flow of current is
accompanied by movement of matter. A substance that is capable of
forming a conducting liquid medium when dissolved or melted.
Electrolysis
Production of chemical changes of the electrolyte by the
passage of current through an electrochemical cell.
Electromotive Force Series (EMF Series)
A list of elements arranged according to their standard
electrode potentials, with "noble" metals such as gold being positive
and "active" metals such as zinc being negative.
Elasticity
The property of certain materials that enables them to
return to their original dimensions after an applied stress.
Electroplating
The electrodeposition of an adherent metallic coating upon
an electrode for the purpose of securing a surface with properties or
dimensions different from those of the substrate material.
Embrittlement
The severe loss of ductility or toughness or both, of a
material, usually a metal or alloy.
Removal of material from a surface due to mechanical
interaction between that surface and a fluid, a multicomponent fluid,
or impinging liquid or solid particles
Associated action involving corrosion and erosion in the
presence of a corrosive substance.
Etch
A roughened surface produced by chemical, electrochemical
or mechanical means. To dissolve unevenly a part of the surface of a
material to highlight microstructure in metallography.
Exfoliation
Corrosion that proceeds laterally from the sites of
initiation along planes parallel to the surface, generally at grain
boundaries or coating interfaces, forming corrosion products that force
metal or coating away from the body of the material, giving rise to a
layered appearance.
Certain materials undergo chemical reactions when
thermally sprayed and produce extra heating. This can be useful in
improving adhesion of the coating to the substrate.
A cumulative effect causing a material 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.
Wear of a solid surface caused by fracture arising from
material fatigue.
Blasting
A pressurised stream of particulates (ceramic, plastic, metal, ,
etc..) applied on a surface to clean, peen or abrade.
Fines
The portion of a powder composed of particles which are
smaller than the specified size
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.
Flame spraying
A thermal spraying process in which the particles are
heated and accelerated in a flame (combustion flame, plasma flame). Old
term for thermal spray process.
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.
Wear arising as a result of fretting (see fretting).
Friction
The reaction force resulting from surface interaction and
adhesion during sliding. The friction Coefficient is defined as the
friction force divided by the load.
A process in which the coating material is deposited by
thermal spraying and then fused by post heat treatment. This can be
done by flame, induction heating, furnace or by laser.
Fused and crushed powder
Powder formed from a fused solid mass which is then
crushed to the appropriate size for spraying.
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.
Galvanic corrosion
Accelerated corrosion of a metal because of an electrical contact
with a more noble metal or non-metallic conductor in a corrosive
electrolyte.
Galvanic Series
A list of metals and alloys arranged according to their
relative corrosion potentials in a given environment.
Gas carburising
See Carburising
Gas flow rate
The flow rate of gas (e.g. litres per minute) through the
spraying torch.
Gas nitriding
see Nitriding
Gas nitrocarburising
See Nitrocarburising
Galvanising
A hot dip process for deposition of zinc for galvanic
corrosion protection of steel.
Gold plating
The electrolytic deposition of gold for decorative or
electrical applications.
Granular powder
Particles having approximately equidimensional
nonspherical shapes.
Grinding
The removal of material by the use of fixed abrasives like
grinding wheels or emery paper.
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
or area of penetration is measured.
A Thermal spray process. The spray powder particles are injected
into a high velocity jet formed by the combustion of oxygen and fuel,
heated and accelerated to the work piece.
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.
Hot dip coating
A metallic coating obtained by dipping the substrate metal
into a molten metal.
Diatomic gas, atomic number 1, The lightest element, very
reactive and powerful reducing agent. Used as a secondary plasma gas in
the plasma spraying process and as a fuel gas in combustion thermal
spray processes (CWS, CPS
and HVOF)
Hydrogen embrittlement
Hydrogen induced cracking or severe loss of ductility caused by
the presence of hydrogen in the metal. Hydrogen absorption may occur
during electroplating, pickling etc.. ( The use of hydrogen as a
secondary gas in plasma spraying does not appear to effect substrates
and the majority of coatings, one exception being titanium coatings.)
Hydrophilic
Tending to absorb water.
Hydrophobic
Tending to repel water or lacking affinity for water
A process of filling the pores of a coating with resin,
wax or oil. (See sealer, vacuum impregnation)
Induction heating
The heating of a electrically conductive material by an induction
coil producing alternating magnetic fields which induce alternating
electric currents to flow in the material and cause heating by
resistance. Used in many heating process (induction fusing, induction
plasma, induction hardening etc...)
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.
A process resulting in a continuing succession of impacts
between (liquid or solid) particles and a solid surface.
Impingement corrosion
a form of erosion-corrosion generally associated with the
impingement of a high velocity, flowing liquid containing air bubbles
against a solid surface.
Interconnected porosity
A network of pores in and extending to the surface of a
coating.
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.
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.
Irregular powder
Particles lacking symmetry.
Intergranular corrosion
Preferential corrosion at or adjacent to the grain
boundaries of a metal or alloy.
Internal oxidation
The formation of isolated particles of corrosion products beneath
the surface of the metal or coating. (This occurs as a result of
preferential oxidation of certain alloy constituents by inward
diffusion of oxygen, nitrogen, sulphur, etc..
Rubbing two surfaces together, with or without abrasives,
for the purpose obtaining extreme dimensional accuracy or superior
surface finish.
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 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.
Liquid impingement erosion
Progressive loss of material from a solid surface due to
continue exposure to impacts by liquid drops or jets.
Localised corrosion
Corrosion at discrete sites, for example, pitting, crevice
corrosion, and stress corrosion cracking.
The hardness of a coating as measured on a macroscopic
scale, which shows the coatings bulk properties.
Magnetron sputtering
See Sputtering. In this PVD process, the sputtering action
is enhanced by intense magnetic fields.
Matrix
The continuous phase of a material or coating in which
separate particles of another constituent are embedded. (Like tungsten
carbide particles in a cobalt matrix)
Usually represented by mechanical interlocking of the
deposited particles with the rough heights on the substrate surface
produced during grit blasting.
The hardness of a coating as measured on a microscopic
scale. Can show the hardness of individual phases within the coating
and avoid the effects of porosity.
Microinch
One millionth of an inch, 0.000001".
Micrometer (µm)
One millionth of a metre, 0.001mm.
Microtrack
A device for measuring powder particle size distributions.
The electrolytic deposition of nickel to form a 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 250µm). Performed at
between 500 and 750oC 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
250µ). Performed at between 500 and 750oC from a gas,
salt bath or plasma glow discharge.
A metal that does not readily tend to furnish ions, and therefore
does not dissolve readily, nor easily enter into such reactions as
oxidation, etc.. The opposite of base metal.
Nodular powder
Irregular particles having Knotted, rounded, or similar
shapes.
Loss of electrons by a constituent of a chemical reaction.
(Also refers to the corrosion of a metal that is exposed to an
oxidising gas at elevated temperatures.)
The elements contained within the particles of a spray
powder.
Particle size
The controlling lineal dimension of an individual particle
as determined by analysis with sieves or other suitable means.
Particle size distribution
The percentage by weight, or by number, of each fraction
into which a powder sample has been classified with respect to sieve
number or microns.
Passivation
The process in metal corrosion by which metals become
passive. (See passive)
Passivator
A type of inhibitor which appreciably changes the
potential of a metal to a more noble (positive) value.
Passive
The state of a metal surface characterised by low
corrosion rates in a potential region that is strongly oxidising for
the metal.
Peening
Blasting process using spherical shaped beads or shot for
cleaning and/or modifying surface properties.
Permeability
A property measured as a rate of passage of a liquid or
gas through a coating
Plus sieve
The portion of a powder sample retained on a sieve of
specified number. (See minus sieve.)
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 and
good surface for painting.
Photo-thermal NDT
An NDT 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.
Pitting--tribology
A form of wear characterised by the presence of surface
cavities the formation of which is attributed to processes such as
fatigue, local adhesion, or cavitation.
Pitting--corrosion
corrosion of a metal surface, confined to a point or small area,
that takes the form of cavities
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 flame or jet.
A thermal spraying process in which the heat source is a
plasma flame.
Plasma Transferred Arc (PTA)
Similar to the plasma spray process in that powder is sprayed
through a plasma, but instead of being heated via a neutral plasma
(carrying no electric current) the arc is transferred to the substrate
(made to be the anode). This is a hot process and produces coatings
similar to fused or weld hardfacing coatings.
Plowing
The formation of grooves by plastic deformation of the
softer of two surfaces in relative motion.
Polyester
A condensation polymer formed by the interaction of
polyhydric alcohols and polybasic acids. They are used in some coatings
and the manufacture of glass-fibres products. See Alkyd resin.
Polymer
Organic 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.
The presence of pores or voids in a coating, usually
expressed as a percentage by volume.
Powder coating
A polymeric coating deposited via electrostatic attraction
Powder injection angle
The angle from which the powder is injected into the
plasma jet in plasma spraying.
Pre-alloyed powder
A powder composed of two or more elements which are
alloyed in the powder manufacturing process and in which the particles
are of the same nominal composition throughout.
Polishing
The smoothing of a material surface by means of the action
of abrasive particles attached usually to a fabric cloth. The final
mechanical step in metallographic preparation.
Propane (C3 H8)
Aliphatic hydrocarbon gas used as a fuel gas in thermal
spray processes.
Propylene (C3 H6)
Hydrocarbon gas used as a fuel gas in thermal spray
processes. Higher flame temperature than hydrogen and propane.
Pull-out occurs when particles are plucked from the
coating during machining or grinding. Also occurs during metallographic
preparation. It is sometimes confused with porosity.
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.
A substance that cases reduction, thereby itself becoming
oxidised.
Reduction
A reaction in which electrons are added to the reactant.
More specifically, the addition of hydrogen or the abstraction of
oxygen.
Resin
A synthetic or naturally occurring polymer
RFI Shielding
Thermal spray coatings of electrically conductive metals
such as zinc, aluminium and copper are used on non-conducting composite
casing materials to shield sensitive electronic devices from radio
frequency electromagnetic interference.
Rhodium plating
The electro-deposition of rhodium for oxidation resistance
combined with surface hardness.
A coating that provides corrosion protection wherein the
coating material corrodes in preference to the substrate, thereby
protecting the latter from corrosion.
Salt Bath Carburising
See Carburising
Salt Bath Nitriding
See Nitriding
Salt Bath Nitrocarburising
See Nitrocarburising
Scoring
A severe form of wear characterised by the formation of
extensive grooves and scratches in the direction of sliding.
Scratching
The mechanical removal or displacement, or both, of
material from a surface by the action of abrasive particles or
protuberances sliding across the surfaces.
Sealant, Sealer
A preparation of resin or wax type materials for sealing
the porosity in coatings.
Sealing
A process which, by absorption of a sealer into thermal
spray coatings, seals porosity and increases resistance to corrosion of
the underlying substrate material.
A name given to thermal spray coatings that are capable of
bonding to clean smooth surfaces. Bond and "one-step" coatings are
normally in this group. These are particularly important where grit
blasting or surface roughening processes must be omitted.
Shrinkage
A decrease in dimensions of a coating during processing.
Shrinkage stress
The residual stress in a coating caused by shrinkage
during processing.
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.
Sieve classification
That portion of a powder sample which passes through a
standard sieve of specified number and is retained by some finer sieve
of specified number.
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 materials being
sprayed.
Silver plating
The electro-deposition of silver for electrical,
decorative or anti-fretting properties.
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.
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
treatment in steam at about 300oC. Improves corrosion
performance and reduces friction.
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.
Stress corrosion cracking
A cracking process that requires the simultaneous action
of a corrodent and sustained tensile stress.
Cleaning and roughening the surface to be sprayed, usually
by grit blasting. This is to increase the adhesion of the coating to
the substrate.
Sulphidation
The reaction of a metal or alloy with a sulphur containing
species to produce a sulphur compound that forms on or beneath the
surface of the metal or alloy.
Surface topography
The geometrical detail of a surface, relating particularly
to microscopic variations in height.
Surfacing
The application of a coating or cladding to a surface to
impart a change in its surface behaviour.
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 forming an insulating barrier to a heat source
to protect the substrate.
Thermochemically formed coatings
A painted, dipped or sprayed chromium oxide based coating
consolidated by repeated deposition and curing cycles (about 500oC).
A process in which coating material is heated and accelerated
from a spray torch towards the work piece. The deposited material forms
a coating on the surface.
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.
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 work piece
and the arc is said to be transferred.
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.
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.
