COLD GAS-DYNAMIC SPRAY PROCESS GLOSSARY

This glossary is intended to foster development of a shared vocabulary within the rapidly evolving field of cold gas-dynamic spray. Defining this terminology is an important and controversial challenge that we hope will lead to a future standard representing industry consensus.

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A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

 

A

 

abradable coating. A sacrificial layer of material applied to a substrate, usually to enable a shape-conforming seal.

 

abrasion. The rubbing or scraping of the surface layer.

 

abrasive. A natural or manufactured substance used to grind, wear down, rub away, smooth, scour, clean, or polish.

 

abrasive blasting. A method of cleaning or roughening a surface by a forcibly projected stream of abrasive particles.

 

abrasive wear. The surface condition resulting from active contact with an abrasive.

 

adhesive strength. A nonstandard term when used for bond strength.

 

agglomerated powder. A substance of clusters of finely divided particles. See also conglomerated powder and flocculated powder.

 

aggregate, n. A mass of particles held together by mechanical forces.

 

air classification. The separation of powder into particle size fractions by means of an air stream of controlled velocity.

 

aligned porosity. A localized array of porosity oriented in a line.

 

alloy. A substance with metallic properties and composed of two or more chemical elements of which at least one is a metal.

 

alloy powder. Powder prepared from a homogeneous molten alloy or from the solidification product of such an alloy. See also powder blend.

 

amorphous. Non-crystalline, or devoid of regular structure.

 

apparent density. The weight of a unit volume of solid, which might not be homogeneous.

 

apparent hardness. The indicated solidity and firmness of a solid, which might not be homogenous.

 

asperity. A small-scale topographical surface irregularity such as a peak, protuberance.

 

atomization. The dispersion of a material into fine particles by a rapidly moving gas, liquid stream, or by mechanical dispersion.

 

atomized powder. A powder produced by the dispersion of a molten material into fine particles by a rapidly moving gas, liquid stream, or by mechanical dispersion.

 

automatic spraying. Spraying with equipment requiring only occasional or no observation and no manual adjustments during its operation. See also manual spraying, mechanized spraying, robotic spraying, and semiautomatic spraying.

 

axial injection. Introduction of a material along an axis parallel or coincident with the axis of the spray jet.

 

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B

 

babbitt metal. Nonferrous bearing alloys consisting mainly of various amounts of copper, antimony, tin, and lead.

 

backing. A material or device placed against the back side of a substrate to facilitate the spray process or support the substrate.

 

bead. See spray deposit bead.

 

binder.  A cementing medium used in producing composite or agglomerated powders.

 

blast helmet. Personal protective device enclosing the person's head in a loose-fitting hard shell, directing fresh air to the wearer, and protecting the head and neck from flying particles generated by abrasive blasting.

 

blast hood. Personal protective device enclosing the person's head and neck in a loose-fitting covering, and protecting the head and neck from flying particles generated by abrasive blasting.

 

blasting. See abrasive blasting.

 

blended powder. Thoroughly intermingled powder containing materials of substantially similar chemical composition. See also mixed powder.

 

block sequence. A combined longitudinal and cross-sectional sequence for a continuous multiple-pass spray deposit in which separated increments are completely or partially sprayed before intervening increments are sprayed. See also cascade sequence, continuous sequence, and cross-sectional sequence.

 

bond. See covalent bond, ionic bond, mechanical bond, and metallic bond.

 

bond coat. A coating layer applied to a substrate to improve the adherence or performance of subsequent layers.

 

bonding force. The attractive force holding atoms together. See also covalent bond, ionic bond, and metallic bond.

 

bond specimen. The test specimen on which a spray deposit has been applied to determine the bond strength and spray deposit strength.

 

bond strength. The force per unit area required to separate a spray deposit from the substrate.

 

bottle. A nonstandard term when used for gas cylinder.

 

bow shock. A flow discontinuity in the spray feedstock-laden spray jet caused by deceleration and deflection of the gas flow ahead of the substrate. See also compressed layer and free jet.

 

brittleness. The tendency of a material to fracture without first undergoing significant plastic deformation.

 

buildup. A surfacing variation in which surfacing material is deposited to achieve the required dimensions. See also buttering, cladding, and hardfacing.

 

buildup sequence. A nonstandard term for cross-sectional sequence.

 

buttering. A surfacing variation depositing surfacing metal on one or more surfaces to provide metallurgically compatible metal for a joint. See also buildup, cladding, and hardfacing.

 

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C

 

carrier gas. A gas conveying powder in the spray process from the powder feeder through the surfacing gun. See also spray feedstock driving gas.

 

cascade sequence. A combined longitudinal and cross sectional sequence in which spray deposits are made in overlapping layers. See also block sequence, continuous sequence, and cross-sectional sequence.

 

cathodic protection. A technique to reduce the corrosion rate of a metal by making it the cathode of an electrochemical cell.

 

cavitation erosion. The progressive loss of material from a solid surface due to the collapse of bubbles or cavities within a liquid containing a gas, vapor, or a mixture of the two.

 

ceramic. A class of inorganic nonmetallic materials subjected to high temperatures during manufacture.

 

cermet powders. A blended or composite powder of metal and ceramic constituents.

 

cladding. A surfacing variation depositing or applying surfacing material, usually to improve corrosion or heat resistance. See also buildup, buttering, and hardfacing.

 

coating. A nonstandard term when used for spray deposit or thermal spray deposit.

 

coating density. A nonstandard term when used for spray deposit density ratio.

 

coating strength. A nonstandard term when used for spray deposit strength.

 

cold gas-dynamic spray (CGSP). A solid-state spraying process using a supersonic jet of compressed gas to accelerate near-room-temperature spray feedstock particles through a nozzle at very high velocities towards a substrate where they plastically deform and consolidate on impact. See high-pressure cold gas-dynamic spray, low-pressure cold gas-dynamic spray and pulsed cold gas-dynamic spray.

 

cold spray. See cold gas-dynamic spray. See also high-pressure cold gas-dynamic spray, low-pressure cold gas-dynamic spray and pulsed cold gas-dynamic spray.

 

composite. A material consisting of two or more discrete materials with each material retaining its physicochemical identity.

 

composite powder. See powder composite.

 

composite spray deposit. A spray deposit made with two or more dissimilar surfacing materials, which may be formed in layers.

 

compressed layer. A high-pressure high-density gas layer formed between the substrate surface and the bow shock creating a resistance to flow. See also bow shock and free jet.

 

compressed layer temperature. See flow stagnation temperature.

 

conformal spray deposit. A spray deposit covering and fitting the shape of the substrate.

 

conglomerated powder. A substance of particles of different materials. See also agglomerated powder and flocculated powder.

 

continuous sequence. A longitudinal sequence in which each spray deposit pass is made continuously from one end of the substrate to the other. See also block sequence, cascade sequence, and cross-sectional sequence.

 

continuous spray deposit. A spray deposit made without interruption.

 

convergent-divergent nozzle. See de Laval nozzle.

 

corrosion. Chemical or electrochemical reaction between a material and its environment which results in deterioration in the properties of the material.

 

cosmetic spray deposit bead. A spray deposit bead used to enhance appearance.

 

cosmetic spray deposit pass. A spray deposit pass resulting in a cosmetic spray deposit bead.

 

covalent bond. A primary bond arising from the reduction in energy associated with overlapping half-filled orbitals of two atoms. See also bonding force, ionic bond, mechanical bond, and metallic bond.

 

cover bead. A spray deposit bead resulting from a cover pass.

 

cover pass. A spray deposit pass or passes resulting in the exposed layer of a multipass spray deposit on the side from which spraying was done.

 

crack. A fracture type discontinuity characterized by a sharp tip and high ratio of length and width to opening displacement.

 

crater. Substrate surface discontinuity caused by mechanical impact such as a particle impacting at less than the critical velocity.

 

critical spray angle. The orientation of spray jet impingement at which the angle of incidence is sufficient to facilitate spray deposition.

 

critical spray velocity. The temperature-dependant (particle and substrate) spray velocity above which there is a transition from erosion to coating formation.

 

cross-sectional sequence. The order in which the passes of a multiple-pass spray process are deposited. See also block sequence, cascade sequence, and continuous sequence.

 

crushed powder. Powder formed from a solid which is crushed to the appropriate size for spraying. See also milled powder.

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D

 

debond. An interface separation of a coating from a substrate. See also delamination.

 

defect. A discontinuity or discontinuities that by nature or accumulated effect render a part or product unable to meet minimum applicable acceptance standards or specifications. The term designates rejectability. See also discontinuity and flaw.

 

degreasing. The removal of grease and oil from a surface.

 

delamination. The separation of a coating into constituent layers. See also debond.

 

de Laval nozzle. A nozzle which converges to a throat and then diverges to allow gas expansion and produce gas acceleration.

 

delay time. A nonstandard term when used for deposition delay.

 

demixing. The act of segregating a powder mixture, sometimes due to overmixing. See also segregation.

 

deposit. A nonstandard term when used for spray deposit.

 

deposition. The process of applying a sprayed material to a substrate.

 

deposition delay. The time interval from initiation of surface treatment by the flow of particles to the beginning of particle attachment to the substrate.

 

deposition efficiency. See spraying deposition efficiency.

 

deposition rate. The weight of material deposited in a unit of time. Usually expressed as kilograms per hour (kg/h) or pounds per hour [lb/h].

 

deposition sequence. A nonstandard term when used for spray deposit pass sequence.

 

deposit sequence. A nonstandard term when used for spray deposit pass sequence.

 

discontinuity. An interruption of the typical structure of a material, such as a lack of homogeneity in its mechanical, metallurgical, or physical characteristics. A discontinuity is not necessarily a defect. See also defect and flaw.

 

dovetailing. A method of surface preparation involving angular undercutting to interlock the spray deposit. See also groove roughening, knurling, rotary roughening, and rough threading.

 

driving gas. See spray feedstock driving gas.

 

ductility. The ability of a material to deform plastically without fracturing.

 

duplex coating. A coating consisting of two layers of two dissimilar materials.

 

dust. Fine dry pulverized particles. See also particle and powder.

 

dynamic spray. A nonstandard term when used for cold gas-dynamic spray.

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E

 

edge loss. Spray deposit lost as overspray beyond the edge of the substrate.

 

elasticity. The property of certain materials enabling them to return to their original dimensions after an applied stress.

 

electromagnetic pulse spray. A solid-state spraying process using electromagnetic force to propel spray feedstock particles through a nozzle at very high velocities towards a substrate where the particles plastically deform and consolidate on impact. See also cold gas-dynamic spray.

 

embrittlement. The severe loss of ductility, toughness, or both, of a material usually a metal or alloy.

 

erosion. Removal of material from a surface due to mechanical interaction between the surface and a fluid, a multicomponent fluid, or impinging liquid or solid particles.

 

erosion-corrosion. Associated action involving corrosion and erosion in the presence of a corrosive substance.

 

etch. To erode a material surface by chemical, electrochemical, or mechanical means to highlight microstructure or create a pattern.

 

exfoliation. Corrosion proceeding 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.

 

exhaust booth. A system of individual units functioning collectively to gather expended spray gases and airborne materials while simultaneously flushing and renewing the air in the working environment. See also spray chamber and spraying booth.

 

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F

 

fatigue. A cumulative effect causing a material to fail after repeated applications of stress none of which exceeds the ultimate tensile strength.

 

fatigue strength. The maximum cyclic stress a material can withstand for a specified number cycles before failure occurs.

 

fatigue wear. Wear of a solid surface caused by fracture arising from fatigue in the material.

 

feeder. See powder feeder.

 

feed hopper. A container used for holding and metering spray feedstock for delivery to the spray device. See also powder feeder.

 

feed hopper pressure. See stagnation pressure.

 

feed rate. The rate at which material passes through the spray device in a given length of time.

 

feedstock. A nonstandard term when used for spray feedstock.

 

field spray deposit. A spray deposit made at a location other than a shop or the place of substrate fabrication.

 

fill bead. A nonstandard term when used for intermediate spray deposit bead.

 

fill pass. A nonstandard term when used for intermediate spray deposit pass.

 

filler. A material added to a product to increase its bulk, weight, viscosity, opacity, strength, or simply to dilute it for economy.

 

filler bead. A nonstandard term when used for intermediate spray deposit bead.

 

filler pass. A nonstandard term when used for intermediate spray deposit pass.

 

fines. The portion of a powder composed of particles which are smaller than the specified size.

 

finish allowance. The amount of excess coating left on the surface for subsequent machining.

 

fixture. A device for holding workpieces in proper relation to each other.

 

flaw. An undesirable discontinuity. See also defect and discontinuity.

 

flocculated powder. Small lumps or loose clusters of loosely aggregated particles. See also agglomerated powder and conglomerated powder.

 

flow rate. The time required for a material of standard weight or volume to flow through an orifice according to a specific procedure.

 

flow stagnation temperature. Temperature of the fluid flow at the compressed layer. See also room stagnation temperature and stagnation temperature.

 

fluidized bed. A contained mass of finely divided solids behaving like a fluid when brought into suspension by a moving gas or liquid.

 

free jet. The jet of spray feedstock-laden carrier gas from the exit of the nozzle to the bow shock. See also bow shock and compressed layer.

 

fretting wear. Material loss resulting from a small amplitude oscillatory motion between two solid surfaces in contact.

 

fused and crushed powder. Powder formed from a fused solid mass subsequently crushed to the appropriate size for spraying.

 

fused coatings. A process in which the coating material is deposited by spraying and then fused by post heat treatment. This can be done by flame, furnace, induction, laser, or resistance heating.

 

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G

 

galvanic corrosion. Accelerated corrosion of a metal because of an electrical contact with a more noble metal or nonmetallic conductor in a corrosive electrolyte.

 

gas-dynamic spraying. See cold gas-dynamic spraying.

 

gas flow rate. The flow rate of gas, typically in liters per minute (lpm) [standard cubic feet per minute (scfm)], through the spraying torch.

 

graded coating. A sprayed deposit composed of mixed materials in successive layers, progressively changing in composition from the material immediately adjacent to the substrate to that at the surface of the sprayed deposit.

 

gradient coating. A nonstandard term when used for graded coating.

 

graduated coating. A nonstandard term when used for graded coating.

 

grain. An individual crystal in a polycrystalline material.

 

grain boundary. A narrow zone corresponding to the transition from one crystallographic orientation to another, thus separating one grain from another.

 

granular powder. A finely divided material having approximately equidimensional but nonspherical, irregular shaped powders.

 

grit. Crushed ferrous or non-metallic abrasive material in various mesh sizes used in abrasive blasting to clean and/or roughen surfaces.

 

grit blasting. A process using a pressurized stream of grit to clean and roughen surfaces.

 

groove roughening. A method of surface preparation in which grooves are made and the original surface is roughened and spread. See also dovetailing, knurling, rotary roughening, and rough threading.

 

gun. A nonstandard term when used for surfacing gun.

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H

 

hardfacing. The application of a cladding or coating of material designed to resist wear. See also buildup, buttering, and cladding.

 

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. See also macrohardness and microhardness.

 

hard surfacing. A nonstandard term for hardfacing.

 

helmet. See blast helmet.

 

heterogeneity. The quality or state of being heterogeneous.

 

heterogeneous. Made up of parts or elements, not unified, compatible, or proportionate. See also homogeneous.

 

high pressure. In cold gas-dynamic spray typically taken to mean the range of 2.5 MPa to 4 MPa [350 psi to 600 psi].

 

high-pressure cold gas-dynamic spray (CGSP-H). A cold gas-dynamic spray process variation employing high-pressure carrier gas and spray feedstock injection before the nozzle throat. See also low-pressure cold gas-dynamic spray and pulsed cold gas-dynamic spray.

 

homogeneity. The quality or state of being homogeneous.

 

homogeneous. Of uniform structure or composition throughout. See also heterogeneous.

 

hood. A nonstandard term when used for blast hood.

 

hydrogen embrittlement. Hydrogen-induced cracking or severe loss of ductility caused by the presence of hydrogen in the metal matrix.

 

hydrophilic. Tending to absorb water.

 

hydrophobic. Tending to repel water or lacking affinity for water.

 

hypersonic. Having a Mach number of greater than 5.0. Some energy of the object goes into exciting the chemical bonds of the fluid. See also subsonic and supersonic.

 

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I

 

impingement. A continuing succession of impacts between a liquid or solid particles and a solid surface.

 

impingement angle. A nonstandard term when used for spray angle.

 

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.

 

impingement zone. A nonstandard term when used for compressed layer.

 

impregnation. A process of filling the pores of a material with sealant.

 

impurity. An unwanted minor constituent or one of an unacceptable concentration level. See also inclusion.

 

incident particles. Those particles transferring most of their potential energy to the substrate. See also reflected particles.

 

inclusion. Entrapped foreign solid material or a physical discontinuity within a material.

 

induction time. See deposition delay.

 

inert gas. A stable gas that does not support combustion and does not form reaction products with other materials. Included are helium, argon, and sometimes nitrogen.

 

injection angle. See spray feedstock injection angle.

 

interconnected porosity. A network of pores in and extending to the surface of a coating.

 

intergranular corrosion. Corrosion occurring preferentially at grain boundaries.

 

intermediate spray deposit bead. The spray deposit resulting from an intermediate spray deposit pass.

 

intermediate spray deposit pass. A spray deposit pass within a cross-sectional sequence lying between the first spray coating pass or layer and the cover pass or layer.

 

internal energy. The sum of an objects kinetic and potential energies. See also kinetic energy and potential energy.

 

internal oxidation. The formation of isolated particles of corrosion products beneath the surface of the metal or coating as a result of preferential oxidation of certain alloy constituents.

 

ionic bond. A primary bond arising from the electrostatic attraction between two oppositely charged ions. See also bonding force, covalent bond, mechanical bond, and metallic bond.

 

irregular powder. Finely divided particles lacking symmetry. See also nodular powder.

 

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J

 

jet. A forceful stream of fluid discharged from a narrow opening or a nozzle.

 

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K

 

kinetic energy. The energy a substance possesses by virtue of its velocity of motion. See also internal energy and potential energy.

 

kinetic spray. A nonstandard term when used for the cold gas-dynamic spray process.

 

knurling. A method of surface preparation in which the surface is upset with a knurling tool. See  also dovetailing, groove roughening, rotary roughening, and rough threading.

 

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L

 

laval nozzle. See de Laval nozzle.

 

layer. A stratum of spray deposit consisting of one or more spray deposit beads.

 

linear discontinuity. A discontinuity with a length substantially greater than its width.

 

localized corrosion. Corrosion at discrete sites, for example, pitting, crevice corrosion, and stress corrosion cracking.

 

low pressure. In cold gas-dynamic spray typically taken to mean the range of 0.5 MPa to 1 MPa [70 psi to 145 psi]

 

low-pressure cold gas-dynamic spray (CGSP-L). A cold gas-dynamic spray process variation employing low-pressure carrier gas and spray feedstock injection after the nozzle throat. See also high-pressure cold gas-dynamic spray and pulsed cold gas-dynamic spray.

 

lubricant. Any substance interposed between two surfaces for the purpose of reducing the friction or wear between them.

 

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M

 

Mach number. The speed of an object relative to a fluid medium divided by the speed of sound in the medium. See also hypersonic, subsonic, and supersonic.

 

macrograph. A graphic reproduction of the image of an object as seen by the naked eye.

 

macrohardness. The result of a hardness test performed on a macroscopic scale to show the bulk property of a material. See also microhardness.

 

manual spraying. A spraying operation with the surfacing gun held and manipulated by hand. Accessory equipment, such as part motion devices may be used. See also automatic spraying, mechanized spraying, robotic spraying and semiautomatic spraying.

 

mask. A material or device used to conceal or screen from a process.

 

matrix. The continuous phase of a material or coating in which separate particles of another constituent are embedded.

 

maximum substrate velocity. The substrate velocity above which substrate activation is insufficient to facilitate particle attachment. See also substrate velocity.

 

mean particle size. The equivalent average spherical particle size.  See also particle size.

 

mechanical bond. The adherence by interlocking such as a spray deposit to a roughened surface. See also bonding force, covalent bond, ionic bond, and metallic bond.

 

mechanized spraying. An operation with equipment requiring manual adjustment by an operator in response to visual observation, with the surfacing gun held by a mechanical device. See also automatic spraying, manual spraying, robotic spraying, and semiautomatic spraying.

 

mesh size. The designated openings in a sieve or screen. See also minus sieve and plus sieve.

 

metal. An opaque, lustrous, elemental chemical substance that is a good conductor of heat and electricity, usually malleable, ductile, and more dense than other elemental substances.

 

metallic bond. The primary bond holding metals together arising from the increased spacing of valence electrons when an aggregate of metal atoms are in close proximity. See also bonding force, covalent bond, ionic bond, and mechanical bond.

 

metallizing. A nonstandard term when used for spraying or the application of a metal spray deposit.

 

metal-matrix composite. A material with nonmetallic reinforcement incorporated in the metallic matrix. The reinforcement may constitute from 10% to 60% of the material. Example reinforcements include graphite, silicon carbide, and refractory metals.

 

micrograph. A graphic reproduction of the image of an object formed by a microscope.

 

microhardness. The result of a hardness test performed on a microscopic scale to determine the property of individual phases within a material and avoid the effects of porosity. See also macrohardness.

 

microinch. One millionth of an inch (0.000001 in) [.0000254 mm].

 

micrometer (µm). One millionth of a meter (0.001 mm) [0.0003937 in].

 

micron. See micrometer.

 

microtrack. A device for measuring powder particle size distributions.

 

mil. One thousandth of an inch (0.001 in) [0.0254 mm].

 

milled powder. Powder or powder mixtures having received the mechanical treatment, such as by ball milling, to alter the size or shape of the individual particles or to coat one component of the mixture with another. See also crushed powder.

 

minus sieve. The portion of a powder sample passing through a standard sieve of specified mesh size. See also plus sieve.

 

mixed powder. Thoroughly intermingled powder of different materials. See also blended powder.

 

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N

 

nanostructured powder. Particles displaying grains or phases whose average size is less than 200 nm.

 

nodular powder. Finely divided particles having a regular shape. See also irregular powder.

 

nozzle. See spray nozzle.

 

nozzle accumulation. Filler metal or surfacing material deposited on the inner surface and on the exit end of the nozzle.

 

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O

 

orifice. The portion of the nozzle containing the throat.

 

orifice throat length. The length of the constricting orifice.

 

overspray. The portion of the spray feedstock not deposited on the substrate.

 

oxidation. Loss of electrons by a constituent of a chemical reaction, or the corrosion of a metal exposed to an oxidizing gas at elevated temperatures.

 

oxidizing. An environment or material promoting oxidation.

 

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