Erosion by mechanical or particulate impact (could be waterjet stripping or abrasive blasting). Also, surface preparation of a substrate that is intended to roughen the surface profile of the material and remove foreign materials.


Material (such as crushed chilled cast iron, crushed steel grit, aluminum oxide, silicon carbide, flint, garnet, or crushed slag) used for cleaning or surface roughening.


Abrasive blasting

A method of propelling abrasive using a compressed gas (typically air) or pressurized liquid (typically water) as the propellant. Also known by terms related to the abrasive media in use, including: sand blasting, shot blasting, grit blasting, bead blasting and blast cleaning.

Abrasive blasting

Air filter

Mechanism for cleaning air of contaminants such as water, oil and solid matter.

Air filter


A substance having metallic properties and being composed of two or more chemical elements of which at least one is metal.

Almen gauge

An instrument using a dial or digital indicator, a plunger and a platform for mounting an Almen strip. The gauge is used to measure the arc height of a peened Almen strip. Digital gauges provide arc height readings to four decimal places (0.0001").

Almen gauge

Almen strip

Thin strips of spring steel used to quickly gauge the shot peening process. Developed by John Almen at General Motors, these strips are used in conjunction with an Almen gauge to determine the intensity of the shot peen stream.


The chemical compound aluminum oxide. A ceramic used in powder or rod form in thermal spraying operations. May also be used as an abrasive grit blasting medium.

Aluminum oxide abrasive

A blast cleaning abrasive manufactured by fusing the mineral bauxite at high temperature. The fused aluminum oxide is crushed, dried, and screened (sieved).


The electrode maintained at a positive electrical potential.


A luminous discharge of electrical current crossing the gap between two electrodes.

Electric arc

Arc gas

The gas introduced into the thermal spraying arc chamber and ionized by the arc to form a plasma gas.

Arc height

A measurement of the amount of deflection or bow in an Almen strip, after it has been shot peened. The measurement is taken at the center of the concave side of the peened Almen strip using an Almen gauge. Readings are normally in thousandths of an inch (0.001"), or in millimeters (mm), while digital gauges can provide readings out to 0.0001".

Arc spraying

A thermal spraying process using an arc between two consumable electrodes of surfacing materials as a heat source and a compressed gas to atomize and propel the surfacing material to the substrate.

Arc spraying


Production of a fine spray of liquid particles.


Blast angle

Angle of a blasting nozzle relative to the surface being blasted with abrasive, shot or waterjet.

Blast nozzle

Device through which abrasive or shot is propelled onto a surface during grit blasting or shot peening. The two primary types of blast nozzles are (1) the straight bore nozzle, which has a small opening and a concentration of power in the center of the blast pattern; and (2) the Venturi nozzle, which has a large mouth, tapered mid-section, and a flared opening.

Blast nozzle

Bond coat

A preliminary (or prime coat) of material that improves adherence of the subsequent spray deposit.

Bond strength

The force required to pull a coating free of a substrate, usually expressed in kPa (psi).

Breakdown rate

The rate at which abrasive or shot particles become too small to be reused after a certain number of impacts (blasting or peening cycles).


A chemical compound formed between carbon and a metal or metals, such as tungsten carbide, tantalum carbide, titanium carbide, and chromium carbide.

Carrier gas

The gas used to carry powdered material from the powder feeder or hopper to the thermal spray gun.


The electrode maintained at a negative electric potential.


A physical mixture of ceramics and metals, such as alumina plus nickel, and zirconia plus nickel.

Cold working

The process of deforming metal plastically beyond its yield strength but below its recrystallization temperature (normally room temperature). Cold working normally sets up residual stresses in the material, and is achieved through stretching, compressing, bending, twisting, cold rolling, cold drawing, and by shot peening.

Composite coating

A coating consisting of two or more dissimilar spray materials which may or may not be layered.

Compressive stress

Force or forces applied toward a common point, for instance a block squeezed in a vise.


The chemical or electrochemical reaction between a metal and its environment that results in the loss of material and its properties. Metals corrode because they exist in chemically unstable states.


The measurement of surface area which has been shot peened as indicated by the degree of overlapping dimples, expressed as a percentage of a complete overlapping of dimples.

Deionized water

Water purified by passing it through ion exchange resins to remove the minerals.


A situation in thermal spray where a coating segment breaks away from the substrate due to stresses and/or poor surface preparation. Also, a process in waterjet stripping where the coating is fractured by the high pressure water and large coating particles spall off the substrate.

Deposition efficiency

The ratio, usually expressed in percentage, of the weight of thermal spray deposit to the weight of the material sprayed.

Deposition rate

In thermal spraying, the weight of material deposited in a unit of time.

Dew point

The temperature at which air becomes saturated with water, that is, when the air is at 100 percent relative humidity. Below this temperature, moisture will condense and produce dew or fog. As air cools, the amount of water vapor it can hold decreases.


Additive that increases the stability of a suspension of powders in a liquid.

Dwell time

The length of time the spray material is exposed to the heat zone which produces and sustains a molten condition.


The adherence of particles of blast cleaning abrasive (or broken shot) on a substrate. The particles cannot be removed by brushing or blowing down with compressed air.

Fatigue failure

The fracture of a material due to cyclic stresses or loads.


A chemical compound or metal alloy that contains primarily iron.

Ferrous metal

Flame spraying

A thermal spraying process in which an oxyfuel gas flame is the source of heat for melting the surfacing material. Compressed gas may or may not be used for atomizing and propelling the surfacing material to the substrate.

Flow meter

A device for indicating the rate of gas flow in a thermal spray system.


A type of wear that occurs between tight-fitting surfaces subjected to cyclic relative motion of extremely small amplitude.



A condition caused by excessive friction between high spots in a material resulting in localized welding with subsequent spalling.

Gradated coating

A thermal spraying deposit composed of mixed materials in successive layers which progressively change in composition from the constituent material lot the, substrate to the surface of the sprayed deposit. Also referred to as graduated or graded coating.

Gradated coatings

High efficiency particulate air (HEPA) filter

An air filter that removes 99.97 percent of all particles larger than 0.3 microns.

HEPA filter


A material not containing iron such as non-iron metals, oxides, glass beads and ceramic particles.

Non-ferrous media


The excess spray material that is not deposited on the part being thermal sprayed.


A chemical compound. The combination of oxygen with a metal forming a ceramic, such as aluminum oxide, zirconium oxide.

Peening intensity

A measurement of the energy imparted to a materials surface by a stream of shot. The intensity is determined from interpretation of an Almen saturation curve. The peening intensity is the first point on a curve (not necessarily a data point) and commonly referred to as "T1." Beyond this point, the curve or arc height of the Almen strip increases by no more than 10% when the peening time is doubled ("2T").

Plasma spraying

A thermal spraying process in which a nontransferred arc is utilized as the source of the heat that ionizes a gas, which melts and propels the coating material to the workpiece.

Plastic deformation

Deformation that remains permanent after removal of the load that caused it.


Cavity type discontinuities within a thermal sprayed coating.

Pressure pot

A closed container that provides a uniform flow of material at a consistent pressure to the blast nozzle in pneumatic blasting and shot peening.

Pressure pot

Primary gas

The major constituent of the arc gas fed to the thermal spray gun to produce the plasma, usually argon or nitrogen.

Ricochet peening

Shot peening of a surface achieved by deflecting shot off from another surface. This occurs in applications where surfaces cannot be reached by normal line-of-sight nozzles or lances.

Saturation curve

A best-fit curve generated from a set of arc height readings produced by shot peening an Almen fixture for different time intervals.

Secondary gas

The minor or second constituent of the arc gas fed to the thermal spray gun to produce the plasma.

Shadow mask

A protective device that partially shields the area of work, thus permitting some overspray to produce a feathering at the coating edge.

Shear stress

Stresses due to forces on an object when the forces are slightly offset from one another; for example, the use of scissors in cutting a material.

Shot peening

A process used to produce a compressive residual stress layer and modify mechanical properties of metals. Shot peening entails impacting a surface with shot (round metallic, glass or ceramic particles) with force sufficient to create plastic deformation.

Shot peening


A process in which abrasives or shot peen media is passed through one or more screens and classified according to particle size.


Solution precursor plasma spray (SPPS)

A thermal spray process where a liquid feedstock solution is heated, precipitated and then deposited onto a substrate.


The flaking or separation of a sprayed coating.

Spalling, spallation

Stress corrosion cracking

Failure by cracking under combined action of corrosion and a tensile stress, either external (applied) or internal (residual).

Suspension plasma spray (SPS)

A form of plasma spraying where a fine powder (normally <10 micron or submicron) is dispersed in a liquid suspension before being injected into the plasma jet.

Suspension plasma spray (SPS)

Tensile stress

Forces applied to a material in opposite directions.

Thermal spraying

A group of processes in which finely divided metallic or nonmetallic surfacing materials are deposited in a molten or semi-molten condition on a substrate to form a spray deposit. The surfacing material may be in the form of powder, rod, cord, or wire.

Thermal spraying

Waterjet stripping

Also known as weater jet cleaning. High pressure water jet stripping or cleaning involves the use of high pressure water propelled at high speeds to clean surfaces and materials of all types.

Waterjet stripping

Wet blasting or wet peening

Combining water and abrasives or ceramic beads in a blast operation for cleaning or shot peening.

Wet blasting