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Thermal Spray FAQs
Courtesy of ASM Thermal Spray Society
NOTE: * asterisk items from AWS A3.0 adapted for use in Thermal Spraying.
What is Alumina and how is it used?
A chemical compound (aluminum oxide);a ceramic used in powder or rod form in thermal
spraying operations. May also be a blasting medium.
*What is Arc Spraying (ASP)?
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.
*What is Atomization?
(1) The division of molten material at the end of the wire or rod into fine particles. (2) The
process used in the manufacture of powder.
What is a Base Material?
Any material to which a thermal spraying deposit is applied.
*What is Blasting?
A method of cleaning or surface roughening by a forcibly projected stream of sharp angular
abrasive.
*What is a Bond Coat?
A preliminary (or prime coat) of material that improves adherence of the subsequent spray
deposit.
*What is Bonding Force?
The force that holds two atoms together; it results from a decrease in energy as two atoms
are brought closer to one another.
*What is a Bond Line?
The interface between a thermal spraying deposit and substrate, or between adhesive and
adherent in an adhesive bonded joint.
*What is Buildup?
A surfacing variation in which surfacing metal is deposited to achieve the required
dimensions.
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*What is Ceramic Rod Flame Spraying?
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A thermal spraying process variation in which the material to be sprayed is in ceramic rod
form.
See Flame Spraying (FLSP).
What is Cermet?
A physical mixture of ceramics and metals; examples are alumina plus nickel and zirconia
plus nickel.
*What is Cladding?
A surfacing variation that deposits or applies surfacing material, usually to improve corrosion
or heat resistance.
*What is a Clad Metal?
A laminar composite consisting of a metal, with a metal of different chemical composition
applied to one or two sides.
What is a Coating?
(1) The act of building a deposit on a substrate, (2) the spray deposit.
*What is Coating Density?
A nonstandard term for spray deposit density ratio.
*What is Collaring?
Adding a shoulder to a shaft or similar component as a protective confining wall for the
thermal spray deposit.
*What is Deposition Efficiency?
The ratio, usually expressed in percent, of the weight of spray deposit to the weight of the
material sprayed.
*What is Deposition Rate?
The weight of material deposited in a unit of time.
*What is Detonation Flame Spraying.
A thermal spraying process variation in which the controlled explosion of a mixture of fuel
gas and oxygen is utilized to melt and propel the material to the workpiece?
*What is Dovetailing?
A method of surface roughening involving angular undercutting to interlock the spray
deposit.
*What is Flame Spraying (FLSP)?
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.
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*What are Fuel Gases?
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Gases such as acetylene, natural gas, hydrogen, propane, stabilized methylacetylene
propadiene, and other fuels, and hydrocarbons, usually used with oxygen for heating.
*What is a Fused Spray Deposit?
A self-fluxing spray deposit which is subsequently heated to coalescence within itself and
with the substrate.
*What is Fusion?
The melting together of filler metal and metal (substrate), which results in coalescence.
*What is a 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.
*What is Hardfacing?
A surfacing variation in which surfacing metal is deposited to reduce wear.
What is HVOF/HVAF?
High Velocity Oxygen Fuel/High Velocity Air Fuel. A high velocity flame spray process.
*What is an Ionic Bond?
A primary bond arising from the electrostatic attraction between two oppositely charged ions.
*What is a Mechanical Bond?
The adherence of a thermal spraying deposit to a roughened surface by the mechanism of
particle interlocking.
*What is a Metallic Bond?
The principal bond that holds metals together and is formed between base metals and filler
metals in all processes. This is a primary bond arising from the increased spatial extension
of the valence electron wave functions when an aggregate of metal atoms is brought close
together. See also Bonding Force, and Ionic Bond.
What is Molten Metal Flame Spraying?
A thermal spraying process variation in which the metallic material to be sprayed is in the
molten condition. See Flame Spraying (FLSP).
*What is an Oxidizing Flame?
An oxyfuel gas flame having an oxidizing effect (excess oxygen).
*What is Plasma Spraying (PSP)?
A thermal spraying process in which a nontransferred arc is utilized as the source of heat
that ionizes a gas which melts and propels the coating material to the workpiece.
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What is Powder?
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Material manufactured into finely divided particles. When explicitly blended for thermal
spraying, powder falls within a specific mesh range, usually finer than 120 mesh (125
microns). Fine powder is usually defined as having particles smaller than 325 mesh (44
microns).
*What is Powder Flame Spraying?
A thermal spraying process variation in which the material to be sprayed is in powder form;
all oxyfuel gas processes. See Flame Spraying (FLSP).
*What is Powder Metallizing?
A nonstandard term for powder flame spraying.
*What is a Protective Atmosphere?
A gas envelope or vacuum surrounding the part to be thermally sprayed, with the gas
composition controlled with respect to chemical composition; dewpoint, pressure, flow rate,
etc. Examples are inert gases, combusted fuel gases, hydrogen and vacuum.
*What is Rotary Roughening?
A method of surface roughening in which a revolving roughening tool is pressed against the
surface being prepared, while either the work or the tool, or both, move.
What are Self-Bonding Materials?
Those materials that exhibit the characteristics of forming a metallurgical bond with the
substrate in the as-sprayed condition.
*What are Self-Fluxing Alloys?
Surfacing materials that "wet" the substrate and coalesce when heated to their melting point,
without the addition of an externally applied flux. These alloys contain boron or silicon, or
both, as fluxing agents.
*What is Shielding Gas?
Protective gas used to prevent or minimize atmospheric contamination. See also Protective
Atmosphere.
What is Splat?
A single thin flattened sprayed particle.
What is Splat Cooling?
Extremely rapid, high rate of cooling, the effects of which can be observed in thermal
spraying deposits leading to the formation of metastable phases and an amorphous
microstructure.
*What is Spray Deposit Density Ratio?
The ratio of the density of the spray deposit to the theoretical density of the surfacing
material. Usually expressed as percent of theoretical density.
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*What is a Substrate?
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Any material to which a thermal spraying deposit is applied.
*What is Thermal Spraying (THSP)?
A group of processes in which finely divided metallic or nonmetallic surfacing materials are
deposited in a molten or semimolten condition on a substrate to form a spray deposit.
The surfacing material may be in the form of powder, rod, cord, or wire.
See also Arc Spraying, Flame Spraying, and Plasma Spraying.
*What is Thermal Stress?
Stress resulting from nonuniform temperature distribution.
*What is Wire Flame Spraying?
A thermal spraying process variation in which the surfacing material is in wire form. See
Flame Spraying (FLSP).
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8175 Kroger Farm Road, Cincinnati, Ohio 45243 USA
Tel 513-831-4284
Fax 513-831-5237
E-Mail aflame@fuse.net