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vacancy
A structural imperfection in which an individual atom site is temporarily unoccupied.
vacuum arc remelting (VAR)
A consumable-electrode remelting process in which heat is generated by an electric arc between the electrode and the ingot. The process is performed inside a vacuum chamber. Exposure of the droplets of molten metal to the reduced pressure reduces the amount of dissolved gas in the metal. See also consumable-electrode remelting.
vacuum carburizing
A high-temperature gas carburizing process using furnace pressures between 13 and 67 kPa (0.1 to 0.5 torr) during the carburizing portion of the cycle. Steels undergoing this treatment are austenitized in a rough vacuum, carburized in a partial pressure of hydrocarbon gas, diffused in a rough vacuum, and then quenched in either oil or gas.
vacuum casting
A casting process in which metal is melted and poured under very low atmospheric pressure; a form of permanent mold casting in which the mold is inserted into liquid metal, vacuum is applied, and metal is drawn up into the cavity.
vacuum degassing
The use of vacuum techniques to remove dissolved gases from molten alloys.
vacuum deposition
Deposition of a metal film onto a substrate in a vacuum by metal evaporation techniques.
vacuum furnace
A furnace using low atmospheric pressures instead of a protective gas atmosphere like most heat-treating furnaces.
vacuum hot pressing
A method of processing materials (especially metal and ceramic powders) at elevated temperatures, consolidation pressures, and low atmospheric pressures.
vacuum induction melting (VIM)
A process for remelting and refining metals in which the metal is melted inside a vacuum chamber by induction heating. The metal can be melted in a crucible and then poured into a mold.
vacuum melting
Melting in a vacuum to prevent contamination from air and to remove gases already dissolved in the metal; the solidification can also be carried out in a vacuum or at low pressure.
vacuum nitrocarburizing
A subatmospheric nitrocarburizing process using a basic atmosphere of 50% ammonia/50% methane, containing controlled oxygen additions of up to 2%.
vacuum refining
Melting in a vacuum to remove gaseous contaminants from the metal.
vacuum sintering
Sintering of ceramics or metals at subatmospheric pressure.
vapor degreasing
Degreasing of work in the vapor over a boiling liquid solvent, the vapor being considerably heavier than air. At least one constituent of the soil must be soluble in the solvent. Modifications of this cleaning process include vapor-spray-vapor, warm liquid-vapor, boiling liquid-warm liquid-vapor, and ultrasonic degreasing.
vapor deposition
See chemical vapor deposition , physical vapor deposition , and sputtering.
vapor plating
Deposition of a metal or compound on a heated surface by reduction or decomposition of a volatile compound at a temperature below the melting points of the deposit and the base material. The reduction is usually accomplished by a gaseous reducing agent such as hydrogen. The decomposition process may involve thermal dissociation or reaction with the base material. See also vacuum deposition.
V-bend die
A die commonly used in press-brake forming, usually machined with a triangular cross-sectional opening to provide two edges as fulcrums for accomplishing three-point bending.
vent
A small opening in a foundry mold for the escape of gases.
vermicular graphite iron
Same as compacted graphite iron.
vibratory finishing
A process for deburring and surface finishing in which the product and an abrasive mixture are placed in a container and vibrated.
Vickers hardness number (HV)
A number related to the applied load and the surface area of the permanent impression made by a square-based pyramidal diamond indenter having included face angles of 136°, computed from: where P is applied load (kgf), d is mean diagonal of the impression (mm), and is the face angle of the indenter (136°).
Vickers hardness test
A microindentation hardness test employing a 136° diamond pyramid indenter (Vickers) and variable loads, enabling the use of one hardness scale for all ranges of hardness–from very soft lead to tungsten carbide. Also known as diamond pyramid hardness test. See also microindentation and microindentation hardness number.
virgin metal
Same as primary metal.
void
(1) A shrinkage cavity produced in castings or weldments during solidification. (2) A term generally applied to paints to describe holidays, holes, and skips in a film.
V process
A molding (casting) process in which the sand is held in place in the mold by vacuum. The mold halves are covered with a thin sheet of plastic to retain the vacuum.