Glossary | N – P (The vocabulary of the coating and heat-treating industries—explained)

Back to Main Page 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


Natural Aging

Spontaneous aging of a supersaturated solid solution at room temperature. Compare with artificial aging.

Navier-Stokes Equations

Equations that relate all of the flow field variables together into nonlinear partial differential equations. The NS equations are basically a reformulation of Newton's 2nd Law of Motion, F=ma. These are probably the most pivotal equations in all of theoretical fluid dynamics.

Neutral Flame

A gas flame in which there is neither an excess of fuel nor of oxygen in the inner flame. Oxygen from ambient air is used to complete the combustion of CO2 and H2 produced in the inner flame.

Neutralization Number

An ASTM number given to quenching oils that reflects the oil's tendency toward oxidation and sludging. See saponification number.

Nickel (Ni)

An element that is used in low alloy steels to reduce their sensitivity to variations in heat treatment and distortion or cracking upon quenching. It also improves low-temperature toughness and hardenability. Nickel is also a base metal for many casting alloys that are resistant to corrosion and high-temperature oxidation. Its melting point is 1455°C (2651°F).

Nickel Plating

(process) The electrolytic deposition of nickel to form a corrosion barrier or reclaim a worn part. Hard ceramic particles are sometimes added to form a wear-resistant composite coating.
(substance) The coating that is applied by the nickel plating process.


Hard, white cast iron containing 4% Ni and 2% Cr. Niobium (Nb) (Columbium - Cb). It lowers the transition temperature and raises the strength of low-carbon steel. Niobium increases strength at elevated temperatures, resulting in finer grain size and forming stable carbides, which lowers the hardenability of the steel.


The process of introducing nitrogen into the surface layer of a solid ferrous alloy by holding it, at a suitable temperature (below Ac1 for ferritic steels), in contact with an appropriate nitrogenous composition. Quenching is not required to produce a hard case. See aerated bath nitriding, bright nitriding and liquid nitriding.


Any of several processes in which both nitrogen and carbon are absorbed into the surface layers of a ferrous material at temperatures below the lower critical temperature and, by diffusion, create a concentration gradient. Nitrocarburizing is done mainly to provide an antiscuffing surface layer and to improve fatigue resistance. Compare with carbonitriding.

Nitrogen (N)

An element that increases the strength, hardness and machinability of steel while decreasing its ductility and toughness. In aluminum killed steels, nitrogen combines with the aluminum to provide grain size control, thereby improving both toughness and strength. Nitrogen can reduce the effect of boron on the hardenability of steels.

Nitrogen (N2)

The diatomic, gaseous form of the element nitrogen. It is used as a primary and secondary gas in plasma spraying and is inert to most materials with some exceptions (e.g. titanium).

Noble Metal

A metal that does not readily tend to furnish ions, and therefore does not dissolve readily or easily enter into such reactions as oxidation, etc. The opposite of base metal.


Used in a numerical simulation to attach the adjacent elements.

Nodular Powder

Irregular particles having knotted, rounded or other, similar shapes.

Non Transferred Arc (Plasma)

The plasma arc which transfers heat energy to plasmagenic gas (argon, helium, hydrogen, nitrogen) in order to promote the plasma state according to Saha's law. This arc strikes between the tungsten electrode (cathode) and the constricting nozzle (anode). The term Pilot Arc is also used in plasma transferred arc processes (PTA welding).


A negative term referring to alloy in which iron is not the predominate metal or solvent.

Normal Steel

Steel in which the pearlite is completely laminated.


Heating a ferrous alloy to a suitable temperature, above its transformation range, and then cooling it in air to a temperature substantially lower than the transformation range.

Notched Coating Adhesion (NCA)

A recent characterization technique; a test used to analyze adhesive bond durability.

Nuclear Reaction Analysis (NRA)

An ion beam technique which profiles light-of-mass elements into materials. It analyses to a depth of up to one micrometer.


The initiation of a phase transformation at discrete sites, the new phase growing on nuclei.


The first structurally-stable particle capable of initiating the recrystallization of a phase or growth of a new phase while possessing an interface with the parent matrix. The term also applies to a foreign particle that initiates such action.


Oil Hardening

A quench-hardening treatment that entails the use of oil for cooling.

Oil Quenching

The type of quenching process that uses oil as a quenchant. Typically, an object being quenched in this way is made of carbon steel. Oils are categorized into conventional, fast, martempering, and hot quenching.

Optical Film

Films that affect the optical transmission or reflection of a surface. They are usually multilayer films, or stacks. They are generally composed of alternating layers of materials that have high (germanium [Ge], Si, TiO2, zirconium dioxide [ZrO2], SiO, cerium dioxide [CeO2]) and low (magnesium fluoride [MgF2], SiO2) indices of refraction. A major application is the antireflection (AR) coatings on lenses. Optical film stacks can be used as optical filters. Neutral density or gray filters reduce the light intensity equally for all wavelengths; broadband filters affect the transmission of radiation over a wide wavelength range, while narrow or monochromatic filters affect transmission over a very narrow wavelength region. Some film stacks are a special type of optical film whose color relates to the angle of observation (OVIDs). These films allow pseudo-holographic imaging. These OVID films are used as security devices to prevent counterfeiting. These films are an outgrowth of the interference-colored films used for decorative films and, when pulverized, for pigment.

Optical Pyrometer

An instrument for measuring the temperature of heated material by comparing the intensity of the emitted light with that of an incandescent lamp filament whose intensity is known.

Orange Peel

A finish resembling the dimpled appearance of an orange peel.

Order-Disorder Transformation

A phase change among two solid solutions having the same crystal structure, but in which the atoms of one phase (disordered) are randomly distributed; in the other, the different kinds of atoms occur in a regular sequence upon the crystal lattice, which is in an ordered arrangement. Compare with dissociation.

Order Hardening

A low-temperature annealing treatment that permits short-range ordering of solute atoms within a matrix, which greatly impedes dislocation motion.

Organic Metal Chemical Vapor Deposition (OMCVD)

A process using metal organic reactants with low cracking temperatures. It allows deposition of metallic carbides such as CrC with a moderated process temperature (∼400°C).

Orsat Analyzer

An atmosphere analysis device in which gases are absorbed selectively (volumetric basis) by passing them through a series of preselected solvents.


Aging under conditions of time and temperature greater than those required to obtain maximum change in a certain property, resulting in the property being altered in the direction of the initial value.


Heating a metal or alloy to such a high temperature that its properties are impaired. When the original properties cannot be restored by further heat treating and/or mechanical working, the overheating is termed burning.


(1) A reaction in which there is an increase in valence resulting from a loss of electrons.
(2) A corrosion reaction in which the corroded metal forms an oxide; usually applied to reaction with a gas containing elemental oxygen, such as air.

Oxidized Surface (on steel)

Surface having a thin, tightly-adhering, oxidized skin (from straw to blue in color) that extends inwards from the edge of a coil or sheet. Sometimes called an annealing border.


The production of a stable oxide layer on a steel component by heating in a controlled atmosphere. Provides corrosion protection and reduced friction.

Oxidizing Agent

A compound that causes oxidation, thereby causing itself to be reduced.

Oxidizing Flame

A gas flame produced with excess oxygen in the inner flame.

Oxygen (O2)

A diatomic, gaseous element used to support the combustion of gaseous fuels in combustion thermal spray processes. Its use achieves much higher flame temperatures than the use of air.

Oxygen Probe

An atmosphere-monitoring device that electronically measures the difference between the partial pressure of oxygen in a furnace or furnace supply atmosphere and the external air.


Pack Carburizing

A method of surface hardening, used on steel, in which the parts are packed with carburizing compound into a steel box and heated to elevated temperatures.

Pack Nitriding

A method of surface hardening, used on steel, wherein parts are packed with nitriding compound into a steel box and heated to elevated temperatures.


A coating composed of resin, a solvent, additives, pigments and sometimes a diluent. Paints are generally opaque, and commonly represent the portion of the industry known as the architectural coating industry.


The application of organic based layers (acrylics, etc) as paint for corrosion protection and decorative purposes.

Partial Annealing

An imprecise term used to denote a treatment given cold-worked material to either reduce the strength to a controlled level or relieve stress. For the term to be meaningful, one must state the type of material, the degree of cold work, and the time-temperature schedule.


A solid, tiny object that, together with other tiny objects, makes up a powder. This powder can be used for plasma spraying.

Particle Chemistry

The elements, and their ratios to one another, that make up one particle.

Particle Size

The controlling lineal dimension of an individual particle. This can be measured, among other methods, by using sieves.

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.

Particles Induced Gamma-ray Emission (PIGE)

An ion beam technique particularly well suited for the determination of light-mass element concentrations into materials. It can analyse to a depth of up to a few micrometers.

Particles Induced X-ray Emission (PIXE)

An ion beam technique used in surface science for stoichiometry analysis and the quantification of trace elements. It is ideal for analysing impurities in coatings.


The post treatment (usually via chromating) of nickel, cadmium or zinc coatings to reduce their corrosion rates.


The process in metal corrosion by which metals become passive.


A type of inhibitor which appreciably changes a metal's potential to a more noble (positive) value.


The state of a metal surface characterized by low corrosion rates in a potential region that is strongly oxidizing relative to that metal's usual properties.


In wiremaking, a heat treatment applied to medium carbon or high-carbon steel before the drawing of wire or between drafts. This process consists of heating to a temperature above the transformation range and then cooling to a temperature below Ae1 in air or in a bath of molten lead or salt.


A metastable, lamellar aggregate of ferrite and cementite, resulting from the transformation of austenite at temperatures above the bainite range.


The full or partial detachment of a coating from its substrate.


A stream of sharp, material particles which break superficial fiber, reducing internal stress fields.

Penetration, Metal

A condition wherein molten metal has penetrated into the sand, resulting in a mixture of metal and sand adhering to the casting.

Perfluro Alkyle Ether (PFA)

Relatively hard, long chain polymer with inert, orientated structure. Applied by spraying and then melt flowing at temperatures above 250°C. Develops non-stick properties and resistance to wear.

Perfuoroether (FEP)

Soft, long chain polymer with an inert, orientated structure. Applied by spraying and then melt flowing at 400°C. Develops excellent non-stick properties.

Permanent Mold

A metal mold of two or more parts—not an ingot mold. It is used repeatedly for the production of many castings of the same form.


A property measured as a rate of the passage of a liquid or gas through a coating.

Phase Diagram

A graphical representation of the temperature and composition limits of phase fields in an alloy system as they actually exist under the specific conditions of heating or cooling (synonymous with constitution diagram). A phase diagram may be an equilibrium diagram, an approximation to an equilibrium diagram, or a representation of metastable conditions or phases.


A conversion process used on steel surfaces to enhance their protection from corrosion. It is often zinc-based.

Phosphorus (P)

An element which is generally restricted to below 0.04 weight percent to minimize its detrimental effect on ductility and toughness. Certain steels may contain higher levels to enhance machinability, strength and/or atmospheric corrosion resistance.

Photothermal NDE (Non-Destructive Evaluation)

An NDE technique for sprayed 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 the thickness of the coating.

Physical Properties

Properties of a metal or alloy that are relatively insensitive to structure and can be measured without the application of force. Example physical properties are density, electrical conductivity, coefficient of thermal expansion, magnetic permeability, and lattice parameter. Chemical reactivity is not a physical property. Compare with mechanical properties.

Physical Vapor Deposition (PVD)

A term that covers all vapor deposition processes, including ion plating. Compare to chemical vapor deposition (CVD).


An operation by which surface oxide (scale) is removed by chemical action. Sulfuric acid is typically used to pickle carbon and low-alloy steels. After the operation, which is carried out in an acid bath, the steel is rinsed in water.

Pin-On-Disk Tribometer

A measuring device used to determine wear characteristics of material samples. A pin, which is a flat or spherical contact, is loaded with precisely-known force onto the disk, which is the test sample. The pin is mounted to a stiff lever designed to transduce force without friction. As the disk rotates, miniscule deflections of the lever (triggered by the action of frictional forces between pin and disk) are measured. Wear coefficients for both the pin and disk material are calculated from the volume of the material lost during a specific friction run. This simple method facilitates the determination and study of friction and wear behavior of almost every solid-state material combination, with variations in time, contact pressure, velocity, temperature, humidity, lubricants etc.


A cavity formed by the shrinkage of metal during solidification, usually occurring in a riser having feeder metal for the casting.

Pirani Gage

An instrument used to measure the pressure inside a vacuum chamber. The gage measures electrical resistance in a wire filament, the temperature of which changes depending on atmospheric pressure.

Pitot Gage

An instrument that measures the stagnation pressure of a flowing fluid, consisting of an open tube pointing into the fluid and also connecting to a device that indicates pressure.

Pitting (Corrosion)

The corrosion of one or more points or small areas on a metal surface, resulting in the formation of cavities on the surface.

Pitting (Tribology)

A form of wear characterized by the presence of surface cavities, the formation of which is attributed to fatigue, local adhesion, cavitation etc.


The fourth state of matter. It is formed when a gas (usually argon, helium, nitrogen, hydrogen) has been heated to a temperature of sufficient heat to cause the gas to become partially ionized and therefore electrically conductive. The term was introduced by Irving Langmuir in 1930.

Plasma Assisted Chemical Vapor Deposition (PACVD)

This process allows coating via CVD to be carried out at greatly reduced temperatures. PACVD's temperature range lies between 150° and 250°C, whereas the temperature range for CVD is 800°–1000°C. The significance of this difference is that the variety of base materials that can be coated expands considerably.

Plasma Carburizing

See ion carburizing.

Plasma Enhanced Chemical Vapor Deposition (PECVD)

Chemical vapor deposition in which the precursor gases are decomposed primarily by a plasma.

Plasma Jet

A jet of plasma usually produced from a plasma torch, which is a tool used to ionize gas (gas turns into a plasma when it is ionized) and then send it in the direction to which it is aimed. An electric arc is struck between a cathode and anode and is then blown through a nozzle to form this jet.

Plasma Nitriding

See ion nitriding.

Plasma Spraying

A thermal spraying process wherein the source of heat is a jet of plasma.

Plasma Transferred Arc (PTA)

Another name for transferred arc.

Plasma-Based Ultra-Fine Particle Synthesis

A process wherein a liquid precursor is atomized and injected into the plasma flame. The plasma-synthesized particles are collected either as a deposit on a substrate or as a powder on an electrostatic precipitator.

Plastic Deformation

Permanent distortion of metals. Plastic, as a descriptive word, is the opposite of elastic. This distortion is the result of stresses being applied to a metal and pushing the strain to beyond the material's elastic limit.

Plenum (Plasma)

A space or chamber in a plasma torch, confined by the inner wall of the constricting nozzle and the cathodic electrode. The shape and size of this annular chamber play the highest role in plasma arc torches (welding, spraying).


The formation of grooves, by plastic deformation, in the softer of two surfaces in motion relative to one another.

Plus Sieve

The portion of a powder sample retained on a sieve of specified number. Compare with minus sieve.


The smoothing of a material surface using the action of abrasive particles, usually attached to a fabric cloth. This is the final mechanical step in metallographic preparation.


A condensation polymer formed by the interaction of polyhydric alcohols and polybasic acids. They are used in the manufacture of glass-fiber products. See alkyd resin.


A substance having large molecules consisting of repeated units. There are a number of natural polymers, such as polysaccharides, and synthetic polymers are used extensively in plastics.

Polymer Film

Films of polymer. Interest is growing in regards to depositing organic and inorganic polymer films in vacuum. These films can be formed by condensation of a monomer, followed by E-beam or UV curing to polymerize the monomer, or by plasma polymerization of the monomer. The monomer precursor can yield a carbon, silicon or boron-based polymer material that often contains hydrogen, chlorine or fluorine. Films that contain fluorine are used to form hydrophobic surfaces.


The property of a chemical substance crystallizing into two or more forms of different structures, such as diamond and graphite.

Polytetrafluorethylene (PTFE)

A long chain polymer with orientated structure, providing low friction. It is applied as a coating (via spraying or dipping and curing) or as powder additions to other coatings (e.g. electroless nickel).


The property of a coating or object in which pores or voids are present. Not the same as pull-out.


Heating weldments immediately after welding. This can be done for tempering, stress relieving, or to provide a controlled rate of cooling to prevent formation of a hard or brittle surface.

Pot Annealing

Another term for box annealing.


The transfer of molten metal from a furnace to a ladle, a ladle to another ladle, or a ladle to a mold.

Powder Coating

Polymeric coatings applied for corrosion protection on low friction. Applied dry via electrostatic attraction to the part.

Powder Gas Flow Rate

In plasma spraying, the flow rate of the gas that propels the powder into the plasma jet.

Powder Injection Angle

In plasma spraying, The angle from which the powder is injected into the plasma jet.

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.

Precipitation Hardening

Hardening caused by the precipitation of a constituent from a supersaturated solid solution. Also see age hardening and aging.

Precipitation Heat Treatment

A type of artificial aging in which a constituent precipitates from a supersaturated solid solution.


Heating that occurs before another thermal or mechanical treatment. It is done differently depending on the material and circumstances. Tool steel is preheated to an intermediate temperature immediately before final austenitizing. Some nonferrous alloys are heated to a high temperature for a long time to Homogenize the structure before working. In welding and related processes, heating is to an intermediate temperature for a short time immediately before welding, brazing, soldering, cutting, or thermal spraying.

Press Quenching

A quench in which hot dies are pressed and aligned with a part before the quenching process begins. The part is then placed in contact with a quenching medium in a controlled manner. This process prevents distortion of the part.

Pretreatment Coating

A coating process wherein the coating contains no more than 12% solids by weight and at least .5% acid by weight and is used to provide surface etching. It is applied directly to metal surfaces to provide corrosion resistance, adhesion and ease of stripping.

Process Annealing

An imprecise term denoting various treatments used to improve workability. For the term to be meaningful, one must state the condition of the material and the time-temperature cycle used.

Profile Tolerances

A system of locating and tolerancing developed to control the orientation of rough parts in machine fixtures. From locating points on the casting, a "perfect profile" is established for all surfaces and features. A tolerance envelope surrounding that profile defines the limitations of an acceptable part.

Progressive Aging

An aging process wherein the temperature is increased either in steps or continuously throughout the aging cycle. Compare with interrupted aging and step aging.

Propane (C3H8)

Aliphatic hydrocarbon gas. It is used as a fuel gas in thermal spray processes.


(1) In a CFD simulation, fluid properties are density, viscosity and volume of expansion; particle properties are density and specific heat of evaporation.
(2) Properties are the characteristics of objects, substances, or processes that make these things unique. See mechanical properties and physical properties.

Propylene (C3H6)

Hydrocarbon gas, used as a fuel gas in thermal spray processes. It produces a higher flame temperature than hydrogen or propane.


See blank carburizing.


See blank nitriding.


The result of particles being plucked from the coating during machining or grinding. This also occurs during metallographic preparation. Not to be confused with porosity.

Pusher Furnace

A type of continuous-type furnace in which parts to be heated are periodically charged into the furnace in containers, which are pushed along the hearth against a line of previously charged containers; thus advancing the containers toward the discharge end of the furnace where they are removed.


A device for measuring temperatures above the range of liquid thermometers.

Back to Top