Term Glossary

Click on a phrase below to see it's definition.

Age hardening:

Also called precipitation hardening, is a type of heat treatment use to strengthen metal alloys.

Aluminum Anodizing:

Anodization changes the microscopic texture of the surface and changes the crystal structure of the metal near the surface. Anodic films are generally much stronger and more adherent than most types of paint and metal plating, but also more brittle. This makes them less likely to crack and peel from aging and wear, but more susceptible to cracking from thermal stress. Aluminum alloys are anodized to increase corrosion resistance, to increase surface hardness, and to allow dyeing (coloring), improved lubrication, or improved adhesion.


Heating steel to, and holding at a suitable temperature, followed by relatively slow cooling. The purpose of annealing may be to remove stresses, to soften the steel, to improve machinability, to improve cold working properties, or to obtain a desired structure.

Black Oxide:

Conversion coating for ferrous materials. It is used to add mild corrosion resistance and for appearance. To achieve maximum corrosion resistance the black oxide must be impregnated with oil or wax. One of its advantages over other coatings is its minimal buildup.


Surface modification technique that is used to increase the surface hardness of a metal, thereby reducing wear. It is is often applied to inexpensive, easily machined low carbon steel.

Case Depth Analysis:

Destructive method specified on many types of parts that require surface fatigue strength and wear resistance. Total case depth is typically measured by sectioning the samples and polishing the surface and etching the sectioned and polished surface with acid to reveal the case depth.

Case Hardening:

Process of hardening the surface of a metal, often a low carbon steel, by infusing elements into the material's surface, forming a thin layer of a harder alloy.

Chemical Analysis:

Performed routinely to ensure that the material is what was specified.

Deep Freeze:

Process that can improve hardness and wear and achieve the proper microstructure. Through the use of a liquid nitrogen system, sub-zero temperatures as low as -320°F are accurately controlled to completely transform austenite into martensite. Conventional deep-freeze methods reach only minus 120°F.

Gas Carburizing:

One of the most widely used case (surface) hardening processes. The process involves diffusing carbon into a low carbon steel alloy to form a high carbon steel surface.

Glass Bead:

Process of removing surface deposits by applying fine glass beads at a high pressure without damaging the surface.

Micro Hardness:

Destructive method used for measuring the hardness of a material on a microscopic scale. A precision diamond indenter is impressed into the material at loads from a few grams to 1 kilogram. The impression length, measured microscopically, and the test load are used to calculate a hardness value. The hardness values obtained are useful indicators of a material’s properties and expected service behavior. The indentations are typically made using either a square-based pyramid indenter (Vickers hardness scale) or an elongated, rhombohedral-shaped indenter (Knoop hardness scale).

Micro Structure:

Destructive method used to determine the shape and alignment of the microscopic components of a metal. A material's microstructure often determines its hardness, toughness, and other properties. Used as a tool in both failure analysis and for routine quality control


Normalization is an annealing process in which a metal is cooled in air after heating in order to relieve stress. This treatment refines the grain size and improves the uniformity of microstructure and properties of hot rolled steel. This technique provides harder, stronger steel which improves the machinability of a component and provides dimensional stability if subjected to further heat treatment processes.


The process of making a material "passive", and thus less reactive with surrounding air, water, or other gases or liquids. The goal is to inhibit corrosion, whether for structural or cosmetic reasons. In the context of corrosion, it is the spontaneous formation of a hard non-reactive surface film that inhibits further corrosion. This layer is usually an oxide or nitride that is a few nanometers thick.

Plating Thickness Analysis:

Destructive method used to determine if it is too thin because then it will not offer enough wear or corrosion resistance and can be equally important in providing good performance.

Precipitation Hardening:

Also called age hardening, is a heat treatment technique used to increase the yield strength of malleable materials, including most structural alloys and some stainless steels.

Powder Coating:

Applied as a free-flowing, dry powder. The powder may be a thermoplastic or a thermoset polymer. It is usually used to create a hard finish that is tougher than conventional paint.


The metal is heated to a specific temperature and rapidly cooled (quenched) in a bath of water, brine, oil, or air to increase its hardness. One drawback of using this method by itself is that the metal becomes brittle. This treatment is therefore typically followed by a tempering process.

Stress Relieving:

A technique used to remove or reduce the internal stresses created in a metal. Typically, the parts that benefit from stress relieving are large and complex weldments, castings with a lot of machining, parts with tight dimensional tolerances and machined parts that have had a lot of stock removal performed.


This process is carried out by preheating previously quenched or normalized steel to a temperature below the critical range, holding, and then cooling to obtain the desired mechanical properties. Also used to reduce the brittleness of quenched steel. Many products that require hardness and resistance to breakage are quenched and tempered. The temperature chosen for the tempering process directly impacts the hardness of the work piece.

Tensile Testing:

Typically, the testing involves taking a small sample with a fixed cross-section area, and then pulling it with a controlled, gradually increasing force until the sample changes shape or breaks. When testing metals, indentation hardness correlates linearly with tensile strength. Ultimate tensile strength (UTS), often shortened to tensile strength (TS) or ultimate strength, is the maximum stress that a material can withstand while being stretched or pulled before necking, which is when the specimen's cross-section starts to significantly contract.

Thru-Hardening Tempering:

The object of this process is to harden parts throughout their cross section. Not only is the surface resistant to wear, but the entire part is more able to resist bending or twisting without failure. Unfortunately as hardness goes up, the ability of the part to withstand shock and bending forces decreases. This latter property is called "toughness."

Vacuum Heat Treating:

A vacuum furnace is a type of furnace that can heat materials, typically metals, to very high temperatures and carry out processes such as brazing, sintering and heat treatment with high consistency and low contamination. Heating metals to high temperatures normally causes rapid oxidation, which is undesirable. A vacuum furnace removes the oxygen and prevents this from happening

Yield Testing:

Involves taking a small sample with a fixed cross-section area, and then pulling it with a controlled, gradually increasing force until the sample changes shape or breaks. Yield strength or Yield point of a material is defined in engineering and materials science as the stress at which a material begins to deform plastically. Prior to the yield point the material will deform elastically and will return to its original shape when the applied stress is removed. Once the yield point is passed, some fraction of the deformation will be permanent and non-reversible.