Glossary

Quick definitions of essential terms in metallurgy, materials science, and testing.

A

Additive manufacturing: Additive manufacturing builds metal parts layer by layer from a digital model, using processes like powder bed fusion or directed energy deposition, enabling complex geometries and reduced material waste. Read more in the article. Wikipedia entry.
Aluminum alloy: Aluminum alloy is a lightweight metal mixed with elements such as copper, magnesium, or silicon to improve strength, corrosion resistance, or formability, categorized by series like 2xxx or 6xxx. Read more in the article. Wikipedia entry.
Annealing: Annealing is a heat treatment that softens a metal by heating it to a specific temperature, holding, then slow cooling, which relieves internal stresses and increases ductility. Read more in the article. Wikipedia entry.
Austenite: Austenite is a face-centered cubic iron phase stable at high temperatures in steel, capable of dissolving significant carbon, and is non-magnetic. Read more in the article. Wikipedia entry.
Austenitizing: Austenitizing is the process of heating steel to a temperature where its microstructure transforms fully to austenite, the first step before quenching and tempering. Read more in the article. Wikipedia entry.

B

Bainite: Bainite is a steel microstructure formed by cooling austenite at rates between those that produce pearlite and martensite, consisting of ferrite and finely dispersed cementite. Read more in the article. Wikipedia entry.
Brass: Brass is a copper-zinc alloy known for good machinability, corrosion resistance, and acoustic properties, with common grades like C360 for machining. Read more in the article. Wikipedia entry.
Bronze: Bronze is primarily a copper-tin alloy offering high strength, wear resistance, and corrosion resistance, often used in bearings, bushings, and marine hardware. Read more in the article. Wikipedia entry.

C

Cementite: Cementite is an iron carbide (Fe3C) phase in steel, hard and brittle, that precipitates in pearlite or during tempering, contributing to strength and wear resistance. Read more in the article. Wikipedia entry.
Creep: Creep is the time-dependent, permanent deformation of a metal under constant load at elevated temperatures, a critical design consideration for high-temperature components like turbine blades. Read more in the article. Wikipedia entry.

D

Ductility: Ductility is a metal's ability to deform plastically under tensile stress without fracturing, commonly measured by percent elongation or reduction of area in a tensile test. Read more in the article. Wikipedia entry.

E

Elastic modulus: Elastic modulus, or Young's modulus, is the ratio of stress to strain in the elastic region of a material, indicating stiffness; a higher value means less deformation under load. Read more in the article. Wikipedia entry.
Eutectoid: Eutectoid is a three-phase reaction in which a solid phase transforms into two different solid phases upon cooling, most notably the austenite-to-pearlite transformation in steel at 727°C. Read more in the article. Wikipedia entry.

F

Fatigue limit: Fatigue limit is the maximum stress amplitude below which a ferrous metal can endure an infinite number of load cycles without fatigue failure, a key design parameter. Read more in the article. Wikipedia entry.
Ferrite: Ferrite is a body-centered cubic iron phase in steel, stable at room temperature, with low carbon solubility, soft, and magnetic. Read more in the article. Wikipedia entry.
Fracture toughness: Fracture toughness quantifies a material's resistance to crack propagation, typically measured as KIC, the critical stress intensity factor for brittle fracture under plane-strain conditions. Wikipedia entry.

G

Galvanic corrosion: Galvanic corrosion occurs when two dissimilar metals in electrical contact are exposed to an electrolyte, causing the more anodic metal to corrode preferentially. Read more in the article. Wikipedia entry.

H

Hardenability: Hardenability is the ability of a steel to form martensite upon quenching, influenced by alloy content and grain size, commonly evaluated by the Jominy end-quench test. Read more in the article. Wikipedia entry.
Hardness: Hardness is a material's resistance to localized plastic deformation, typically measured by indentation tests such as Rockwell, Brinell, or Vickers, and correlates with strength. Read more in the article. Wikipedia entry.
Heat treatment: Heat treatment involves controlled heating and cooling of metals to alter their microstructure and achieve desired mechanical properties, such as hardening, softening, or stress relief. Read more in the article. Wikipedia entry.
Hot isostatic pressing: Hot isostatic pressing (HIP) applies high temperature and isostatic gas pressure to consolidate metal powders or heal internal porosity in castings, improving density and mechanical properties. Read more in the article. Wikipedia entry.

I

Iron-carbon phase diagram: The iron-carbon phase diagram maps the equilibrium phases of iron and carbon alloys as a function of temperature and carbon content, essential for understanding steel microstructures and heat treatment. Read more in the article. Wikipedia entry.

M

Martensite: Martensite is a hard, brittle steel microstructure formed by diffusionless shear transformation of austenite during rapid quenching, characterized by a body-centered tetragonal lattice and high strength. Read more in the article. Wikipedia entry.

N

Nickel-based superalloy: Nickel-based superalloy is a high-performance alloy designed for extreme temperatures and stresses, retaining strength and resisting creep and oxidation in jet engines and gas turbines. Read more in the article. Wikipedia entry.
Normalizing: Normalizing is a heat treatment that refines grain structure by heating steel above its upper critical temperature and air cooling, producing a uniform, fine pearlitic microstructure. Read more in the article.

P

Pearlite: Pearlite is a lamellar microstructure of alternating ferrite and cementite layers formed by slow cooling of eutectoid steel, providing a balance of strength and toughness. Read more in the article. Wikipedia entry.
Powder metallurgy: Powder metallurgy is a manufacturing process where metal powders are compacted and sintered to produce near-net-shape parts, offering material efficiency and the ability to alloy immiscible elements. Read more in the article. Wikipedia entry.
Precipitation hardening: Precipitation hardening, or age hardening, strengthens alloys by forming fine, dispersed precipitates that impede dislocation motion, achieved through solution treatment, quenching, and aging. Read more in the article. Wikipedia entry.

Q

Quenching: Quenching is rapid cooling of a metal from a high temperature, typically in water, oil, or polymer, to form a hard microstructure like martensite in steel or to retain a supersaturated solid solution. Read more in the article. Wikipedia entry.

R

Recycling: Recycling of metals involves collecting, sorting, and remelting scrap to produce secondary metal, significantly reducing energy consumption and mining waste compared to primary production. Read more in the article. Wikipedia entry.

S

S-N curve: An S-N curve, or Wöhler curve, plots stress amplitude (S) against the number of cycles to failure (N) for a material, used to determine fatigue life and endurance limits. Read more in the article. Wikipedia entry.
Selective laser melting: Selective laser melting (SLM) is an additive manufacturing process that uses a high-power laser to selectively melt and fuse metal powder layers, building dense, complex parts directly from CAD data. Read more in the article. Wikipedia entry.
Sintering: Sintering is a thermal process that bonds powder particles together by atomic diffusion below the melting point, increasing strength and density of powder metallurgy compacts. Read more in the article. Wikipedia entry.
Stainless steel: Stainless steel is an iron-based alloy containing at least 10.5% chromium, which forms a passive chromium oxide layer providing corrosion resistance, with grades classified by microstructure. Read more in the article. Wikipedia entry.
Stress corrosion cracking: Stress corrosion cracking (SCC) is the brittle failure of a susceptible alloy under tensile stress in a specific corrosive environment, often occurring without significant general corrosion. Wikipedia entry.

T

Tempering: Tempering is a heat treatment following quenching that reheats steel to a moderate temperature to reduce brittleness, relieve stresses, and adjust hardness and toughness. Read more in the article. Wikipedia entry.
Tensile strength: Tensile strength, or ultimate tensile strength (UTS), is the maximum engineering stress a material can withstand while being stretched before necking, a key value on data sheets. Read more in the article. Wikipedia entry.
Titanium alloy: Titanium alloy is a lightweight, high-strength metal with excellent corrosion resistance, often used in aerospace and medical implants, with common grades like Ti-6Al-4V. Read more in the article. Wikipedia entry.
Toughness: Toughness is a material's ability to absorb energy and plastically deform without fracturing, often measured by the area under the stress-strain curve or impact tests like Charpy. Read more in the article. Wikipedia entry.

Y

Yield strength: Yield strength is the stress at which a material begins to deform plastically, typically determined by the 0.2% offset method on a stress-strain curve, critical for structural design. Read more in the article. Wikipedia entry.