PE Metallurgical key terms

The stress at which a material begins to deform permanently, commonly reported as the 0.2% offset value from a stress-strain curve.

A measure of stiffness equal to the slope of the linear elastic part of the stress-strain curve; higher values mean less elastic strain for a given stress.

The extent to which a material can deform plastically before breaking, often expressed as percent elongation or percent reduction in area in a tensile test.

The amount of energy a material absorbs before fracture, reflecting a combination of strength and ductility; measured by impact tests or the area under a stress-strain curve.

A material's resistance to localized plastic deformation, such as indentation or scratching, commonly measured by Rockwell, Brinell, or Vickers tests.

Time-dependent plastic deformation under a sustained load, especially at temperatures above roughly one-third of the absolute melting temperature.

The stress amplitude below which a material, typically steel, can endure an effectively infinite number of load cycles without fatigue failure.

A material property describing resistance to growth of an existing crack, expressed as the critical stress intensity factor K_Ic; important for fail-safe design.

Strengthening caused by plastic deformation, which multiplies dislocations and makes further deformation harder; also called work hardening.

Strengthening from dissolved alloy atoms that distort the crystal lattice and impede dislocation motion; depends on size and concentration differences between atoms.

The face-centered cubic phase of iron that exists at high temperature and can dissolve substantial carbon; it transforms to other phases on cooling.

A hard, brittle phase formed when austenite is cooled too fast for carbon to diffuse, producing a supersaturated, distorted crystal structure.

A lamellar two-phase microstructure of ferrite and cementite that forms when austenite cools slowly through the eutectoid temperature.

Strengthening by fine second-phase particles that form during aging after a solution heat treatment, blocking dislocation motion; used in aluminum and nickel alloys.

An iron-based alloy containing at least about 10.5% chromium, which forms a passive oxide film that provides corrosion resistance.

An iron-carbon alloy with more than about 2% carbon, often containing graphite flakes or nodules, used for its castability and damping capacity.

A high-performance alloy, usually nickel-, cobalt-, or iron-based, designed to retain strength and resist oxidation at elevated temperatures.

The temperature at which an amorphous polymer changes from a hard, glassy state to a softer, rubbery state as molecular motion increases.

A polymer that softens when heated and can be remelted and reshaped repeatedly because its chains are not chemically crosslinked.

A polymer that cures into a permanently crosslinked network and cannot be remelted; often used for adhesives and composite matrices.

A material combining strong fibers in a matrix to carry load, giving high stiffness and strength along the fiber direction with low density.

Deliberate addition of small amounts of impurity elements to a semiconductor to control its electrical conductivity and charge-carrier type.

A heat treatment that heats a material and cools it slowly to soften it, relieve residual stresses, and produce a more equilibrium microstructure.

Rapid cooling of a heated metal, often in water, oil, or air, to suppress diffusion and form hard phases such as martensite.

Reheating a quenched steel to a moderate temperature to reduce brittleness and relieve stresses, trading some strength for improved toughness.

Plastic deformation performed below the recrystallization temperature, which increases strength and hardness while reducing ductility.

Consolidating a powder compact by heating it below the melting point so particles bond and pores shrink, increasing density and strength.

The region of base metal next to a weld that is thermally altered but not melted, often where properties or cracking problems occur.

A manufacturing route in which metal powders are compacted into a shape and then sintered to form a solid part.

The ratio of a material's strength to its density; a key measure for lightweight design such as aerospace structures.

A chart of one material property against another, used with performance indices to compare material classes and guide selection.

The ratio of a material's allowable or failure strength to the maximum stress expected in service, providing margin against uncertainty.

A test that pulls a specimen along one axis until it breaks, measuring strength, ductility, and elastic modulus from the stress-strain curve.

A test in which a swinging hammer breaks a notched bar, measuring absorbed energy and revealing toughness and ductile-to-brittle transition behavior.

An imaging technique that scans a focused electron beam over a sample to reveal surface topography and microstructure at high magnification and depth of field.

An analytical technique that identifies crystalline phases and measures lattice spacing by the angles at which X-rays diffract from atomic planes.

Crack growth caused by the combined action of a tensile stress and a corrosive environment, often occurring below the alloy's normal yield strength.

Loss of ductility and premature cracking caused by hydrogen absorbed into a metal, often during plating, welding, or service in corrosive environments.

Accelerated corrosion of one metal when it is electrically connected to a more noble metal in the presence of an electrolyte.

The study and interpretation of fracture surfaces to identify the failure mode, such as ductile overload, fatigue, or brittle cleavage.