4 - Strengthening Mechanisms - Flashcards

This set of flashcards covers key concepts, terminology, and mechanisms related to materials engineering and strengthening techniques for metals that are essential for the AERO 481 course.

Strengthening Mechanisms for Metals

A set of methods aimed at enhancing the strength and hardness of metals by manipulation of dislocation mobility.

Dislocations

Defects in the crystal structure of metals that allow for plastic deformation.

Grain Size Reduction

A strengthening mechanism that increases the number of grain boundaries, acting as barriers to dislocation motion.

Hall-Petch Equation

An equation that relates the yield strength of polycrystalline materials to their average grain diameter.

Solid-Solution Strengthening

A mechanism where small amounts of alloying elements are added to a host metal, which increases its strength.

Substitutional Solid Solution

A type of solid solution where atoms of similar size replace some of the host atoms.

Interstitial Solid Solution

A solid solution where smaller atoms fit into the interstitial spaces of the host metal's lattice.

Strain Hardening

A process where metals become stronger and harder as they are deformed plastically, primarily through dislocation interactions.

Dislocation Density

The number of dislocations in a given volume of material, which increases with cold working.

Recovery

A heat treatment process that allows dislocations to move and reduce internal stress in cold-worked metals.

Recrystallization

The process of forming new, strain-free grains in a cold-worked material when heated past a certain temperature.

Grain Growth

The process by which new grains grow larger over time at elevated temperatures, often undesired in metal processing.

Martensitic Transformation

A diffusional transformation that occurs in steel when it is rapidly cooled, creating a hard yet brittle phase, martensite.

Pearlite

A mixture of ferrite and cementite that forms in steel during slow cooling; it has desirable mechanical properties.

Bainite

A phase that forms in steel during a cooling rate faster than that needed for pearlite, consisting of elongated Fe3C particles.

Spheroidite

A microstructure formed when pearlitic or bainitic steel is held at a temperature below eutectoid for an extended time.

Austenite

A face-centered cubic phase of iron stable at high temperatures and capable of dissolving carbon.

Ferrite

A body-centered cubic form of iron that is soft and ductile.

Cementite

An iron-carbon compound (Fe3C) that is hard and brittle.

Eutectoid Reaction

A reaction where a solid phase transforms into two new solid phases at a specific composition and temperature.

Heat Treatment

A controlled process of heating and cooling metals to alter their mechanical properties.

Aging (Precipitation Hardening)

A heat treatment process that allows fine precipitates to form within a metal matrix, enhancing strength.

Cold Working

Deforming metal below its recrystallization temperature, usually to increase strength.

Hot Working

Deforming metal above its recrystallization temperature to avoid strengthening while maintaining ductility.

Ductility

The ability of a material to undergo significant plastic deformation before rupture.

Yield Strength

The stress at which a material begins to deform plastically.

Tensile Strength

The maximum stress that a material can withstand while being stretched or pulled.

Plastic Deformation

Permanent deformation that occurs when stress exceeds the yield strength of a material.

Annealing

A heat treatment process used to soften a material and improve its ductility by allowing for recovery and recrystallization.

Quenching

Rapidly cooling a hot metal to set its microstructure, often used in hardening processes.

Temper

A heat treatment following quenching to reduce brittleness while maintaining strength in metals.

Oxide Particles

Hard particles dispersed in a matrix that impede dislocation movement, contributing to dispersion strengthening.

Fiber Reinforced Composites

Materials made from fibers embedded in a matrix, providing enhanced strength and toughness.

Phase Boundaries

Interfaces between different phases in a material, which can impede dislocation movement.

Lattice Strain

Deformation of the crystal lattice due to the presence of dislocations or other defects.

Slip Plane

The plane along which dislocations move, influencing a material's ductility.

Grain Boundaries

Interfaces separating individual grains (crystals) in polycrystalline materials.

Schematic Diagram

A simplified representation of a structure or process used for illustrative purposes.

Material Constant

A unique property of a material that remains unchanged under specified conditions.

Atomic Mobility

The ability of atoms in a material to move or rearrange, affecting properties like diffusivity.

Chemical Reactivity

The tendency of a substance to undergo chemical reactions, often influenced by grain boundaries.

Dislocation Motion

The movement of dislocations through a material under applied stress.

Hardness

A measure of a material's resistance to localized plastic deformation.

Alloy

A mixture of two or more elements, with at least one being a metal, designed to enhance properties.

Cross-Sectional Area

The area of the intersection of a material, relevant when calculating mechanical properties.

Resistance to Deformation

The ability of a material to withstand changes in shape without permanent deformation.

Creep Resistance

The ability of a material to resist slow, permanent deformation under persistent stress.

Interfacial Area

The surface area that separates distinct phases in a composite material.

Diffusion

The process by which atoms or molecules spread from areas of high concentration to areas of lower concentration.

Impurity Atoms

Atoms of one element that are present in small amounts within a host material, influencing its properties.

Thermodynamically Stable

A state where a system is at its lowest energy configuration and is unlikely to change spontaneously.

Elastic Loading

The application of stress to a material in such a way that it returns to its original shape upon unloading.

Microstructure

The structure of a material observed at a microscopic scale.

Mechanical Properties

Characteristics that describe a material's behavior under mechanical loads.

Phase Diagram

A chart showing the phases present at different temperatures and compositions of a material.

Aging Temperature

The specific temperature at which aging (precipitation) heat treatment occurs.

Solid Solution

A homogeneous mixture of two or more substances where the solute is incorporated into the solvent's lattice.

Grain Refinement

The process of reducing grain size to enhance strength and toughness.

Tensile Deformation

Deformation that occurs in a material as it is being stretched.

Ash Reduction

A process used in material science to remove impurities for improved properties.

Micrograph

A photograph taken with a microscope to show the microstructure of materials.

Coherent Precipitates

Precipitates that maintain a structural relationship with the surrounding matrix, enhancing strength.

Overaging

A condition where precipitates in an alloy become too large, resulting in decreased strength.

Metal Matrix Composites

Materials composed of a metal matrix with dispersed particles to enhance properties.

Heat Treatment Cycle

The sequence of heating and cooling processes applied to a metal to alter its properties.

Substitutional Alloy

An alloy where the atoms of the solute take the place of solvent atoms in the lattice.

Interstitial Alloy

An alloy where solute atoms occupy voids between the solvent's atoms in the crystal structure.

Friction Stir Welding

A solid-state joining process that uses friction to generate heat and join materials without melting.

Phase Transformation

A change in the arrangement of atoms in a material, leading to different phases.

Quench Hardening

A process of hardening steel by rapid cooling after heating.

Work Hardening

An increase in strength and hardness due to plastic deformation.