Materials Science Midterm 2

Hot working of metals

permanent deformation of metals and alloys above the temperature at which a stain-free microstructure is produced continuously (recrystallization temperature)

Cold working of metals

permanent deformation of metals and allows below the temperature at which a strain-free microstructure is produced continuously (recrystallization temperature). causes a metal to be strain-hardened

Percent cold reduction

% cold reduction = change in cross-sectional area / original cross-sectional area * 100%

Annealing

heat treatment used on a metal to soften it

Extrusion

plastic-forming process which a material under high pressure is reduced in cross section by forcing it through an opening in a die

Forging

primary-processing method for working metals into useful shapes in which the metal is hammered or pressed into shape

Wire drawing

process which wire stock is drawn through one or more tapered dies to the desired cross section

Deep drawing

metal-forming process for shaping flat sheets of metal into cup-shaped articles

Elastic deformation

if a metal deformed by a force returns to its original dimensions after the force is removed

Engineering stress σ

average uniaxial force divided by original cross-sectional area

Engineering strain ϵ

change in length of sample divided by original length of sample

Shear stress τ

shear force S divided by the area A over which the shear force acts

Shear strain γ

shear displacement a divided by the distance h over which the shear acts

Engineering stress-strain diagram

experimental plot of engineering stress versus engineering strain; σ on y-axis, ϵ on x-axis

Modulus of elasticity E

stress divided by strain in the elastic region of an engineering stress-strain diagram for a metal

Yield strength

stress at which a specific amount of strain occurs in the engineering tensile test. yield strength is determined for 0.2% strain

Ultimate tensile strength (UTS)

maximum stress in the engineering stress-strain diagram

Hardness

measure of the resistance of a material to permanent deformation

Slip

process of atoms moving over each other during the permanent deformation of a metal

Slipbands

line markings on the surface of a metal due to slip cause by permanent deformation

Slip system

combination of a slip plane and a slip direction

Deformation twinning

plastic deformation process that occurs in some metals and under certain conditions. a large group of atoms displaced to form a region of a metal crystal lattice that is a mirror image of a similar region along a twinning plane

Hall-Petch relationship

empirical equation that relates the strength of a metal to its grain size

Strain hardening (strengthening)

hardening of a metal or alloy by cold working. dislocations multiply and interact, leading to an increase in the strength of the metal

Solid-solution hardening (strengthening)

strengthening a metal by alloying additions that form solid solutions. dislocations have more difficulty moving through a metal lattice when atoms are different in size and electrical characteristics

Annealing

heat-treatment process applied to a cold-worked metal to soften it

Recovery

first stage in annealing process that results in removal of residual stresses and formation of low-energy dislocation configurationsR

Recrystallization

second stage of annealing process which new grains start to grow and dislocation density decreases significantly

Grain growth

third stage of annealing process which new grains start to grow in equiaxed manner

Superplasticity

ability of some metals to deform plastically by 1000% to 2000% at high temperatures and low loading rates

Nanocrystalline metals

metals with grain size smaller than 100 nm

Ductile fracture

mode of fracture characterized by slow crack propagation. surfaces of metals are usually dull with a fibrous appearance

Brittle fracture

mode of fracture characterized by rapid crack propagation. surfaces of metals are usually shiny and have granular appearance

Transgranular fracture

type of brittle fracture which the crack propagates across the grain

Intergranular fracture

type of brittle fracture which the crack propagates along the grain boundary

Ductile-to-brittle transition (DBT)

observed reduced ductility and fracture resistance of a material when temperature is low

Fatigue

phenomenon leading to fracture under repeated stresses having a maximum value less than the ultimate strength of the materialF

Fatigue failure

failure that occurs when a specimen undergoing fatigue fractures into two parts or otherwise has been significantly reduced in stiffness

Fatigue life

number of cycles of stress or strain of a specific character that a sample sustains before failure

Fatigue crack growth rate da/dN

rate of crack growth extension caused by constant amplitude fatigue loading

Creep

time-dependent deformation of a material when subjected to a constant load or stress

Creep rate

slope of the creep-time curve at a given time

Creep (stress)-rupture strength

stress that will cause fracture in a creep (stress-rupture) text at a given time and in a specific environment at a particular temperature

Larsen-Miller (L.M.) parameter

time-temperature parameter used to predict stress rupture due to creep

Phase

physically homogeneous and distinct portion of a material system

Equilibrium

if no macroscopic changes take place with time in a system

Equilibrium phase diagram

graphical representation of the pressures, temperatures, and compositions for which various phases are stable at equilibrium. temperature versus composition

System

portion of the universe that has been isolated so that its properties can be studied

Degrees of freedom F

the number of variables (temperature, pressure, and composition) that can be changed independently without changing the phase of phases of the system

Number of components of a phase diagram

the number of elements of compounds that make up the phase-diagram system

Cooling curve

plot of temperature versus time acquired during solidification of a metal, provides phase change information as the temperature is lowered

Thermal arrest

region of the cooling curve for a pure metal where temperature does not change with time (plateau), representing the freezing temperature

Isomorphous system

phase diagram which there is only one solid phase

Liquidus

temperature at which liquid starts to solidify under equilibrium conditions

Solidus

temperature during the solidification of an alloy at which the last of the liquid phase solidifies

Lever rule

weight percent of the phases in any two-phase region of a binary phase diagram can be calculated using this rule if equilibrium conditions prevail

Tie line

horizontal working line drawn at a particular temperature between two phase boundaries to be used to apply the lever rule

Cored structure

type of microstructure that occurs during rapid solidification or nonequilibrium cooling of a metal

Homogenization

a heat-treatment process given to a metal to remove undesirable cored structures

Eutectic point

L —> two new solids

Hypoeutectic

left of eutectic point

Hypereutectic

right of eutectic point