manufacturing midterm terms

Allotropism

Many shapes

• appearance of one or more type of crystal types

• Important in heat treatment, metal working, and welding

Anisotropy

a physical property that has a different value when measured in different direction

• ex wood is strong along grain than across

basal plane

largest flat surface within a layered crystalline material 

Body centered cubic (BCC) def and characteristics

atoms at each of its 8 corners and one atom in the center

• 48 possible slip systems

• required high shear stress for slip, but many slip areas to happen

• good strength, moderate ductility

• can have higher ductility at higher temps

face centered cubic (FCC) def and characteristics

atoms located at the eight corners of the cube and at each center of the six faces

• 12 slip system, so chance of slip moderate

• shear stress required for slip is low 

• moderate strength, good ductility

hexagonal close packed (HCP) def and characteristics

hexagonal prism with three layers, 6 corner atoms on top and bottom bases and 3 atoms int he middle of the prism, and 2 center atoms on the faces. 6 atoms per unit cell.

• 3 slip systems, low probability of a slip

• slip more active at higher temps

• brittle at room temps

cold working

plastic deformation carried out at room temp

covalent bond

sharing of electrons to achieve stable configuration

creep

gradual time dependent deformation of material under constant load or stress, accelerated by elevated temps

dislocation

a linear defect in a crystalline solid responsible for plastic deformation

elastic deformation

returns to OG shape after force is removed

embrittlement

process where a material, including metal, loses ductility and toughness, becoming brittle and more prone to cracking

grain

individual crystal within a polycrystalline structure like a metal

grain boundary

in polycrystalline materials is the boundary surface between adjacent crystals (grains)

grain growth

if temperature of the metal is raised the grains begin the grow and exceed the OG grain size

• larger grains lead to rougher surface

• adversely affect mechanical properties

grain size influence

• smaller grain size increases a material’s strength and hardness as it creates more grain boundaries, impeding dislocation movement

• larger grain size increases ductility by allowing for easier dislocation movement, can improve high temp creep resistance

homologous temp

T/Tm ratio where T is working temp and Tm is melting point

• dimensionless

hot shortness

metal becoming brittle and prone to cracking when heated to high temp

hot working

when deformation occurs above the recrystallization temp

imperfections

• point defects

• linear defects

• planar defects

• volume defects

• strengthening mechanisms

ionic bond

bond from oppositely charges ions formed when once atom completely transfers one or more electrons to another

mechanical fibering

• type of anisotropy resulting from inclusions, impurities, and voids during deformation

• impurities will weaken grain boundaries, so piece of metal will be weaker

metallic bond

force that holds metal atoms together in a solid formed by positive charges metal ions

nucleation

the initial stage of crystal formation

orange peel

rough surface appearance on sheet metals produced by larger grains

plastic deformation

permanent deformation - does not return to its original shape when the force is removed

polygonization

formation of subgrain boundaries 

recovery

stressed in highly deformed regions of metal piece are relieved, subgrain boundaries begin to form with no significant change in mechanical properties

recrystallization

the “reset button” after being bent or stretched — when heated to the right temperature, it forms new, smooth, strain-free grains that replace the old, deformed ones, making the metal softer and more ductile again

shear stress

force acting parallel to area of material, causing planes within material to slide past each other

slip system

combination of a slip plane and its direction of a slip

slip plane

the adjacent plane of which a plane of atoms slips over under shear stress

work hardening/strain hardening

When more shear stress is needed to overcome obstacles in the metal’s structure, its overall strength and hardness increase

twinning

A deformation process where part of a crystal forms a mirror image of the rest, helping the metal change shape under stress (HCP structures)

vacancy

atom missing from a normally occupied position

interstitial 

atom present in a position that is normally unoccupied 

van der waals force

A weak attraction between molecules caused by temporary or uneven distribution of electric charges

Bauschinger Effect

When a metal is stretched and then compressed, it becomes easier to deform in the opposite direction — this is called strain softening or work softening

brittle fracture

no plastic deformation before fracture

compression

A force that pushes or squeezes a material, making it shorter or more compact

creep

time dependent deformation under load

deformation rate

speed at which a tension test is being carried out

disk test

A test where a disk is squeezed between two flat plates until it splits in half, showing how the material breaks under tension

ductile fracture

relatively large amounts of plastic deformation before fracture

elongation

measure of ductility of a material

ductility

ability of a material to stretch or deform before fracture

engineering strain

The amount a material stretches compared to its original length

egnineering stress

applied load divided by the original cross-sectional area of a material σeng​=F/A₀

true stress

applied load divided by the actual (instantaneous) cross-sectional area as the material deforms σtrue​=F/A_{instantaneous}

true strain

natural (logarithmic) strain considering continuous deformation εtrue​=ln(​L/L₀)​

fatigue

failure at relatively low stress levels

hardness

resistance to indentation

modulus of rupture

stress at fracture in bending

poisson’s ratio

relationship between axial and transverse strain

residual stresses

stresses that reaimin within a part after it has been formed and all the external forces are removed

strain rate

how quickly a material stretches, shorter specimens stretch faster than longer ones under same conditions

strain rate sensitivity exponenet

slope of temp and strain rate curves 

superplasticity

ability of a material to undergo large uniform elongation before necking and fracture

tension

a force that pulls or stretches material

toughness

measure of the ability of a material to absorb energy up to fracture

ultimate tensile strength 

max stress a material can withstand while being stretched before deformation

yield stress

stress at which a material starts to permanently deform

thermal conductivity

indicates the rate at which heat flows within and through a material as temp changes

• metals have higher thermal conductivity

• ceramics and plastics poor conductivity

• materials with high electric conductivity typically have high thermal conductivity

thermal expansion

expansion or contraction of a material with change in temp

thermal stresses

thermal expansion creates stress, can also be caused by anisotropy of thermal expansion (uneven expansion)

thermal fatigue

caused by thermal cycling (heating, cooling, heating…) can cause surface cracks to form

conductors

materials with high electrical conductivity such as metals

super conductors 

phenomenon of near-zero electrical resistivity that occurs in some metals and alloys below a critical temperature

• application is high power magnets

semiconductors

extremely sensitive to temperature and impurities so by controlling these properties we can control electrical conductivity

• used in microelectronics

electrical conductivity

material’s ability to conduct electrical current

dielectric strength 

largest electric field an electrically insulating material can encounter without degrading or losing its insulating properties

ferromagnetism

high permeability and permanent magnetization that are due to the alignment of iron, nickel, and cobalt atoms into domains

• used in electric motors, electric generators, etc

piezoelectric effect

Some materials change shape when electricity is applied, and produce electricity when pressed

Magnetostriction

expansion or contraction of a material when it is subjected to a magnetic field

galvanic corrosion

One metal corrodes faster when touching a different metal in water or electrolyte

stress corrosion cracking

Cracks form in metal under tension and a corrosive environment.

general corrosion

Metal corrodes evenly over its surface, like rust.

localized corrosion (pitting)

Small spots corrode faster than the rest of the metal.

caustic agent corrosion

Metal is damaged by strong chemicals like acids or bases.

pure metals

all atoms are the same type, except very small % of impurity atoms 

• 99% pure minimum 

alloys

a composition of two or more chemical elements, at least
one of which is a metal

interstitial solid solution

impurities are located in the spaces between the solvent atoms (interstices)

substitutional solid solution

impurities are located in sites normally occupied by solvent atoms

inter metallic compounds

structures consisting of two metals in which solute atoms are present among solvent atoms in certain proportions

• typically strong, hard, and brittle

phase diagram

A diagram that shows which phases exist in an alloy at different temperatures and compositions when the system is stable

tie line

A horizontal line drawn at a specific temperature across a two-phase region on a phase diagram. It intersects the phase boundaries to show the compositions of the coexisting phases

ferrous

iron based

steel

iron alloyed primary with carbon but can be with Cr, Mo, Ni, etc

raw materials 

iron ore, limestone, coke

blast furnace

A large furnace used to smelt iron from its ore by heating it with a combination of coke, limestone, and air, producing molten iron and slag

electric arc furnaces

A furnace that melts steel using a continuous electric arc between electrodes and the metal, typically from steel scrap, in a few hours

basic oxygen furnace

A steelmaking furnace where pure oxygen is blown into molten iron and scrap to remove impurities, producing steel and slag quickly and efficiently

• fastest and far most common in the world

carbon steels

steels with carbon

• low less than 0.3%

• medium 0.3-0.6%

• high higher than 0.6%

complex phase steels

very fine grain microstructures of ferrite and high volume of martensite and bainite

• UTS strengths of 800 MPa

continuous casting 

A process where molten metal is poured into a mold and solidified while being continuously pulled through rollers to form long, uniform shapes

continuous casting

A process where molten metal is poured into a mold and solidified while being continuously pulled through rollers to form long, uniform shapes

dual phase steels

mixed ferrite and martensite strcutre

• high work hardening exponent

• improved ductility and formability

High Strength Low Alloy Steels (HSLA)

steels with low carbon content less than 0.3%

• fine grain ferrite as one phase and a hard second phase of martensite and austenite 

ignot

solid form of molten steel

martensitic steels

Stainless steels that are hardenable by heat, magnetic, very strong and hard, with good fatigue resistance and moderate corrosion resistance