MAT SCI FINAL

Structure

how atoms come together to form geometric features

Processing

how do I make/fabricate materials with desired stuctures

Ductile

Capacity of a material to undergo plastic deformation, stress before fracturing

Brittle

Tendancy to break or snap

Metals

Strong, Dectile, high thermal abd conductivity, opaque and reflective

Polymers/Plastic

Soft, ductile, low strenth, low thermal and conductivity

Ceramic

Hard, brittle, metallic and nonmetallic elements

Alloy

combining 2 or more elements to make a new material

Ionic Bonds

is transfer of electrons, metals donate electrons to nonmetals, large bond energy (ceramics)

Covalent Bonds

Sharing of electrons. Variable bond energy, ceramics, and polymers.

Van der Walls

come from attractive forces between negative and positive, low bond energy, ceramics

Stress

the measure of force intensity

Tensile Stress

stretching the body

Compressive Stress

compressing the body

Elastic behavior

the ability of a material to deform under applied force and automatically return to its original shape and dimensions when that force is removed

Yield Strenth

the maximum stress a material can withstand without undergoing permanent deformation

tensile strenth

the maximum stress a material can withstand while being stretched or pulled before breaking

Fracture Stress

the maximum stress or load it can withstand before a fracture occurs

Ductility

measure of the degree of plastic deformation that has been sustained at fracture

Brittle

Material that experiences very little or no plastic deformation

Resilliance

Capacity of a material to absorb energy when deformed elastically and release the energy upon unloading, are of the slope of the stress strain curve

Toughness

ability for a material to absorb energy without fracturing, area under the curve of the stress strain curve

Hardness

a material's resistance to localized plastic deformation, such as denting, scratching, abrasion, or cutting

Ductile Fracture

slow cracking followed by significant folds without warning

Brittle

rapid cracking, little or no plastic deformation, breaks without warning

Intergranular Crack vs Transgranular Crack

Intergranular crack is between the grains while the Transgranular Crack is through the grians

Fatigue

Failure under lengthy period of repeated stress or strain

Fatigue striations

microscopic fracture

Creep

measures deformation (strain) vs time at constant stress

Deformation

The change in size or shape of a component due to applied external loads, such as force or temperature.

Stages of Creep

Primary Creep - slope decreases with time

Secondary Creep - steady state, steady slope

Tertiary Creep - increasing slope

Conduction

heat transfer by motion of atoms and molecules

Convection

energy exchange between a surface and adjacent fluid

Radiation

emission of electromagnetic waves

Heat Capacity

the energy required to produce a unit raise in temp for 1 mol of material

Photon

single quantum of vibrational energy

Thermal expansion

Materials change size when temperature is changed, expand when heated, contracted when cooled

Asymmetric Curve vs Symmetric Curve

In a Asymmetric Curve atoms vibrate longer distances, in a Symmetric Curve atoms vibrate smaller distances

Thermal conductivity

Ability for a material to transport heat

Electron Bond Energy

how valence electrons (outermost electrons) behave when atoms are packed close together in a solid

Energy Band

In a solid, when atoms get close, their energy levels split into many tiny levels and merge into bands. Electrons need to jump between these energy bands. Large band gaps require more energy to jump so fewer jumps = less conductive

Band Gap of Materials

Insulators - have a large band gap

Semiconductors - have a small band gap

Metals - have no band gap

Fermi Energy

The highest energy level occupied by electrons

Intrinsic Semiconductor vs Extrinsic Semiconductor

Intrinsic semiconductors are inherent in pure materials, and extrinsic semiconductors behaviors dictated by impurity atoms (artificial)

Free Electron Vs Hole

free electrons have a negative charge and are in the conduction band,

holes have a positive charge and a vacant electron state in the valence

N type vs P type (extrinsic semiconductors)

N type Electron# > Hole#

P type Hole# > Electron#

Dense vs Nondense Packing

Dense ordered packing tends to have lower energies than random nondense packing

Crystaline

materials with atoms arranged periodically

Non Crystaline

materials with no periodic arrangement “Amorphous” = noncrystalline

Bravars Lattice

There are only 14 ways to arrange points in a crystal

Simple Cubic Structure

center of the atom at the 8 corners of the cube

Body Centered Cubic

8 cube corners and a single center atom

Face Centered Cubic

8 cube corners and 6 faces

Vacancies

vacant atom sits in the structure of a gap

Self interstitial

extra host atom positioned in the interstitial position between atoms

Most metals are alloys

impurity atoms are added to modify specific properties/characteristics

Linear id defects

one-dimensional, line-shaped irregularities in the ordered structure of crystalline materials

Edge Dislocation

there is an extra half plane of atoms

Screw Dislocation

Slipped/Sheared plane within a crystal, a spiral within the lattice structure

Burgers Vector

a vector that represents the magnitude and direction of lattice distortion

4 Ways to Strengthen a Metal

Solution Hardening, Work Hardening, Precipitation Hardening, Hall Petch Strengthening

Dislocations

are defects in the crystal structure that let atoms “slip” past each other when a material is deformed

Solution Hardening

Add impurity atoms, differently sized, smaller atoms in between cracks, making it harder for dislocations to move

Work Hardening

deforming the metal plastically, bending, rolling, and stretching creates more dislocations making it harder to move

Precipitation Hardening

You heat, quench, and age the material, forming tiny particles, blocking dislocations

Hell Petch Strengthening

you make grains smaller, more grains = more boundaries = block dislocations

Diffusion

Net Movement of atoms, molecules or any other molecule form a region of high concentration to low

Interdiffusion

diffusion of atoms from one material to another

Self diffusion

atomic migration in a pure material

Vacancy Diffusion

atoms and vacancies exchange positions

Stiffness

Slope of the rising line in the stress vs strain curve