Final Exam Flashcards
Equation
true stress and true strain (plastic region to point of necking)
What is a crystal structure
The manner in which atoms, ions, or molecules are spatially arranged
2
2 engineering strain
Phase diagram
a graph representing the states of a material by composition and temperature
Equation
Interplanar spacing for crystals having cubic symmetry
mechanisms of diffusion for gases, liquids, and solids
gases & liquids - random (Brownian) motion
solids - vacancy diffusion or instititial diffusion
What is a crystal lattice?
A three dimensional array of points coinciding with atom positions or sphere centers
types of imperfections
point defects
- vacancy atoms
- interstitial atoms
- substitutional atoms
line defects
- dislocations
area defects
- grain boundaries
Equation
Fick’s first law
steady-state diffusion independent of time
flux proportional to concentration gradient
6
6 yield point
Eutectic reaction
liquid is transformed into two solids
Equation
engineering stress
solubility limit
maximum concentration for which only a single phase solution exists
8
8 elastic deformation / elastic region
5
5 proportionality limit
point at which there is deviation from linearity
What types of materials form crystalline structures
All metals, many ceramic materials, and certain polymers under normal solidification conditions
grain boundaries
regions between crystals where there is a transition from one lattice to that of another
11
11 necking
conditions for substitutional solid solutions
- difference in radius < 15%
- lowest difference in EN
- same or higher no. of valent electrons
- same crystal structure
Which is faster Dinterstitial or Dsubstitutional and why?
Dinterstitial >> Dsubstitutional
Name the correlations between bonding type and material
Polymers – covalent
Metals – metallic
Ceramics - ionic/mixed ionic-covalent
Molecular solids – van der Waals
Semi–metals – mixed covalent–metallic
Intermetallics – mixed metallic–ionic
isomorphous system
complete solubility of one component in another
7
7 yield strength
Equation
temperature dependece of diffusion coefficient
Phase
homogeneous state of matter that has uniform physical and chemical characteristics
What does tensile strength represent and what point is it on the engineering stress strain curve?
It represents the maximum tensile stress that can be sustained by a specimen
It is taken as the stress level at the maximum point on the engineering stress-strain curve
components
the elements or compounds which are present in the alloy
Material Science
Materials science involves investigating the relationships that exist between the structures and propterties of materials
Equation
atomic packing factor (APF)
Equation
true stress
Name the types of point defects
Vacancies
Interstitials
Substitutions
tie line (isotherm)
connects the phases in equilibrium with each other
Equation
engineering strain
4
4 ultimate strain or fracture point
Equation
Fick’s second law
non-steady state diffusion where the concentration of diffusing species is a function of both position and time
How is yield strength determined and what is it indicative of
From a stress-strain plot using the .002 strain offset technique
It is indicative of the stress at which plastic deformation begins
What is a crystalline material?
One in which atoms are situated in a repeating or periodic array over large atomic distances–that is, long-range order exist, such that upon solidification, the atoms will position themselves in a repetitive three-dimensional pattern, in which each atom is bonded with its nearest neighbor atoms
9
9 plastic deformation / plastic region
Equation
unit cell edge length for BCC
Materials engineering
Materials engineering involves, on the basis of these structure-property correlations, designing or engineering the structure of a material to produce a predetermined set of properties
types of dislocations (describe)
edge dislocation - extra half plane of atoms inserted in a crystal structure [perpendicular]
screw dislocation - spiral planar ramp resulting from shear deformation [parallel]
Equation
number of atomic sites per unit volume
Name the types of materials
Metals (metallic elements)
Ceramics (compounds between metallic and nonmetallic elements)
Polymers (compounds composed of carbon hydrogen and other non-metallic elements)
Composites (composed of at least two different types of materials)
What types of point defects are not allowed in ceramic / ionic compounds and why?
Vacancies and substitutions. They lead to charge imbalances in the system.
Equation
ductility, percent reduction in area
Equation
Bragg’s law; wavelength-interplanar spacing-angle of diffracted beam
What is ductility?
A measure of the degree to which a material plastically deforms by the time fracture occurs
Name the point defects in ionic systems
Schottky (pair of vacancies) and Frankel (atom relocates to an interstitial site)
Equation
ductility, percent elongation
Equation
modulus of elasticity (Hooke’s law)
peritectic reaction
solid transforms into a liquid and another solid
Equation
diffusion flux
1
1 engineering stress
eutectoid reaction
solid transforms into two other solids
10
10 ultimate strength
Equation
unit cell edge length for FCC
3
3 youngs modulus
How is ductility measured?
In terms of percents elongation (%EL) and reduction in area (%RA)
burger’s vector
b
a measure of lattice distortion
What happens on an atomic level during plastic deformation
Atomic bonds stretch as they go through elastic deformation. Slipping along interatomic crystal planes occurs past the yield point, increasing overall elongation
Equation
number of vacancies per unit volume
What happens on an atomic level during elastic deformation?
Atomic bonds are stretching. Interatomic separation increases with increasing stress and returns to equilibrium when no longer under tension
Why does D have exponential dependence on T
An increase in temperature increases the number of vacancies. An increase in vacancies increases the rate of diffusion and decreases activation energy.
12
12 strength hardening
Describe elastic deformation on an atomic level
Elastic deformation corresponds to the stretching of interatomic bonds and corresponding slight atomic displacements
linear defects (dislocations)
one dimensional defects around which atoms are misaligned
Equation
true strain
unit cell
smallest repeating volume which has a complete crystal lattice pattern
APF for a simple cubic structure
0.52
APF for a body-centered cubic structure
0.68
APF for a face-centered cubic structure
0.74
Equation
density
vacancy diffusion
atoms exchange with vacancies
applies to substitutional impurities atoms
rate depends on number of vacancies and activation energy to exchange
interstitial diffusion
smaller atoms diffuse between attoms
case hardening
diffusion of carbon atoms onto the surface of a host iron atom
free energy
A thermodynamic quantity that is a function of both the internal energy and entropy (or randomness) of a system. At equilibrium, it is at a minimum.
diffusion is faster for
_____ structures
materials w/_____ bonding
_____ diffusing atoms
_____ density materials
diffusion is faster for
open crystal structures
materials w/secondary bonding
smaller diffusing atoms
lower density materials
diffusion is slower for
_____ structures
materials w/_____ bonding
_____ diffusing atoms
_____ density materials
diffusion is slower for
close-packed structures
materials w/covalent bonding
larger diffusing atoms
higher density materials
microconstituent
An element of the microstructure that has an identifiable and characteristic structure. It may consist of more than one phase, such as with pearlite.
interstitial solid solution
A solid solution in which relatively small solute atoms occupy interstitial positions between the solvent or host atoms.
solute
One component or element of a solution present in a minor concentration. It is dissolved in the solvent.
atomic number (Z)
the number of protons within the atomic nucleus
Exhibiting different values of a property in different crystallographic directions.
anisotropy
shear
A force applied that tends to cause two adjacent parts of the same body to slide relative to each other in a direction parallel to their plane of contact
fracture toughness
the measure of a material’s resistance to fracture when a crack is present
fatigue strength
The maximum stress level that a material can sustain without failing, for some specified number of cycles.
equilibrium
The state of a system in which the phase characteristics remain constant over indefinite time periods. At equilibrium the free energy is a minimum.
A dislocation that has both edge and screw components.
mixed dislocation
Atomic migration in pure metals
self-diffusion
one of the two phases found in the eutectic structure
eutectic phase
Miller indices
A set of three integers (four for hexagonal) that designate crystallographic planes, as determined from reciprocals of fractional axial intercepts
creep
The time-dependent permanent deformation that occurs under stress; for most materials it is important only at elevated temperatures.
The increase in hardness and strength of a ductile metal as it is plastically deformed below its recrystallization temperature.
strain hardening
The combination of unit cell edge lengths and interaxial angles that defines the unit cell geometry.
lattice parameters
polymorphism
The ability of a solid material to exist in more than one form or crystal structure.
The increase in average grain size of a polycrystalline material; for most materials, an elevated-temperature heat treatment is necessary.
grain growth
vacancy
A normally occupied lattice site from which an atom or ion is missing.
area defects
grain boundaries
twins
stacking faults
Alloy
A metallic substance that is composed of two or more elements
Interstitial solid solution
A solid solution in which relatively small solute atoms occupy interstitial positions between the solvent or host atoms.
imperfection
A deviation from perfection; normally applied to crystalline materials in which there is a deviation from atomic/molecular order and/or continuity.
The capacity of a material to absorb energy when it is elastically deformed.
