Material Science Flashcards
Crystallography
How many types of crystalline structures are there?
What are these called?
14 types
Bravais Lattices
Cry
Crystallography
What are the three cell systems that most common metallic crystals form?
body-centered cubic (BCC(, face-centered cubic (FCC), hexagonal close-packed (HCP)
Material Testing
What is engineering stress (σ)?
load per unit original area.
F/Ao
Material Testing
What is engineering strain (ε)?
elongation of the test specimen xpressed as a percentage or decimal fraction of the orginal length.
ΔL/Lo
Stress-Strain Curve
What is Hooke’s law?
The relatinship between the stress and the strain represented as σ=Eε, where E represents the Modulus of elasticity.
Stress-Strain Curve
What is Young’s modulus?
Young’s monulus is also called the modulus of elasticity, and is represented by E. It is the slope of the initial straight line segment in the stress-strain curve.
Stress-Strain Curve
What is permanent set?
Permanent deformation.
Stress-Strain Curve
Most nonferrous materials do not have well-defined yield points, and the yiield piont is usually taken as the stress that will cause a what in the material?
2% parallel offset (i.e. a plastic strain of 0.002)
Stress-Strain Curve
What is ductility?
The ability of a material to yield and deform prior to failure.
ductility = εf/ εy (ultimate failure strain / yielding strain)
Stress-Strain Curve
What is percent elongation?
Short for percent elongation at failure. It is the total plastic strain at failure.
percent elongation = ΔL/Lo * 100% = εf (final) * 100%
Stress-Strain Curve
Are brittle materials ductile?
No
Endurance Test
What is fatique failure?
The condition where a material can fail after repeated stress loadings even if the stress level never exceeds the ultimate strength.
Endurance Test
What is the “fatigue life” of a material?
The number of cycles (Np) required to cause failutre for a particular stress level (Sp) on a specimen.
Impact Test
What is toughness?
A measure of a material’s ability to yield and absorb highly localized and rabidly applied stress.
A touch material will be able to withstand occasional high stresses with
Impact Test
What is the definition of modulus of toughness?
It is the strain energry, or work per unit volume required to cause fracture. This is the total area under the stress-strain curve.
Impact Test
What is notch toughness?
The impact energy that causes the norched sample to fail.
Impact TEST
What is a Charpy test?
It is an impact test to measure the tou ghness of the materila - localized and rapidly applied stress.
A standardized beam specimen is given a 45-degree notch, is centered on simple supports with the notch facing down, and a falling pendulum strikers hits the center of the specimen. This is repeated multiple times at different heights and specimens until a sample fractures.
Endurance Test
What is the maximum stress called that can be repeated indefinitely without causing the speciment to fail?
Endurance Stress / Endurance Limit / Fatigue Limit
Corrosion
What is corrosion?
An undesirable degradation of a material resulting from a chemical or physical reaction with the environment.
Corrosion
What is galvanic action?
Results rom the difference in oxidation potentials of metallic ions.
The greater the difference, the greater the corrosion.
Corrosion
Which metal will corrode (act as an anode) in a galvanic cell?
The more electropositive metal.
Corrosion
What is a galvanic cell?
A device that produces electrical current by way of an oxidation-reduction reaction = that is, chemical energy is converted into electrical energy.
Diffusion
What are the three types of crystal imperfections?
Point, line, and planar (grain boundary) imperfections.
Diffusion
What are point dvects?
vacant lattice sites, ion vacancies, substitutions of foreign atoms into lattice points or interstitial points, and occuration of interstitial pionts by atoms.
Diffusion
What are line devects?
Imperfections that are repeated consistently in many adjacent cells and have extension in a particular direction.
Diffusion
What are grain boundary defects?
The interfaces between two or more crystals. Almost always a mismatch in crystalline structures.
Diffusion
All point devects can move individually and independently from one position to another through what?
Diffusion
Diffusion
What usually causes diffusion?
Activation energy, such as heat and/or strain.
It is governed by Fick’s laws.
Diffusion
What is Fick’s first law?
The prediction of the number of defects that will move across a unit surface area per unit time. This number is knows as the “devect flux, J.
Diffusion
What is the defect flux, J, equation?
J = -D dC/dx
where D is the diffusion coefficient, and dC/dx is the devect concentration gradient.
Diffusion
What three things is the divvusivity (also knows as diffusion coefficient, D) dependent on?
Material, activation energy, and temperature.
Diffusion
What is the formula for the diffusion coefficient, D?
D=Do e^(-Q/RT)
Binary Phase Diagrams
What is a phase diagram called? What does it show?
Equilibrium diagram
The regions on the diagram illustrate the various allooy phases. The phases are plotted agtainst temperature and composition.
(diagram is only applicable during slow cooling.)
Binary Phase Diagrams
What is the “eutectic composition?”
For a limited solubility alloy, it is the point on an equilibrium diagram where the components are perfectly miscible.
Lever Rule
What is the lever rule?
IT is an interpolation technique used to find the relative amounts of solid and liquid phase at any composition.
(These perfecntages are given in fraction (or percent) by weight.)
Lever Rule
Fraction solid formula
= n/w = 1 - fraction liquid
Lever Rule
Fraction liquid formula
= m/w = 1 - fraction solid
Iron-Carbon Phase Diagram
What are allotropes?
Has the same composition but different atomic structures, volumes, electrical resistances, and magnetic properties.
Hardness and Hardenability
What three factgors primarily affect hardenability?
Carbon content, grain size, and thickness.
Hardness and Hardenability
What is austenite?
Gamma-iron
Iron-Carbon Phase Diagram
What are allotropic changes?
Reversible changes that occur at the critical pionts. (i.e. critical temperatures.)
Iron-Carbon Phase Diagram
What three primary allotropic forms does iron exist in?
What causes these forms?
alpha-aron, delta=iron, and gamma-iron.
The changes are brought about by varying the temperature of the iron.
Gibb’s Phase Rule
What is the Gibb’s phase rule?
It defines the relationship between the number of phases and elements in an equilibrium mixture.
P + F = C + 2
(P = # of phases)
(F = # of independent variables)
(C = # elements in the alloy)
Thermal Processing
What is thermal processing?
A process used to obtain a part with desireable mechanical properties.
Examples of processes: hot working, heat treating, and quenching, etc
Thermal Processing
What do “hot working” and “cold working” imply?
Hot working implies that the forming process occurs ABOVE the “recrystallization temperature.”
Cold working implies that the forming process occurs BELOW the “recrystallization temperature.”
Thermal Processing
What is “heat treatment?”
The raising of the temperature of a part to slightly above the recrustallization temperature after it has been worked.
Used to relieve stresses, increase grain size, and recrystallize the granes.
This operation is also knows as “annealing.”
And stress relief is also knows as “recovery.”
Thermal Processing
What is “quenching?”
Method used to control the microstructgure of steel by preventing the formation of equilibrium phases with undesirable chracteristics.
Can be performed with gases, oil, water, or brine.
Thermal Processing
What are Time-Temperature-Transformation (TTT) curves used for?
To determine how fast an alloy should be cooled to obtain a desirable microstructure.
They are NOT equilibrium diagrams.
Hardness and Hardenability
What is “hardness?”
Hardness is the measure of resistance \a material has to plastic deformation.
Examples of hardness tests: Brinell, Rockwell, Meye, Vickers, Knoop
Hardness and Hardenability
What is “hardenability?”
A relative measure of the ease by which a material can be hardened.
