Chapter 2 Flashcards
How many crystal structures exist?
14
What is a unit cell?
The simplest repeating unit in a crystal
What is a close packed plane?
Planes containing the highest atom density
Name some 0-dimensional defects?
Vacancy, Interstitials, Impurities
What rules determine solid solutions or precipitation?
Hume Rothery rules
What are the Hume Rothery rules?
(1) atom radius difference not more than 15%
(2) Similar crystal strucutre
(3) Small electronegativity difference
(4) similar number of valence electrons
What happens to solubility with increasing valence electrons?
Solubility decreases
What is electronegativity?
chemical potential of an element describing the tendency of a material to attract electrons
What is the electronegativity a function of? and what is the ranking use?
Function of distance to the nucleus and number of electrons. Ranking on Pauling scale
What could happen if the electronegativity difference between two components in a solution is more than 0
They will form intermetallic compound instead of a substitutional solid solution.
What is the principal product of neutorn irradiation of the structural metals in the LWR?
Highly non-equilibrium concentrations of vacancies and self-interstitials.
What types of fields does vacancies cause on neighboring atoms?
Attractive forces of neighboring atoms into vacancy creates tensile stress (strain) field, which is elastic isotropic. The strain field is nearly spherical and short range
Does vacancy density increases or decreases with temperature?
Vacancy density increases with temperature
Does electrical resistivity increases or decreseas with vacancy concentration
Electrical resistivity increases with increasing vacancy concentration.
Name three mechanisms by which we can increase vacancies?
Quenching, deformation, irradiation
Name the five recovery stages for V&I with increasing temperature.
I: Collapse of close frenkel pairs, correlated and uncorrelated recombination
II: Interstitial clusters grow leading to small interstitial loops.
III: Vacancies migrate and adulate at interstitial clusters
IV: Vacancy clusters surviving III grow in size and then dissociate thermally
What is the max. size of interstitial in bcc tetrahedron space?
0.29R
What is the max. size of interstitial in bcc octahedron space?
0.154R
What is the max. size of interstitial in fcc tetrahedron space?
0.225R
What is the max. size of interstitial in FCC octahedron space?
0.414R
What is a frekel pair?
Vacancy + SIA
What is the usual average vacancy formation energy?
1.5 +- 0.5 eV
What is the usual average vacancy formation energy?
3e_V = 5 eV
What must point defects in ionic crystals must mantain?
Local electrical neutrality
What is a schottky defect?
anionn vacancy + cation vacancy
What is a cation frenkel pair?
cation interstitial and vacant cation site
What is an Anion Frenkel Pair?
anion interstitial + vacant anion site
Name the 1 dimensional defect
Dislocations
What is the energy per atom of a dislocation?
7 eV
What does the burgers vector describes?
It describes the direction and the amount the dislocation moves
Where do dislocations end?
At interfaces or form loops
What does introducing dislocations in the crystal leads to?
Leads to shape change of crystal leading to elastic stress in the lattice.
What are some 2 dimensional defects?
Grain Boundaries, Interfaces, etc
What has better mechanical properties: small or large grains?
small grains
What are twins?
highly symmetrical with slight miss orientation where atoms are shared.
Why do twins occur mainly?
Occurs if not enough slips systems are avaliable for deformation twinning
What does youngs equation regarding grain boundaries represent?
Single phase material the material attempts to minimize its surface energy tryhing to equate angles.
Name some 3D defects?
Precipitates, pores, particles, inclusions
What are the 7 main crystal structure groups?
Cubic, Tetragonal, Monoclinic, Orthorombic, Rhombohedral, Hexagonal, Triclinic
