Imperfections in solids Flashcards
What are the three point defects?
Vacancy, Interstitial, Substitutional
What are the two main line defects?
Edge and Screw Dislocation
What are the 4 Hume-Rothery Rules for the formation of an alloy?
Atomic size factor, Crystal Structure, Electronegativity, Valences.
What are the area Defects?
Grain boundaries.
What is meant by a Self interstitial?
an atom that is crowded into an interstitial site (a small void that under ordinary circumstances is not occupied)
what is alloying in metals used for in metals?
to improve mechanical strength and corrosion resistance.
what does the addition of impurity atoms to a metal result in?
the formation if a solid solution and/or a new second phase.
what is a solvent?
the element or compound that is present in the greatest amount. (Sometimes called host atoms)
what is a solute?
element or compound present in minor concentration.
What is a Substitutional atom?
an atom which causes bonds to tighten up, it is an atom which is not of the same size as its surrounding atoms.
How do you express the composition of an alloy in terms of its constituent elements?
Weight % and Atom %
What Letter and number are used for weight percent?
C1
What Letter and number are used for atom percent?
Cā1
What is an edge dislocation?
it is a linear defect that centers on the line that is defined along the end of the extra half plane of atoms.
What is a screw dislocation?
atoms are arranged in a helical pattern that is normal to the direction of the stress.
How are grain sizes measured?
Area method and linear intercept method
The bigger the grain size the
smaller the number
how is the linear intercept method performed?
lines are drawn randomly through the grains. grain boundaries which are intercepted by the line segments are counted.
what are the four other defects not studied in this course
Interfaces, Grain Boundaries, Phase boundaries, Twin Boundaries.
A crack that progresses exclusively through grains results in a fracture called
transgranular fracture.
for an internal crack, the smaller the radius of the crack tip, the lower the magnification of the applied stress
False
