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This document delves into the world of imperfections in solids, exploring various types of defects such as point defects (vacancies, interstitials, and substitutional atoms), line defects (dislocations), and area defects (grain boundaries). It examines the impact of these imperfections on material properties, including their influence on strength, ductility, and conductivity. The document also discusses the mechanisms of solidification, the formation of grain structures, and the role of grain boundaries in material behavior. It provides a comprehensive overview of the subject, making it a valuable resource for students of materials science and engineering.
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CHAPTER 4:
IMPERFECTIONS IN SOLIDS
Imperfections in Solids
Adapted from Fig.4.14 (b), Callister 7e.
nuclei crystals growing grain structure
liquid
Polycrystalline Materials
region to that of the other
boundaries
Adapted from Fig. 4.7, Callister 7e.
Types of Imperfections
Boltzmann's constant
(1.38 x 10
J/atom-K)
(8.62 x 10
eV/atom-K)
v
v
No. of defects
No. of potential
defect sites.
Activation energy
Temperature
Each lattice site
is a potential
vacancy site
Equilibrium Concentration:
Point Defects
from
an experiment.
v
v
Measuring Activation Energy
v
exponential
dependence!
v
ln
v
/ k
slope
microscope view of
a (110) surface of NiAl.
surface island of
atoms to grow.
conc. increases via atom
motion from the crystal
to the surface, where
they join the island.
Reprinted with permission from Nature (K.F. McCarty,
J.A. Nobel, and N.C. Bartelt, "Vacancies in
Solids and the Stability of Surface Morphology",
Nature, Vol. 412, pp. 622-625 (2001). Image is
5.75 m by 5.75 m.) Copyright (2001) Macmillan
Publishers, Ltd.
Observing Equilibrium Vacancy Conc.
Island grows/shrinks to maintain
equil. vancancy conc. in the bulk.
Two outcomes if impurity (B) added to host (A):
phase (usually for a larger amount of B)
Substitutional solid soln.
(e.g., Cu in Ni)
Interstitial solid soln.
(e.g., C in Fe)
Second phase particle
--different composition
--often different structure.
Point Defects in Alloys
Substitutional solid solution
Hume-Rothery rules are as follows:
no more than 15%:
same valency.
[2]
vice versa.
[3] [4] [5]
the electronegativity difference is too great, the metals tend to
form intermetallic compounds instead of solid solutions.
Interstitial solid solution rules
x 100
1 2
1
1
m m
m
C
m 1
= mass of component 1
1 2
' 1
1
m m
m
n m
= number of moles of component 1
Schematic of Zinc (HCP):
slip steps
Line Defects
Adapted from Fig. 7.8, Callister 7e.
