last lecture introduction to materials science and engineering atoms / electron configuration
TRANSCRIPT
last lecturelast lecture
Introduction to materials science and engineering
Atoms / electron configuration
todaytoday
Bonding in solids
Structure of crystal solids
Bonding Forces and EnergiesBonding Forces and Energies
re p u ls iv e
a ttra c tiv e
n e t e n e rg y
e n e rg y /fo rc e
r 0
in te ra to m ic fo rc e
distance r
The Periodic TableThe Periodic Table
METALS NONMETALS
INTERMEDIATE
increasing electronegativity
Ionic Bonding Ionic Bonding Covalent Bonding Covalent Bonding
e.g. sodium chloride e.g. methane
Metallic BondingMetallic Bonding
+
d isc re te e n e rg y le v e ls o f e le c tro n sE
1
23
4
rn u c le u s+ +
1
2
n u c le u s
e n e rg y b a n d s = > fre e e le c tro n s
+
+
+
+
+
+
+
+
+ +
+ +
+ +
+ +
-
-
-
-
-
-
-
-
-
io n c o re s se a o f e le c tro n s
Bonding EnergiesBonding Energies
low
high
Crystalline StructuresCrystalline Structures
Crystalline StructuresCrystalline Structures
amorphous crystalline
Example: GlassExample: Glass
quartz(crystalline)
quartz glass(amorphous)
Si4+O2-
glass(amorphous)
Crystalline StructuresCrystalline Structures
simple cubicbody-centered cubic (bcc)
bcc
fcc
Hexagonal Crystal StructuresHexagonal Crystal Structures
hcp unit cell
Stacking Sequence of Stacking Sequence of Close-Packed StructuresClose-Packed Structures
first plane Afirst plane A and second plane Bfirst plane A, second plane B and third plane C: fccfirst plane A, second plane B and third plane A: hcp
FCC and BCC Solid Sphere ModelFCC and BCC Solid Sphere Model
fcc unit cell bcc unit cell
R
R = atomic radiusa = unit cell length / lattice constant
a a
Crystalline Structures of MaterialsCrystalline Structures of Materials
Lattice ParametersLattice Parameters
a
b
c
x
y
z
Crystal SystemsCrystal Systems
Crystal SystemsCrystal Systems
How to define a directionHow to define a direction
Vector of convenient length (pass through origin)
Project the vector to the axes (and measure in a, b, and c)
Multiply or divide these numbers by common factor to get smallest set of integers
Write them down as [uvw]
Miller Indices: Miller Indices: Crystallographic DirectionsCrystallographic Directions
a
b
c
x
y
z
a
b
c
x
y
z
Miller Indices: Crystallographic Miller Indices: Crystallographic Directions (Miller Bravais)Directions (Miller Bravais)
a 1
a 2
a 3
z
[0 001 ]
[111 0 ]
How to define a planeHow to define a plane
Plane may not include origin!
Determine the intercepts with appropriate axes as a, b, and c
Take reciprocals (no intercept means infinity reciprocal of infinity = 0)
Multiply or divide these numbers by common factor to get smallest set of integers
Write them down as (hkl)
Miller Indices: Miller Indices: Lattice PlanesLattice Planes
x
z
y
(0 11 )
x
z
y
= > (111 )
x
z
y
intersection points: 1/2 a, 1/2b, 1/2creciprocal values: (222)
DefectsDefects
Point defects
Linear defects
2-dimensional defects
Point DefectsPoint Defects
self-interstitial vacancy
Impurity AtomsImpurity Atoms
interstitial substitutional
Dislocations: Edge DislocationDislocations: Edge Dislocation
Burgers vectorinserted half plane
dislocation line
Dislocations: Screw DislocationDislocations: Screw Dislocation
Burgers vector
dislocationline
Grain BoundariesGrain Boundaries
Ni-Base Superalloy Waspalloy
50µm
high-angle grain boundary (>15°)
low-anglegrain boundary
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Properties of materials