Concept of crystal geometry

1
Concept of crystal geometry
Body centre cubic (bcc)
Face centre cubic (fcc)
Hexagonal close packed (hcp)

• There are three basic types of crystal
  structures in metals

z
z
a3
y
y
a2
x
x
a1
Corners 1/8 x 8 1 atom Centre 1
atom Total atoms 2 atoms
Corners 1/8 x 8 1 atom Faces 1/2 x 6
3 atoms Total atoms 4 atoms
Corners 1/6 x 6 1 atom Centre 1
atom Total atoms 2 atoms
Ex a - Fe, Ta, Cr, Mo, W
Ex Al, Cu, Pb, Au, Ni
Ex a - Ti , Zn, Mg, Cd
2
Close packed structures
FCC and HCP structures ? close-packed structures
APF 0.74, BCC structure has APF 0.68 Simple
cubic unit has APF 0.52.
(111) plane
Close-packed plane stacking sequence of FCC
structure. ABCABC ? 111 plane.
(a) Close-packed plane stacking ABC
(1000) basal plane
(b) Close-packed plane stacking AB
Close-packed plane stacking sequence of HCP
structure. ABAB ? (1000) basal plane.
3
Slip planes

• Plastic deformation is confined to the low-index
  planes, which has higher density of atom per unit
  area (most widely spaced planes)

Slip
http//en.wikipedia.org/wiki/Plasticity_(physics)
Straight slip lines in copper

• Dislocation movement can be considered analogous
  to the distortion produced in a deck of cards.

Shear stress
500 x
4
Hardness measurement

• Hardness tests can be used for many engineering
  applications to achieve the basic requirement of
  mechanical property.
• For examples
• ? surface treatments where surface hardness has
  been much improved.
• ? Powder metallurgy
• ? Fabricated parts forgings, rolled plates,
  extrusions, machined parts.

www.nitrexmetaltech.com
Hardness variation of nitrided part
Nitrided part
www.automation.com
5
Vickers hardness
Materials Hv
http//www.brycoat.com/hardness.htm
Tin 5 Aluminium 25 Gold
35 Copper 40 Iron 80 Mild steel
230 Full hard steel 1000 Tungsten
carbide 2500
6
Rockwell hardness
Brale indenter, 120o diamond cone
1.6-3.2 mm diameter steel ball indenter
Diamond tip
7
Fatigue of metals
Fatigue failure in a bolt
www.corrosionlab.com
Fatigue initiation
Beach mark
8
Fatigue of metals
www.btinternet.com
Fatigue failure occurs at the outer rim of the
wheel
Fatigue fracture area in a shaft caused by
corroded inside area
9
Creep
http//cheweb.tamu.edu/orgs
High temperature applications
www.bv.com
Subjected to high stress at high temperature
http//en.wikipedia.org
Oil refinery
Steam power plant
www.ideas-eng.com
Steam turbine used in power plant
Process plant
10
Metallographic preparation
Cutting
Mounting
cold
hot
www.materials.co.uk
Grinding
Polishing
11
Grain size measurement
1 inch
1 inch
www.inspecttest.com
N ????????????????????????? n ASTM grain size
number
12
Grain size measurement image analysis
www.paxit.com
13
SEM Operation
14
SEM and OM images
www.msm.cam.ac.uk
/www.globalspec.com
Optical image
SEM image
15
Slip planes
16
Slip planes
17
Slip planes