Transcript Chapter 8: Deformation and Strengthening Mechanisms of

Team 1
CHEN 313
Add Figure(s)
Summary 8.2
• In the 1930s It was theorized that the that
the discrepancy in in mechanical
strengths was due to the different types of
linear crystalline defect which is known as
“dislocation.”
• Only after the 1950 were the ability to see
with the electron microscopes possible,
making it possible to visualize
dislocations.
Add Figure(s)
Summary 8.3
• The motion of dislocations due to an
applied shear stress causes plastic
deformation; this process is termed
“slip”. There are three types of
dislocations: edge, screw, and
mixed.
Add Figure(s)
Summary 8.4
•
•
•
•
Lattice Strain-Compressive, shear, and tensile
stresses in the lattice are formed as a
dislocation travels through the lattice.
Stress fields around dislocations include
compressive and tension.
When dislocations are in the same plane, they
can either repel each other if they have the
same sign, or destroy each other if they have
opposite signs.
Deformations cause the number of dislocations
to increase.
Summary 8.5
• The combination of both the preferred slip plane
and directions forms the slip system.
• Slip plane is generally taken as the closest
packed plane in the system.
• Slip direction is the direction on the slip plane
with the highest linear density.
Summary 8.6
• Slip in single crystals:
• When a shape of a single crystal changes under a
tensile stress, plastic deformation will occur by slip on
parallel crystal planes.
• During the deformation sections of the crystal slide
to one another, causing the geometry of the single
crystal to change as shown in the following diagram.
Summary 8.7:
Because the grain boundaries are arranged
randomly the direction of the slips would be in
different directions, and the dislocation would
occur towards the highest shear stress.
When the material is deformed by plastic
deformation the grain boundaries is
maintained and the grains itself are
constrained in a shape depending on the
grains that are next to it.
Summary 8.8
• Under particular conditions, two or more
intergrown crystals are formed in a symmetrical
fashion. Twinning is important because the
crystallographic reorientation makes the slip
process more favorable.
Summary
Add Figure(s)
• What is strengthening of a metal? Strengthening
of a metal is the ability of a metal to deform
plastically due to the motion of a large number
of dislocations.
• Three types of mechanisms to strengthen a
metal:
• Strengthening by grain size reduction
• Solid-solution strengthening
• Strain hardening
Add Figure(s)
Summary 8.9
• Dislocation motion is restricted by a larger area of
grain boundaries (finer grains)
• Slower cooling results in courser grains
• Grain size may be regulated by the rate of
solidification from the liquid phase and by plastic
deformation
• Hall-Petch equation: sy = sy + ky/ d
• Yield strength increases with decreasing grain size
Edit equations and/or use symbols but do not insert equations a graphics
Instead of usuing summary as title, use a title more related the topic
Summary 8.10
Interstitial Atoms
Substitutional Atoms
•Impurity atoms may be substitutional or interstitial. Substitutional atoms that
are larger than the host atoms will impose a compressive stress on the
surrounding lattice. Conversely interstitial atoms that are smaller than the host
atoms will cause tensile stresses in the lattice.
•The stress fields associated with impurity atoms interact with the stress fields
associated with dislocations and restrict their movement.
Summary 8.11
Each slide have to be self-explanatory
• It is the increase in the
strength and hardness of a
metal due to a mechanical
deformation in the metal's
microstructure.
• Any material with a
reasonably high melting
point such as metals and
alloys can be strengthened
in this fashion
Add Figure(s)
DEFORMATION MECHANISMS
FOR METALS
Earlier theoretical strengths of perfect crystals were
computed from early materials that were studied
• It was theorized that the that the
discrepancy in in mechanical strengths was
due to the different types of linear
crystalline defect which is known as
“dislocation”
Add Figure(s)
• Electron microscope was used to
visualize the dislocation which
then proved it’s existence.
Name this file according to the guidelines posted on the web site