Chapter 7 Deformation and strengthening mechanisms Flashcards
dislocation motions
enables atoms in metals to slide readily by one another, facilitating the plastic deformation that blunts the advance of cracks.
dislocation and material classes
Metals (Cu, AL):
Covalent Ceramics ( Si, diamond):
Ionic Ceramics (NaCI) :
slip plane
and
slip direction
slip plane = is the large displacement of one part of a crystal relative to another part along crystallographic planes and directions.
slip direction = the direction in which the dislocation moves, which is the direction of the Burgers vector for edge dislocations.
* quick reference *
dislocation motions
Resolved shear stress (RSS)
is the shear component of an applied tensile or compressive stress resolved along a slip plane that is other than perpendicular or parallel to the stress axis.
critical resolved shear stress
is the component of shear stress, resolved in the direction of slip, necessary to initiate slip in a grain.
single crystal slip
When a single crystal is deformed under a tensile stress, it is observed that plastic deformation occurs by slip on well-defined parallel crystal planes
example deformation of a single crystal
polycrystals stronger than single crystals
grain boundaries are barriers to dislocation motion
anisotropy in σ y
what are the four strategies for strengthing
1) reduce grain size
2) form solid solutions
3) precipitation strengthing
4) cold work ( strain hardening )
strategy for strengthening
reduce grain size
decreases the amount of possible pile up at the boundary, increasing the amount of applied stress necessary to move a dislocation across a grain boundary
strategy for strengthening
form solid solutions
is a type of alloying that can be used to improve the strength of a pure metal. The technique works by adding atoms of one element to the crystalline lattice of another element, forming a solid solution.
strategy for strengthening
precipitation strengthing
is a heat treatment technique used to increase the yield strength of malleable materials, including most structural alloys of aluminium, magnesium, nickel, titanium, and some steels and stainless steels.
strategy for strengthening
cold work
shaping the workpiece at a temperature below its recrystallization temperature, usually at ambient temperature. … The cold working of the metal increases the hardness, yield strength, and tensile strength.
dislocation density formula ( during cold work )
impact of cold
as cold work is increases
yield strength -
tensile strength -
ductility -
what are the values of yield strength, tensile strength, and ductility for Cu
Summary of this chapter
