Chapter 5 Flashcards
Basal Slip
Deformation that occurs on the basal plane of HCP crystals as a result of dislocation motion.
Burger’s circuit
A circuit drawn around a dislocation through defect-free material that would normally close if there were no dislocation inside of the circuit.
Burger’s Vector
The vector that joins the end to the start of the Burger’s circuit. The Burger’s vector is an invariant property of a dislocation.
Critical resolved shear stress
The shear stress resolved in the slip plane in the slip direction at which plastic deformation occurs.
Dislocation
A linear defect in a crystalline solid that is responsible for plastic deformation.
Dislocation Climb
The motion of an edge dislocation that occurs when vacancies migrate to the edge of the extra half plane. Climb results in the dislocation being displaced to a parallel slip plane. Climb requires mass transport.
Dislocation Glide
The motion of a dislocation on its slip plane (defined by the Burger’s vector and the unit tangent vector
Edge dislocation
a dislocation that is formed (figuratively) by the insertion of an extra half plane into an otherwise perfect region of a crystal.
Flow Stress
the stress required to continue plastic deformation. The stress at which plastic deformation first occurs is a specific value of the flow stress and is referred to as the yield stress.
Grain Boundary
occurs when two crystals of arbitrary orientation to each other are joined along an arbitrary surface. A grain boundary is a planar defect.
Normal Stress
The force divided by the normal to the force
Petch-Hall Equation
The equation that provides the relationship between the grain size and the yield stress. The yield stress increases with decreasing grain size according to the Petch-Hall equation.
Plastic deformation
deformation that is permanent; for example, a metal part that has been permanently bent is said to have undergone plastic deformation.
Precipitation hardening
The hardening or strengthening of an alloy by the presence of fine, uniformly distributed precipitate
Schmid’s Law
The equation that relates the orientation of a crystal and the normal stress to the shear stress at which plastic deformation occurs.
Screw Dislocation
a dislocation that may be formed by making a cut in a crystal and displacing the top half of the cut region relative to the bottom half in a direction parallel to the cut. The Burger’s vector of a screw dislocation is parallel to the dislocation line.
Shear Stress
The force divided by the area of the plane in which the force acts. Shear stresses are responsible for the motion of dislocations.
Slip direction
the direction in which atoms are displaced across the slip plane when a dislocation passes over the slip plane. The slip direction is parallel to the Burger’s vector of the dislocation responsible for the slip being considered.
Slip Plane
The plane on which a dislocation moves by glide. It is defined by the Burger’s vector and the unit tangent vector.
Slip System
refers to any combination of slip direction and slip plane on which deformation can occur. For example, in FCC metals the family of all slip systems is represented by {1 1 1}.
Stacking fault
a variation in the normal stacking sequences of close-packed planes. For example, in FCC crystals the normal stacking sequence is ABCABC…, and if in some region of the crystal the stacking is ABCBCABC…, that region is said to contain a stacking fault.
Strain hardening
hardening that occurs as a result of deforming a metal. During strain hardening, dislocations are generated and the high dislocation density makes it difficult for other dislocations to move.
Stress
The force per unit area
Surface tension
the energy per unit area associated with internal or external surfaces. It has units of energy/area, which is equivalent to force/length.
Tilt boundary
a boundary composed of edge dislocations of the same sign stacked vertically above one another. As a result of all of the extra half planes being in one portion of the crystal, a tilt is created.
Twin
The portion of a crystal in which all of the atoms are in mirror-image positions compared with atoms in the bulk of the crystal.
Twist boundary
a boundary that is composed of a grid of screw dislocations of like sign on the same plane. As a result of the displacements around the grid, a twist is created.
Unit tangent vector(t)
a vector that is locally tangent to the direction of a dislocation at the point of interest.
Void
a volumetric defect in which there is no matter.
Yield stress
The stress at which deformation becomes permanent in a tensile test.
