Chapter 5

Question 1

Basal Slip

Answer 1

Deformation that occurs on the basal plane of HCP crystals as a result of dislocation motion.

Question 2

Burger’s circuit

Answer 2

A circuit drawn around a dislocation through defect-free material that would normally close if there were no dislocation inside of the circuit.

Question 3

Burger’s Vector

Answer 3

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.

Question 4

Critical resolved shear stress

Answer 4

The shear stress resolved in the slip plane in the slip direction at which plastic deformation occurs.

Question 5

Dislocation

Answer 5

A linear defect in a crystalline solid that is responsible for plastic deformation.

Question 6

Dislocation Climb

Answer 6

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.

Question 7

Dislocation Glide

Answer 7

The motion of a dislocation on its slip plane (defined by the Burger’s vector and the unit tangent vector

Question 8

Edge dislocation

Answer 8

a dislocation that is formed (figuratively) by the insertion of an extra half plane into an otherwise perfect region of a crystal.

Question 9

Flow Stress

Answer 9

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.

Question 10

Grain Boundary

Answer 10

occurs when two crystals of arbitrary orientation to each other are joined along an arbitrary surface. A grain boundary is a planar defect.

Question 11

Normal Stress

Answer 11

The force divided by the normal to the force

Question 12

Petch-Hall Equation

Answer 12

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.

Question 13

Plastic deformation

Answer 13

deformation that is permanent; for example, a metal part that has been permanently bent is said to have undergone plastic deformation.

Question 14

Precipitation hardening

Answer 14

The hardening or strengthening of an alloy by the presence of fine, uniformly distributed precipitate

Question 15

Schmid’s Law

Answer 15

The equation that relates the orientation of a crystal and the normal stress to the shear stress at which plastic deformation occurs.

Question 16

Screw Dislocation

Answer 16

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.

Question 17

Shear Stress

Answer 17

The force divided by the area of the plane in which the force acts. Shear stresses are responsible for the motion of dislocations.

Question 18

Slip direction

Answer 18

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.

Question 19

Slip Plane

Answer 19

The plane on which a dislocation moves by glide. It is defined by the Burger’s vector and the unit tangent vector.

Question 20

Slip System

Answer 20

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}.

Question 21

Stacking fault

Answer 21

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.

Question 22

Strain hardening

Answer 22

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.

Question 23

Stress

Answer 23

The force per unit area

Question 24

Surface tension

Answer 24

the energy per unit area associated with internal or external surfaces. It has units of energy/area, which is equivalent to force/length.

Question 25

Tilt boundary

Answer 25

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.

Question 26

Twin

Answer 26

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.

Question 27

Twist boundary

Answer 27

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.

Question 28

Unit tangent vector(t)

Answer 28

a vector that is locally tangent to the direction of a dislocation at the point of interest.

Question 29

Void

Answer 29

a volumetric defect in which there is no matter.

Question 30

Yield stress

Answer 30

The stress at which deformation becomes permanent in a tensile test.