Chapter 4 defects in solids

Question 1

why are defects important

Answer 1

defects have a huge impact on the various properties of materials

• defects are responsible for color and price of a diamond
• forging a metal tool introduces defects and increases the strength of the tool

Question 2

defects can be introduced or removed during ________

Answer 2

Processing

Question 3

point defects

Answer 3

are lattice defects of zero dimensionality, i.e., they do not possess lattice structure in any dimension. Typical point defects are impurity atoms in a pure metal, vacancies, and self-interstitials.

Question 4

vacancies

Answer 4

is a type of point defect in a crystal where an atom is missing from one of the lattice sites.

Question 5

interstitial defect

Answer 5

is a type of point crystallographic defect where an atom of the same or of a different type, occupies a normally unoccupied site in the crystal structure.

Question 6

point defects in metals

Answer 6

Question 7

equilibrium concentration

Answer 7

Equilibrium is when the rate of the forward reaction equals the rate of the reverse reaction. All reactant and product concentrations are constant at equilibrium.

Question 8

Boltzmann’s constant

Answer 8

Question 9

activation energy

Answer 9

the minimum quantity of energy which the reacting species must possess in order to undergo a specified reaction.

Question 10

measuring activation energy

Answer 10

Question 11

estimating vacancy concentration

Answer 11

Question 12

observing vacancy ( continued )

Answer 12

Question 13

impurities

Answer 13

are foreign atoms that replace some of the atoms making up the solid or that squeeze into the interstices

atoms that are different from the host

Question 14

a homogeneous material

Answer 14

or system has the same properties at every point

Question 15

solids with impurities

Answer 15

Question 16

substitutional impurity

Answer 16

An atom or ion which is not normally found in a solid, but which resides at the position where an atom or ion would ordinarily be located in the lattice structure and replaces it.

Question 17

three types of point defects

Answer 17

Vacancy - in crystal an atom is missing from one of the lattice sites (point defect)

Interstitial - in crystal an atom of the same or different type occupies a normally unoccupied site in the lattice

Substitutional- same as interstitial but a different type of atom resulting in strain

Question 18

*quick reference *

imperfections in metals

Answer 18

Question 19

W Hume Rothery rules

Answer 19

are a set of basic rules that describe the conditions under which an element could dissolve in a metal, forming a solid solution.

Question 20

solubility

imperfections in metals

Answer 20

Question 21

Dislocations ( dislocation lines )

Answer 21

are linear defects. the interatomic bonds are significantly distorted only in the immediate vicinity of the dislocation line. this area is called the dislocation core.

Question 22

burgers vector

Answer 22

Question 23

edge dislocation

Answer 23

is a defect where an extra half-plane of atoms is introduced midway through the crystal( burger vector is perpendicular to dislocation line)

Question 24

Screw dislocation

Answer 24

a spiral planar ramp is inserted ( burger vector is parallel to dislocation line)

Question 25

mixed / partial dislocations

Answer 25

Question 26

where do dislocations come from

Answer 26

the number of dislocations in a material is expressed as the **dislocation density** ( the total dislocation length per unit volume or the number of dislocations intersecting a unit area )

Question 27

plastic deformation

Answer 27

is the ability of a solid material to undergo permanent deformation, a non-reversible change of shape in response to applied forces.

Question 28

dislocations and crystal structures/ plastic deformation

Answer 28

Question 29

grain boundaries

Answer 29

is the interface between two grains, or crystallites, in a polycrystalline material. Grain boundaries are 2D defects in the crystal structure and tend to decrease the electrical and thermal conductivity of the material.

Question 30

solidification

Answer 30

result of casting of molten material

Question 31

steps of solidification

Answer 31

Question 32

grain boundaries properties

Answer 32

Question 33

interaction between grain boundaries and dislocation

Answer 33

Question 34

bulk or volume defects

Answer 34

Three-dimensional macroscopic defects. They generally occur on a much larger scale than the microscopic defects. -these include cracks, pores, foreign inclusions, and other phases.

Question 35

**_Summary of this chapter_**

Answer 35