Chapter 4 - Imperfections in Solids

Question 1

interfacial defects definition

Answer 1

boundaries that have two dimensions and normally separate regions of the materials that have different crystal structures or crystallographic orientations

Question 2

interfacial defects (5)

Answer 2

1. external surfaces
2. grain boundaries
3. phase boundaries
4. twin boundaries
5. stacking faults

Question 3

external surface

Answer 3

the boundary along which the crystal structure terminates, higher energy state which gives rise to surface energy

Question 4

grain boundaries

Answer 4

the boundary separating two small grains or crystals having different crystallographic orientations in polycrystalline materials, magnitude of energy is a function of the degree of misalignment (large angle being greater energy), more chemically reactive than the grains, density remains the same

Question 5

tilt boundary

Answer 5

small angle grain boundary, when a plane of atoms is inserted

Question 6

twist boundary

Answer 6

small angle grain boundary, when the angle of disorientation is parallel to the boundary

Question 7

phase boundaries

Answer 7

exist in multiphase materials where a different phase exists on each side of the boundary

Question 8

twin boundaries

Answer 8

type of grain boundary where the lattice structure is mirrored across the boundary, region of materials between the boundaries is called a twin, result from applied mechanical shear forces (BCC, HCP) or during annealing heat treatments following deformation (FCC)

Question 9

catalyst

Answer 9

a substance that speeds up the rate of a chemical reaction without participating in the reaction itself (it is not consumed)

Question 10

adsorption

Answer 10

the adhesion of molecules of a gas or liquid to a solid surface

Question 11

absorption

Answer 11

the assimilation of molecules into a solid or liquid

Question 12

stacking faults

Answer 12

found in FCC metals where the ABCABC… stacking sequence is interrupted

Question 13

atomic vibrations

Answer 13

the fact that every atom is vibrating very rapidly around its lattice position, can be thought of as an imperfection or defect

Question 14

microscopy

Answer 14

the use of optical, electron and scanning probe microscopes to investigate the microstructure features of all material types, can take pictures on a photomicrograph

Question 15

microscopic techniques (3)

Answer 15

1. optical microscopy
2. electron microscopy
3. scanning probe microscopy

Question 16

optical microscopy

Answer 16

light microscope is used to study the microstructure, basic elements are optical and illumination systems, upper limit approximately 2000x magnification

Question 17

metallographic

Answer 17

investigations using optical microscopy where a light microscope is used in a reflecting mode and contrasts are visible due to the differences in reflectivity

Question 18

etching

Answer 18

procedure where the microstructure is revealed by using a surface treatment of an appropriate chemical reagent

Question 19

electron microscopy

Answer 19

capable of much higher magnifications, formed using beams of electrons, transmission and scanning

Question 20

transmission electron microscope (TEM)

Answer 20

formed by an electron beam that passes through the specimen, details of internal microstructure features are observable, differences in beam scattering or diffraction create contrasts, material must be very thin, 10^5x magnification

Question 21

scanning electron microscope (SEM)

Answer 21

surface of a structure is scanned with an electron beam and reflected, image represents the surface features of the specimen, surface must be electrically conductive, 10-50,000x magnification

Question 22

scanning probe microscope (SPM)

Answer 22

neither light nor electrons are used to form an image, microscope generates a 3D topographical map on an atomic scale representing the surface features and characteristics of the specimen, 10^9x magnification

Question 23

grain size determination

Answer 23

determined when the properties of a polycrystalline material is under consideration, average grain volume, diameter or area, photographed at a magnification of 100x,

Question 24

crystalline defect

Answer 24

a lattice irregularity having one or more of its dimensions on the order of an atomic diameter

Question 25

point defect

Answer 25

defects associated with one or two atomic positions

1. vacancy
2. self-interstitial

Question 26

vacancy

Answer 26

a lattice site that is normally occupied from which an atom is missing, all crystalline solids have vacancies

Question 27

self-interstitial

Answer 27

an atom from the crystal that is crowded into a space that is not normally occupied

Question 28

alloy

Answer 28

metals into which immunity atoms have been added intentionally to impart specific characteristics to the material

Question 29

solid solution

Answer 29

formed when as impurity atoms are added to a metal the crystal structure is maintained, compositionally homogeneous

Question 30

solvent

Answer 30

the element or compound that is present in the greatest amount, also called host atoms

Question 31

solute

Answer 31

an element or compound present in a minor concentration

Question 32

substitutional point defect

Answer 32

solute or impurity atoms replace or substitute for the host atoms, depends on Atomic Size Factor, Crystal Structure, Electronegativity, and Valences

Question 33

interstitial point defect

Answer 33

impurity atoms fill the voids among host atoms

Question 34

composition or concentration

Answer 34

weight percent or atom percent of constituent elements

Question 35

weight percent

Answer 35

the weight of a particular element relative to the total alloy weight

Question 36

atom perecent

Answer 36

the number of moles of an element in relation to the total moles of elements in the alloy

Question 37

dislocation

Answer 37

linear or one-dimensional defect

Question 38

edge dislocation

Answer 38

when an extra half plane of atoms is inserted in, linear defect that centers on the line that is defined along the end of the extra half-plane of atoms, edge dislocation is perpendicular to the plane of the page, burgers vector perpendicular to the dislocation line

Question 39

screw dislocation

Answer 39

shear stress is applied to produce a shift in atomic distances, can make a spiral or helical path, burgers vector is parallel to the dislocation line

Question 40

burgers vector

Answer 40

the magnitude and direction of the lattice distortion associated with a dislocation