Chapter 4 (imperfections)

Question 1

what is solidification

Answer 1

the result of casting of molten material

Question 2

steps of solidification:

Answer 2

1. Nuclei form
2. Nuclei grow
3. grain structure is achieved (not considered a step)

Question 3

what do we call grains that are of equal length

Answer 3

equiaxed

Question 4

what do we call grains that have been elongated

Answer 4

columnar

Question 5

List the types of point defects

Answer 5

1. Vacancy
2. interstitial
3. substitutional

Question 6

how can we increase the number of vacancies

Answer 6

increase temp

Question 7

solvent:

Answer 7

host element

Question 8

solute:

Answer 8

minor element

Question 9

list the conditions for solid subsitution, and what is this law called?

Answer 9

1. difference in atomic radius must be less than 15%
2. similar electronegativities
3. same crystal structure
4. Valency
   this law is called the W. Hume-Rothery rule

Question 10

plastic deformation is produced by what type of defect

Answer 10

line defects, more specifically dislocations

Question 11

where would impure atoms go?

Answer 11

interstitial spaces

Question 12

Linear Defect:

Answer 12

1D misalignment

Question 13

Edge Dislocation

Answer 13

extra half plane is inserted (b vector is perpendicular to dislocation line)

Question 14

screw dislocation

Answer 14

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

Question 15

3 properties of grain boundaries

Answer 15

1. high mobility
2. high diffusivity
3. high chemical reactivity

Question 16

how are grain boundaries produced

Answer 16

by the solidification process

Question 17

how can we explain the causing of equiaxed grains

Answer 17

there a greater delta T near the wall during formation

Question 18

what kind of defect is a grain boundary

Answer 18

Area defect

Question 19

which factors can cause vacancies?

Answer 19

solidification process, heating, neutrons, working

Question 20

what is substitutional solid solution

Answer 20

when a host atom is replaced by another atom which can be either larger or smaller. note: DO NOT CONFUSE WITH SUBSTITUTIONAL DIFFUSION!!!

Question 21

what is an insterstitial solid solution

Answer 21

same as substitutional except it goes between atoms and is typically smaller

Question 22

what do these (S.S.S) cause?

Answer 22

distortions to the lattice

Question 23

will a metal have a greater tendency to dissolve another metal of lower or higher valency?

Answer 23

higher

Question 24

if you have both a screw and edge dislocation, what is this referred to as?

Answer 24

mixed dislocation

Question 25

put in order of reactivity/energy: surface, bulk, boundary

Answer 25

surface>boundary>bulk

Question 26

give a few examples of bulk defects

Answer 26

cracks, holes

Question 27

list 4 methods to observe grain boundaries in metals/ceramics

Answer 27

1. section and grind the sample
2. polish it with diamond paste
3. etch it chemically
4. microscope

Question 28

briefly describe the intercept method to determine the size of grain boundaries

Answer 28

draw random equal length lines through the photomicrograph. count the number of grains crossed per line and get the average. grain size=(line length/avg grains crossed)/(magnification)