Chapter 3

Question 1

crystalline materials…….
atoms pack in ____
-typical of __________,_________,__________

Answer 1

pack in periodic 3D arrays

typical of metals, many ceramics, some polymers

Question 2

noncrystalline materials…..
atoms have ____________
-occurs for __________,_______________

Answer 2

atoms have no periodic packing

occurs in complex structures, rapid cooling

Question 3

“amorphous”=_____________

Answer 3

noncrystalline

Question 4

unit cell is __________________________________

Answer 4

is the smallest repetitive volume which contains the complete lattice pattern of a crystal

Question 5

there are _ crystal systems and ___ crystal lattices

Answer 5

7 crystal systems

14 crystal lattices

Question 6

a,b, and c are __________

Answer 6

lattice constants

Question 7

metallic crystal structures tend to be _____ packed

Answer 7

densly

Question 8

what are the reasons for dense packing?

Answer 8

• typically, only one element is present, so all atomic radi are the same
• metallic bonding is not directional (it can bond in all directions)
• nearest neighbor distances tend to be small in order to lower bond energy
• electron cloud shields cores from each other

Question 9

metallic crystal structures have the _____ crystal structures

Answer 9

simplest crystal structures

Question 10

simple cubic structure (SC)

this structure is _______ due to the low packing density.

___ directions are the cube edges

whats its coordination number?????
APF=?

how many atoms/unit cell=?

Answer 10

this is rare

closed-packed direction

coordination number = 6

APF= .52

1 atom /unit cell

Question 11

what is the coordination number for simple cubic structure?

Answer 11

6

Question 12

APF=

Answer 12

volume of atoms in unit cell/volume of unit cell

Question 13

Body center cubic structure (BCC)

atoms touch each other along __________
coordination number =____________

how many atoms per cell? ____

APF=?

Answer 13

along cube diagonals

coordination number =8

2 atoms/unit cell

APF= .68

Question 14

face centered cubic structure (FCC)

atoms touch each other along ___________

what is the coordination number?

how many atoms/unit cell?

APF=???/

Answer 14

atoms touch each other along face diagonals

coordination number=12

4 atoms/unit cell

APF=.74

Question 15

hexagonal close-packed structure (HCP)

what is the coordination number=

APF=

how many atoms per cell?

Answer 15

coordination number = 12
APF=.74

6 atoms/unit cell

Question 16

density=p=?

Answer 16

mass of atoms in unit cell/total volume of unit cell

Question 17

density of materials classes?

________>__________>___________

Answer 17

metals(most dense)>ceramics>polymers

why?
metals- have close-packing (metallic bonding), often large atomic masses

ceramics- have less dense packing, often lighter elements, polymers have low packing density (often amorphous), lighter elements

however, composites have intermediate values

Question 18

_________________for unit cell CENTER are a/2, b/2, c/2:

1/2,1/2,1/2

Answer 18

point coordinates

Question 19

point coordinates for unit cell _________ are 111

a,b,c

Answer 19

CELL CORNER

Question 20

What is the algorithm to find the crystallographic directions

Answer 20

1. find the head and tail point coordinates
2. subtract tail point coordinates from head point coordinates
3. adjust to smallest integer values
4. enclose in square brackets, no commas {uvw]

Question 21

what is the formula for linear density =LD

Answer 21

LD=number of atoms/unit length of direction vector

Question 22

all parrallel planes have _____________________

Answer 22

same Miller indices

Question 23

what is the algorithm of crystallographic planes?

Answer 23

1. read off intercepts of plane with axes in terms of a, b,c
2. take reciprocals of intercepts
3. reduce to smallest integer value
4. enclose in parentheses, no commas

Question 24

some engineering applications require single crystals:

such as:

• _________________
• ___________________

Answer 24

diamond single crystals for abrasives

turbine blades

Question 25

properties of crystalline materials often related to _________

Answer 25

crystal structure

Question 26

most engineering materials are ____________-

Answer 26

polycrystals

Question 27

each “_____” is a single crystal

Answer 27

grain

Question 28

if grain are randomly oriented, overall component properties are not ___________.

grain size typ. range from 1nm to 2cm.

Answer 28

directional

Question 29

single crystals??

Answer 29

vary with direction:anisotropic.

Question 30

poly crystals??

Answer 30

• properties may/may not vary with direction
• if grains are randomly orientated: ISOTROPIC
• if grains are textured: ANISOTROPIC

Question 31

atoms may assemble into ____ or ________ structures

Answer 31

crystalline or amorphous

Question 32

common metallic crystal structures are _______,___________, and _________

Answer 32

FCC, BCC, HCP

Question 33

we can predict the density of a material, provided we know the _________,_______,__________

Answer 33

atomic weight, atomic radius, and crystal geometry

Question 34

_____________ points, directions and planes are specified in terms of indexing schemes. ___________ directions and planes are related to atomic linear densities and PLANAR DENSITIES

Answer 34

crystallographic directions

Question 35

materials can be ________ or ___________. Material properties generally vary with single crystal orientation (they are ___________) but are generally non-directional (they are _________) in polycrystals with randomly oriented grains

Answer 35

can be single crystals or polycrystalline

single crystals=anisotropic

non-directional=isotropic