Lecture 3 and 4- Crystal structure in metals

Question 1

Which arrangement has an atom in each corner and one in the middle of each face?

Answer 1

FCC face-centered cubic

Question 2

Which arrangement has a hexagonal shape?

Answer 2

HCP hexagonal close packed metals

Question 3

Which arrangement has an atom in each corner and one in the middle of the cube?

Answer 3

BCC body centered cubic

Question 4

What is the packing order of FCC?

Answer 4

ABC: different layers each time

Question 5

What is the packing order of HCP?

Answer 5

ABA: identical layers with different layer in the middle

Question 6

whats the difference between HCP/FCC and BCC?

Answer 6

HCP/FCC are tightly packed arrangements, BCC is non close packed

Question 7

Name 2 FCC metals

Answer 7

-Aluminium
-Copper

Question 8

Name 2 HCP metals

Answer 8

-Magnesium
-Titanium

Question 9

Name a BCC metal

Answer 9

• Iron at room temperature

Question 10

Put these 3 arrangements in order of ductility

Answer 10

FCC>BCC>HCP

Question 11

Put these 3 arrangements in order of strength

Answer 11

HCP>BCC>FCC

Question 12

What is the maximum atomic packing factor, and which arrangement has it?

Answer 12

0.74 FCC

Question 13

As iron is heated to really high temperatures state the arrangement change pattern

Answer 13

BCC-> FCC-> BCC

Question 14

Are most metals single-crystal or polycrystalline? what does polycrystalline mean?

Answer 14

polycrystalline, each crystal is called a grain, which is separated by grain boundaries

Question 15

What is creep?

Answer 15

deformation due to high temperature and stress

Question 16

what makes creep more likely to happen

Answer 16

defects in the structure

Question 17

what are 4 defects in metals

Answer 17

• vacancies
  -extra atoms
  -dislocations
  -grain boundaries

Question 18

What are vacancies?

Answer 18

gaps where atoms should be

Question 19

What are dislocations?

Answer 19

extra half planes that occur in the structure

Question 20

what are grain boundaries?

Answer 20

when atoms are structured non uniformly, theres planes facing different directions, and where they meet is the grain boundary

Question 21

How many elements are ceramics comprised of? What kind of bonding occurs in ceramics?

Answer 21

-2 or more
-ionic

Question 22

describe the atomic structure of plastics

Answer 22

long chain molecules made of carbon and hydrogen that are covalently bonded

Question 23

What is a non-crystalline or amorphous polymer? example?

Answer 23

a polymer whose chains are arranged/folded randomly. rubber

Question 24

What are the crystalline regions in a polymer?

Answer 24

regions where chains are carefully folded

Question 25

What happens when a semicrystalline structure is stretched?

Answer 25

amorphous regions stretch, crystalline regions stay folded

Question 26

What is polymorphism? give 2 examples

Answer 26

when a material changes structure by changing the temperature or pressure of that same composition.

Carbon-graphite-diamond

shape memory alloys (nitinol-braces)