Lecture 3 and 4- Crystal structure in metals Flashcards
Which arrangement has an atom in each corner and one in the middle of each face?
FCC face-centered cubic
Which arrangement has a hexagonal shape?
HCP hexagonal close packed metals
Which arrangement has an atom in each corner and one in the middle of the cube?
BCC body centered cubic
What is the packing order of FCC?
ABC: different layers each time
What is the packing order of HCP?
ABA: identical layers with different layer in the middle
whats the difference between HCP/FCC and BCC?
HCP/FCC are tightly packed arrangements, BCC is non close packed
Name 2 FCC metals
-Aluminium
-Copper
Name 2 HCP metals
-Magnesium
-Titanium
Name a BCC metal
- Iron at room temperature
Put these 3 arrangements in order of ductility
FCC>BCC>HCP
Put these 3 arrangements in order of strength
HCP>BCC>FCC
What is the maximum atomic packing factor, and which arrangement has it?
0.74 FCC
As iron is heated to really high temperatures state the arrangement change pattern
BCC-> FCC-> BCC
Are most metals single-crystal or polycrystalline? what does polycrystalline mean?
polycrystalline, each crystal is called a grain, which is separated by grain boundaries
What is creep?
deformation due to high temperature and stress
what makes creep more likely to happen
defects in the structure
what are 4 defects in metals
- vacancies
-extra atoms
-dislocations
-grain boundaries
What are vacancies?
gaps where atoms should be
What are dislocations?
extra half planes that occur in the structure
what are grain boundaries?
when atoms are structured non uniformly, theres planes facing different directions, and where they meet is the grain boundary
How many elements are ceramics comprised of? What kind of bonding occurs in ceramics?
-2 or more
-ionic
describe the atomic structure of plastics
long chain molecules made of carbon and hydrogen that are covalently bonded
What is a non-crystalline or amorphous polymer? example?
a polymer whose chains are arranged/folded randomly. rubber
What are the crystalline regions in a polymer?
regions where chains are carefully folded
What happens when a semicrystalline structure is stretched?
amorphous regions stretch, crystalline regions stay folded
What is polymorphism? give 2 examples
when a material changes structure by changing the temperature or pressure of that same composition.
Carbon-graphite-diamond
shape memory alloys (nitinol-braces)
