week 3: Metals 1

Question 1

What are the four different metals?

Answer 1

1. stainless steel
2. cobalt chromium
3. titanium + alloys
4. nitinol

Question 2

What are the 5 general properties of metals?

Answer 2

1. good conductors
2. opaque
3. dense
4. strong
5. mostly solid at room temp

Question 3

What does Nickel provide for stainless steel?

Answer 3

strength

Question 3

How are Cobalt based alloys formed?

Answer 3

by casting or forging

Question 3

What are two properties of stainless steel?

Answer 3

1. poor conductors of electricity
2. hard due to Nickel and Chromium content

Question 3

What does Chromium provide for stainless steel?

Answer 3

protective oxide layer for corrosion resistance

Question 4

What are 4 characteristics of Cobalt-alloys?

Answer 4

1. high tensile strength
2. high fatigue strength
3. high corrosion resistance
4. high levels of Carbon = most wear resistance

Question 5

What are 4 characteristics of Titanium alloys?

Answer 5

1. excellent corrosion resistance
2. low elastic modulus
3. strong osseointegration tendency
4. poor wear resistance

Question 6

What 2 characteristics does Nitinol exhibit?

Answer 6

1. unique shape memory effect
2. elasticity

Question 7

What is nitinol used for?

Answer 7

1. dental
2. stents

Question 8

What are some qualities you should look for in metals to design a hip replacement stem?

Answer 8

1. biocompatibility
2. strength
3. low elastic modulus
4. high fatigue strength
5. corrosion resistance
6. osseointegration

Question 9

Why would you want a biomaterial with a lower elastic modulus for a hip replacement stem?

Answer 9

to avoid stress shielding

Question 10

Why is stainless steel used in biomedical applications instead of steel?

Answer 10

it’s an alloy so its properties are better than iron.
- stronger
- corrosion resistance

Question 11

If I want to make a rod but the metal is weak and too ductile, what treatment should I use without alloying?

Answer 11

cold working through strain hardening to increase the yield and tensile strength of the rod while reducing its ductility.

Question 12

What are some ideas we need to consider when designing with any material?

Answer 12

replacement
development
therapeutic
prevention
diagnosis

Question 13

What are the 6 properties needed for a biomaterial?

Answer 13

1. biocompatibility
2. mechanical strength
3. wear resistance
4. cellular integration
5. weight/density
6. ductility

Question 14

What are crystalline metals?

Answer 14

highly ordered atoms arranged in periodic 3D layer

Question 15

What are non-crystalline metals?

Answer 15

disordered/amorphous atoms have no periodic arrangement.

Question 16

What does a high atomic packing factor mean?

Answer 16

more ductility

Question 17

What are the 3 properties that the atomic packing factor influence?

Answer 17

1. density
2. strength
3. melting temp.

Question 18

What are the crystal structure for SS, CoCr, and Ti?

Answer 18

SS = BCC, FCC
CoCr = FCC
Ti = HCP, BCC, or mix

Question 19

Describe the densities of the 3 types of biomaterials.

Answer 19

1. metals = large density, large atomic masses
2. ceramics = often lighter
3. polymers = low packing density, amorphous, lightweight elements

Question 20

Anisotropy

Answer 20

property value depends on crystallographic direction of measurement

Question 21

Isotropy

Answer 21

polycrystals - properties may/may not vary with direction

Question 22

What are the 2 point defects?

Answer 22

1. vacancy - found at lattice site where an atom would normally be present 2. self-interstitial - atom from crystal is crowded within the interstitial space between surrounding atoms, occupying space that would normally be empty.

Question 23

What do impurities cause?

Answer 23

lattice strain

Question 24

What are 3 things alloys do?

Answer 24

1. increase strength 2. increase corrosion resistance 3. improve electrical properties

Question 25

solid state diffusion

Answer 25

movement of atoms into vacancies

Question 26

What are 3 reasons why solid state diffusion occurs?

Answer 26

1. movement from high to low concentration 2. temperature 3. during metal processing

Question 27

Vacancy diffusion

Answer 27

atoms and vacancies exchange placesinter

Question 28

interstitial diffusion

Answer 28

small interstitial atoms move from one interstitial position to an adjacent one

Question 29

Which type of diffusion is more rapid?

Answer 29

interstitial

Question 30

What are the 3 ways to change mechanical properties of metals?

Answer 30

1. composition 2. surface 3. processing

Question 31

How do alloys change the composition of metals?

Answer 31

by diffusion

Question 32

How does grain size change the composition of metal?

Answer 32

by annealing and then quenching

Question 33

What surface characteristics change mechanical properties of metals?

Answer 33

cracks and scratches

Question 34

tensile strain

Answer 34

created on surrounding environment if the impurity atom is smaller than the base metal

Question 35

compressive strain

Answer 35

created on surrounding environment if the impurity atom is bigger than the base metal atom

Question 36

What type of treatment causes alloying?

Answer 36

grain size refinement by annealing or quenching

Question 37

annealing

Answer 37

form of heat treatment in which the material is exposed to high temperature for long period of time

Question 38

quenching

Answer 38

material is cooled after annealing

Question 39

strain hardening

Answer 39

material becomes stronger as it deforms

Question 40

How is strain hardening achieved?

Answer 40

by mechanical working a metal above its yield strength

Question 41

On the atomic level, how is strain hardening achieved?

Answer 41

it is the result of dislocations interacting with other dislocations and causes entanglements that further enhance strength

Question 42

What is the purpose of hot-working?

Answer 42

to weaken the material

Question 43

What is the purpose of cold-working?

Answer 43

to strengthen the material

Question 44

What does cold-working reduce?

Answer 44

1. ductility 2. corrosion resistance