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BME 312 Exam 1 > week 3: Metals 1 > Flashcards

week 3: Metals 1 Flashcards

1
Q

What are the four different metals?

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

What are the 5 general properties of metals?

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

What does Nickel provide for stainless steel?

A

strength

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3
Q

How are Cobalt based alloys formed?

A

by casting or forging

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3
Q

What are two properties of stainless steel?

A
  1. poor conductors of electricity
  2. hard due to Nickel and Chromium content
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3
Q

What does Chromium provide for stainless steel?

A

protective oxide layer for corrosion resistance

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4
Q

What are 4 characteristics of Cobalt-alloys?

A
  1. high tensile strength
  2. high fatigue strength
  3. high corrosion resistance
  4. high levels of Carbon = most wear resistance
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5
Q

What are 4 characteristics of Titanium alloys?

A
  1. excellent corrosion resistance
  2. low elastic modulus
  3. strong osseointegration tendency
  4. poor wear resistance
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6
Q

What 2 characteristics does Nitinol exhibit?

A
  1. unique shape memory effect
  2. elasticity
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7
Q

What is nitinol used for?

A
  1. dental
  2. stents
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8
Q

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

A
  1. biocompatibility
  2. strength
  3. low elastic modulus
  4. high fatigue strength
  5. corrosion resistance
  6. osseointegration
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9
Q

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

A

to avoid stress shielding

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10
Q

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

A

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

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11
Q

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

A

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

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12
Q

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

A

replacement
development
therapeutic
prevention
diagnosis

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13
Q

What are the 6 properties needed for a biomaterial?

A
  1. biocompatibility
  2. mechanical strength
  3. wear resistance
  4. cellular integration
  5. weight/density
  6. ductility
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14
Q

What are crystalline metals?

A

highly ordered atoms arranged in periodic 3D layer

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15
Q

What are non-crystalline metals?

A

disordered/amorphous atoms have no periodic arrangement.

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16
Q

What does a high atomic packing factor mean?

A

more ductility

17
Q

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

A
  1. density
  2. strength
  3. melting temp.
18
Q

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

A

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

19
Q

Describe the densities of the 3 types of biomaterials.

A
  1. metals = large density, large atomic masses
  2. ceramics = often lighter
  3. polymers = low packing density, amorphous, lightweight elements
20
Q

Anisotropy

A

property value depends on crystallographic direction of measurement

21
Q

Isotropy

A

polycrystals - properties may/may not vary with direction

22
Q

What are the 2 point defects?

A
  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.
23
Q

What do impurities cause?

A

lattice strain

24
Q

What are 3 things alloys do?

A
  1. increase strength
  2. increase corrosion resistance
  3. improve electrical properties
25
Q

solid state diffusion

A

movement of atoms into vacancies

26
Q

What are 3 reasons why solid state diffusion occurs?

A
  1. movement from high to low concentration
  2. temperature
  3. during metal processing
27
Q

Vacancy diffusion

A

atoms and vacancies exchange placesinter

28
Q

interstitial diffusion

A

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

29
Q

Which type of diffusion is more rapid?

A

interstitial

30
Q

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

A
  1. composition
  2. surface
  3. processing
31
Q

How do alloys change the composition of metals?

A

by diffusion

32
Q

How does grain size change the composition of metal?

A

by annealing and then quenching

33
Q

What surface characteristics change mechanical properties of metals?

A

cracks and scratches

34
Q

tensile strain

A

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

35
Q

compressive strain

A

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

36
Q

What type of treatment causes alloying?

A

grain size refinement by annealing or quenching

37
Q

annealing

A

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

38
Q

quenching

A

material is cooled after annealing

39
Q

strain hardening

A

material becomes stronger as it deforms

40
Q

How is strain hardening achieved?

A

by mechanical working a metal above its yield strength

41
Q

On the atomic level, how is strain hardening achieved?

A

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

42
Q

What is the purpose of hot-working?

A

to weaken the material

43
Q

What is the purpose of cold-working?

A

to strengthen the material

44
Q

What does cold-working reduce?

A
  1. ductility
  2. corrosion resistance

BME 312 Exam 1 (4 decks)

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