Uc Biomaterials Quiz 4: Metals

Front 1

What are 4 types of biomaterials?

Back 1

1. Metals

2. Polymers: synthetic and natural

3. Ceramics

4. Composites

Front 2

What are 6 applications metals are used for as biomaterials?

Back 2

1. Bone and joint replacement

2. Dental implants

3. Maxillo and cranio/facial reconstructure

4. Cardiovascular devices

5. External prostheses

6. Surgical instruments

Front 3

What are 6 physical properties of metals?

Back 3

1. Luster (Shininess)

2. Good electrical and heat conductors

3. High density (Heavy for their size)

4. High melting point

5. Ductile (Drawn into thin wires)

6. Malleable (Hammered into thin sheets)

Front 4

What are 4 chemical properties of metals?

Back 4

1. Easily lose electrons

2. Surface reactivity

3. Loss of mass (Corrode easily)

4. Change in mechanical properties

Front 5

Describe the chemical nature of metals.

Back 5

- Crystalline solids composed of elements

- Positively charged ions in a cloud of electrons

Front 6

What is the basic microstructure of a metal?

Back 6

The basic architecture is a crystalline structure

Front 7

What are 3 examples of metallic crystal structures?

Back 7

1. Body Centered Cubic (BCC)

2. Face Centered Cubic (FCC)

3. Hexagonal Close Packed (HCP)

Front 8

What are two terms that refer to the activities and processes that change the shape of a metal workpiece by deforming it or removing metal from it.

Back 8

1. Machining

2. Metal Fabrication

Front 9

What are two factors that strongly affect the mechanical properties of a metal?

Back 9

1. Heat

2. Plastic Deformation

Front 10

What are two general steps in metal processing?

Back 10

1. Molten metal is cooled to form a solid

2. The solid metal is then mechanically shaped to form a particular product.

Front 11

What are three general states that a metal exhibits during cooling from a molten state?

Back 11

1. Liquid

2. Liquid and solid solution

3. Polycrytstalline solid

Front 12

In what direction do crystals form in free state growth?

Back 12

Crystals form simultaneously in all three axes

Front 13

How does solidification proceed during casting processes?

Back 13

Nucleation begins at the edges where it is coolest and grows inward

Front 14

This term refers to the solidification of the first unit cells during crystal formation of metals.

Back 14

Nucleation

Front 15

This term refers to new unit cells attaching to already existing unit cells during crystal formation in metals.

Back 15

Growth

Front 16

What are the area called where two or more crystals meet/interfere/impinge?

Back 16

Grain boundaries

Front 17

This term refers to a homogeneous part or aggregation of the material that differs from another part due to a difference in structure, composition, or both.

Back 17

A Phase

Front 18

What are these structures?

Back 18

1. Grain boundaries

2. Grains

Front 19

What does the alignment of internal planes between unit cells during crystal formation give rise to?

Back 19

Slip planes

Front 20

What are these types of crystal defects?

Back 20

1. Vacancy

2. Interstitial Atom

Front 21

What type of defect occurs due to the application of shear stress?

Back 21

Dislocation

Front 22

What type of plastic deformation is this?

Back 22

Slip

Front 23

What type of plastic deformation is this?

Back 23

Twinning

Front 24

What are 4 stages of fatigue failure?

Back 24

1. No harm

2. Small cracks

3. Clam Shell Effect

4. Fracture

Front 25

What term refers to the maximum stress that a metal will withstand w/o failure for a specified large number of cycles?

Back 25

Fatigue Limit

Front 26

What effect does grain size reduction typically have on metals?

Back 26

Improved toughness

Front 27

What effect do grain boundaries have on slip and dislocations?

Back 27

Grain boundaries resist dislocation and slip

Front 28

What are two ways that grain size be controlled?

Back 28

1. Slowing the rate of solidification

2. Plastic deformation after solidification

Front 29

What are these structures?

Back 29

1. Grain

2. Grain Boundary

3. Slip Band/Dislocation

Front 30

What are the benefits of grain boundaries?

Back 30

- Stop dislocation movement

- strengthen the material

Front 31

What are single crystals considered to be less strong than polycrystals?

Back 31

Single crystals do not have grain boundaries to resist dislocations.

Front 32

What are 4 drawbacks of grain boundaries?

Back 32

1. Sites for precipitation of impurities

2. More grain boundaries leads to lower conductivity (Electrical and thermal)

3. Site for corrosion initiation

4. Creep deformation

Front 33

What are two ways of increasing metallic strength?

Back 33

1. Cold working

2. Controlling grain size

Front 34

The metal strengthening techniue involves loading the material past it's yield point and unloading which leads to an increase in strength, but a decreas in ductility. It also results in texture which can be viewed on an SEM.

Back 34

Cold working

Front 35

What types of steel were early steel implants made out of prior to the 1950s?

Back 35

- 302 series steel (Formerly 18-8)

- 316 series steel (Formerly 18-8sMo)

Front 36

What is the crystal structure of 316L SS?

Back 36

FCC

Front 37

Why does 316L have a high ductility?

Back 37

Low carbon concentration

Front 38

Why are chromium levels kept above 12% in 316L SS?

Back 38

To avoid chromium carbide formation.

Front 39

This element is added ot steel to mprove hot working properties and increase strength, toughness, and hardenability.

Back 39

Manganese

Front 40

This element is added to steel to improve machinability, aid in corrosion resistance. The drawback is that it may lead to cracking during welding.

Back 40

Phosphorous

Front 41

This element is added to steel to improve machinability.

Back 41

Sulphur

Front 42

This element is used as a deoxidizing agent during the melting of steel.

Back 42

Silicon

Front 43

Why does adding chromium to steel lead to corrosion resistance?

Back 43

Surface chromium bonds with oxygen to form a protective chromium oxide layer.

Front 44

What does levels of carbon above 0.03% typically result in?

Back 44

Inhibition of chromium oxide formation (due to chromium carbide formation)

Front 45

What is a protective oxide layer coating a metal called?

Back 45

Passivation layer

Front 46

What element, when added to steel enhances resistance to pitting corrosion?

Back 46

Molybdenum

Front 47

What is the purpose of nickel in stainless steel? Why is it necessary?

Back 47

- It stabilizes the FCC austenitic structure of steel.

- The addition of too much Chromium, Molybdenum, and Silicon results in a BCC structure

Front 48

Which ASTM standard stabilizes the composition and processing of 316 SS?

Back 48

ASTM F138

Front 49

How much cold working is applied to most 316L SS implants?

Back 49

About 30%

Front 50

What are 3 types of common failures seen in 316L implants?

Back 50

1. Design

2. Materials

3. Manufacturing

Front 51

What are 4 design related failures seen in 316L SS implants?

Back 51

1. Overload failure (Stresses exceeded)

2. Fatigue failure

3. Fracture

4. Wear

Front 52

What is a prevalent materials related failure seen in 316L SS implants?

Back 52

Corrosion

Front 53

What are 3 manufactuing failures typically seen in 316L SS implants?

Back 53

1. Heat treatment

2. Defects

3. Surface treatments

Front 54

What are 4 sources of corrosion failure?

Back 54

1. Improper alloy composition

2. Incorrect heat treatment

3. Improper implant selection and handling

4. Mismatched components

Front 55

At what temperature does chromium carbide formation take place?

Back 55

600C to 950C

Front 56

What are two steps that take place after heat treatment?

Back 56

1. Polishing to a mirror finish

2. Surface is cleaned, degreased, and passivated in HNO3 (ASTM F86)

Front 57

What are three precautions to take during heat treatment?

Back 57

1. Quenching and heat treatment to avoid chromium carbide formation (Keep temperature out of 600-950 carbide formation temperature range)

2. Ensure uniformity of heating to avoid heat distortion

3. Chemically and mechanically etching oxide scales on the surface resulting form heat treatment

Front 58

Name one other type of stainless steel used in medical devices other than 316L?

Back 58

400 Series - Martensitic Chromium Steels (Body Centered Tetragonal (BCT) Crystals)

Front 59

What are the characteristics of martensitic chromium steel?

Back 59

1. Very hard

2. Low toughness (Can be increased by tempering)

3. Carbon content above 0.03%

4. Chromium content varies from 11-18% depending on specific grade w/i 400 series

Front 60

What is a type of metal is frequently used in medical instruments?

Back 60

Series 420 Steel

Front 61

What is a metal comprised of two or more elements (At least on being metallic)?

Back 61

Alloys

Front 62

What are two ways that metals mix to form alloys?

Back 62

1. Substitutional

2. Interstitial

Front 63

What type of alloy/defect is this?

Back 63

Interstitial Alloy

Front 64

What type of alloy/defect is this?

Back 64

Substitutional Alloy

Front 65

In a solid solution, which element is seen as the solvent and which the solute?

Back 65

The more abundant element is the solvent, all others are the solutes

Front 66

What are 3 conditions for substitutional solid solutions?

Back 66

1. The atomic radii of the two elements is similar

2. Their lattice types are the same

3. The lower valency metal becomes the solvent

Front 67

What are the mechanical characteristics of BCC crystals?

Back 67

1. Ductile

2. High plasticity (Many slip planes)

Front 68

What are the mechanical characteristics of FCC crystals?

Back 68

1. Ductile

2. Moderate plasticity (Medium slip planes)

Front 69

What are the mechanical characteristics of HCP crystals?

Back 69

1. Low plasticity (Few slip planes)

Front 70

What are 3 dental alloys?

Back 70

1. Gold-Silver Alloy

2. Silver-Copper Alloy

3. Silver-Tin Alloy

Front 71

Why is atomic size a major factor in interstitial alloys?

Back 71

solute atoms must e small in size to fit into the spaces between the larger solvent atoms.

Front 72

What are 5 important interstitial atoms?

Back 72

1. Carbon

2. Hydrogen

3. Boron

4. Nitrogen

5. Oxygen

Front 73

What is the mechanism behind strain hardening?

Back 73

When ductile metals are plastically deformed below melting temperature, dislocations occur. As dislocation density increases, further dislocation formation is hindered, thus strengthening the material (Resisting further plastic deformation).

Front 74

What is the process of heating a metal to increase diffusion and enhance dislocation motion to relieve the internal strain energy and reduce the number of dislocation.

Back 74

Annealing

Front 75

Why is titanium commonly used in joint implants?

Back 75

Total resistance to attack by body fluids and it has high strength and low modulus.

Front 76

What is the ASTM standard for commercially pure titanium?

Back 76

ASTM F67

Front 77

Why is titanium a good biomaterial?

Back 77

It forms a layer of titanium oxide which a stable and reactive interface that becomes coated with plasma proteins.

Front 78

What are 3 benefits of titanium?

Back 78

1. TiO2 passivation layer provides high corrosion resistance

2. Strength-to-weight ratio is high compared to other metals

3. Oxidized surface leads to osseointegration where bone contacts TiO2 without fibrotic capsule

Front 79

What is an example extracellular glycosylated bone phosphoprotein with a polypeptide backbone?

Back 79

Osteopontin (OPN)

Front 80

What are 5 functions of osteopontin?

Back 80

1. It binds calcium and interacts with the vitronectin receptor

2. It binds covalently to fibronectin

3. Enhances osteoclast and osteoblast adhesion

4. Protects against bacterial infection

5. maintains tissue integrity and biomechanical strength during bone remodelling

Front 81

What are the pros and cons of Co-Cr?

Back 81

Pros:

- Higher corrosion resistance than SS

Cons:

- High modulus leads to stress shielding

Front 82

What are the advantages of casting?

Back 82

Near net shape parts

Front 83

What are the disadvantages of casting?

Back 83

- Defects

- Grain size is not optimal

- Low fatigue strength

Front 84

This process combines pressure and temperature to produce parts with substantially better properties than other methods.

Back 84

Hot Isostatic Pressing