What are the four types of materials or classification of materials used for biomaterials?
- Metals
- Ceramics (including glasses)
- Composites
- Polymers
What kinds of properties make metals ideal for use as biomaterials in the body, and conversely what are the problems associated with the long term in vivo application of metals within the body?
- Strength and toughness
- Problem:
- Inflammation and Implant loosening
Name three metals used as bio-metallic implants?
- Stainless steel
- Titanium
- Cobalt allloys
Name three applications for metals as implants
- Bone and joint replacement
- Dental Implants
- Cardiovascular Devices
- Surgical Instruments
Distinguish between ionic and covalent bonding. What bonding is more prevalent in metallic structures?
- Ionic:
- Occurs between + and - ions
- Requires electron transfer
- Large difference in electronegativity required
- Predominant bonding in ceramics
- Ex. NaCl
- Large bond energy
- Covalent:
- Similar electronegativity - share electrons
- Bonds determined by valence - s & p orbitals dominate bonding
- Ex. CH4
- Variable bond energy
State and describe two types of imperfections of metallic structures
- Point Defects
- Vancacy atoms (Vacancies)
- Vacant atomic sites in a structure
- Distortion of planes - Interstitial atoms (Self-Interstitials)
- “Extra” toms positioned between atomic sites
- Distortion of planes
- Vancacy atoms (Vacancies)
- Line Defects
- Dislocations
- Slip between crystal planes result when dislocations move
- Produce permanent (plastic) deformation - Area Defects
- Grain Boundaries (Interfacial Defects)
- Regions between crystals
- Transition from lattice of one region to that of the other
- Slightly disordered
- Low density in grain boundaries
- high mobility
- high diffusivity
- high chemical reactivity
State the difference between crystalline and non-crystalline materials
- Crystalline materials:
- Atoms pack in periodic, 3D arrays
- Typical of:
- Metals
- Many ceramics
- Some polymers
- Noncrystalline materials: (amorphous)
- Atoms have no periodic packing
- Occurs for:
- Complex structures
- Rapid cooling
Define unit cell as it relates to metallic lattice structure of a metal.
-Smallest repetitive volume which contains the complete lattice pattern of a crystal
~Relates to metals because they have crystal structure
Name and schematically draw a structure that represents a way that microstructure of metallic atoms could be arranged.
- Simple Cubic Structure (SC)
- Rare due to low pacing density (only Po has this structure
- Closed-packed directions are cube edges
- Coordination # = 6
- Body Centered Cubic Structure (BCC)
- Atoms touch each other along cubic diagonals
- Coordination # = 8
- Face Centered Cubic Structure (FCC)
- Atoms touch each other along face diagonals
- ABCABC……Stacking sequence
- 2D projection
What information does the characterization technique XRD give.
- XRD = X-Ray Diffraction Pattern
- tells you what the unit (crystal) structure is
Name and describe two types of metallic crystal defects
- Point Defects
- Vancacy atoms (Vacancies)
- Vacant atomic sites in a structure
- Distortion of planes - Interstitial atoms (Self-Interstitials)
- “Extra” toms positioned between atomic sites
- Distortion of planes
- Vancacy atoms (Vacancies)
- Line Defects
- Dislocations
- Slip between crystal planes result when dislocations move
- Produce permanent (plastic) deformation - Area Defects
- Grain Boundaries (Interfacial Defects)
- Regions between crystals
- Transition from lattice of one region to that of the other
- Slightly disordered
- Low density in grain boundaries
- high mobility
- high diffusivity
- high chemical reactivity
Define Alloy and describe two ways that alloys could be formed
-A metal compromised of two or more elements, at least one of which is metallic
- Substitution
- Dissolved atoms replace host atoms
- Ex. Brass - Interstitial
- Small atoms fit between larger hosts
- Ex. Steel
State and describe two types of diffusion mechanisms
- Interdiffusion
- In an alloy, atoms tend to migrate from regions of high concentration to regions of low concentration
- Vacancy diffusion
- Atoms exchange with vacancies
- Rate depends on:
- Number of vacancies
- Activation energy to exchange - Interstitial Diffusion
- Smaller atoms can diffuse between atoms
- More rapid than vacancy diffusion
Differentiate between elastic and plastic deformation of metals
- Elastic deformation
- Reversible
- Plastic deformation
- Permanent
Define and describe in detail any two of the following mechanical properties of metals (young’s modulus, ductility, toughness and hardness)
- Tensile Stress (sigma)
- Perpendicular force (N/m^2) - Shear Stress (tao)
- Parallel force (N/m^2) - Tensile strain, Lateral strain and shear strain (all curvy E)
- Change in length
- No units - Modulus of Elasticity (E) - Young’s Modulus
- A measure of the stiffness of a solid material
- Stress/Strain - Ductility
- Measure of degree of plastic tensile strain (deformation) at failure - Toughness
- Energy to break a unit volume of material
- Approximate by the area under the stress-strain curve - Hardness
- Resistance to permanently indenting the surface
- Large hardness means:
- Resistance to plastic deformation or cracking in compression
- Better wear properties
What are the two fundamental types of dislocations
- Edge dislocation
- Dislocation moves in direction of applied stress
- Extra half-plane of atoms is inserted in the crystal structure
- Burger’s vector is perpendicular to dislocation - Screw dislocation
- Dislocation motion is perpendicular to applied shear stress
- Spiral planar ramp form shear deformation
- Burger’s vector is parallel to the dislocation
State and describe in detail two mechanisms of strengthening in metals
- Reduce Grain Size
- Grain boundaries are barriers to slip
- Barrier “strength” increases with increasing angle of misorientation
- Smaller grain size: more barriers to slip
- Solid Solutions
- Impurity atoms distort the lattice and generate stress
- Stress can produce a barrier to dislocation motion
- Smaller substitutional impurity
- Impurity generates local stress at A and B that opposes dislocation motion to the right
- Larger substitutional impurity
- Impurity generates local stress at C and D that opposes dislocation motion to the right.
- By Alloying
- Small impurities tend to concentrate at dislocations
- Reduce mobility of dislocation - increase strength - Precipitation Strengthening
- Hard precipitates are difficult to shear - Cold Work (%CW)
- Room temperature deformation
- Common forming operations change the cross sectional area
- Forging
- Rolling
- Drawing
- Extrusion
- As cold work is increased
- Yield strength increases
- Tensile strength increases
- Ductility decreases
State and describe two types of fracture mechanisms
- Ductile fracture
- Occurs with plastic deformation
- Warning before fracture
- One piece
- Large deformation
- Cup-an-cone fracture
- Brittle fracture
- Little or no plastic deformation
- Catastrophic
- No warning before fracture
- Many pieces
- Small deformation
What is creep.
- Sample deformation at a constant stress vs. time
- Primary Creep: slope (creep rate) decreases with time
- Secondary Creep: steady-state (constant slope)
- Tertiary Creep: slope increases with time (acceleration of rate)
