Metals Flashcards
What is fatigue failure?
Failure below the ultimate tensile strength of the material related to repetitive loading
What is the endurance limit?
The maximal stress at which the material is immune to fatigue failure
Name 3 different types of corrosion?
Galvanic
Fretting
Crevice
Mechanism behind crevice corrosion?
Fatigue cracks lead to differences in oxygen tension
What is fretting corrosion?
Corrosion ar a contact site from relative micro motion of two materials or two components
Titanium favoured for?
Nails
Advantages of titanium? 3
Biocompatible
Corrosion resistant
Closest Youngs modulus to bone (therefore load sharing)
Main disadvantage of Ti
NOTCH SENSITIVITY
Poor resistance to wear
Components of stainless steel?
Iron carbon alloy Chromium Molybendum Managanese Nickel
Advantages of stainless steel? 2
Very stiff
Fracture resistant
2 main disadvantages of steel?
Stress shielding
Susceptible to corrosion
Components of cobalt? 3
Cobalt
Chromium
Molybendum
Advantages of cobalt? 2
Strong
Better resistance to corrosion than steel
What is a passivation layer?
Oxidization layer that prevents against corrosion
Strength of a metal dependant on?
- Crystalline structure
- Grain size (smaller better)
- Density
- Defects (intragranular imperfections - vacancies/dislocations)
3 Microscopic structure of pure metals?
- Hexagonal close packed (marbles - ABA)
- Body centred cubic (ABC)
- Face centred cubic
Main forging processes of metals?
- Cold working
- Strain hardening
- Hot working
What is strain hardening?
Strengthening of a metal by plastic deformation
What is annealing?
Heating to just below melting temperature - cooling - then cold working
What does annealing do?
Decreases free radicles
Heat increases ductility
What does cold working do to a metal?
Induces strain hardening by increasing dislocations within the material crystal structure
What is ti made from? 3
Titanium
Alumnium
Vanadium
