Metallurgy Flashcards
What is wrought metal
Cast metal or alloy that is permanently deformed
What is malleabilty
Ability to form thin shset by hammering or roling
What is dictility
Ability to stretch into wire
What is effect of strain/work hardening/cold working
Increase hardness, ultimate tensile strength (ie harder to elongate), increase brittleness
Decrease ductility and corrosion resistance
How does cold working make metal harder
Dislocation tends to happen at grain boundaries. Atomic slip occurs on intersecting slip planes, point defects increase and grains are distorted. More stress required for firther slip
What happens if there is further increase in cold work
Fracture as atoms get more detached from one another, weakened
Are orthodontic wires prone to work hardening
No. Bending force is generally within working range
How does proportional limit relate to elastic deflection
Increased proportional limit, higher elastic deflection
Relationship between elastic deflection and force applied
For given elastic modulus, elastic deflection is proportional to force applied
Is nickel titanium easy to shape
Hard to bend, does not undergo plastic deformaiton easily. Can be shaped with increase in temperature
What does it mean that nickel titanium ahs no shape memory
When force is applied, atoms will find and hold the new position
What is shape memory
Ability to return to original shape thermally induced eg deform at rtp (20-25ºC), return to original shape at 500ºC or 37ºC over a long time
What features enable shape memory
No dissociation of grains (change shape eg sqaure torhombus but atom arrangement and position same)
Twinning
What is super elasticity
Transition from austenite (fcc) to martensite (highly strained tetragonal form) induced by stress
At the same temperature, when stress is released, go back to orginial shape
Grains do not dissociate. Twinning responsible
Stress memory vs superelasticity
Stress memory thermally induced
Superelasticity stress induced
