Coldworking Flashcards
(33 cards)
What type of deformation provides strengthening of a material?
What happens to tensile strength and yield strength?
What happens to Ductility?
-plastic deformation
- They both increase
-Ductility decreases
What does the application of stress greater than the yield strength provide?
It increases dislocations, and dislocation density increases.
What should we expect for the strain hardening exponents of metals?
It should be low doe HCP metals, and higher for BCC and FCC metals
What does plastic deformation do to thermoplastic polymers?
It strengthens them
When stress applied is greater than yield strength, what force between polymer chains is impaired?
Van der waals force
What does strain hardening do to polymer chains?
The chains straighten and become aligned in the direction of the applied stress.
What happens to dislocations in ceramics?
Dislocations are usually not mobile
What characteristic do ceramics have, and how does it make them act?
Ceramics contain voids, and it makes brittle
What is cold working?
It is the deformation of metal below recrystallization temperature.
What are advantages of cold working?
- Allows metals to be strengthened & at the same time the desired shape to be generated
- Offers excellent dimensional tolerances and surface finish
-It is a cheap method of manufacturing small parts in bulk - Some deformation processing techniques can only occur if the material is strain hardened or cold worked.
What are some disadvantages of coldworking
- Some materials can be cold worked
only up to a small degree such as HCP
magnesium - Ductility, electrical conductivity &
corrosion resistance are reduced - Lack of control over residual stresses
can impair the material properties - Cold working for strengthening can’t
be used for parts exposed to high
temperatures during operation
What is annealing?
Heating to a specific elevated temperature & cooling the material very slowly.
What are the three stages in annealing?
Recovery, Recrystallization, and Grain growth
What occurs during recovery?
Low temperature process
- Heat causes the dislocations to move
- Dislocations move and form the
boundaries of a polygonised sub grain
structure
- Residual stress is removed due to
rearrangement of dislocations
- This process is sometimes called stress
relief anneal
- Dislocation density is unchanged
What does recovery do to electrical conductivity, and corrosion?
It restores high electrical conductivity, and improves corrosion resistance.
What is recrystallization? What happens to dislocation density?
- Process of nucleation of new small grains at the cell boundaries of the polygonised structure by heat treatment
- Dislocation density is reduced.
What is recrystallization temperature?
Temperature at which new small grains with low dislocation density appear
What is grain growth?
It is the phenomenon of increased grain size at high enough temperature.
What do favored grains do to smaller grains?
They consume them
What happens to grain boundary area?
It decreases
Is it a desirable or undesirable phenomenon?
It is undesirable
Are recovery and recrystallization necessary for grain growth?
They are not necessary
What is hot working? Cold working? Warm working?
- Deformation process conducted above 0.6 times the melting temperature of a metal in Kelvin
- Deformation below 0.3 times
- Deformation between 0.3-0.6 times melting temp
What does repeated cold work and annealing cycle allow us to do?
Increase the total amount of deformation
