Kmu479 son hafta Flashcards
(20 cards)
What is strain hardening?
Strain hardening is the phenomenon whereby a ductile metal becomes harder and stronger as it is plastically deformed.
What are other names for strain hardening?
Strain hardening is sometimes called work hardening or cold working.
At what temperature do most metals strain harden?
Most metals strain harden at room temperature.
How is percent cold work (%CW) defined?
Percent cold work (%CW) is defined as the degree of plastic deformation expressed as a percentage.
What happens to yield and tensile strength with increasing cold work?
Steel, brass, and copper increase in yield and tensile strength with increasing cold work.
What is the trade-off for increased hardness and strength in metals?
The price for this enhancement of hardness and strength is a decrease in ductility.
What microstructural changes occur during plastic deformation?
Plastic deformation produces changes such as a change in grain shape, strain hardening, an increase in dislocation density, and stored energy.
What is recovery in the context of metal deformation?
Recovery is the process where some stored internal strain energy is relieved by dislocation motion at elevated temperatures.
What happens to ductility and hardness after recovery?
After recovery, ductility increases, hardness decreases slightly, and toughness increases.
What is recrystallization?
Recrystallization is the formation of a new set of strain-free and equiaxed grains with low dislocation densities.
What drives the formation of new grains during recrystallization?
The driving force is the difference in internal energy between the strained and unstrained material.
What happens to mechanical properties during recrystallization?
Mechanical properties that were changed due to cold working are restored to their precold-worked values.
What is the recrystallization temperature?
The recrystallization temperature is the temperature at which recrystallization just reaches completion in 1 hour.
How does impurity affect recrystallization?
Impurity atoms can segregate at recrystallized grain boundaries, decreasing their mobility and raising the recrystallization temperature.
What is grain growth?
Grain growth is the phenomenon where strain-free grains continue to grow if the metal is left at elevated temperatures.
What drives grain growth?
Grain growth is driven by the reduction in total energy as the total boundary area decreases.
How does grain size change over time?
As time progresses, the average grain size increases, with larger grains growing at the expense of smaller ones.
What is the relationship between temperature and grain growth rate?
Grain growth proceeds more rapidly as temperature increases due to the enhancement of diffusion rate.
Why do some metals not strain harden at room temperature?
Some metals, like lead and tin, do not strain harden when deformed at room temperature due to their inherent properties.
Can ceramic materials experience recrystallization?
Ceramic materials typically do not experience recrystallization due to their structural characteristics.
