Strengthening mechanisms Flashcards
What is the main principle of strengthening metallic alloys?
Preventing dislocation motion.
What are some methods of strengthening mechanisms?
Cold working, grain size reduction, solution hardening, precipitation hardening.
How does solid solution hardening work?
By introducing alloys. This can result in stresses within the crystal lattice (compressive - bigger atoms or tensile - smaller atoms). These stresses LOCALLY DISTORT THE LATTICE and hinder dislocations. Furthermore, the new atoms decrease mobility.
How does precipitation hardening work?
Through austenitizing (bringing the material into the austenite region to obtain a homogenous solution), quenching the material will result in a supersaturated solution, the last step, aging, focuses on the fine distribution of precipitates, in the material so that dislocations are effectively impeded.
Overaging the material can result in a decrease in the material’s strength and hardness.
Why does grain size reduction help strengthen the material?
Smaller grains result in more grain boundaries, providing more obstacles for the movement of dislocations. More stress is required to deform the material.
How does cold work strengthen the material?
Plastic deformation increases the dislocation density and decreases the distance between dislocations. This creates residual stresses within the material.
How are smaller grains beneficial in high-temperature applications?
In high-temperature applications, it is important to maintain fine grains to preserve strength and resistance to recrystallization.
How do the properties of the material change during cold working?
Cold working increases strength and hardness.
Cold working decreases ductility and machinability. (tempering can help regain some ductility)
Anisotropy might be an issue.
What is martensitic hardening?
Achieved through the formation of martensite in steels as a result of fast cooling. This is the result of diffusionless transformation. The strained martensite lattice BCT creates a strong and hard material but very brittle. Ductility can be induced in the material through tempering.
Among the hardening mechanisms, which is the only one that has the potential to
preserve ductility while increasing strength?
Grain size reduction
