Strengthening Flashcards
(35 cards)
What is yield strength
The ability to resist plastic deformation
What is plastic deformation
Permanent deformation
Governed by dislocation movemnet
Why does materials tend to break via dislocation slip
Easier to break a set of bonds and reform with neighbours then breaking all bonds and shifting over and thus plastic deformation tends to happen via dislocation slip
How is the strength of a material increased?
By adding obstacles (other defects) to interact and thus block dislocation movement
Ductility in relation to dislocations
Ductility is the capability to plastically defrom
Governed by how much dislocations are allowed to move freely
Why does strength and ductility need to be balanced
They are contradictory and thus as strength increases, duality decreases
Want to balance for optimal results
What is an alloy
A metal with other elements added- this can be as a solute or precipitate
What is strain hardening/work hardening
Introducing dislocations and increasing their density within a materials crystal structure by deforming it at cold temperatures (bellow recrystallization temperature)
Dislocations multiply and tangle, hindering movement
Increases strength since it dislocations block other dislocations, more resistant to plastic deformation
Strnegthing material by deforming it
What is grain boundary strengthening
Strengthening by reducing grain size
This increases the size of GB and thus strength as GB impede dislocation movement - harder to cross
What is solid solution strengthing
Strengthen by alloying, adding solutes which block movement through created strain field as dislocations are attracted to it, this means dislocations need more energy to break bond between solute and surroundings and drag it or energy needed to separate from the solute
Also energy needed to go through the particle
What is particle strengthing
Strengthening from the addition of a 2nd phase (alloying)
(T/F) Particle Strengthening can be manipulated and controlled via heat treatment
T
What happens to the energy imposed on a material to deform it
Most is lost as heat
Only about 10% remains in sample and is stored by increasing the defect population
Effects of cold working
Increased dislocation density
Change in grain geometry to a finer geometry
YS goes up with more cold work
Tensile strength also goes up
Elongation to failure (ductility) decreases
What is the relationship between strain hardening, cold working and work hardening
Synonyms for the same thing
They are the same
What is the goal of quenching and termpering
To produce a tougher steel or iron
What are the three main phases of quench and tempering of steel
- Austenitizing or Normalizing
- Quenching
- Tempering
What is Austenitizing
The first stage of strengthening steel
The steel is heated up to high temperatures above the recrystallization tempreture
Here austenite is formed
Relieves stress, thus highest ductility and almost lowest strength
What Is austenite
The FCC structure form of Iron/steel
Can be gamma-Fe
What is quenching
Typical second step in strengthening steel
Forming of martensite
Rapid cooling increases dislocation density very fast, strongest point
What is tempering
Typically final step in strengthening steel
Tempers the martensite - manipulates it to get desired properties
Brings material properties to a comfortable middle point of strength and ductlity
In the quenching process, when is the material the strongest and when is it the most ductility
Most ductile when austenitizing and least ductile after quenching
What is age hardening
Precipitation hardening
Also known as aging or age hardening
Uses aging process to increase strength
Typically done on alumium
Steps to age hardening
- Solution heat treatment or solutionizing: Heated past recrystallizing temp, turns system into complete solid solution, relieves stress
- Quenching - results in a super saturated solid solution at the end of this as the solubility decreases rapidly with the drop in temperature, creating precipitates
- Precipitation Heat treatment: control the precipitation of the beta phases (the aging stage)
