Chapter 2 L05 Flashcards
What is a single crystal?
It is a crystaline solid that has a perfect arrangement of atoms throughout the entire specimen, where the unicells fit perfectly and have the same orientation.
What is a polycrystalline material?
Materials composed of many small crystal/ grains with different orientations, separated my grain boundaries
What is anisotropy and isotropy?
- Anisotropy: materials in which measured properties are dependent of the crystal direction
- Isotropy: materials in which measured properties are independent of the crystal direction
Can a polycristalline material be isotropic?
Yes. Even though the individual grains may be anisotropic, the set of all grains (poly. mat.) may be isotropic.
Advantages of big and small grains.
- Big: ↑Melting tmp ↑Elastic Modulus
- Small: ↑Toughness/Strength
How are Steels normally, single crytals or polycrysatlline?
Polycristalline
How is the structure from non-crystalline materials?
They lack of regular arrangement of atoms. They are amorphous
What is Difussion? Give an example
It is a phenomenon in which material is transported at an atomic level. It is used to improve material properties. Example: Case hardening or nitriding
Explain how diffusion works? Name some diffusion factors
Join 2 bars of «different metals», heat them under the melting points «tempertature», cool them down.
What are binaray alloys?
Those that contain 2 components
What do phase diagrams represent?
They represent the physical state and transformations as a f() of % of components and temperature
What is a phase?
Solid, liquid, mixture
What are phase diagrams used for?
Thay are used for :
- Relating microstructures and mechanical properties
- Predict phase transformations (physical states)
What are the names of the lines separating different phases?
Liquidius line
Solidius line
How does the lever rule for liquid/solid phase work?
(% of one phase at 2 phases)
“Notes”
Label important parts in the iron-iron carbide diagram
“Notes”
Which carbon contents define iron, steel and cast iron?
- Iron: C < 0.008%
- Steel: 0.008% < C < 2.14%
- Cast Iron: 2.14% < C < 6.70%
What is heat treatment? Name important steps and factors
- It is a process of heating and cooling metals to change their microstructure for obtaining better mechanical properties.
- Heat, hold, cool
- Important factors: Temperature and cooling rates
What is the difference between Hardening and Annealing?
They are two types of heat treatments:
- Hardening: Very fast cooling
- Annealing: Slow cooling rates
Fill annealing areas in the iron carbide diagram
“Notes”
Name 5 typical alloy elements of steel
Carbon, Manganese, Chromium, Phosphorus and Sulfur
What %C do low, medium and high carbon steels have?
Low-Carbon Steel: C < 0.25%
Medium-Carbon Steel: 0.25% < C < 0.6%
High-Carbon Steel: 0.6% < 1.4%
Why is not always high-carbon steel used?
Although they are the hardest and strongest steels, they are also the least ductile, tough and are expensive to produce
What is the main advantage of stainless steel?
acero inoxidable
They are highly resistent to corrosion and rusting (oxidacion)
Why is stainless steel corrosion resistant?
Because of the chromium concentration (11% at least)
