Single crystal and poly crystal metal

In summary, a single crystal would have a lower yield stress, directional stiffness, and Young's modulus.
  • #1
helloy
8
0
What difference would you observe about the yield stress, young modulus,etc if your material were a single crystal? Explain the difference.
 
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  • #2
Please show your own work first. Also, it looks like this and your other questions would be a better fit in the homework forum.
 
  • #3
my ans is:If the material were a single crystal, the yield stress would be lower. The dislocation could move easily because there is only 1 crystal. In addition, single crystal metals have directional stiffness. But I'm not sure about that
 
  • #4
Sounds good. To fill this in further, I'd mention the relative difference between the yield stress and Young's modulus for the two types of samples (i.e., is [itex]\sigma_y[/itex] half as much for a single crystal? A thousandth as much? Similarly, does the Young's modulus in different directions vary by a factor of two? A factor of a thousand?).
 
  • #5
Thax, I'll think about it
 
  • #6
I came to this forum to learn more about single crystal casting/properties/etc. Sooooo, instead of starting a new thread I will just continue this one.

Mapes said:
Sounds good. To fill this in further, I'd mention the relative difference between the yield stress and Young's modulus for the two types of samples (i.e., is [itex]\sigma_y[/itex] half as much for a single crystal? A thousandth as much? Similarly, does the Young's modulus in different directions vary by a factor of two? A factor of a thousand?).
And the answer to this barrage was? I've taken my fair share of materials courses and the only time single crystals are brought up, it is just to discuss that they are used for fan blades. Or that processing is """expensive""" with no comparative examples.

Can single crystal structures be heat treated to different phases? If they have dislocations, this implies that they can be forged/annealed/work hardened/etc, no? How would the UTS and modulus in the preferred (maximum value) direction compare to a polycrystalline sample of the same dimensions?

I know cost is a big prohibitor, but why have we not seen single crystal casting methods used to create parts in applications like MotoGP, F1, and others? It seems that their only purpose is to make fan blades and computer chips.
 
  • #7
Any help here? Seems like I couldn't find anything on my own for a reason...
 
  • #8
The advantage of single crystals (in mechanics) is that grain boundary creep is removed as a creep mechanism. If grain boundary creep isn't the dominant cause of failure, then nobody's going to spend money to grow a single metal crystal part.
 
  • #9
Mapes said:
The advantage of single crystals (in mechanics) is that grain boundary creep is removed as a creep mechanism. If grain boundary creep isn't the dominant cause of failure, then nobody's going to spend money to grow a single metal crystal part.
Seems to me like they could find a place in IC engines...if anyone knew more about them.
 

1. What is the difference between single crystal and polycrystal metal?

Single crystal metal is a metal that has a uniform and continuous internal structure, with all of its atoms arranged in a single crystal lattice. Polycrystal metal, on the other hand, is composed of multiple small crystals or grains that are randomly oriented and joined together.

2. How are single crystal and polycrystal metals formed?

Single crystal metals are typically formed through a process called directional solidification, where the metal is cooled at a controlled rate to allow for the formation of a single crystal lattice. Polycrystal metals, on the other hand, are formed through processes such as casting, rolling, or extrusion, where the metal is subjected to mechanical deformation and creates multiple grains.

3. What are the properties of single crystal and polycrystal metals?

Single crystal metals have anisotropic properties, meaning they exhibit different physical and mechanical properties depending on the direction in which they are measured. Polycrystal metals, on the other hand, have isotropic properties, meaning they exhibit the same properties in all directions. Single crystal metals also tend to have higher strength and ductility compared to polycrystal metals.

4. What are the applications of single crystal and polycrystal metals?

Single crystal metals are commonly used in high-performance applications such as turbine blades, jet engine components, and electronic devices. Polycrystal metals are widely used in everyday applications such as construction materials, household appliances, and automotive parts.

5. How do researchers study the properties of single crystal and polycrystal metals?

Researchers use various techniques such as X-ray diffraction, microscopy, and mechanical testing to study the crystal structure, properties, and behavior of single crystal and polycrystal metals. These techniques allow for a better understanding of the materials and aid in the development of new and improved metal alloys.

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