Single Crystal materials

[MechatroPro]

i'm a little bit confused about single crystal alloys, and have some questions about them:

*Why single crystal material are used in the form of alloys?

is right it right to say that:

*pure substances like Fe,Cu are Not suitable because they are unstable and do not show strong mechanical properties?

*each phases in a multiphase single crystal superalloy, is single crystal?

*all superalloys are single crystal materials?

 

[TVP]

As far as I know, there is only one commercially developed application that uses single crystal materials: investment cast blades for high temperature gas turbine applications. The materials used for these are superalloys. So, the answer to your questions are as follows:

1. Alloys have better mechanical and physical properties.
2. Pure substances like Fe and Cu have low mechanical properties. I would not characterize them as unstable.
3. You are confusing some terms. In a superalloy single crystal casting, there is only one crystal, and it is only one phase.
4. All superalloys are NOT single crystals. Single crystal castings represent a small fraction of the total usage of superalloys.

 

[IRstuff]

I think that you are attempting to generalize where there is no "there."

The bottom line is that alloys are used when there's an advantage, whatever that might be, strength, chemical resistance, electrical properties, shine, etc. Not everything is about strength or "stability." GaAs is an annoyingly unstable material at high temperatures, but it possesses a superb electron mobility, and is therefore the material of choice for certain electronic devices.

Likewise, silicon is extremely stable, but in order to make usable electronic devices, we add toxic materials the degrade the perfectness of the silicon crystal.

TTFN

FAQ731-376

 

[EdStainless]

There are two reasons to use SC blades for high temp turbine applications.
1: You remove the grain boundaries which are the weakest part of the alloy.
2: You use the alloy in the crystal orientation that has the highest properties.

In the SC blades the matrix is a single crystal, but the secondary phases are dispersed throughout in order to give the required properties.

As to other applications for single crystal technologies, semiconductors (Si substrate), optics (sapphire lenses), jewelry (star sapphire)

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[mighoser]

Add to EdStainless Post:

High Temp Creep: Turbine Blades must not elongate beyond the clearance they are allocated based upon thermal expansion and tolerance. Single crystals minimize grain boundary assocated creep mechanism which dominates in most alloys.