Cast vs Wrought Superalloy 2

[ebuntario]

What is the difference between Cast and Wrought on a Nickel-base Superalloy?

I read on "Superalloy: The Technical Guide" by Michael J. Donachie stating that "the highest creep-rupture strength at elevated temperatures can be achieved in nickel-base superalloy castings for high-stress, high-temperature turbine blade applications". How is this possible? Thank you

 

[mrfailure]

This is because superalloys can be cast as single crystals with no grain boundaries. Elimination of boundaries produces higher strength and inhibits formation of creep voids.

Aaron Tanzer

http://www.lehightesting.com

 

[ebuntario]

My bad. The quotation I meant was this, " The coarse grain size of PC (polycristalline) castings, as compared to finer-grained forgings, favors strength at high temperatures". So, I guess it's not because of the single crystals.

 

[lidbasky]

I think it is because of that cast Ni base superalloys could have more volume fraction of gamma prime phase than wrought superalloys, which make cast one stronger.

 

[metengr]

This is a complex subject that cannot be easily answered in a forum. I performed an internet search myself on this subject partly out of interest and because I am not an expert on Ni-base superalloy design and processing. I can tell you this from the results of my search that the choice of wrought over cast is based on final near net shape, cost, and desired mechanical and creep rupture properties. In other words, it is case by case specific on use of cast versus wrought versus P/M (powdered metal) - you might as well throw this into the mix for consideration.

 

[EdStainless]

In all alloys you have higher creep strength in coarse grain material.
This applies to stainless steel and alloy carbon steels.

With Ni superalloys you have the chemistry along with the other factors.
Yes the cast alloys are different from the wrought versions.

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Plymouth Tube

 

[ebuntario]

I know it's to complicated for this forum. Yet, all these answers gives great insight.

Anyways, does grain size really affect the strength?

 

[TVP]

Yes, grain size affects strength at high temperature. Larger grain size generally leads to improved resistance to creep and stress rupture. Here is one link with background including a summary on page 8:

http://www4.ncsu.edu/~murty/MAT450/NOTES/creep.pdf