Understanding the Role of Aluminum in High Temperature Super Alloys

[Pkruse]

Is anyone interested in starting a discussion on this topic? I use them in designs, but don't understand the metallurgy very well.

In particular, how does adding Al to Ni increase the melting point of Ni? It also improves a number of other desirable characteristics. The peak of the melting temperature curve on the phase diagram is at a 50-50 mixture. (Counting moles, not weight.) The resulting mixture is half aluminum, which we who work with refractory metals call "butter" due to its incredibly low melting point; yet the melting point of this mixture is much higher than pure Ni.

 

[Astronuc]

Is anyone interested in starting a discussion on this topic? I use them in designs, but don't understand the metallurgy very well.

In particular, how does adding Al to Ni increase the melting point of Ni? It also improves a number of other desirable characteristics. The peak of the melting temperature curve on the phase diagram is at a 50-50 mixture. (Counting moles, not weight.) The resulting mixture is half aluminum, which we who work with refractory metals call "butter" due to its incredibly low melting point; yet the melting point of this mixture is much higher than pure Ni.

Superalloys is an extraordinarily interesting topic, and in fact TMS (The Metallurgical Society) has hosted a conference Superalloys on a three year period. One of the key editors of the series, Ed Loria, passed away recently (https://www.physicsforums.com/showthread.php?t=402572).

TMS Superalloys Archive - http://knowledge.tms.org/superalloys.aspx

See also - http://www.tms.org/meetings/specialty/superalloys2000/superalloyshistory.html

The high melting point can be attributed to NiAl, an intermetallic compound.

See the Ni-Al phase diagram here - http://www.ias.ac.in/sadhana/Pdf2003Apr/Pe1064.pdf

The challenge is that there are several different phases that can form during the freezing of a melt, so one possibility is to produce a rapid solidified powder, which then must be hot pressed.

 

[Pkruse]

Thanks, Joe. Now I have to go do some studying before I can ask further questions.