Dear Ahmad,

Good afternoon!

There is no monotectic reaction in the Cu-Fe equilibrium diagram...

The one you attached, is part of the article " Rapid solidification of bulk undercooled hypoperitectic Fe–Cu alloy ", DOI: 10.1016/j.jallcom.2006.03.012, where it is clear it is a " Fe–Cu phase diagram including calculated metastable miscibility dome (dot line) ".

Thank you!

Andre

André Vicente

Thanks for your reply. I was referring to the paper by Muntiz (also attached). I just attached the phase diagram as a reference. Muntiz writes "Solidification of Fe-Cu alloys exhibits a monotectic reaction, involving the liquid separation into two melts within the miscibility gap. Directionally grown monotectics may be classified into two microstructural types, according to the ratio of the monotectic temperature (TM) to that of the upper consolute temperature (Tc)." Then it is continued that "The Fe-Cu has a TM/Tc ratio of 0.82. 34 It thus belongs to a type A microstructure".

So, are these statements in the article wrong, or does the monotectic reaction happen when cooling/solidification is rapid?

Thanks,

Ahmad

Ahmad Zafari

I wouldn't say it is wrong... I would only suggest to review the text emphasizing that it is a metastable model of monotectic reaction that was observed and that looks like to happen for higher cooling rates, but never it would be the equilibrium condition that could be plot as a phase diagram. It could be a "matastable phase diagram" like in the case of the classic Fe-Fe3C metastable phase diagram...

In this case, I understand that a possible monotectic reaction of fashion L1 --> L2 + gama-Fe, would happen exactly at the dotted line, and for for different chemical compositions it would happen at different temperatures...

Very nice discussion! Thank you for bringing such good questions to the forum!

Andre

André Vicente

Thanks. Indeed interesting. I actually found a paper confirming what you discussed above that the monotectic reaction happens only upon rapid solidification (non-equilibrium). The paper is Luo et. al Acta Materialia 69 (2014) 355–364. Article A comparative study of dendritic growth within undercooled l...

Just one more question. You mentioned exactly at the dotted line. Do you mean where the liquid separation starts? Does that mean that liquid first separates to L1+L2 and then L1--> L2+gama-Fe? And again, does this mean that the gama phase field expands upon rapid cooling that gama can actually exist in a temperature within L1+L2 phase field?