Martensites

Hello all, Here's an interesting discussion my colleagues and I have been having for some time now. I'd like to know what people think about this.
It's been surmised and "reported" that the precursor to some martensitic transformations is the formation of the tweed structure. Although it's a diffusionless process, the transformation shows characteristics of second order transformations (where the tweed structure fluctuates and strains the matrix) until you form martensite at some critical strain (first order latent heat). This might be best described as a hybrid transformation. The question is, is this tweed structure a spinodal? I say no because there's no change in composition, just structure. Although others claim that over a few unit cells, you get local fluctuations of structure AND composition. Admittedly, this is one of those classification/"I R smarter than you" debates over a few beers, but I just wonder what others think. Let the name calling begin!
-SrvClapton
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I should say that I am not an expert in the martensic transformation but I have been working on the second order transformation in the Y123. Our model is described at
Simultaneous assessment of the YBa2Cu3O6+z thermodynamics under the linear error model. J. Phys. Chem. Ref. Data, 1998, v. 27, N 5, p. 855-888. http://evgenii.rudnyi.ru/doc/papers1/98jpcrd_y123.pdf
It was possible to introduce the spinodal there, well, as a function of oxygen concentration. Usually, if you have a critical phenomenon, you have a spinodal. Hope this helps.
Best wishes,
Evgenii Rudnyi
--
http://www.imtek.uni-freiburg.de/simulation/mor4ansys /


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