MICRESS Forum

Hello Bernd,

I hope this message finds you well.

I am currently studying the phase transformation of polygonal ferrite using MICRESS, with elastic stress coupling enabled. I would like to seek some clarification regarding the influence of external stress on the transformation behavior.

In my simulations, I applied both tensile and compressive stresses. I observed that the transformation kinetics are affected: the transformation start temperature and the overall transformation time change noticeably. However, the crystallographic orientation (or growth morphology/orientation selection) of the polygonal ferrite does not seem to change under different loading conditions.

In my current setup, the interface properties are isotropic and no crystallographic anisotropy is introduced.

I am wondering:

Why do tensile and compressive stresses influence the transformation kinetics, but not the orientation or growth direction of polygonal ferrite?

Is this behavior expected for polygonal ferrite transformations in MICRESS?

Could this be related to the use of isotropic interface properties or the formulation of elastic energy (e.g., volumetric eigenstrain only)?

If anyone has insights or relevant references on this topic, I would greatly appreciate your guidance.

Thank you very much for your time and help.

Best regards,
Zelin Zhang

Dear Zelin Zhang,

In order to get an anisotropic effect of elastic stress or strain on a phase transformation, I think three conditions must be fulfilled:

1.) There must be a difference on molar Volume between the phases

2.) Stress/strain must be anisotropic, i.e. e.g. uniaxial

3.) There must be a difference in the elastic properties of the two phases.

If all conditions are fulfilled, but the difference of the shear modulus (c11-c12)/2 between the two phases is not large enough, the effect still may be too small to be easily detected. Then you might need to use high stress values or check for the equilibrium shape after long holding times rather than for the phase transformation.

Bernd