Prof Tomonari Inamura, Tokyo Institute of Technology, Japan

Effect of incompatibility on martensite microstructure in shape memory alloy
When Jan 15, 2018
from 02:00 PM to 03:00 PM
Where LR8
Contact Name
Contact Phone 01865-283446
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Martensitic transformation is a shear-dominant, lattice distortive and diffusionless solid-solid transformation occurring by nucleation and growth. Shape memory alloy is a typical material that has the transformation. At the transformation temperature, a high temperature (parent) phase discontinuously transforms to a low temperature (martensite) phase through a cooperative motion of atoms.  The loss of some symmetry elements in the high temperature phase results in the formation of crystallographically equivalent variants of the low temperature phase.  The domains of a low symmetry phase are interfaced with each other to reduce the overall strain; a typical martensite microstructure appears.

 

In the classical theory of martensite crystallography, only the compatibility between parent and martensite phases is considered. However, after Ball and James, the importance of the compatibility (rank-1 connection) of all the interfaces involved in the microstructure has been recognized. Recently, to improve the mechanical property of the shape memory alloys for several new applications, a mathematical guiding principle to control the martensite microstructure is extensively investigated based on the rank-1 connection. However, roles of the compatibility on the formation and geometry of microstructure, defects and mobility of domain-walls, fatigue mechanism have not been understood enough; these topics are new aspects of martensite microstructure emerged from the advances in the mathematical theory.

 

In this talk, effects of the deviation from the compatibility condition on the geometry and the formation process of martensite microstructure are analyzed in some shape memory alloys by various microscopy techniques including in-situ observation.  Especially, how the incompatibility at interfaces governs the nucleation of martensite and final microstructure is focused.