Formation of Nanostructured Steels by Phase Transformation

T. Yokota, C. Garcia-Mateo and H. K. D. H. Bhadeshia


A thermodynamic criterion is developed to define the finest grain size that can be achieved during phase transformation, as a function of the driving force, interfacial energies and the parent phase grain size. It is found that at large undercoolings below the equilibrium temperature, the grain size achieved in practice is far greater than predicted theoretically. This is because of the heat of transformation, which causes recalescence and reduces the effective undercooling. Whereas these conclusions apply generally, there is a special effect associated with displacive transformations, \ie the plastic accommodation of the shape deformation, which limits the growth of grains but which has yet to be modelled quantitatively.

Scripta Materialia, Vol. 51 (2004) 767-770.

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Bulk nanostructured metal


(Dr) Tomoyuki Yokota Graduates

Tomoyuki Yokota obtained his Ph.D. degree from Waseda University, for a thesis entitled Ultra grain refinement in 9%Ni steels through spontaneous reverse transformation due to adiabatic deformation heating.

Degree ceremony at Waseda University in Tokyo, Japan
The party.
With the proud parents.

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