Effect of grain size on the thermal hysteresis in martensitic transformations

P. LA ROCA

Paris

Exposición; Oral presentation, Laboratoire de M´etallurgie Structurale, Ecole Nationale Superieure de Chimie de Paris; 2013

Laboratoire de M´etallurgie Structurale, Ecole Nationale Superieure de Chimie de Paris

In a thermally induced martensitic transformation, thermal hysteresis is generated due to dissipative processes. In materials with large grain size (g), the martensitic transformation hystéresis to a monoclinic 18R structure is about 10 ° K. However, when the grain size decreases there is an effect which modifies the hysteresis width. To study this effect, ribbons with reduced grain size were obtained by rapid solidification techniques. This work shows that for grain size below 100 μm, the hysteresis increases. To understand the effect of grain size, a dissipation model has been proposed. Recarte et al showed that during the martensitic transformation, if two crystallographically structures are not compatible, an irreversible deformation is generated between two structures. Similarly, in the case of the 18R structure and grain boundaries, during the martensitic transformation generates irreversible strains affecting the hysteresis width. Based on this phenomenon, a model was developed which correctly fit with the experimental results