Surface effects in displacive phase transformations studied by X-ray specular reflectivity

We report the first application of specular reflectivity to measure the formation of surface relief resulting from displacive phase transformations. It is demonstrated for the martensitic transformation of Ni62.5Al37.5 and the two step transformation of Ni2MnGa that reliefs heights ranging from the nanoscopic to the mesoscopic scale can be characterized by reflectivity experiments. Since a mesoscopic surface relief shows up as a dip below the critical angle, this opens up the opportunity to study displacive phase transitions at the intensity level of total external reflection. The application of the technique to surface nucleation problems is discussed