SURFACE EFFECTS IN DISPLACIVE PHASE-TRANSFORMATIONS STUDIED BY X-RAY SPECULAR REFLECTIVITY

We report the first application of specular reflectivity to measure th e formation of surface reliefs resulting from displacive phase transfo rmations. It is demonstrated for the martensitic transformation of Ni6 2.5Al37.5 and the two step transformation of Ni2MnGa that relief heigh ts ranging from the nanoscopic to the mesoscopic scale can be characte rized by reflectivity experiments. Since a mesoscopic surface relief s hows up as a dip below the critical angle, this opens up the opportuni ty to study displacive phase transitions at the intensity level of tot al external reflection. The application of the technique to surface nu cleation problems is discussed. (C) 1998 Elsevier Science B.V. All rig hts reserved.