Investigation of the Initiation of Solid State Structural Phase Transformations at Crystal Surfaces by Law-Energy Electron Diffraction (LEEDS).

摘要

This is a report on the LEED investigations of the role of a free surface in the initiation of Martensitic phase transformations where restricted to principally cobalt surfaces and iron and titanium surfaces. The aim was to study the possible occurrence of surface localized soft phonon modes active in nucleation, however, it was first determined by LEED studies of both pre and post transformed cobalt that the traditional operational nucleation mechanism localized to a surface (surface localized 'frozen in' embryos or nuclei) and proposed faulting mechanisms were unapplicable to the cobalt system. Detailed low-energy electron-diffraction (LEED) work on the (0001) surface of cobalt has indicated no existence of surface localized different phases or embryos that could act as nuclei for the martensitic transformation. The atomic structure of the cobalt surface was shown to be eqivalent to that of the bulk in both the high temperature and low temperature phases. The soft-mode idea could therefore be examined by LEED in detail as a viable mechanism for martensitic transformation nucleation at the surface of cobalt and other transforming materials. (Author)