Orientation determination by EBSP in an environmental scanning electron microscope

Abstract

Remarkable progress has been made in the single orientation measurement of polycrystalline materials using scanning electron microscopy (SEM) (1,2,3). The automation of this technique in the form of Orientation Imaging Microscopy (OIM) provides materials scientists with a reliable technique of texture and micro-texture characterization of materials at high vacuum conditions (4,5). The technique is based on the acquisition of Electron Backscattered Diffraction Patterns (EBSP) in the chamber of an SEM. These diffraction patterns are formed in the same manner as Kikuchi patterns in the TEM, but result from backscattering of electrons out of the top surface of the sample. Hence they can be obtained from bulk samples. In this paper we will discuss some of the unique capabilities provided by EBSP analysis at elevated pressures and temperatures in an Environmental Scanning Electron Microscope (ESEM). It was possible to obtain patterns with good quality for water vapor pressures as high as 6 Torr for single crystals, and 3 Torr for polycrystalline materials (NiAl grains with diameter up to 64 microns were examined). With increasing pressure, polycrystalline diffraction patterns degrade at a much higher rate than single crystal patterns.