Stress Measurement and Precision Diffraction Angles on Large Grained Specimens

Extract

This note describes a diffractometer technique that is successful on specimens that yield sharp diffraction peaks but that have grain sizes somewhat too large to give reliable results with the usual powder diffraction methods, owing to the peak profiles being distorted or displaced by having too few grains reflecting, Such specimens are not uncommon in stress analysis and the errors encountered are sometimes reduced by oscillating the specimen through an angle range, Δβ, of a degree or so about the diffractometer axis, thereby increasing the number of recorded reflections. The technique discussed here is basically a single crystal technique rather than a powder technique, and with a diffractometer capable of measuring reflections at high angles on both sides of the initial beam this technique would amount to W. L. Bond's precision method. For the usual diffractometer, however, high diffraction angles must be measured on one side only, even though some instruments permit the lower angle reflections to be measured on both sides for accurately locating the zero of the 2θ scale. We are discussing a technique as applied to these usual types of diffractometers.