High-Resolution Single-Grain Diffraction of Polycrystalline Materials

Polycrystalline bulk materials are ubiquitous in everyday life, including biological, geological, and engineered structural and functional materials. Their fundamental units are individual grains, which are characterized by their microstructure; i.e., the arrangement of lattice defects. The microstructure usually influences the materials properties critically.
It has been demonstrated that, by using high-energy synchrotron radiation, diffraction peaks off individual grains can be recorded in-situ during processing. Important information such as the orientation, average strain, and size of individual grains can be obtained, even if the peak shapes are commonly not analyzed. However, it is also well-known that the shape of diffraction peaks, if observed with sufficient resolution, contains significant information about the microstructure. While the intensity distribution in reciprocal space of a perfect lattice consists of delta functions located at the reciprocal lattice points, defects induce characteristic peak broadening. In order to exploit the wealth of microstructural information contained in broadened diffraction peaks, the intensity distribution has to be characterized in all three dimensions of reciprocal space. Distinguished directions are the radial direction, parallel to the reciprocal lattice vector g and quantified by differences in the scattering angle 2θ, and the azimuthal directions, perpendicular to the reciprocal lattice vector and quantified by the angles η and ω (Figure 1). Conventional radial profile (line shape) analysis techniques average over many grains with possibly significantly different microstructure. Under conditions of single-grain diffraction, these limitations are overcome and the intensity distributions along all three directions of reciprocal space are accessible.