FEATURE A D V A N C E D M A T E R I A L S & P R O C E S S E S | J U L Y / A U G U S T 2 0 2 2 6 3 to some extent. The problem of quantitative phase analysis in textured material is one of obtaining the integrated intensity averaged over all orientations of the specimen with respect to the x-ray beam. Methods of averaging involve randomizing the intensities by mathematical or mechanical means. Several methods of averaging the intensities have been proposed for the quantitative phase analysis of textured materials[3]. Any electromagnetic radiation interacts with the material through either absorption and energizing the material system and expelling neutrons from atoms; or diffusion, during which the radiation is diffused by the matter and the electromagnetic waves associated with it change direction of propagation. This change can be accompanied by energy exchanges between photons and matter. The technique of x-ray diffraction is based on coherent elastic scattering: the macroscopic phenomenon of diffraction arises from the coherent sum of all the electromagnetic waves diffused by the atoms found along the same family of reticular planes. To manifest itself, it necessarily requires the presence of a reticular order, as found in crystals or in crystalline materials. The incoming beam (upper left in Fig. 7) scatters, re-radiating a small portion of its intensity as spherical wave. If this happens symmetrically at a discrete distance d, the waves are in synchrony (constructive mode) only in the direction where their path-length difference 2dsinθ is equal to an integer multiple of the radiation wavelength λ. This creates a diffracted beam at an angle measuring 2θ producing a figure called diffraction pattern that can be collected and represented as follows in function of the detecting method. In addition to phase analysis, x-ray diffraction can also be used to analyze microstructural features such as texture, residual stress, and grain size. Texture produces systematic deviations of peak intensity from the characteristic diffraction pattern of a phase. The intensity deviation can be used to quantify the fraction of grains in a certain orientation by tilting and rotating the sample in the diffractometer as shown in Fig. 7. With the x-ray measurement, the diffraction plane is crucial: only the grain in the lattice nhkl are registered. Therefore, the sample has to be turned and tilted and is measuring the intensity at multiple angle positions. CARBIDE CORRECTION Carbide presence can have an influence on the determination of RA%Vol. The influence is given by the presence of overlapped or adjacent carbide peaks that can interfere and alter the intensity of the ferrite or austenite peaks. Standard algorithms based on the evaluation of the region of interest, can lead to an erratic evaluation of the RA%Vol since it can be totally or partially considered in the peak integration. Using the full profile approach, it is possible to consider the influence of this peak and do not consider it, as well as all the other peaks of carbides that can interfere. ORIENTATION Measurements of retained austenite using x-ray diffraction are often employed despite the caveat that these methods only apply to uniform (random) texture distributions. Due to the strong crystallographic texture causedbydeformation during processing, these assumptions Fig. 6 — Scattering schematics. 13 Fig. 7 — Schematics and rotating the sample while measuring with x-ray.
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