Refinements in phase fraction determination of textured alloys from transmission diffraction data

Abstract

The use of high-energy synchrotron X-ray diffraction sources has become increasingly common for high-quality phase fraction measurements and microstructural evolution experiments. While the high flux, large volume illuminated and large number of diffraction vectors should reduce common sources of uncertainty and bias, the distribution of the diffraction vectors may still cause bias in the phase fraction measurement. This hypothesis of bias was investigated with example experimental data and synthetic data. The authors found that there may be bias depending on the sample texture, the distribution of diffraction vectors and the hkl planes used in the phase fraction measurement, even for nearly complete coverage of a pole figure. The authors developed a series of geometry-based correction values that reduced the measurement bias due to sampling scheme and texture in the phase fraction measurement by an order of magnitude. The efficacy of these corrections was demonstrated with application to both experimental and synthetic data.

A method for pole figure measurements via a dynamic segmented spiral scheme

“…Following the work described by Creuziger et al (2021Creuziger et al ( , 2018a, 20 common texture components for rolled steel sheets were used to assess the accuracy of the ODFs. These texture components are separated into seven face-centered cubic components for the austenite () phase and 13 body-centered cubic components for the ferrite () phase.…”

“…The phase fraction calculations follow the equations laid out by Creuziger et al (2021). ODFs were used to calculate pole figures for a selection of hkl planes.…”

“…As with the ODF reconstruction, the particular hkl planes used to calculate the phase fraction can affect the accuracy of phase fraction measurement (Creuziger et al, 2021(Creuziger et al, , 2018a. Common approaches include using intensity data from a select list of measured peaks or fitting the entire spectrum of data (i.e.…”

“…Phase fraction and stability are often functions of composition and processing, necessitating measurements on the material as produced. When diffraction data are recorded, the phase fraction data are often calculated from a simple summation (Jatczak et al, 1980;Creuziger et al, 2021) over all diffraction vectors (i.e. positions on a pole figure) measured.…”

“…positions on a pole figure) measured. However, as shown by Creuziger et al (2021Creuziger et al ( , 2018a, summation alone can lead to bias in the phase fraction. Bias errors were found to be negligible when a series of diffraction vectors were evenly distributed over a pole figure.…”