Abstract
Separation of size and strain effects on diffraction line profiles has been studied in a round robin involving laboratory instruments and synchrotron radiation beamlines operating with different radiation, optics, detectors and experimental configurations. The studied sample, an extensively ball milled iron alloy powder, provides an ideal test case, as domain size broadening and strain broadening are of comparable size. The high energy available at some synchrotron radiation beamlines provides the best conditions for an accurate analysis of the line profiles, as the size-strain separation clearly benefits from a large number of Bragg peaks in the pattern; high counts, reliable intensity values in low-absorption conditions, smooth background and data collection at different temperatures also support the possibility to include diffuse scattering in the analysis, for the most reliable assessment of the line broadening effect. However, results of the round robin show that good quality information on domain size distribution and microstrain can also be obtained using standard laboratory equipment, even when patterns include relatively few Bragg peaks, provided that the data are of good quality in terms of high counts and low and smooth background.
Highlights
X-ray diffraction (XRD) line profile analysis (LPA) is frequently used to gain insight into the microstructure of crystalline materials, often complementing evidence provided by electron microscopy
The present work is mostly focused on (i), to assess the real possibility of separating size and strain effects and how the result is influenced by the quality and quantity of information available from experiments performed with different optics and X-ray wavelengths, using both commercially available equipment and synchrotron radiation (SR) XRD instruments
It is ideal to collect data by SR XRD up to high q, encompassing tens of peak profiles with good statistics, with high instrumental resolution and at different temperatures for a reliable assessment of the temperature diffuse scattering (TDS) contribution; but the present results clearly demonstrate that an effective and even reliable size– strain separation can be achieved with much less information, on accessible laboratory instruments equipped with conventional sources, and even with the few peaks observable by relatively low energy X-rays (e.g. 4CoK 1 data), provided that the measurement statistics are good
Summary
X-ray diffraction (XRD) line profile analysis (LPA) is frequently used to gain insight into the microstructure of crystalline materials, often complementing evidence provided by electron microscopy. The present work is mostly focused on (i), to assess the real possibility of separating size and strain effects and how the result is influenced by the quality and quantity of information available from experiments performed with different optics and X-ray wavelengths, using both commercially available equipment and synchrotron radiation (SR) XRD instruments To this end we studied a ball milled metal powder which we consider as a nearly ideal specimen, as it is stable, is available in large amounts from the same production batch, and shows comparable broadening effects of finite domain size and strain caused by plastic deformation.
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