It is well known that the properties of metallic materials can be controlled by there being multiple phases. The most notable examples include the precipitation hardening and transformation induced plasticity which is mainly generated from finely dispersed secondary phase particles and a large amount of retained austenite phase in the ferrite or bainite structures. The development of multi-phase materials is one of the hot topics today in the metal industry. When it comes to multi-phase materials, among the crucial parameters affecting their microstructure, is their phase fraction. This is defined as the ratio of the volume or weight fraction for a given phase. Specifically, the fraction of austenite retained in transformation-induced plasticity steels has in recent times drawn exemplary attentions from scholars and researchers. Consequently, many techniques for determining the fraction of retained austenite have been suggested.
However, the fractions obtained by the various available techniques often differ over a wide range. As a resolve, this has been seen to hinder the comprehension of the microstructures and the mechanisms that control the properties of materials based on a quantitative evaluation of the phase fraction. There are three main groups of techniques for determining the phase fraction, namely: diffractometry, microscopy and bulk property measurement. All these techniques have their pros and cons, however, the Rietveld method has the ability to overcome such setbacks uncertainly being introduced by the texture.
Yusuke Onuki and colleagues at the Frontier Research Center for Applied Atomic Sciences- Ibaraki University in Japan proposed a study on the application and verification of the Rietveld texture analysis using diffractograms acquired by iMATERIA from the viewpoint of phase fraction measurement in steel. They aimed a presenting a detailed discussion on the effects of texture on the phase fraction, as analyzed, using conventional X-ray diffraction technique. Their research work is now published in Journal of Materials Science.
The research team commenced their experimental procedure by preparing model samples consisting of laminations of ferritic and austenitic stainless-steel sheets. They then used the models to verify the accuracy of the phase fraction determined by time-of-light neutron diffraction measurement at iMATERIA. During this process, the team applied the Rietveld texture analysis technique, based on 132 diffractograms, as the main analysis method.
The authors of this paper mainly observed that the analyzed volume fractions of austenite agreed well with the prepared fractions portraying a maximum error of only 5% relative to the prepared fractions. They also noted that the quality of the texture analysis for the austenite phase became poorer at volumes lower than 5%. More so, the team realized that by ignoring the texture of the austenite, the analyzed phase fractions exhibited deviations from the true values.
In their study a comprehensive report on the investigation of the use of Rietveld texture analysis by using time-of-flight neutron diffraction data measured at iMATERIA, J-PARC MLF as a tool for determining the phase fraction of steel, has been presented. The measurements that were undertaken were for the samples comprising of sheets of ferritic and austenitic stainless steels, for which the overall phase fractions are well known. From the results presented within, it is clear that the multi-diffractogram-based Rietveld texture analysis is an effective technique of determining the phased fractions in textured steels.
Yusuke Onuki, Akinori Hoshikawa, Shigeo Sato, Toru Ishigaki, and Toshiro Tomida. Quantitative phase fraction analysis of steel combined with texture analysis using time-of-flight neutron diffraction. J Mater Sci (2017) Volume 52: page 11643–11658.
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