As austenite and ferrite are not compounds, how do we identify their presence. Plz enlighten me about the procedure for such XRD analysis. For example: A sample of duplex steel has only two phases and as such no other compounds are present, how to match peaks corresponding to these two phases?
I understand ferrite and austenite as phases and they are part of any (inorganic) database. "compound"? It should be clear that pure iron is comparatively unlikely, if you investigate duplex steel since the phase diagram tells you that at room temperature only bcc (ferrite) is stable. This means, in case you have duplex steel you are dealing with Fe-alloys. However, the lattice parameters do not change that much during alloying so that for your investigation you can use ferrite as well as austenite as starting phases. The peak positions nearly match and can be (manually) adjusted if they deviate more than a half of a peak width.
The experimental procedure is roughly: use NO Cu radiation (fluorescence) but Co, better shorter wave length like Mo radiation since then you can observe about 7 peaks within some ten degrees. These are commonly used to approximately determine the phase fraction. Since there are several other effects also affecting the reflex intensities (e.g. preferred orientation) the results are only correct in first approximation if during refinement (full pattern refinement, sometimes also misleadingly called Rietveld refinement) bigger deviations between the calculated and measured intensities occur.
If you want play a bit around with phases, angle ranges, wave length...use PowderCell. It offers many options in order to optimize measurement conditions and also contain a simple full pattern refinement. For more advanced refinement you should test Fullprof or Maud. From my point of view, the best (but also a bit challenging in the beginning) is BGMN (also free available) which has a user interface as well. This software determines automatically when the consideration of texture mathematically makes sense (if case of a small fraction).
I understand ferrite and austenite as phases and they are part of any (inorganic) database. "compound"? It should be clear that pure iron is comparatively unlikely, if you investigate duplex steel since the phase diagram tells you that at room temperature only bcc (ferrite) is stable. This means, in case you have duplex steel you are dealing with Fe-alloys. However, the lattice parameters do not change that much during alloying so that for your investigation you can use ferrite as well as austenite as starting phases. The peak positions nearly match and can be (manually) adjusted if they deviate more than a half of a peak width.
The experimental procedure is roughly: use NO Cu radiation (fluorescence) but Co, better shorter wave length like Mo radiation since then you can observe about 7 peaks within some ten degrees. These are commonly used to approximately determine the phase fraction. Since there are several other effects also affecting the reflex intensities (e.g. preferred orientation) the results are only correct in first approximation if during refinement (full pattern refinement, sometimes also misleadingly called Rietveld refinement) bigger deviations between the calculated and measured intensities occur.
If you want play a bit around with phases, angle ranges, wave length...use PowderCell. It offers many options in order to optimize measurement conditions and also contain a simple full pattern refinement. For more advanced refinement you should test Fullprof or Maud. From my point of view, the best (but also a bit challenging in the beginning) is BGMN (also free available) which has a user interface as well. This software determines automatically when the consideration of texture mathematically makes sense (if case of a small fraction).
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