Direct Comparison Method is used to calculate the volume fractions of two phases distributed throughout a material, by using XRD patterns. I have faced two questions in respect of this method:
1) There is a parameter, named "R", for each phase. To calculate this parameter you need to know the values of temperature factors and multiplicity. Can temperature factor and multiplicity be considered as the same for both phases? If no, how can I calculate them in order to obtain the value of R for each phase?
2) To calculate the volume fractions of the two phases, it is required to choose a pair of XRD lines (one line for phase 1 and another one for phase 2). How are these peaks (lines) selected? I know that different pairs of lines can be chosen and the differences between volume fractions derived from different pairs are viewed as errors, but I still do not know how each pair of lines are chosen.
I would appreciate it if you would clarify these two points for me.
This method is often used for measuring the amount of retained austenite in dual phase steels. In this case, the temperature factor is defined for iron as a function of sinθ/λ. The temperature factor-sinθ/λ curve of iron at 20 degrees centigrade is presented in "Elements of X Ray Diffraction (edition 1956), Fig.14-5". The Multiplicity factor can be defined as the number of planes in a family that have the same spacing. For example, the multiplicity factor for the {100} family of planes of a cubic crystal is 6. So, this factor is dependent on the crystal structure of phase and plane which a certain peak belongs to.
When the microstructure contains martensite and retained austenite, Suitable austenite lines are the 200,220, and 311 lines; these may be compared with the 002-200 and 112-211martensite doublets. But when the microstructure contains ferrite (bainitic or Widmanstätten), the 111, 200, 220 and 311 peaks of retained austenite and the 110, 200, 211 and 220 peaks of ferrite are chosen.
Thanks Sadjad, but what you explained was about steels. I'm going to use this method for titanium alloys.
Why u wanna use that method instead of using Rietveld?
What is ur material and how many elements?
Temperature factor has different value for different element, because X-ray interact with the electron clouds. Multiplicity is same for same structure.
It is doubtful if u only compare 1 or 2 peaks specially for metal that that usually had a prefered orientation.
Is there any reference article or book on this topic that someone can share?
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