Having studied Elements of XRD book and indexed an alloy profile, it remains some doubts, some of them are ordinary because the lack of knowledge of mine. I would kindly ask someone to explain or give directions.
First, the profiles I have (20 to 120°) are low quality, so it would cause some deviation from precise measurement, but it seems to me the basic analysis would be similar. I could indexed a bcc structure. The alloy has 7 elements all in high content form 11 to 25 at%.
1. Must I have to use Kalpha 1.540562 or the medium value 1. 541838?
2. The main peak is very intense, 100%=8000 counts, while the 2nd is only 4.3% and the remaining below 1%. What could this means?
3. The 220 and 310 reflections for bcc are missing. Why?
4. From alloy density, the number of atoms per cell was found from 3.20 to 3.30, say, maybe 3 atoms per cell is close to reality, or a multiple of that like 10?... What kind of unit cell can show that? Or can I consider a superlattice of how may cells, based on it?
5. The cell parameter is higher than one calculated from Vegard's Rule: 3.22-3.27 against 3.05 Angstrons. What does it mean?
The profile is attached. I believe the alloy is well homogenized even because a previous lower quality cast showed the same main peaks with other reflections that do not appear now.
Hi Thomas, since you have two phases, from the intensity profile I can say alpha phase is more than beta phase and your polycrystalline sample has directional growth along the [110] direction of that alpha phase. What kind of analysis are you looking for? Since the sample is textured I would suggest you to do pole figure measurement or electron back scatter diffraction (EBSD) for texture analysis, Thanks.
Many thanks Pinku Roy
The alloy was chill casted over a thick copper tray (~30mm) that was rather hot due to plama torch, maybe near 600°C. So the colling rate was high or middle to high. So how can it had directional growth? The microstructure does not show any direction but I am not sure... I send you a microstructure from SEM where you can see 2 phases and dendrites for as-cast alloy.
Hi Thomas, though temperature of the copper tray is ~600 C , I think it is far below the melting point of your alloy and since copper is a very good thermal conductor, it extracted heat from the liquid in such a way that it formed dendritic structure of 10 micron or less as per the microstructure. At room temperature or below, copper tray would have produced larger dendrites.
Hello Thomaz Augusto Guisard Restivo. You said that the alloy has 7 elements all in high content, but you did not mention these elements in detail. X-ray diffraction analysis (XRD) is a useful technique for knowing the presence of certain elements or not by showing the characteristic peaks, especially for crystalline compounds. if your alloy contains Si, Fe, Au, Ti3AlC2 or Ti3C2(OH)2, then these articles will be useful for you. You should compare your obtained data with that of well-known published ones.
Best Wishes...
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thank you Mohammad Hegazy
Actually my material is a solid solution metallic alloy containing Fe, Cr, Nb and more 4 metals all in high content from 6 to 20wt.%. Only transition metal elements. The strange things are the big bcc (110) peak, being others bcc peaks very weak or absent, and the Nu. of atoms per cell of 3 ! I was wondering if these have any meaning in terms of structure. Pinku said the first is caused by directional growth.
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