If I have titanium-based alloy subjected to different thermal treatments, Is there any database (such as Tables or ...) illustrates: [the (2 theta) versus the peaks] and the specific type of the phase related to this peak i.e., alpha, alpha' and alpha''? or this process depend on the understanding of the nature of the composition and thermal treatment, any help please.
Dear Yasser, if you have the unit-cell parameters (i.e. space group, lattice parameters, and the occupation of the unit cell with the different atoms of the alloy), then you may easily calculate the related diffraction pattern (i.e. peak positions and intensities). You may do that by yourself using e.g. the powder-cell software that is freely available! Good luck, Dirk
Dear Yasser,
The identification of phases by XRD for Ti alloys is a real challenge. Due to the difference in the crystal structures, the alpha (hcp) and beta (bcc) phases are easily distinguishable by XRD, but alpha and alpha 'requires auxiliary techniques, such as syncroton or neutron diffraction. The alpha" can also be easily distinguished from the others, because of its orthorhombic structure. The omega phase is generally more difficult to detect, because of their small volume fraction. Special attention should be taken primarily on the peaks around 40º, where most usually the phases have high intensity peaks.
Good Luck!
I can only agree: as first approximation use the structure data and simulate a diffraction pattern (e.g. using PowderCell). You can immediately see which peaks overlap and which peak width is still acceptable for a reliable differentiation of the phases. Sometimes structures look different from their crystallographic description but they are not because of pseudo-symmetry. In that case one has to change the lattice description (e.g. instead of hexagonal an orthorhombic description is required because the hexagonal symmetry is not exactly fullfilled), and then nearly all atomic coordinates will change as well so that the description looks different. This you can also do in PowderCell by pressing a button and selecting the wished subgroup description. Everything else is done automatically.
A microstructure consisting of alpha prime has a smaller HCP unit cell compared to the alpha phase in (alpha+beta) microstructures (where the beta phase has a large volume fraction.) Thus comparing the two in XRD; the alpha prime peaks will be slightly to the right of the alpha peaks. This is due to te difference in alloying element concentration.
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