Let's say Ni-20 Cu and Ni-30Cu. How the peak of each alloy varies in XRD. Can I be able to simulate the peaks or is there any package/software available for it?
using Vegard's law is the way to resolve this issue.
In the base PDF4 + 2016 from the ICDD, I have been able to find the case Cu0.25Ni0.75 04-004-4502, the cases that you are looking for, you can obtain them by means of the Vegard's law from the pure cases (Cu 04-004-0386, Ni 04-004-0850), representing the combination of phases in % of the position of the peaks of the pure phases for example with Excel or Origin.
Vegards rule is a rule and no law. There are several mixtures which do not match to a simple linear interpolation between two constituents. One famous example is Au-Ag. In case of Cu and Ni it seems to be not critical.... see the attached link, however I have to admit that if you take the shown diagram and add the lattice parameter of Ni = 3.524A, the derived slope in the diagram will finally end in a lattice parameter for Ni which is considerably smaller than the correct one. Therefore, it might be that there is also a small deviation from vegards rule. I would suggest to look for some experimental data. Look e.g. the attached pdf.
or the last reference.
Article Pulsed electrodeposition of nanocrystalline Cu–Ni alloy film...
Article Cu–Ni materials prepared by mechanical milling: Their proper...
The TOPAS or LEPTOS (BRUKER) software packages are useful for the simulation of such kind of coatings or alloy formation. TOPAS & LEPTOS are the curve fitting softwares of Bruker which considers all the instrument parameters as well as the provided crystal structure parameters in . str format for the curve fitting. After the curve fitting it will directly give you the percentage of the specific phase in the given powder sample. Topas is mainly used for powder samples & LEPTOS is used for the Thin films. In Leptos thickness of multilayered thin films, stress generation in it and surface morphology of the sample can be studied. I have used TOPAS mainly so I don't have that much idea about the Leptos, please google Bruker's webinar presentations related to Leptos & Topas for more info.
For simulating the patterns corresponding to the question, DIFFRAC.EVA must be enough, is posible to do with DIFFRAC.TOPAS also, both from Bruker. There are others software available, for example Expert HighScore from Panalytical, Rigaku software,Match!...