Mechanical alloying of the elemental powder mixture of copper and yttrium is performed in a high-energy planetary ball mill. The equiatomic YCu compound with full ordered CsCl-type structure is synthesized by use of powder-metallurgy methods for the first time. Phase transformations taking place at Y–Cu mixture milling are studied by x-ray diffraction methods. An expanded description of original software package for the automated DRON apparatus is presented. This software is used for analysis and interpretation of the obtained x-ray diffraction data. This package is intended for solving different tasks, namely: determination of both peak positions and integral intensities of the Bragg reflections by means of full profile analysis; carrying out the qualitative and quantitative phase analyses using PDF (Powder Diffraction File) data for phase identification and the least square method for lattice-constants’ refinement; testing the structure models and refining crystal-structure parameters (including coordinates, atomic position filling, texture, etc.). The effect of oxygen on the phase composition of milling products is analysed. As revealed, the mixture of two oxides (Y$_{2}$O$_{3}$ and YCuO) is forming at the last stage of the milling in the air. So, the phase transformation during milling of the equiatomic Y–Cu charge in the air follows the reaction Y + Cu $\rightarrow$ YCu + YCu$_{2}$ $\rightarrow$ YCu$_{2}$ + O$_{2}$ $\rightarrow$ Y$_{2}$O$_{3}$ + YCuO + YCu$_{5}$. Only the first stage of this transformation is realized in the case of synthesis under argon atmosphere.