The structures of Co–W alloys in the region of solid solutions (0–13.06 at.% W) and intermetallic compound Co$_3$W are studied by the methods of X-ray diffraction analysis using Fe$K_\alpha$-radiation. As found, the initial structure of the cast alloy consists of 1/3 of a solid solution of $\beta$-Co with f.c.c. lattice and 2/3 of $\alpha$-Co with hexagonal close-packed crystal lattice. Annealing of the alloy leads to the decomposition of the solid solution with the precipitation of intermetallic Co$_3$W, and the redistribution of the amount of solid solutions in favour of $\alpha$-Co. Electrospark doping of the surface with a tungsten electrode leads to an increase the tungsten in the solid solution and as a consequence to increase the intensity of the cellular reaction.