Metastable phases in the Co-W system traced from elemental Co and W powders

► Structural similarities in metastable phases of Co and W has been revealed. ► The η-phase with 11.037 Å was depicted in annealed W and Co-W mixture. ► FCC phases of milled and annealed Co powder with 3.506 Å and 4.162 Å were obtained. ► FCC phases of milled and quenched W with 3.510 Å and 4.177 Å were obtained. ► HCP phase a = 2.73 Å; c = 4.32 Å was depicted after annealing W powder at 1000 °C.