Ball milling and annealing of Co-50 at% W Powders

Abstract

Broadening and height reduction of X-ray diffraction peaks were observed after cold-pressing of unmilled Co-W pow- der mixture. It seems the effect of cold pressing has slightly reduced the lattice parameter of W from 3.165 to 3.143 Å. Consequent annealing of unmilled compacts yielded metastable phases. Upon 10 and 20 h ball milling of Co-W powder, no alloying was obtained. Although milling did not yield significant crystal changes in W and Co ground state struc- tures, its effect is evident during subsequent annealing. An eta phase is obtained for the first time from unmilled-an- nealed Co-W powder mixture in the absence of interstitial elements like carbon, while the milled counterpart yielded the rhombohedral Co(sub7)W(sub6-)type phase with composition deviated from stoichiometric value.