Effect of Mechanical Milling and Cold Pressing on Co Powder

[摘要] Cold pressing (CP) of the amorphous-like Co powder suppressed most of the XRD peaks, in particular the peak along (100) plane. The DSC curve of unmilled CP Co powder has shown a distinct sharp exothermic peak at615C°. Upon annealing at700C°, only the FCC phase with lattice parameter of 3.51 Å was detected by XRD. Our results implied that the exotherm at615C°corresponds to compaction-pressure-assisted HCP to FCC first-order phase transition. The XRD analysis of 30 h milled powder revealed for the first time the FCC phase witha=3.80 Å. However, due to presence of (100) and (210) peaks, this phase is thought to be FCT with lattice parametersa=b=3.80andc=3.07 Å. Consequently, the high-energy milling carried out in the current work induced for the first time HCP to FCT transition in Co. Upon CP of milled powder, the lattice parameterashrunk from 3.80 to 3.75 Å. However, during annealing of the CP milled Co powder at750C°, the FCT to FCC transition occurred, yielding the FCC phase witha=3.51 Å.

[学科分类] 工业化学