UFG Microstructure Processing by ECAP from Double Electron-Beam Melted Rare Metal

Abstract:

High purity (99.99, wt %) niobium ingots were received by double electron beam melting technology. The specimens of pure metals with cast microstructure were processed using cold equal-channel angular pressing (ECAP) followed by a heat treatment at around 1080 °C in vacuum furnace for 2 h. Shear bands and microstructure evolution was studied in shear region at first pass and at next passes of ECAP. Microstructure processing characterization was performed using light optical and field emission scanning electron microscopy. Accompanied to microstructure the changes of mechanical properties were determined by micro- and universal hardness testing. The shear bands forming, evolution of large crystals to elongated laminar and dislocation fine-grain structures during processing was characterized and discussed in view of metal hardening-softening and viscoplastic behavior under subsequent hard cyclic straining.