Microstructure and Mechanical Properties of Electron Beam Melted Nb-W and Nb-W-Zr Alloys

The present work deals with microstructure evolution and room temperature mechanical properties of electron beam melted Nb-10 wt.% W (Nb-W) and Nb-10 wt.% W-2.5 wt.% Zr (Nb-W-Zr) alloys. The consumable electrodes were prepared through mechanical mixing, cold isostatic pressing and vacuum sintering using the raw materials in the form of powders. These electrodes were used for the preparation of ingots through electron beam melting. The ingots were forged at 1250 degrees C; subsequently, they were subjected to warm rolling at 1000 degrees C and cold rolling at 25 degrees C with an intermediate annealing. The alloys were characterised by optical microscope, scanning electron microscopy, electron backscattered diffraction and room temperature tensile test. The results show that both alloys exhibit a single-phase microstructure. The Nb-W-Zr alloy displays a higher tensile strength as compared to the Nb-W alloy. The Nb-W alloy under warm rolled and annealed condition shows a sharp yield point during tensile test, while such a sharp yield point is not observed for Nb-W-Zr alloy. The fracture surfaces of tensile tested samples reveal that Nb-W alloy shows a completely transgranular cleavage fracture. A mixed mode of fracture consisting of both dimple and cleavage is observed for Nb-W-Zr alloy.