The role of addition of Mo and Nb on microstructure, phase and mechanical properties in tungsten heavy alloys

Abstract

This study attempts to analyse the effect of Nb and Mo addition on sinterability, microstructural features, phase evolution, and mechanical properties in a W-Ni-Fe composition-based alloy. The base alloy (90W-7Ni-3Fe) and the alloy compositions with Mo and Nb addition of (1.25, 2.5, & 3.75 wt%) independently were sintered in a reducing atmosphere at 1500 degrees C for 60 min. Nb was selected for its lower thermal conductivity and specific heat, whereas Mo was selected for its grain refinement capabilities. Microstructural analysis by SEM revealed tungsten grain refinement from 28.60 mu m for the base alloy to 18.21 mu m upon 3.75 wt% Mo addition, while Nb addition, on the contrary, leads to a slight tungsten grain growth to 32.75 mu m. The grain size increase was directly proportional to contiguity variation and inversely proportional to dihedral angle variation. Microstructure and phase analysis revealed Nb addition resulted in the formation of NbO2 along with the emergence of Nb rich - Fe lean phases (relative to matrix) with channel and stripped morphology. A maximum hardness value of 385.78 f 25.4 HV1 was found for the alloy with 3.75 wt% Nb addition, while the least hardness value of 296.65 f 9.15 HV1 was found for the base alloy. An increment in compressive strength was seen with the addition of Mo and Nb to the base alloy, further Nb addition resulted in a higher compressive strength as compared to Mo addition in the alloy. The addition of Nb, a novel aspect of this study, could serve as a foundation for its inclusion as a viable alloying element in tungsten heavy alloy.