The influence of Mo and Nb on liquid phase sintering and mechanical properties of W-Ni-Fe-Co based tungsten heavy alloy

Abstract

Efforts to enhance the self-sharpening properties of tungsten heavy alloy based kinetic energy penetrators have led to innovations in its compositions and processing techniques. Mo and Nb are the two potential alloying elements for tungsten heavy alloys (WHA) due to their grain refinement capabilities and lower thermal properties respectively. Accordingly, this research investigates the influence of Mo and Nb addition to a WHA of composition 90 W- (6,2,2)(Ni:Fe:Co) in concentrations of 1.25, 2.5 and 3.75 wt%. The alloys were sintered at 1500 degrees C in a reducing hydrogen atmosphere for 60 min. The results demonstrated tungsten grain refinement with Mo addition, whereas Nb addition resulted in a slight grain growth. Ni-Nb binary eutectic reactions at 1175 degrees C lead to an early liquid phase formation expanding the time regime for tungsten grain growth. Additionally, Nb addition caused NbO2 formation and Nb-rich Fe-lean strips and channels to form in the matrix. Increase in contiguity and dihedral angle was observed with increase in Mo and Nb concentration due to higher undissolved tungsten in the alloy. Mo addition resulted in enhanced compressive strength due to refined tungsten grain size, matrix solid solution strengthening and increased tungsten contiguity. Whereas Nb addition resulted in poor compressive strength at lower Nb concentrations due to pore formation, however the compressive strength was found to increase at higher Nb concentration due to solution strengthening, increase in contiguity and minimized porosity.