Enhanced plasticity in laser additive manufactured Nb-reinforced bulk metallic glass composite

Abstract

The microstructures and mechanical properties of 50 wt% Nb-reinforced Zr-based bulk metallic glass composites, (BMGCs), manufactured via laser directed energy deposition (LDED) with two different laser powers, P , are investigated and compared with those of LDED manufactured monolithic bulk metallic glass (BMG). Results show that both BMGCs have a multi-component microstructure that includes dual-sized Nb particles and devitrification-induced nano crystals at the melt-pool boundaries whereas the monolithic BMG contains only the latter. The nanocrystals at the melt-pool boundaries embrittle the LDED manufactured monolithic BMG, which reflects as a higher yield strength but negligible plastic deformation in uniaxial compression. In contrast, both BMGCs undergo significant plastic deformation as the Nb-reinforcements, besides improving plasticity by arresting propagating shear bands, reduces the enthalpy of relaxation, Δ H rel , of the matrix and decreases the volume fraction of the nanocrystallites, V nc , at the melt-pool boundaries. However, amongst the two, the BMGC manufactured at higher P exhibits much higher shear band plasticity, despite having higher V nc and lower Δ H rel . This is rationalized by analyzing the load transfer characteristics of the Nb-BMG matrix interfaces in the two BMGCs. • LDED manufactured Nb-reinforced Zr-based BMGCs have significantly improved plasticity. • Nb induced plasticity improvement is achieved through limiting the structural relaxation of amorphous matrix. • Higher thermal diffusivity of Nb can minimize the devitrification induced brittle phases and thus enhance plasticity. • Partially dissolving Nb in the amorphous matrix by sufficient laser power can maximize shear band arresting capabilities.