Enhancing the Mechanical Properties of a Zr-Based Bulk Metallic Glass via Laser Powder Bed Fusion Process Control

Laser powder bed fusion (LPBF) enables the fabrication of large-dimensioned bulk metallic glass (BMG) components; however, we are only just learning how to control the LPBF process to obtain specific mechanical properties. LPBF was used to produce dense and fully amorphous Zr_59.3Cu_28.8Nb_1.5Al_10.4 BMG samples from two different starting powders. One powder had a relatively finer particle size range of 10-45 μm and the other had a relatively coarser particle size range of 25-63 μm. Fully amorphous samples were achieved for both powders within a large processing window of laser power and scanning speed combinations. When the LPBF volumetric energy density was raised above ~30-33 J/mm³, high relative density (> 99%) was maintained along with devitrification and embrittlement. Low LPBF energy densities below ~20 J/mm³ produced low relative density (< 99%) and fully amorphous samples. Strength and hardness generally increased with increasing LPBF energy density while the relaxation enthalpy, ductility, and fracture toughness decreased. Furthermore, the coarser powder had four times lower oxygen content and gave better glass forming ability, compression ductility up to 6% plastic strain, and fracture toughness up to ~38 MPa√m. These findings demonstrate that it is possible to tailor the structure and mechanical properties of BMGs by tuning the LPBF process parameters within a wide processing window and by controlling the feedstock powder oxygen content.