Production of gas-atomized powders of [(Fe0.6Co0.4)0.75B0.2Si0.05]96Nb4 glass-forming alloy and their consolidation by hot extrusion

The present work is focused on the production of gas-atomized powders of the [(Fe0.6Co0.4)0.75B0.2Si0.05]96Nb4 (at%) glass-forming alloy and their consolidation within the supercooled liquid interval by hot extrusion. The thermal history of the powders during gas atomization was modeled using momentum and energy conservation equations. While these calculations predicted that the atomized droplets were subjected to solidification rates over 103 K/s, some crystalline phases were still experimentally observed in the atomized powders. The crystalline structure of these phases was determined using synchrotron x-ray diffraction experiments. The atomized powders with diameters between 53 and 75 µm were encapsulated in copper cans and hot extruded at 565 °C using an extrusion ratio of 3:1. The extrusion produced deformed powders, suggesting that the process was successfully conducted between the glass transition and crystallization temperatures. Minimal crystallization occurred during consolidation, as quantified by optical microscopy and differential scanning calorimetry techniques. Nanocrystals of about 10 nm, dispersed in a glassy matrix, were observed in the extruded powders. Furthermore, a discontinuous layer of α-(Fe, Co) phase was present between the extruded particles. The presence of hard micro-size crystalline particles among the powders led to a highly heterogeneous flow during extrusion. Due to stress concentration at the interface between glassy and crystalline particles, cracks sometimes nucleated and grew along the boundaries between the extruded particles. The results shown in this work give an important contribution to the understanding of the effect of crystalline particles on the processing of metallic glass matrix composites within the supercooled liquid interval.