Approach of the spark plasma sintering mechanism in Zr57Cu20Al10Ni8Ti5 metallic glass

Research highlights: → SPS allows manufacturing bulk parts from metallic glass powders. → Regarding the sintering conditions, SPSed samples exhibit mechanical properties similar to the quenched BMG. → Sintering of MG by SPS is likely divided into two steps: first, over-heating at particles necks leads to partial devitrification and consolidation; second, viscous flow of the metallic glass is reached and total densification is fulfilled. - Abstract: Spark plasma sintering (SPS) was used to sinter gas-atomized Zr57Cu20Al10Ni8Ti5 amorphous powder. Systematic analyses were performed to study particle size and annealing time effects on the parts structure and properties. Partial devitrification and particles welding were observed and correlated to particle size and thermal conditions. Mechanical testing, through compression and micro-hardness, reveals that the sintered parts show strength similar to a quenched bulk metallic glass and damaging before failure. However, the pulsed current input does not seem the most relevant way to sinter amorphous powders: during the sintering initial stages (when necks are small), excessive over-heating is generated in the vicinity of particles necks, and is responsible for partial devitrification; further current input at large necks leads to complete densification. Effects of the stress, the thermo- and electro-transports on the sintering are evaluated to provide a better understanding of the SPS mechanisms of densification of metallic glasses.