Processing of Hf based bulk metallic glass through Spark Plasma Sintering (SPS) process

Abstract

The present work describes fabrication of cylindrical cross section bulk specimens of Hf-based bulk metallic glass by spark plasma sintering. Initially amorphous ribbons were made by vacuum melt spinning and different milling techniques such as planetary ball milling, high energy ball milling and cryo-milling were employed for converting ribbons into powders. Planetary ball milling of as spun ribbons did not yield powder. While powders (particle size<500 µm) were successfully obtained following high energy ball milling, partial crystallization of powder particles was also observed. Cryo-milling in select conditions fulfilled both the objectives as it successfully converted ribbons into powder retaining the amorphous phase. Powder produced by cryo-milling was divided into two broad size range (>75 µm and<25 µm) which were used to study the effect of particle size and its distribution on the consolidation behavior of the amorphous powder. The relative densification of spark plasma sintered pellets prepared using powder particles (>75 µm and<25 µm) is around 96–98%, whereas densification as high as 99.8% has been achieved with a blend of>75 µm and<25 µm powders. Complete amorphous phase is formed only when the compaction experiment is performed at 460 °C and 480 °C at 800 MPa. Sintering at higher temperature has resulted in presence of nano crystallites. Hardness values of the compacts containing amorphous phase are relatively lower as compared to those containing the crystallite phase. Present study has demonstrated the potential of spark plasma sintering in consolidation of amorphous powders to near full density cylindrical pellets.