Pressure-assisted sintering of Al-Gd-Ni-Co amorphous alloy powders

The influence of pressure (0-764 MPa), on the densification and crystallization behavior of Al84Ni 7Gd6Co3 glassy powders during sintering has been studied by hot pressing the amorphous alloy powders within the supercooled liquid region. The applied pressure significantly influenced the densification process: decreased the porosity level, changed the area of the inter-particle region and varied the volume fraction of alpha-Al in the inter-particle regions. The main densification mechanisms operating were particle (re)arrangement, plastic flow, viscous flow, and Al diffusion from the amorphous matrix to the inter-particle region at the surface. Furthermore, pressure affected the thermal stability of the amorphous powders during consolidation, influenced the amount of crystalline phases in the amorphous matrix, and the subsequent crystallization of the retained glassy phase. With increasing pressure, the primary crystallization of alpha-Al was hindered whereas crystallization of the intermetallic phases was promoted. This indicated that amorphous powders sintered at lower pressures allowed one to obtain higher volume fraction of alpha-Al and suppress the formation of brittle intermetallic phases. This study provides new and deep insights into pressure-assisted sintering of amorphous alloy powders and allows an innovative way of designing novel and advanced alloys with superior properties.