Applying the Brazil-nut approach to manufacture W-Cu-graded materials

• DOI: 10.1007/s10035-004-0176-8
• Publication Date: 2019-12-12T03:45:33Z
• Authors: Jorge Fiscina; Dragana Jankovic ...; Frank Mücklich
• Keywords: 0103 physical sciences; 01 natural sciences

W-Cu graded packings were produced under gravity and vertical vibration, from a granular medium (GM) formed by tungsten and copper agglomerates with agglomerate size distributions, which do not overlap. These bimodal packings were processed by powder metallurgy techniques to manufacture W-Cu graded pseudo-alloys with a variety of textures of the order of one millimeter. We present and discuss the temporal evolution of the W-Cu GM bed through photographs of two case- studies with frequencies of 600 and 900 Hz. Pre-sintered W-Cu-graded materials corresponding to vibration treatments of different duration are characterised by a SEM, and the tungsten concentration profiles are estimated by area analysis. Using a LASER dilatometer, we measured the temporal registers for the height of the GM bed for a wide range of frequencies and accelerations. Depending on the excitation level of the vibrated GM bed, three types of segregation regime were identified, as follows: segregation due to convection rolls, geometrical segregation aided by surface convection, and geometrical segregation. Only at low enough excitation, through geometrical segregation, does the GM bed reach a graded packing. This occurs due to the diffusive nature of this process, where the smaller agglomerates change their configurations through hopping in a potential energy gradient.