Electrical and elastic properties of Cu-W graded material produced by vibro compaction

Abstract

Self-formed W graded preform was produced by size segregation of weakly vibrated tungsten bimodal granular medium. The bimodal granular media bed was initially set up with larger W agglomerates placed on the bottom and with smaller agglomerates on the top of the container. During the vibro-compaction treatment the granular bed progresses through three distinguished compaction stages: percolation, diffusion like or hopping, and non-equilibrium steady state, which exhibit different packing factor and structures. Shorter vibration time results in a skeleton type of microstructure, while a graded structure was formed when the system reaches a non-equilibrium steady state. The vibrated beds were uniaxially pressed to manufacture sintered W preform with a graded interconnected porosity. High temperature sintering treatments complete the evolution of a steeper gradient in porosity predominantly through coalescence process. Electrical and elastic properties of the final materials, produced by infiltration of Cu into the sintered W preforms, are strongly influenced by the W microstructural evolution. It has been shown that the optimal microstructure for electrical properties consists of a highly 3D interconnected Cu phase (skeleton type of microstructure), while the graded structure exhibits higher E-modulus. This work was undertaken to better understand the nature of the graded structure and to study the relationship between the self-formed microstructure types, electrical and elastic materials properties.