W-Cu graded alloys produced by size segregation of agglomerates induced by vertical vibration at high frequencies

摘要

In this paper we introduce the particle size segregation of powders induced by vertical vibration as a new method of forming graded microstructures, which is based on the physics of a vibrated granular medium (GM) under gravity [1-5]. We applied this method to a GM formed by W and Cu agglomerates to produce W-Cu composites with graded microstructures in the range of millimeters. Tungsten and copper powders were agglomerated using a poly-vinyl-butyral polymer (PVB). Copper agglomerates with sizes from 40 to 45 μm and tungsten agglomerates greater than 250 μm were placed respectively in the higher and lower gravitational positions of a container. Under gravity and vertical vibration, the larger agglomerates move up and the smaller agglomerates move down. The gradient in agglomerate size is self formed in a geometrical segregation regime aided by convection at the surface of the GM [6,7]. Afterwards this graded GM is pressed into a green body and pre-sintered at 1070 ℃ in a dynamic nitrogen atmosphere.