The influence of silicon and other elements in controlling interparticle friction and sintering of beryllium powder

The effect of small additions of activating elements such as silicon on the consolidation behaviour of beryllium powder has been investigated. Evidence is given that compacts of activated powder have more uniform high density than those produced from non-activated material. Studies carried out on prepared beryllium discs show that silicon modifies the micro-structure of the surface layer of beryllium oxide and, in consequence, affects its sliding behaviour and bonding characteristics. From these results a model is proposed to account for the observations made on both sintered and hot-pressed beryllium which leads to the conclusion that, in addition to interparticle bonding, some measure of metal particle rearrangement is necessary for maximum densification. Activating elements may, in modifying the surface characteristics of the individual powder particles, assist in achieving an improved balance between particle sliding on the one hand and interparticle bonding on the other. In taking into account the bulk consolidation characteristics as well as the micromechanics of the process, the model also explains the observed influence of particle-size distribution on porosity in the compact. The extent to which friction and sliding can influence compaction has been demonstrated by using a system of coloured Plasticine balls to simulate individual powder particles. Analysis of the behaviour of the Plasticine compacts substantiates the proposed model of the hot pressing of beryllium powder.