FURTHER NOTES ON THE PRESSURE-SINTERING (HOT PRESSING) OF BERYLLIUM

Abstract

SMALL additions of activating elements to beryllium powder have been shown to improve the vacuum hot-pressing characteristics of the metal at 1100°C (1375 K). Compared with the behaviour of non-activated powder, the improvement is most clearly evidenced as an increase in density throughout the compact, and is particularly marked as the distance from the platen exceeds a length: dia. ratio of 1. Fig. l(d) of Ref. (1) contrasts the hot pressibility of a beryllium powder with and without the addition of 500 ppm silicon as an activator. It is apparent from these densification curves that in the absence of an activator the particles have been tightly compacted together only in the region close to the moving platen. As the distance from the platen becomes greater, the transmission of load via the consolidated powder particles to the lower, loosely packed, region has been impeded by particle welding at points of contact. This causes high interparticle friction, thereby enhancing densification in the uppermost parts by plastic deformation of the particles and leading to non-uniform compaction. An important consequence, therefore, of adding an activator, is to promote bulk:flow of particles and facilitate their arrangement into more closely packed positions, to give the excellent uniform densification observed in the figure. Under these easy :flowconditions, the transmission of load from the moving platen through the powder is improved, since the particles are able to slide past one another without adhering appreciably at points of contact as is usual in a sintering process. Further work has established that this lack of adhesion between particles results from the existence of the intervening oxide layer * Manuscript received 1 January 1970. Oral contribution to a Symposium on Lubrication, Friction, and Wear (Tribology) in Powder Metallurgy, held in Eastbourne on 24-26 November 1969. These notes are complementary to an earlier paper, identified by Ref. (1). t International Nickel Limited, forIl!erly at A.W.R.E., Aldermaston. t Bath University of Technology, fOrmerly at A.W.R.E., Aldermaston.