Advances in pressureless densification of boron carbide

Abstract

The coarsening processes which occur concurrently with the sintering of B₄C were deduced using differential dilatometry, weight loss and grain size measurements. B₂O₃ coatings on B₄C particles stalled the onset of densification until these coatings decomposed away at 1840°C. Oxide gaseous species formed in this process were postulated to be one conduit of particle coarsening. At higher temperatures, the volatilization of B₄C itself were interpreted to be the second vapor phase coarsening mechanism, starting at temperatures above 2000°C. Carbon additions or soaking the compact in a hydrogen-containing atmosphere at 1350°C removed the oxide coatings at temperatures below those in which sintering or coarsening occurred. Accelerating densification above 2130°C was attributed to nonstoichiometric volatilization, leaving carbon behind to facilitate activated sintering.