Effect of powder purification by heat-treatment on the creep behaviour of dense boron carbide monoliths

Abstract

High temperature compressive creep tests have been performed at 1650−1750 °C under applied stresses of 50−150 MPa on sintered boron carbide samples exhibiting high relative density and a mean grain size of 0.5 μm. The creep behaviour of two types of materials, sintered by spark plasma sintering from both raw and heat-treated powders, are characterized. For both materials, the identification of creep parameters (i.e. apparent activation energy and stress exponent values) coupled with TEM structural observations suggest a power law creep regime controlled by dislocation glide, which is limited by the presence of twins. However, the TP material exhibits lower stationary strain rates. This improved creep resistance seems to be directly correlated to the stoichiometry modification of the carbide induced by the powder pre-heat treatment, i.e. increase of structural carbon content and slight decrease of oxygen amount.