KINETICS OF NONISOTHERMAL PRESSURE SINTERING OF ZIRCONIUM DIBORIDE POWDER WITH ADDITIVES OF BORON AND CHROMIUM CARBIDES IN VACUUM

Abstract

The analysis of the experimental data on the kinetics of nonisothermal pressure sintering of zirconium diboride-based powder mixtures with the addition of boron and chromium carbides in vacuum showed a separation of the sintering temperature mode into low-temperature and high-temperature zones. The separation is clearly observed when the temperature increases at a rate of 20 °C/min. In the low-temperature zone, the densification occurs slowly and hardly depends on the temperature. In the high-temperature zone, the viscous flow of the matrix of the porous material is controlled by the secondary creep of the matrix forming the porous body with an activation energy of 394 kJ/mol. A twofold increase in the heating rate leads to acceleration of low- and high-temperature strain of the matrix and increase in the apparent activation energy to 581 kJ/mol, indicating the cascade connection of additional mechanisms of material flow. The investigation of the structure and properties of materials showed that the formation of new boron–carbide phases and eutectic that disappears during sintering activates the densification of the porous material. It is found out that under low pressure nonisothermal sintering, a superplasticity phenomenon can occur, which results in the densification of the porous body to a virtually non-porous state.