Densification kinetics of higher molybdenum and tungsten borides in hot pressing

Final‐stage densification kinetics of direct current–sintered ZrB2

“…The 1900°C diffusion coefficient is similar to the value of 2.4 × 10 −6 cm 2 /s calculated by Kalish for final‐stage sintering of HfB 2 32 . The dislocation diffusion coefficients are also consistent with self‐diffusion in Zr, which validates Koval'chenko's conclusion that dislocation movement is limited by the self‐diffusion of the metallic species in the metallic sublattice 28,46 . Taken together, the values of the diffusion coefficients and activation energies are consistent with the final stage of densification of ZrB 2 being controlled by stress‐assisted dislocation motion.…”

“…Final grain sizes were used as it was assumed that no significant grain growth 32 The dislo-cation diffusion coefficients are also consistent with selfdiffusion in Zr, which validates Koval'chenko's conclusion that dislocation movement is limited by the self-diffusion of the metallic species in the metallic sublattice. 28,46 Taken together, the values of the diffusion coefficients and activation energies are consistent with the final stage of densification of ZrB 2 being controlled by stress-assisted dislocation motion. Future studies utilizing analysis transmission electron microscopy could confirm this mechanism.…”

“…5 Since then, several studies have reported dislocation motion in the borides. [24][25][26][27][28][29] Koval'chenko studied densification kinetics of molybdenum and tungsten borides and reported that activation energies were independent of pressure, which is indicative of the dislocation glide process. Koval'chenko concluded that dislocation movement was limited by the self-diffusion of the metallic species in the metallic sublattice.…”

“…Kalish ultimately concluded that interstitial diffusion of B or grain boundary diffusion of Hf was the predominant mechanism in the final stage of densification of HfB 2 5 . Since then, several studies have reported dislocation motion in the borides 24–29 . Koval'chenko studied densification kinetics of molybdenum and tungsten borides and reported that activation energies were independent of pressure, which is indicative of the dislocation glide process.…”

“…Koval'chenko studied densification kinetics of molybdenum and tungsten borides and reported that activation energies were independent of pressure, which is indicative of the dislocation glide process. Koval'chenko concluded that dislocation movement was limited by the self‐diffusion of the metallic species in the metallic sublattice 28 . Bhakhri estimated an activation energy for dislocation movement in ZrB 2 of 154 ± 96 kJ/mol using indentation experiments and assuming the Burger vector to be along the 〈1 0 0 0〉 direction 24 …”