Occurrence and Distribution of Boron‐Conitaining Phases in Sintered ş‐Silicon Carbide

Abstract

A variety of optical and analytical instruments have been employed to observe and characterize the microstructure and composition of the B-containing phases which occur in sintered a-Sic as a result of either their use as a densification aid or that which evolves as a result of annealing well below the sintering temperatures. The former have been identified as B,C containing a small amount of Si. The latter occur as =20-nm precipitates which have also been tentatively identified as B,C and are believed to contain trace quantities of Si. No B phase was observed on the BC grain boundaries; furthermore, the precipitate formation was not enhanced by the application of stress.

Elevated Temperature Strength Enhancement of ZrB2–30 vol% SiC Ceramics by Postsintering Thermal Annealing

“…Further, Rudy and Windisch predicted a B exchange reaction between the transition‐metal diborides and monocarbides with associated crystallographic volume change . The solubility of B in SiC (and of Si in B 4 C) has been well‐established, and though not specifically investigated, it is conceivable that there exists a limited solubility of B in SiC for the ZrB 2 –SiC system. This solubility is another possible source of change in stress state of the grain‐boundary interfaces during heat treatment, due to changes in lattice parameter associated with solid solution formation.…”

Defects created in N-doped 4H-SiC in the brittle regime: Stacking fault multiplicity and dislocation cores

“…In one model, the Philosophical Magazine 1263 4H!3C phase transformation provides the energy of formation and glide of PDs, hence expanding the corresponding trailed cubic layer. We suggested this thermodynamic force as a possible extra driving force in our experiments [12,27] because it is known that N-doping stabilises the 3C structure [28][29][30], particularly in the temperature range being considered. However, if N-doping stabilises the 3C structure, one would expect a negative sf in N-doped 4H-SiC and thus the formation of large cubic layers of various thicknesses, as long as nucleation sites for PDs are available.…”

Structural characterization of double stacking faults induced by cantilever bending in nitrogen-doped 4H-SiC

“…They have found that E f2 ¼ 4.7 mJ m À2 , which is significantly lower than E f1 ¼ 17.7 mJ m À2 . A negative SF energy E f2 is even likely because it is well known that the 3C structure is more stable than the 4H structure in that temperature range, particularly for nitrogen-doped SiC [36][37][38]. Therefore, when a partial dislocation is created to release the applied stress, the formation of a second partial dislocation in the adjacent plane suitable for creating a DSF is favoured.…”