Investigation of Phase Stability in the System Sic-AlN

Abstract

Dense samples of several compositions in the system Sic-AIN were fabricated by hot-pressing. The SIC-AIN powder was prepared by carbothermal reduction of an intimate mixture of alumina, silica, and carbon in a nitrogen atmosphere. X-ray diffraction and electron and optical microscopy were used to determine the chemical and microstructural characteristics of the hot-pressed specimens. Materials with bulk compositions between 15 and 75 wt% AIN were found to be nonhomogeneous when hot-pressed below 2100°C. These materials were determined to be a mixture of Sic-AIN solid solutions with different compositions. The observed compositional variations were distinctly bimodal. The source of the inhomogeneity was the starting Sic-AIN powder. The powders, as well as the hot-pressed samples, consisted of a mixture of small crystals rich in S i c and large AIN-rich crystals. Compositions outside the 15 to 75 wt% AIN region were found to be single phase and to have the wurtzite structure. Hot-pressing SIC-AIN in the intermediate composition range at 230OOC produced an optically and chemically homogeneous material. The precipitation of an Sic-rich phase from a 75 wt% AIN solid solution and the precipitation of an AIN-rich phase from a 47 wt% AIN alloy when annealed at 1700°C are strong indications that a miscibility gas exists in the system Sic-AIN.

Evaluation on microstructure and dissolution behavior of SiC-AlN composites fabricated by SPS process

“…Taking into account the similarity of α-SiC and AlN in the crystallographic structure (2H phase), a β to α transformation of SiC phase occurred, 5) and then, mutual dissolution occurred between α-SiC and AlN phases. 15) Subsequently, the densifications of the composites proceeded with grain-growth of 2Hss.…”

“…Therefore, if homogeneous SiC-AlN solid solutions can be obtained, the composites are expected as superior high-temperature semiconducting materials, for example, variable wide band-gap semiconductors. 4) Rafaniello et al 5) fabricated optically and chemically homogeneous SiC-AlN solid solutions using hot-pressing at 2300°C. Kobayashi et al 6) fabricated porous SiC-AlN solid solutions by pressureless sintering at 2000°C.…”

First principles phase diagram calculations for the wurtzite-structure quasibinary systems SiC-AlN, SiC-GaN and SiC-InN

“…10,11 In spite of an apparently strong tendency for immiscibility it is possible to synthesize wurtzite-structure solid solutions (SiC) 1ÀX (AlN) X as thin films or single crystals of arbitrary bulk composition, X (Refs. 1, 2 and 9).…”

Thermal decomposition, densification and mechanical properties of AlN–SiC(–TiB2) systems with and without B, B4C and C additives

“…23 In the present study, weight loss due to the decomposition of AlN was strongly enhanced at 2200 • C in Ar (2-3% at 2000 • C, 3.5-4.5% at 2100 • C and 8.3-9.2% at 2200 • C). 24 Consequently, the sintering temperatures applied in the following experiments were set at and below 2100 • C.…”

“…23 The Young's modulus, fracture toughness and hardness of near-stoichiometric AlN-SiC solid solution (AlN content: 65.4-74 wt%) 23,33 was reported to be 307 34 -352 GPa, 33 3.3 23 -5.7 MPa m 1/2 , 35 and 17-21 GPa, 23,36 respectively.…”