Synthesis of tailored 2D SiCf/SiC ceramic matrix composites with BN/C interphase through ICVI

Synthesis of 2D SiCf /SiC composites for applications in fusion reactors is a challenging task due to the stringent specification requirements on various mechanical and thermo-mechanical properties, chemical compatibility (with Pb–Li), oxidation resistance and irradiation resistance. Three types of SiCf/SiC composites with C interface and BN interface, with and without intermediate heat treatment are prepared through isothermal and isobaric chemical vapor infiltration process. Dense SiC seal coat applied to the composites has improved their oxidation resistance. The tensile, flexural and fracture toughness values of composite with BN interface were found to be improved by stabilizing the BN interface through thermal treatment. The electrical and thermal conductivity values obtained for composites with C interface are in the range of 10–29 S/m and 2.5–3.25 W/mK for the temperature range 500–900 �C as required for fusion reactor applications

Effect of Si on morphology of alumina scales

Hot dip aluminised coatings with pure Al, Al-3Si and Al-7Si melts had been produced on 9Cr-1Mo steels and subsequently heat treated at 900 degrees C for 5 h under oxidising conditions to generate alumina films over Fe-Al diffused case. The characterisation of these samples by X-ray diffraction and SEM-EDX techniques indicated reduction in the post-heat treated aluminide case depth with increasing Si concentration. Further, it was observed that after oxidation heat treatment, pure Al coated samples indicated gamma-Al2O3 and theta-Al2O3, while Al-7Si coated samples revealed transformation of metastable theta-Al2O3 phase to stable alpha-Al2O3 phase. The present paper describes change in morphology of oxide after thermal oxidation from gamma to theta and theta to alpha as a function of the Si content of Al melt in hot dip aluminised 9Cr-1Mo steels. The effect of Si on the diffused aluminide case depth is also discussed

STUDY OF ALUMINUM-OXIDE FILMS FORMED BY PLASMA ANODIZATION

Anodic oxidation plays an important role in microelectronics as well as in thin film devices. Oxide films obtained on metals such as aluminium and tantalum by anodization using a gaseous electrolyte are found to be superior to those formed by using aqueous solution. Earlier researchers have shown that anodization can be carried out more efficiently at an optimum pressure of 6.7 Pa (50 mTorr) and an optimum bias voltage of 5V. It is also reported that the optimum pressure depends on the system geometry. This work was carried out to determine the effect of cylindrical geometry. It is observed that the optimum pressure for the cylindrical geometry is 26.8 Pa (200 mTorr) while the optimum bias voltage is found to be 5V. Formation of Al2O3 is confirmed by using electron spectroscopy for chemical analysis. Small-angle X-ray diffraction results indicate the formation of the gamma-Al2O3 phase at low bias voltages whereas the beta-Al2O3 phase is more dominant at higher bias voltages

GLANCING-ANGLE X-RAY-DIFFRACTION AND X-RAY PHOTOELECTRON-SPECTROSCOPY STUDIES OF NITROGEN-IMPLANTED TANTALUM

Polycrystalline tantalum thin foils are implanted with molecular nitrogen ions.X-ray photoelectron spectroscopy results show preferential nitrogen loss during implantation and argon sputtering