Si/SiC-Based Layer Deposited on Boron Carbide Particles via CVD

Abstract

The application of B4C as structural materials has been restricted largely because of its poor sinter-ability. Compared with pressure-less and hot pressing methods, sintering the B4C via the reaction-bonded boron carbide (RBBC) can to great extent circumvent such problem, which can even be conducted at low temperature, when Si/Si-based alloy was used as binding phase. However molten Si/Si-based alloy infiltrated into performs of bare B4C powders can strongly react with and significantly consume B4C particles based on molten infiltration reaction method. The present study aims to encapsulate B4C particles with a protective layer to block off its contact with molten Si/ Si-based alloy via chemical vapor deposition (CVD) method in CH3SiCl3(MTS)-H2-Ar system at low temperature (900-1100 °C) under atmospheric pressure. The phase composition and surface morphology of encapsulated B4C particles were studied using X-ray diffraction (XRD) , scanning electron microscopy (SEM) plus energy dispersive spectrometer (EDS), respectively. It was found that the deposition temperatures have a significant effect on microstructure and composition of deposited coating. The studies on surface morphology revealed that spine-like crystals, nodular growth, island structure and whiskers can be deposited onto the surface of boron carbide particles. When deposited at 900-1000 °C,the coatings is Si + SiC co-deposition, while pure SiC coatings form only at as high deposition temperature at 1050 °Cand 1100 °C.