Papers by Keyword: Si Infiltration

Abstract: B₄C-SiC-Si ceramic composites were fabricated based on molten silicon infiltration method. The influence of preforms^' forming pressure on the microstructure and mechanical properties of B₄C-SiC-Si ceramic composites was studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron universal testing machines, etc. The results showed that the ceramic consists of B₄C, B₁₂(C,Si,B)₃, SiC and Si phases. The microstructure analysis showed that: the volume percent of free silicon decreased with the increase in forming pressures. The Vikers-hardness of B₄C-SiC-Si ceramic composites increased, while the bending strength and fracture toughness both increased initially and then decreased with the increase in forming pressures of which the optimal pressure is 200 MPa. The optimum bending strength, fracture toughness and Vikers-hardness of the obtained B₄C-SiC-Si ceramic composites are 319±13 MPa, 4.9±0.1 MPa·m^1/2 and 24±1 GPa, respectively. The volume density and open porosity of the obtained B₄C-SiC-Si ceramic composites are 2.58 g/cm³ and 0.19 %, respectively.

Abstract: Polycrystalline SiC-diamond composites have been fabricated by high pressure and high temperature, HPHT, sintering conditions using a Si infiltration method. However, infiltration of liquid Si around the diamond particles results not only in SiC but also in free Si, which causes deterioration of the composite properties. In this work, a novel sintering procedure was developed to avoid the formation of free Si in the composite structure. A disk composed of a mixture of graphite and Si was first press-molded at room temperature. The disk was then placed above the diamond powder inside a high pressure chamber used for the HPHT sintering process. This arrangement permitted to preferentially form liquid SiC, which infiltrates in between the diamond particles. Using this procedure, free Si formation is inhibited and the SiC-diamond composite forms a rigid structure with improved properties.