Liquid Silicon Infiltration for SiC and CMC Part Manufacturing - White Paper

Silicon carbide (SiC) is a versatile material, suitable for high temperature applications. In powder form, it is used in abrasive powders, grinding wheels, and cutting tools due to its exceptional hardness, high thermal conductivity, and thermal stability; when sintered, it is used in applications such as heat exchangers, furnace linings, and electrical components, leveraging its chemical resistance and ability to withstand extreme temperatures. Furthermore, SiC can be used in ceramic matrix composites (CMCs), especially in aerospace and energy sectors, where it enhances mechanical strength and thermal resistance in structural components.

Traditionally, SiC is fabricated through standard ceramic processes such as pressing, followed by pressureless sintering or hot pressing. This manufacturing route means that producing complex shapes can be challenging. Pressureless sintering also requires relatively high temperatures of above 2000°C (3632°F) for solid state sintering, and hot pressing can only be performed using specialized equipment.

Liquid silicon infiltration (LSI) offers a practical and advantageous route for fabricating complex SiC parts, in which a porous carbon preform is shaped to the desired geometry and then infiltrated with molten silicon. The silicon reacts with carbon to form SiC, producing near net-shape, mechanically strong parts with intricate geometries and reduced machining needs.

Usually a mix of SiC-C is used as the preform for infiltration, producing a material referred to as reaction bonded SiC (RBSC). As a result, the final material will usually contain primary α-SiC grains bonded with the reaction-formed β-SiC. 

In this white paper, we will focus on the LSI process for both bulk SiC and composite materials, the various methods of fabrication preform for bulk SiC components, and the influence of several processing parameters on the LSI process.