Additive Manufacturing of SiC-SiC CMCs

SiC-SiC ceramic matrix composites (CMC) offer significantly lower density and higher resistance against high temperature oxidation than conventional materials. They are widely used in aerospace and energy production industry in shrouds, combustor liners, blades, jet tabs and vanes, blast tubes, and nozzle throats. CMC use in aircraft engines is projected to double over the next five years.It is necessary to reduce the cost of SiC-SiC CMC production and to increase durability of CMC components. There are different SiC-SiC CMC fabricating technologies, each of which has its advantages and disadvantages. Melt infiltration approach provides the greatest opportunities for commercialization/mass production, but it suffers with a drawback of residual free silicon, which invariably remains in the matrix, volatilize at high temperatures and form cracks. The excessive silicon may also react with environmental water vapor resulting in deterioration in service properties. All production methods are time and labor consuming and thus, expensive.It is proposed to use laser assisted additive manufacturing (AM) process to build layer by layer near net shape preform 3D structures as well as to implement laser assisted AM infiltration of a SiC + C preform with molten silicon. It is also proposed to almost fully eliminate free silicon in SiC-SiC CMC by bonding Sifree into compounds with high energy of formation. Silicon carbide fabric/carbon preform will be infiltrated with the alloyed silicon melt which results in dense SiC matrix targeting free silicon content of le;0.5%. The compositions of the preform and infiltrating melt will be optimized by analyzing the microstructures and phase compositions and by measuring density, flexural strength and fracture toughness of the consolidated CMC. Mechanical properties will also be measured after temperature aging tests.