Development of Near-Net Shape Casting Technology for MGC Components

Abstract

Much attention has been paid to unidirectionally solidified ceramic composites as a candidate for a high-temperature structural material. Eutectic composites, known as Melt Growth Composites (MGCs), have recently been developed. The MGCs (Al2O3/YAG, Al2O3/GAP binary and Al2O3/YAG/ZrO2 ternary systems) have a novel microstructure consisting of three-dimensionally continuous and complexly entangled single-crystal Al2O3 and single-crystal oxide compounds (YAG or GAP or YAG and ZrO2). Therefore, the MGCs have excellent high-temperature strength characteristics, creep resistance, superior oxidation resistance and thermal stability in an air atmosphere at very high temperatures. Manufacturing processes for the MGCs (Al2O3/YAG and Al2O3/GAP binary systems) are being examined under a Japanese national project, scheduled from 2001–2005. The molybdenum mold for near-net-shaped casting of the gas turbine component was fabricated by plasma spraying the molybdenum powders on the copper model. Near-net-shape casting of MGCs is being examined under the NEDO project using the plasma sprayed mold and a new Bridgman-type furnace.