Alloy Design of Ultra High-Tempreature and Ultra Environmental Resisitance insitu Cr_2X-Based Intermetallic Compound Composites

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To develop Cr_2X (X : Nb, Zr, Hf, Ta and Ti)-based Intermetallic compound composites that have low-temperature fracture toughness and ultra high-temperature strength, and also are highly resistive to environment, the studies were performed. The following results were obtained.1) Cr-Nb-W and Cr-Nb-Ti ternary alloy phase diagrams were constructed. The phase fields of Cr_2Nb Laves phase were determined. Also, it was determined that V substitutes for Cr sites while Mo, W and Ti substitute for Nb sites.2) Microstructure and phase diagram of Cr-Zr binary alloy were investigated. Defect structures in Cr_2Zr were determined and discussed in association with atomic size concept. Also, the low-temperature fracture toughness, high-temperature compressive strength and oxidation behavior were investigated, discussed in relation to microstructure and defect structures, and also compared with those in other Laves alloys.3) Deformation microstores of Cr_2Nb and V-added Cr_2Nb were investigated by TEM. It was shown that those alloys were deformable above 1300 K and deformation is not due to mechanical twinning but to glide/climb motion of dislocations.4) Microstructure, low-temperature fracture toughness, high-temperature compressive strength and oxidation behavior of Cr_2Zr and Cr_2Nb alloys fabricated by powder metallurgy were investigated, and shown to be superior to those fabricated by ingot metallurgy.5) Microstructure, phase diagram and low-temperature fracture toughness of Cr_2Zr-Cr_2Nb and Cr_2Zr-Cr_2Hf pseud binary alloys were investigated. The low-temperature fracture toughness was much improved at specific alloy compositions.