Processing for multi-functions・Materials development

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Strength, fracture toughness and oxidation resistance were selected among many properties for high temperature structural materials and harmonic material design was studied.In-situ composites consisting of ductile particle-dispersion refractory intermetallics and ceramics in which both the phases are thermodynamically equilibrated were synthesized by controlling alloying behavior and microstructure. Directionally solidified eutectic ZrC/Mo in-situ composite, which is prepared by the high frequency floating zone melting method, shows the room temperature fracture toughness of about 20 MPam^<1/2> and high strength at 1500C of 420 MPa. The high fracture toughness is attributable to crack deflection arising from decohesion between ZrC and Mo and the high strength at 1500C is due to solid solution strengthening and microstructure refinement.High temperature strength of Mo-Si-B alloys is shown to increase significantly by alloying without sacrificing room temperature fracture toughness. The new concept of "pseudo in-situ composite" is presented and pseudo in-situ Mo-Si-B-O composite is found to exhibit excellent oxidation resistance at 1400C.Based on the fundamental research of the diffusion bonding, clad hot rolling is successfully carried out using Fe_3Al base alloys and CrMo steel. The clad hot rolled sheet shows harmonically high strength, good oxidation resistance and high fracture toughness.