Takehiro Ohno

Development of low thermal expansion superalloys

Alloy 903 and Alloy 909 are well-known Fe-Co-Ni-Al-Ti-Nb alloys with controlled low thermal expan-sion, but they have some properties that can be improved. To improve stress-accelerated grain boundary oxidation embrittlement of Alloy 903 and instability of theγ phase of alloy 909, two new alloys with good stress-rupture ductility, high creep-rupture strength, high tensile strength at high temperature, and good controlled thermal expansion were developed. These property improvements were accomplished by the combination of optimizing the Fe-Co-Ni ratio of the matrix and stabilizing theγ phase with the addition of aluminum.

Long-Term Oxidation Behavior of Fe-Cr Ferritic Alloy ZMG232L for SOFC Interconnects

Fe-Cr ferritic alloys are applied for interconnects of solid oxide fuel cells (SOFCs) operated at around medium temperatures. The long-term oxidation behavior of Fe-22%Cr ferritic alloy, ZMG232L, was investigated. The oxidation rate of thin sheet was much higher than that of thick one. The effect of Cr content on oxidation resistance of ZMG232L was also investigated. The oxidation rate of low Cr alloy was higher than that of high Cr one. Therefore it was found that such accelerated oxidation occurred because Cr content decreased under oxide layer of edge part of thin sheet and Cr oxide became unstable and Fe was mainly oxidized.