Abstract
Although Ni-based superalloys meet the gas turbine needs of today, they are used very close to their melting range. To meet the future demands of gas turbines new materials with higher application temperatures are needed. Addition of Re increases the melting temperature of Co-based alloys and they show promise to supplement Ni-superalloys for ultra high temperature applications. The Co-Re alloy development strategy is first discussed here briefly. Unlike single crystal Ni-superalloys with the &gama;-&gama;´ structure, the Co-Re alloys have complex microstructure with many different phases present in diverse morphology. MC type carbides are the main hardening precipitate particularly used for high temperature creep resistance. Further, Cr and Si additions in Co-Re alloys provide oxidation resistance. Designing optimal microstructure and ensuring its stability is an essential task of high temperature alloy development. In our alloy development program neutron and synchrotron measurements are extensively used. It allows monitoring the microstructure evolution in-situ at high temperatures and thereby helps in understanding the relatively unexplored Co-Re alloy system. Recent results on the effect of C/Ta ratio on the TaC morphology in Co-Re-based alloys are presented as well.

Key words
Co-base alloy, scanning electron microscopy (SEM), neutron scattering

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