Intermetallic Compounds

Developing more efficient fossil energy conversion technologies with less environmental impact require high-performance structural materials of long-term reliability that can be used in aggressive environments. Next generation gas turbines combusting hydrogen-rich fuels and oxy-fuels are predicted to have inlet temperatures higher than the current gas turbines. The current gas turbines utilize state-of-the-art nickel-based superalloys in the hottest sections. These materials possess excellent creep strength because they contain high volume fraction of γ’ precipitates coherent with the γ matrix and excellent high-temperature oxidation resistance due to ability to form protective oxide scales on the surface. However, these alloys perform at their temperature capability limit, and there is not much room left for improvement since the application temperatures are already very near their melting points. Chromium alloys present a potential for development of new high-temperature materials. Precipitation characteristics of a Cr–5Ni–5Al–0.5Ti (at.%) alloy were investigated utilizing a series of heat treatments. XRD, SEM, and analytical TEM were used to characterize the microstructure. This study has shown that the small spherical B2-NiAl precipitates forming below 1345 °C are highly coherent and have a well-defined orientation relationship with the Cr-matrix. Also, some evidence has been presented for the formation of L21-Ni2AlTi phase within the B2-NiAl phase.