A metallurgical evaluation was performed on centrifugal and static 20Cr, 32Ni, 1Nb castings after 21 months aging at 1565°F (852°C) in a hydrogen reformer. The aged microstructures contained secondary precipitates at both the periphery of the eutectic niobium carbides and at intradendritic locations. Chemical analysis indicated the precipitates were M2306 chromium carbides and intermetallic
niobium-nickel-silicides. Electron probe X-ray microanalysis indicated the niobium-nickel-silicides were predominately G-phase (Ni16Nb6Si7)
as well as...
Key words: intermetallic silicides, G-phase, Ni16Nb6Si7, Nb3Ni2Si, heat resistant castings, mechanical properties