Solidification and segregation characteristics of Ni-based superalloy C700R-1 for ultra-supercritical steam turbine rotor

Abstract

The solidification characteristics of C700R-1 alloy was investigated by DSC analysis, in-situ observation, quenching experiment and Thermo-Calc calculation. The segregation behavior during solidification was analyzed by Scanning Electron Microscope and Electron Probe Microanalysis. At the initial stage of solidification, the volume fraction of liquid experienced a steep decrease, accompanied by a rapid formation of dendrites. The residual liquid solidified slowly due to segregation at the final stage. Al, Ni, W and Co elements segregated in the dendrite stems, while Ti, Nb and Mo were enriched in the interdendritic, in which MC carbides also precipitated. At the end of solidification, the segregation of Mo and Cr is further aggravated, resulting in extremely low solidus and formation of eutectic region. The study on the solidification characteristics of C700R-1 alloy demonstrates that aggravation of segregation leads to deterioration of the solidification conditions. • DSC, in situ, quenching experiment and Thermo-Calc calculation were applied. • L→γ at 1370 ℃; L→γ + MC at 1298 ℃; L→γ + μ at 1217 ℃. • The solidification interval is widened due to the addition of Ti, Nb, Mo and W. • The segregation of Mo and Cr leads to the formation of multiple eutectic phases.