Effect of rare earth metals on solidification behaviour in nickel based superalloy

Abstract

The effect of rare earth metals (REMs) on the microstructure and segregation during solidification in a highly alloyed Ni based superalloy was investigated. Rare earth metals considerably decrease the amounts of coarse columnar grains and increase the amounts of equiaxed grains. They are segregated to the interdendritic regions mainly as the precipitate of Ni₅Ce. Both the dimension and distribution of γ′ particles and MC carbide are modified by REM. Eutectic (γ+γ′), Laves phase, δ phase and σ phase are precipitated in the interdendritic regions because of the serious segregation of niobium and titanium aggravated by REM. The differential thermal analysis indicates that the precipitation temperature of phases and the solidification sequence of the superalloy can be changed due to the additions of REM.