The effect of cerium on high temperature tensile and creep behavior of a superalloy

The presence of trace impurities such as S and O can cause embrittlement during elevated and high temperature deformation of iron or nickel-base alloys. In this study various amounts of Ce, ranging from 0 to 0.24 wt pct, have been added to an iron-nickel base superalloy, Udimet 901, in order to study its role in the refining process of S and O in the melt, hot workability, creep and stress rupture, and microstructure. It is found that Ce addition decreases the 0 and S content in the melt and improves both the hot workability and creep ductility. An optimum residual Ce content of 30 ppm was found for which ductilities are maximum. Higher residual cerium contents result in deleterious hot embrittlement. SEM as well as TEM/STEM microscopy combined with X-ray EDS spectroscopy were used to determine the inclusion content present in the alloy as well as the fine spatial microchemistries, especially at grain boundaries.