Influence of Ru Addition on Microstructure, Creep and Rupture Properties of Nickel based DS Superalloy☆

Abstract The effect of Ru addition on the microstructure, creep and rupture properties of the directionally solidified (DS) Ni based superalloy, DMD4 has been evaluated. The microstructural characterization of the alloys has been carried out using scanning electron microscopy and electron microprobe analysis. The morphology of γ′ precipitates was more cuboidal in the Ru-bearing superalloy as compared to the Ru-free superalloy. Further, Ru addition was found to increase the volume fraction of γ′ precipitates from 51% to 54% and decrease the width of the γ channels from 90 nm to 76 nm. Creep and rupture properties, evaluated at stress/temperature combinations ranging between 90-500 MPa/850-1100 °C, showed significant improvement in rupture life of the Ru containing superalloy over that of the Ru free alloy, at all combinations of stress and temperature. Such enhancement in the rupture life can be attributed to the formation of a well elongated rafted structure and the inherent higher volume fraction γ′ precipitates in the Ru-containing alloy. Larson-Miller plots derived from the creep tests suggest that addition of Ru enhanced the temperature capability of the alloy by about 11 °C for 100 hrs life at 140 MPa.