Influence of Ru on Solidification Behavior, Microstructure and Hardness of Re-free Ni-based Equiaxed Superalloys with High Cr Content

The effect of Ru addition on solidification behavior, microstructure and hardness of Re-free Ni-based equiaxed superalloys with high Cr content has been investigated. With the increase of Ru, the solidus temperature of the alloys and the γ′ solvus temperature decreased, respectively. However, the liquidus temperatures of the alloys had no obvious change. The microstructure of the as-cast alloys was mainly composed of γ, γ′, γ/γ′ eutectic and MC carbides. The γ/γ′ eutectic was completely dissolved after the heat treatment. The morphology of γ′ was more cuboidal in heat-treated alloys with increasing Ru. Furthermore, the volume fraction of γ′ in the as-cast and heat-treated alloys diminished upon the increase of Ru. It was noted that Ru addition changed the segregation behaviors of Cr and Mo in the alloys from positive segregation element to negative segregation element and promotes the segregation degree of W. As the Ru content increased, the magnitude of segregation of the positive segregation elements Ta and Ti increased accordingly. Meanwhile, the magnitude of Al segregation decreased and Ru tended to segregate in the dendrite core. In addition, the hardness of the alloys improved and their porosity reduced with increasing amount of Ru.