Realistic Advancement for Nickel-Based Single Crystal Superalloys by the d-Electrons Concept
Superalloys 1992 (Seventh International Symposium)
We have proposed the d-electrons concept for the design and development of nickel-based single crystal superalloys. In this concept, two alloying parameters has been determined by the molecular orbital calculation (DV-Xa cluster calculation). The one is the d-orbital energy level (Md) of alloying transition element, and the other is the bond order (Bo) between atoms. The compositional average of Md and Bo parameters are denoted as M?l and l35, respectively. In this study, several alloying
... eral alloying effects on the high temperature properties were investigated with the aid of these d-electrons parameters, m and I35 For example, it was found that the y solvus temperature was predictable by using these parameters. An idea about alloying vectors was introduced newly to the d-electrons concept. Using this idea, the trend for the partitioning of the alloying elements between the y and the y phases could be understood consistently. Also, the alloying effects of Cr, Co, Re, Ti and Hf were shown on the creep-rupture property and the hot-corrosion resistance of superalloys. In addition, it was found that the realistic advancement for nickel-based superalloys was well recognized using the m-573 diagram. All the single crystal superalloys so far developed and the high strength conventional cast alloys were localized in a very small region in the BZ-I&I diagram. On the basis of these results, a proposal was discussed for the development and the modification of single crystal superalloys, in particular, of the Re-containing single crystal superalloys.