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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 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.

The influence of a number of alloying elements on the electronic structure of aluminium has been investigated by the DV-X, cluster method. The energy level structure was modified remarkably by alloying. For transition metals, for instance. this modification was mainly due to the appearance of the virtual bound state of d electrons near the Fermi energy level. Except for a few elements, the ionicities of alloying elements change monotonically following the electronegativity. The bond order between atoms largely depends on the alloying elements, while the activation energy for the 3d impurity diffusion in aluminium can be related to the calculated bond order. An increment of the residual resistivity, due to the 3d impurities doped into aluminium, also correlata well with the virtual bound stale densityat the Fermienergylevel. Inaddition, it isshown fromcalculations that Mn and Cr are probably the magnetic impurities in aluminium.

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