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The ultimate tensile strength of 250 MPa, 0.2% proof stress of 150 MPa, and fracture strain of 10% at the as-cast condition for Al-1.5Mn-X alloys, were objective in this development. As ternary elements, Ca, Mg, Ti and Zn were initially chosen and the values in ¦Mk of the s-orbital energy level in alloys were adjusted to be less than 0.017. Their proof stress and fracture strain increased and decreased as ¦Mk increased, respectively. The composition of promising alloy was decided to Al-1.5Mn-2.4Mg with ¦Mk of 0.029 on the basis of the relation between tensile properties and ¦Mk. This as-cast alloy showed the · uts · 0.2 and ¾ f of 270, 135 MPa and 18% showing excellent corrosion resistance in the NaCl solution, which resulted in the approximate satisfaction of the objective. The interaction between the proof stress and dislocation density or hindrance for dislocation migration at the constant strain could be explained by ¦Mk, which might lead to the indication of solid solution hardening level using this parameter for Al-1.5Mn-X ternary alloys.

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.

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The + type Ti-5.5Al-2Fe and type Ti-2.5Fe-2Mn-2Zr alloys have been theoretically designed, for the modification of Ti-6Al-4V and the achievement of the high tensile strength more than 1000 MPa at the solution treatment state, respectively, using ubiquitous alloying elements in order to establish the strategic method for suppressing utilization of rare metals. The utilization of the cold crucible levitation melting (CCLM) is very useful for the production of ingots, because titanium is very chemically reactive at high temperature. The experimental alloys with high purity and without contaminations from a crucible were prepared, and the homogeneous melt was also achieved by the diffusion mixing effect of CCLM. The microstructure, phase stability, strength, corrosion-resistance and workable properties of the design Ti-5.5Al-2Fe alloy, were comparable to those of Ti-6Al-4V. In contrast, the solution heat treated Ti-2.5Fe-2Mn-2Zr alloy showed the tensile strength of 1200 MPa, and the 1.3 times increase in the specific strength compared with Ti-15Mo-5Zr-3Al. The alloy design can be successfully carried out even using ubiquitous alloying elements by the d-electrons concept, which leads to the establishment of one method for the strategic utilization of rare metals.

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