Design of super-heat-resisting structural materials using a d-electron alloy theory (II)

not registered; Morinaga, Masahiko*; Saito, Junichi*  ; not registered; not registered

[PURPOSE] For structural materials serviced in the Li environments, both Nb-based and Mo-based alloys are selected as the candidate materials. In this study, a simple method was proposed for evaluating the high temperature strength of these alloys. Also, the corrosion resistance in liquid metals was investigated in order to get fundamental information for the design and development of high performance alloys. [EXPERIMENTAL AND CALCULATING METHODS] With a variety of ternary alloys high temperature micro-hardness was measured systematically. The results were analyzed by referring to the relationship between the hardness and the tensile strength reported in previous publications. Also, some alloys designed last year were exposed to the liquid Na at 650 C, and the attendant changes were examined with respect to the weight, microstructure and local composition of alloys. Some of the results were understood in terms of the free energy for the oxide formation of Na and other elements in alloys. Another effort to understand the corrosion properties was made by the molecular orbital calculation of the electronic states of various elements in liquid Li, K and Na. [RESULTS] The high temperature tensile strength of both the alloys was found to be predictable by using a linear relationship between the hardness and the tensile strength of room temperature to 1200 C. The corrosion resistance was much poorer in the Nb-based alloys than in the Mo-based alloys. This is partially due to the enhancement of corrosion by the preferred oxidation of Nb and Ta in the Nb-based alloys, whereas no such oxidation took place in the Mo-based alloys. In addition, it was found from the molecular orbital calculation that Li is the liquid metal of more strongly-bonded with every alloying element, compared to K and Na liquid metals. Futhermore, it was shown that the hardness of each alloy correlated well with the atomic-size difference and also the young's modulus difference ...