To improve the creep strength of Ni-base superalloys, Re and Ru additions were investigated with using 2nd generation single crystal superalloy TMS-82+ which contains 2.4 mass%Re, as the base alloy. When Re and Ru were added at the same time, creep strength was improved at lower and higher temperature. We suppose that these were caused by the solution strengthening due to Re at lower temperature, and the stabilization of γ/γ′ structure at higher temperature by Ru addition. Further more, in the case of Re addition, creep strength at lower temperature was improved, and creep strength at higher temperature became worse due to the TCP phase formation. Also, in the case of Ru addition, creep strength at lower and higher temperature became worse, although TCP phase formation was completely suppressed. This is because Ru is not an effective element for the solution strengthening at high temperature.
The XAFS spectra of the Mo K-edge were investigated regarding molybdenum ions in sodium potassium silicate glasses. In all the measured glasses the molybdenum ions are considered to be in the 6+ oxidation state. We evaluated the Mo-O correlation and concluded that Mo 6+ ion forms the MoO 4 2- tetrahedron. The Mo-O distance is approximately 0.177 nm. This configuration is stable in the investigated composition range. The results indicate that the MoO 4 2- tetrahedra are located outside the Si-O network anions. These MoO 4 2- characteristics were discussed with the acid-base concept of the oxide glasses.
Ni-base directionally solidified (DS) superalloys have the advantage of production costs over the single crystal (SC) superalloys because of better yield rate of casting and a simpler heat treatment compared with SC superalloys. In our previous work, we developed a third generation DS superalloy TMD-103 which exhibits good creep strength, equivalent with second generation SC superalloys. In this study, we attempt to develop a fourth generation DS superalloy that have better creep strength than TMD-103. To strengthen the grain boundaries of the new DS alloys, C and B were added to the fourth generation SC superalloy, TMS-138, that has good phase stability and a long creep life by Ru and Mo addition. Creep behavior of the as-cast and heat-treated new DS alloy is investigated. As a result of creep tests at 1100 degrees centigrade under a load of 137 MPa, the creep time at 1% strain in the heat-treated alloy is twice as long as that of TMD-103.
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