| Research Abstract |
In this study, to develop the Cr_2Nb intermetallics which can be used at 1473K and the enough fracture toughness at ambient temperature, the mechanical properties of the alloys prepared by alloy design, microstructural control and advanced process were investigated. The following results were obtained.
1) Structures of Cr_2Nb Laves alloy were observed by x'-ray and (HR) TEM.High temperature compressive deformation behavior was investigated, and discussed in correlation with the activated dislocation structures. Consequently, the deformation begins at 1473K,and accomplished by an activation of the Schockley partials of 1/2 <011> dislocations, or the dynamic recrystallization.
2) The isothermal phase diagrams of Cr-Nb-V,Cr-Nb-Mo and Cr-Nb-W ternary alloy systems at 1623K were clarified. It was shown that the C15 Cr_2Nb Laves phases are directly equilibrated with bcc solid solution without forming any ternary intermediate compounds.
The effect of ternary alloying elements such as V,Mo, W and Ti on the alloying behavior, the lattice properties and the phase stability of the C15 Cr_2Nb was investigated. It was shown that the solubility of V and W are more than 10at%, that of W is about 5at%, and Ti forms the continuous solid solution range toward to Cr_2Ti. The ALCHEMI determined that V occupies the sublattice of Cr, Mo, Ti and W do the sublattices of Nb. Also, TEM observation on the microstructure of the alloys with ternary elements suggested that V enhance the stability of C15 structure but Mo, W and Ti reduce the stability of the C15 structure.
4) The mechanical properties of the ternary alloys consisting of the Cr_2Nb and the bcc solid solution were investigated by compression test in a wide range of test temperature. High fracture toughness at low temperature was observed on the alloys consisting of the C15 phase and Cr-rich bcc solid solution, while high strength at high temperature was observed on the alloys consisting of the C15 phase and Nb-rich bcc solid solution.
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