The electrochemical Dy-alloying behaviors of Inconel 600 and Hastelloy C-276 were investigated in a molten LiFCaF 2 DyF 3 (0.30 mol%) system at 1123 K. Cyclic voltammetry and open-circuit potentiometry suggested the formation of several phases of DyNi alloys. Potentiostatic electrolysis was conducted to prepare alloy samples using Inconel 600 and Hastelloy C-276 plate electrodes at 0.20 V vs. Li + /Li for 60 min. Cross-sectional scanning electron microscopy revealed that DyNi alloys were formed in both samples. X-ray diffraction analysis confirmed the formation of DyNi 2 as the predominant phase for both the samples. Phase separation of the alloy layer into the DyNi 2 phase and formation of the agglomerated CrFe and CrFeMo phases were indicated by EDX mapping analysis. [
The electrochemical Dy-alloying behaviors of NiCr and NiMo alloys were compared with those of NiCrMo alloy and pure Ni in a molten LiFCaF 2 DyF 3 (0.30 mol%) system at 1123 K. The effects of chromium and molybdenum as constituent elements of the Ni-based alloys were investigated. Cyclic voltammetry and open-circuit potentiometry indicated the formations of DyNi alloys for all the Ni-based electrodes, as well as for the pure Ni electrode. XRD analysis confirmed the formation of DyNi 2 and DyNi 3 phases for all the electrodes electrolyzed at 0.20 V (vs. Li + /Li) for 60 min. SEM/TEM-EDX analysis of the sample prepared from NiCrMo alloy revealed that the Dy-alloyed layer consists of Cr-rich CrMo and Mo-rich MoCr phases, as well as a DyNi(Fe) matrix phase. The shear stress measurements of the Dy-alloyed samples showed that the NiCrMo alloy is the most suitable substrate to improve mechanical strength, which is explained by precipitation strengthening by both the CrMo and MoCr phases.
In order to develop nondestructive evaluation procedure of fatigue damage in Inconel 718 which is used for components of H-II rocket engine, we investigated correlation between the fatigue life fraction and cracks and slip bands which were observed on the etched cross sectional surface of the fatigued specimens. The main results obtained are as follows. (1) The number of cracks and maximum crack depth become large with increased the fatigue life fraction N/Nf. However, maximum crack depth does not remarkably increase in early stage of the fatigue life, while cracks propagate rather fast in the latter half of the fatigue life. (2) The slip band density can be uniquely correlated with the fatigue life fraction N/Nf. The fatigue damage represented by N/Nf can be evaluated by the chemical etching technique and the damage can be evaluated from the early stage to the last stage of fatigue life.
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