Interaction of trapped hydrogen with dislocations at low-temperature in deformed Pd

Phase-behavior;Trapping;Hydrogen;Dislocation;Palladium (Pd)

Ju, Hyunsu

关键词: Phase-behavior;    Trapping;    Hydrogen;    Dislocation;    Palladium (Pd);   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/18279/JU_HYUNSU.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Segregation of solute atoms to dislocations occurs due to the elastic interaction with thehydrostatic stress of edge dislocations and also due to the dislocation core-solute interaction.The characteristics of the local segregation at dislocations, Cottrell atmosphere, at lowtemperature and low concentration have not been investigated until the phase transformationof the deformed PdH0.0008 was recently observed at low temperature. The purpose of thisstudy was to investigate the phase behavior of the trapped solute influenced by the distorteddislocation environment.The phase behavior of the Cottrell atmosphere in deformed Pd was investigated as a functionof temperature by incoherent inelastic neutron scattering (IINS) and small angle neutronscattering (SANS) measurements. The IINS measurements of the deformed PdH0.00134presented the characteristic vibrational density-of-states (VDOS) of hydrogen trapped atdislocation, while the spatial profile of the trapped hydrogen in the deform PdH0.00134 wasdetermined by the SANS measurements.The VDOS of hydrogen in the deformed PdH0.00134 was obtained at 4, 100, 200, and 295 Kby the IINS measurements. The VDOS at 4 K exhibited the primary peak of approximately57 meV associated with hydrogen-rich-Pd hydride phase. The characteristic peak of theVDOS at 295 K corresponded to dilute solid-solution-Pd hydride phase, appearing atapproximately 68 meV. Coexistence of the beta-phase and the alpha-phase was observed at100 and 200 K. This suggests that hydrogen trapped at dislocations undergoes the phasetransformation upon temperature change from 295 to 4 K in the deformed PdH0.00134.The spatial characterization of the Cottrell atmosphere was performed by the SANS measurements at 15, 100, and 200 K. The cylindrical geometry with the radius of 9 andthe length of 50 was obtained and the dislocation density was 1.2×10−11 cm−2. Basedon the spatial profile, the local concentration of the trapped hydrogen was estimated asapproximately 0.2 [H]/[Pd] even at 200 K, which exceeds the dilute solid-solution regime(∼0.01 [H]/[Pd] at room temperature). Correlation between the local concentration and thephase behavior verified the condensation of the hydrogen-rich phase along the dislocations.Given such low hydrogen concentration in the heavily deformed Pd, this behavior isrepresentative of hydrogen trapped at dislocations at low temperature. Correlating thespatial and the vibrational characterization of the Cottrell atmosphere demonstrated thephase behavior of the trapped solute interacting with dislocations at the distorted dislocationenvironment.