Hydriding and structural characteristics of thermally cycled and cold-worked V–0.5 at.%C alloy

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• 作者：Dhanesh Ch ; ra ; Archana Sharma ; Raja Chellappa ; William N. Cathey ; Franklin E. Lynch ; Robert C. Bowman Jr. ; Joseph R. Wermer ; Stephen N. Paglieri
• 关键词：Metal hydrides ; Domain structure ; Thermal cycling ; Cold-working ; V– ; 0.5 at.%C alloy
• 刊名：Journal of Alloys and Compounds
• 出版年：2008
• 期刊代码：45_09258388
• 类别：ms
• 出版时间：20 March 2008
• 卷：452
• 期：2
• 页码：312-324
• 文件大小：1408 K

摘要

High pressure hydrides of V_0.995C_0.005 were thermally cycled between β₂- and γ-phases hydrides for potential use in cryocoolers/heat pumps for space applications. The effect of addition of carbon to vanadium, on the plateau enthalpies of the high pressure β₂ + γ region is minimal. This is in contrast to the calculated plateau enthalpies for low pressure (c="http://www.sciencedirect.com/scidirimg/entities/204e.gif" alt="greek small letter alpha" title="greek small letter alpha" border="0"> + β₁) mixed phases which showed a noticeable lowering of the values. Thermal cycling between β₂-and γ-phase hydrides increased the absorption pressures but desorption pressure did not change significantly and the free energy loss due to hysteresis also increased. Hydriding of the alloy with prior cold-work increased the pressure hysteresis significantly and lowered the hydrogen capacity. In contrast to the alloy without any prior straining (as-cast), desorption pressure of the alloy with prior cold-work also decreased significantly. Microstrains, c="http://www.sciencedirect.com/scidirimg/entities/2329.gif" alt="left angle bracket" title="left angle bracket" border="0">c="http://www.sciencedirect.com/scidirimg/entities/25b.gif" alt="var epsilon" title="var epsilon" border="0">²c="http://www.sciencedirect.com/scidirimg/entities/232a.gif" alt="right-pointing angle bracket" title="right-pointing angle bracket" border="0">^1/2, in the β₂-phase lattice of the thermally cycled hydrides decreased after 778 cycles and the domain sizes increased. However, in the γ-phase, both the microstrains and the domain sizes decreased after thermal cycling indicating no particle size effect. The dehydrogenated c="http://www.sciencedirect.com/scidirimg/entities/204e.gif" alt="greek small letter alpha" title="greek small letter alpha" border="0">-phase after 778 thermal cycles also showed residual microstrains in the lattice, similar to those observed in intermetallic hydrides. The effect of thermal cycling (up to 4000 cycles between β₂- and γ-phases) and cold working on absorption/desorption pressures, hydrogen storage capacity, microstrains, long-range strains, and domain sizes of β₂- and γ-phase hydrides of V_0.995C_0.005 alloys are presented.