International Journal of Hydrogen Energy, Vol.44, No.36, 20133-20144, 2019
Hydrogen desorption/absorption properties of the extensively cold rolled beta Ti-40Nb alloy
beta Ti-Nb BCC alloys are potential materials for hydrogen storage in the solid state. Since these alloys present exceptional formability, they can be processed by extensive cold rolling (ECR), which can improve hydrogen sorption properties. This work investigated the effects of ECR accomplished under an inert atmosphere on H-2 sorption properties of the arc melted and rapidly solidified beta Ti40Nb alloy. Samples were crushed in a rolling mill producing slightly deformed pieces within the millimeter range size, which were processed by ECR with 40 or 80 passes. Part of undeformed fragments was used for comparison purposes. All samples were characterized by scanning electron microscopy, x-ray diffractometry, energy-dispersive spectroscopy, hydrogen volumetry, and differential scanning calorimetry. After ECR, samples deformed with 40 passes were formed by thick sheets, while several thin layers composed the specimens after 80 passages. Furthermore, deformation of beta Ti-40Nb alloys synthesized samples containing a high density of crystalline defects, cracks, and stored strain energy that increased with the deformation amount and proportionally helped to overcome the diffusion's control mechanisms, thus improving kinetic behaviors at low temperature. Such an improvement was also correlated to the synergetic effect of resulting features after deformation and thickness of stacked layers in the different deformation conditions. At the room temperature, samples deformed with 80 passes absorbed similar to 2.0 wt% of H-2 after 15 min, while samples deformed with 40 passes absorbed similar to 1.8 wt% during 2 h, excellent results if compared with undeformed samples hydrogenated at 300 degrees C that acquired a capacity of similar to 1.7 wt% after 2 h. The hydrogen desorption evolved in the same way as for absorption regarding the deformation amount, which also influenced desorption temperatures that were reduced from similar to 270 degrees C, observed for the undeformed and samples deformed with 40 passes, to similar to 220 degrees C, for specimens rolled with 80 passes. No significant loss in hydrogen capacity was observed in the cold rolled samples. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.