Nb35Hf32.5Co32.5 dual-phase alloy: Hydrogen permeability degradation due to the microstructural changes caused by annealing. (26th April 2021)

• Record Type: Journal Article
• Authors: Liu, Wei; Yan, Erhu; Wang, Hao; Zhao, Ping; Huang, Renjun; Cheng, Jian; Ge, Xiaoyu; Chu, Hailiang; Zou, Yongjin; Xu, Fen; Sun, Lixian
• Is Part Of: International journal of hydrogen energy. Volume 46:Number 29(2021)
• Page Start: 15609
• Page End: 15623
• Publication Date: 2021-04-26
• Subjects: Nb-Hf-Co alloy -- Microstructural stability -- Annealing -- Hydrogen permeability; Hydrogen as fuel -- Periodicals; Hydrogène (Combustible) -- Périodiques; Hydrogen as fuel; Periodicals; 665.81
• DOI: 10.1016/j.ijhydene.2021.02.046
• Languages: English
• ISSNs: 0360-3199

Abstract

Abstract: Nbx Hf(100-x)/2 Co(100-x)/2 (30 ≤ x ≤ 50) alloys are a type of typical dual-phase materials with advantages of excellent hydrogen permeability, high intensity, and low cost, which are at the forefront of the development trends of new materials used for hydrogen separation. However, changes in the microstructure and hydrogen permeability after annealing of the hypereutectic alloys were unknown until now. To this end, the effect of annealing on the microstructure and hydrogen permeability of Nb35 Hf32.5 Co32.5 alloy is investigated in this paper. The results show that this alloy still possesses a hypereutectic structure after short-time annealing, but the above microstructural characteristics gradually disappear with an increase of annealing time (or temperature), and some new impurity phases (e.g. Co2 Nb, Co2 Hf and Co6 Nb7 ) are formed. With this change, the alloys show a gradual reduction in hydrogen permeability, which is mainly attributed to the transition of the bcc-(Nb, Hf) phase in the eutectic structure, from a continuous thin layer to discontinuous granules. Furthermore, brittle fracture occurs in the alloy membranes after long-time annealing at various temperatures due to the formation of the above impurity phases. This study demonstrates that annealing cannot improve the hydrogen permeability, and on the contrary, it deteriorates the hydrogen embrittlement resistance of the Nb-Hf-Co hydrogen permeable alloys. Highlights: The microstructure of the as-cast Nb35 Hf32.5 Co32.5 alloy changes greatly after annealing. The lamellar-rod transition in eutectic caused by annealing degradates the hydrogen permeability. The hydrogen permeation mechanism was constructed by combining the effective medium theory model. Annealing can not improve the hydrogen permeability of the as-cast Nb-Hf-Co alloy.