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In this work, a practical numerical model with few parameters was proposed for the prediction of environmental hydrogen embrittlement. The proposed method adopts hydrogen enhanced plasticity-based mechanism in a fracture strain model to describe hydrogen embrittlement. Fracture toughness degradation of three commercial steels SA372J70, AISI4130 and X80 in high pressure hydrogen environment were investigated. Firstly, governing equations for hydrogen distribution and material damage evolution was established. Hydrogen enhanced localized flow softening effect was coupled within fracture strain dependency on stress triaxiality. Then, the numerical implementation and identification process of model parameters was described. Model parameters of the investigated steels were determined based on experiment results from literatures. Finally, with the calibrated model, fracture toughness reduction of the steels was predicted in a wide range of hydrogen pressure. The prediction results were compared with experimental results. Reasonable accuracy was reached. The proposed method is an attempt to reach balance between physical accurate prediction and engineering practicality. It is promising to provide a simplified numerical tool for the design and fit for service evaluation of hydrogen storage vessels. • Hydrogen embrittlement prediction model with few parameters was proposed. • Identification of model parameters with a few support of experiments. • Simplified Fracture toughness prediction model with acceptable accuracy. [ABSTRACT FROM AUTHOR]

In this study, AZ61 alloy processed by equal channel angular pressing (ECAP) method, is presented. This research seeks to find out the relationship that exists between the microstructure of the AZ61-magnesium alloy doped with SiC and Ni and processed by ECAP in terms of hydrogen storage properties. The results indicate that grain size reduces nearly 10 times after 4 passes of ECAP. Homogeneous distribution of the SiC in the metal matrix composite (MMC) and dynamic recrystallization are also observed. There is a gradual reduction in the grain size when the number of ECAP passes are increased. This microstructural refinement induced by ECAP improves the storage capacity and reaction kinetics of the alloy. Besides, the addition of Ni catalyst achieves faster absorption and desorption kinetics. However, it does not change its capacity. Ni reacts with Mg to form an intermetallic, which is hydrogen-absorbing, which in turn, catalyzes the reaction. Apart from introducing defects, the ECAP process also produces Mg/Al intermetallic, which acts catalytically. It is shown that SiC-doped AZ61-magnesium alloy can absorb and desorb 6.8 wt% H 2 at 648 K and 50 atm. • AZ61 with SiC and Ni additives prepared by gravity stir casting method. • Dispersion characteristics of the particles influences the rate limiting factors. • AZ61-1 wt%SiC achieves a hydrogen capacity of 6.8 wt%. • Performance declines to 6.5 wt% when Ni catalyst is added. • Combining SiC and Ni shows improved kinetics. [ABSTRACT FROM AUTHOR]

In this study, the hydrogen storage performance of commercial AZ31-Mg alloys combined with various allotropes of carbon was investigated and the microstructural modifications with respect to plastic deformation and high energy milling techniques investigated, with the aim of obtaining enhanced hydrogen storage efficiency. The hydrogen storage performance of alloys prepared with different weight ratios of carbonaceous materials as a catalyst was monitored in order to explore the effective improvement in hydrogen storage performance through microstructural modification. Additionally, the effects of different processing methods such as equal channel angular pressing (ECAP) and high energy ball milling (HEBM) were also observed. AZ31 Mg based composites with various carbon additives were produced through gravity resistance casting and their micrographic structures examined through optical Microscopy (OM), X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS). The average particle size distributions of the sample powders were also measured. The rate of hydrogenation kinetics was calculated by a Sievert's type apparatus. Significant enhancement of the hydrogenation performance was obtained with the addition of carbonaceous materials. Overall, the hydrogen storage performance after ECAP deformation of the AZ31-3CB (carbon Black) composite showed a gain in the maximum capacity of 6.72 ± 0.05 wt%. Similar, after milling of the AZ31-3G (Graphene) composite materials, a maximum potential capacity of 6.83 ± 0.04 wt% was attained within 792 ± 144.34 s, with desorption of the entire H 2 content in 143.2 ± 26.09 s. The obtained results revealed significant improvement in the hydrogen storage capacity of AZ31-Mg alloys with the addition of carbon materials and with respect to plastic deformation and milling techniques. Graphical illustration of sample preparation process flow. Image 1 • AZ31/Carbonaceous additives fabricated by Gravity resistance casting method. • Carbonaceous addition modifies the microstructure of AZ31 alloy. • AZ31-3G (Graphene)-HEBM reaches the H 2 capacity of 6.83 ± 0.04 wt% in 792 s. • HEBM exhibits enhanced hydrogenation properties than ECAP for AZ31-3G (Graphene). [ABSTRACT FROM AUTHOR]

Abstract In this work, the hydrogen sorption properties of AZ31 magnesium alloys with various additions of nickel (Ni) (i.e., Ni (X = 0, 2, 4) wt.%) were investigated. Cast ingots with different AZ31/Ni P compositions were fabricated using a gravitating mechanical stir casting (GMSC) method. Two different processes, namely, equal channel angular pressing (ECAP) and high energy ball milling (HEBM) were performed to improve its hydrogen storage properties. The particle size of the sample powders were measured by laser diffraction analysis. The microstructures, powder morphologies, and phase transformation were characterized by optical microscopy (OM), scanning electron microscopy (SEM) and x-ray diffraction (XRD) analysis. The hydrogen sorption kinetics were measured by a Sievert's type apparatus. The results showing the impact of the ECAP and HEBM processes on the hydrogen storage properties were compared. The AZ31-4 Ni ECAP processed sample showed a maximum hydrogen storage capacity of 7.0 wt.% at 2322 s with complete desorption of all the hydrogen in less than 5 min at a temperature of 375 °C. On the other hand, the pure AZ31 alloy which was treated with the HEBM process showed the maximum hydrogen capacity of 6.5 wt.% at 2393 s with desorption of all the hydrogen within 6 min. In addition, the activation energy, as illustrated by the Kissinger plot, revealed that the activation energy of the ECAP processed AZ31-4 Ni was 104.73 (KJ/mol), obviously lower than the material processed by HEBM and pure MgH 2. Graphical abstract Image 1 Highlights • Alloy composition fabricated by GMSC method. • AZ31-4Ni-ECAP reaches the H 2 storing capacity of 7.0 wt.%. • AZ31-4Ni-ECAP alloy exhibits activation Energy of (104.73 kJ/mol). • ECAP shows better results than HEBM. [ABSTRACT FROM AUTHOR]

Cast commercial AZ61 magnesium alloys were processed through equal channel angular pressing (ECAP) and were comminuted into chips by filing with a rasp in order to measure their hydrogen storage properties. The effects of the number of ECAP passes and the processing route of ECAP on the hydrogen storage properties of AZ61 magnesium alloys were investigated. ECAP processing led to severe dynamic recrystallization and grain refinement of the AZ61 alloys. Of the analyzed samples, the AZ61 alloy processed via the Bc ECAP route with eight passes exhibited the smallest grain size, the fastest hydrogen absorption and desorption rates, and the highest gravimetric hydrogen storage capacity of 6.2 wt%. [ABSTRACT FROM AUTHOR]