Relationship between activation energy for hydrogen permeation and hydrogen permeation properties of amorphous Cu50Zr50 and Cu65Zr35 membranes

We investigate the role of hydrogen solubility and diffusivity on the activation energy for hydrogen permeability and the relationship between the hydrogen permeability and resistance to hydrogen embrittlement in amorphous membranes, Cu₅₀Zr₅₀ and Cu₆₅Zr₃₅. The membrane with the lower activation energy for permeation showed higher hydrogen permeability, but it showed lower durability under hydrogen atmosphere. This relationship between the two properties is discussed on the basis of the nature of the short-range ordered (SRO) structures constituting amorphous membranes under hydrogen ambient.     

Hydrogen permeation and structural features of melt-spun Ni–Nb–Zr amorphous alloys

Amorphous (Ni_0.6Nb_0.4)_100−xZr_x (x = 0, 20, 30, 40 and 50 at.%) alloys were prepared by the melt-spinning technique, and the hydrogen permeation through those alloy membranes was examined. The local atomic structure in these alloys was also investigated by radial distribution function (RDF) analysis. Moreover, hydrogen solubility and diffusivity were also measured in order to discuss the mechanism for hydrogen permeation. The permeability of the Ni–Nb–Zr amorphous alloys increases with Zr content and temperature. The maximum hydrogen permeability is 1.59 × 10⁻⁸ mol m⁻¹ s⁻¹ Pa^−1/2 at 673 K for the (Ni_0.6Nb_0.4)₅₀Zr₅₀ amorphous alloy. The (Ni_0.6Nb_0.4)₅₀Zr₅₀ amorphous alloy showed larger hydrogen solubility and diffusivity than the (Ni_0.6Nb_0.4)₇₀Zr₃₀ amorphous alloy. As the result, the (Ni_0.6Nb_0.4)₅₀Zr₅₀ amorphous alloy showed higher hydrogen permeability than the (Ni_0.6Nb_0.4)₇₀Zr₃₀ amorphous alloy at 673 K. The RDF analysis shows that the atomic distance between the Zr atoms increases by hydrogenation. The chemical ordering such that the number of Zr coordinates is much higher than that of Ni and Nb coordinates was found in the (Ni_0.6Nb_0.4)₇₀Zr₃₀ and (Ni_0.6Nb_0.4)₅₀Zr₅₀ amorphous alloys. The relation between the amorphous local structure and the permeation was discussed in detail.     

Effect of Co on the degradation of the hydrogen permeability of Ni-Nb-Zr amorphous membranes

The variation of the hydrogen permeability with time was monitored during the permeation of hydrogen through metallic amorphous membranes of Ni_45?XNb₃₀Zr₂₅Co_X (X=0, 7.5, and 15 at%) in the temperature range of 350 to 450 °C. For tests performed between 3 and 5 bars, the alloy with the medium content of Co, i.e., 7.5 at%, had the most pronounced degradation while the alloy without Co showed less of a decrease in the hydrogen permeability with time. The change in the hydrogen permeability with the Co content was discussed in connection with the difference in the activation barrier energy for crystallization in the alloys.     

Embrittlement of Pd-coated Ni−Nb−Ti−Zr amorphous alloys during hydrogen permeation

In this study, we report results of an investigation into the failure of Ni₆₀Nb₁₅Ti₁₅Zr₁₀ amorphous alloys occurring during hydrogen permeation performed at 473 K and 573 K. However, the amorphous membrane did not fail during test performed at higher temperatures (673 K and 773 K). The failure of the Pd-coated Ni₆₀Nb₁₅Ti₁₅Zr₁₀ amorphous ribbon is attributed to the cracking of the hydrogenated Pd coating induced by the formation of α′ hydride phase in the low temperature range. 0     

Hydrogen permeation properties of Pd-coated Ni−Nb−Ti−Zr amorphous alloys

Hydrogen permeability of Pd-coated Ni₆₀Nb₁₅Ti₁₅Zr₁₀ and Ni₆₀Nb₂₀Ti₁₅Zr₅ amorphous alloys was measured in the temperature range of 673 K to 773 K and was compared with the results obtained using Ni₆₀Nb₄₀, a binary amorphous alloy. The permeability thus measured was found to increase moderately increasing temperature. A long-term permeation test for the Pd-coated Ni₆₀Nb₁₅Ti₁₅Zr₁₀ amorphous alloy revealed high permeation stability up to 16.6 h.     

Electrochemical investigation of hydrogen absorption in a duplex stainless steel

Hydrogen permeation through and hydrogen desorption from duplex stainless steel membranes of various thickness were studied by the electrochemical technique. During the permeation experiments, one side of a membrane was charged with hydrogen by galvanostatic cathodic polarisation in 0.1M NaOH at 25 °C. After an interruption of the hydrogen charging, the desorption rate of hydrogen was measured at both sides of the membrane. The obtained permeation and desorption rates were analysed in terms of the real values of the hydrogen diffusivity (D_α) and the length of diffusion paths (L_α) in the ferrite phase. The total amount of absorbed hydrogen consists mainly of the hydrogen dissolved in the ferrite matrix (diffusible hydrogen) and the hydrogen dissolved in the austenite phase (reversibly trapped hydrogen). Amounts and concentrations of these two forms of hydrogen were evaluated. Some peculiarities and limitations as regards the usefulness of the permeation–desorption measurements for studying hydrogen in the duplex stainless steel membranes are given.     

Synthesis of La-based in-situ bulk metallic glass matrix composite

An in-situ dendritic crystalline α-La reinforced bulk metallic glass matrix composite was successfully synthesized by chill casting a La₆₆Al₁₄Cu₁₀Ni₁₀ alloy into copper mould with a rod diameter as large as 12 mm in diameter. The critical cooling rates for the formation of the in-situ composite determined by Bridgman solidification and for complete glass formation are 15 K/s and 450 K/s respectively. The thermal stability of the residual amorphous in the composite is higher than that of the fully amorphous sample of the same alloy.     

Zr65Al7.5Ni10Cu17.5和Zr65Al10Ni10Cu15合金的非晶和晶态薄带吸氢行为研究

研究两种不同成分具有较大过冷液相区的四元合金Zr65Al7.5Ni10Cu17.5和Zr65Al10Ni10Cu15，非晶和晶态薄带吸氢行为，结果表qt两种薄带的吸氢量均随着温度的升高而增大，非晶薄带的吸氢量要小于同等条件下的晶态薄带的吸氢量且只有在673K吸氢后形成了氢化物，Zr65Al7.5Ni10Cu17.5非晶和晶态薄带吸氢后分别生成了Zr2NiH4.7和ZrH2；而Zr65Al10Ni10Cu15非晶和晶态两种薄带最后生成的氢化物同为ZrH2。     

氢渗透合金膜的研究现状及发展趋势

氢渗透合金膜是一种重要的氢气提纯材料。本文简要介绍了目前存在的几种氢渗透合金膜的研究进展和各自的优缺点,重点讨论了氢渗透合金膜的工作原理、氢渗透性能和制备方法;详细分析了影响氢渗透性能的关键因素,包括氢渗透系数、氢扩散系数、氢溶解系数和氢脆性,提出了通过改善氢渗透合金膜的微观结构以提高膜材料的抗氢脆性、提高氢渗透系数和扩散系数的方法,最后对合金膜的发展趋势进行了探讨。     

The impact of different volume fractions of crystalline structures on the electrochemical behaviour of Mg67Zn29Ca4 alloys for biomedical applications

ABSTRACT

In this work, the influence of various volume fractions of the crystalline phase in an amorphous matrix of Mg₆₇Zn₂₉Ca₄ alloys was investigated for its corrosion resistance for biodegradable applications. An amorphous Mg₆₇Zn₂₉Ca₄ alloy was successfully fabricated using melt casting into a copper mould. Then, to obtain different ratios of the crystalline phase in an amorphous matrix, the obtained amorphous rods with 3?mm diameters were annealed at 190, 230, 250, and 400°C. The volume fraction of the crystalline phase was measured by X-ray diffraction, and the microstructures of the obtained alloys were determined based on scanning electron microscopy images. Electrochemical testing was conducted in simulated body fluid at 37°C. This report shows that the ratio of the volume fractions of amorphous and crystalline phases in alloy microstructures strongly influences their corrosion behaviours. The alloy with a fully amorphous structure was the most resistive in the analysed media.     

化学镀Pd膜的结构及其对Nb-Ti-Ni体系氢分离膜的氢渗透催化研究

采用碱性化学镀在Nb-Ti-Ni合金膜片表面和载玻片上沉积了Pd膜,利用X射线衍射(XRD),能谱(EDS)、扫描电子显微镜(SEM),示差扫描量热仪(DSC)等手段对Pd沉积膜的相结构、成分、形貌及热稳定性进行了分析。结果表明,制备的Pd沉积膜为非晶态结构,膜层呈现球状颗粒密排沉积形态,颗粒尺寸在1μm左右,膜中的P含量在3%～4%(质量分数,下同)。膜的热稳定性研究表明,在经675K热处理后,膜层仍保持其初始的颗粒密排沉积特征,随着温度的升高,颗粒尺寸有轻微增大的趋势,出现Pd相和Pd6P相。电化学测试结果表明,制备的非晶态Pd膜可显著提高合金膜片的氢渗透电流密度,相应的氢扩散系数增大,而非晶膜层经热处理后,其氢扩散系数有较明显的降低。     

Fabrication of a Cu36Zr48Al8Ag8 bulk metallic glass sheet by atmosphere-controlled vertical twin roll strip casting

Large-scale fabrication of Cu₃₆Zr₄₈Al₈Ag₈ amorphous alloy sheets having with lengths above 250 mm was performed using atmosphere-controlled twin roll strip casting. By constructing a continuous cooling transformation diagram, the critical cooling rate was determined to be 212.6 K/s. The size and morphology of the crystalline phases within the amorphous matrix, which was Al-rich and Ag-depleted, were confirmed by scanning electron microscopy. The presence of a small volume fraction fine dendritic crystalline phase was necessary for the improved plasticity of the amorphous strip under tensile deformation mode.     

Nanocrystallization of Zr61Al7.5Cu17.5Ni10Si4 metallic glass

The primary nanocrystallization behavior and microstructural evolution of the Zr₆₁Al_7.5Cu_17.5Ni₁₀Si₄ alloy during annealing were investigated by isothermal differential scanning calorimetry, X-ray diffractometry and transmission electron microscopy. During continuous heating of the 4Si and the base (contains no Si) amorphous alloys at a heating rate of 10 K/min, the saturation point of nucleation for the 4Si amorphous alloy occurs at a crystallization fraction of 78%, which is significantly higher than 65% for the base alloy, implying that these metalloid atoms would extend the nucleation stage and refine crystalline particles. The sequence of crystallization phase from the amorphous matrix for the isothermally annealed 4Si amorphous alloy at 703 K is observed to be Zr₂Cu and Zr₂Ni at the early stage, Zr₃Al at an intermediate stage, and Zr₂Si at the final stage. Moreover, enrichment of Si atoms at the interface between Zr₂Cu crystal and the amorphous matrix is detected. This may result in increasing the thermal stability of the remaining amorphous phase and retardation of the crystal growth of Zr₂Cu particles.     

In-situ XAFS study on structures and devitrifications of Ni–B nano-amorphous alloys

The local structures and the devitrifications of Ni₇₀B₃₀ nano-amorphous alloys prepared by chemical reduction method were studied by in-situ X-ray absorption fine structure (XAFS). The results indicate that the preparation temperature strongly affects the local structures of Ni₇₀B₃₀ amorphous alloys. The coordination geometry surrounding Ni atoms is a structure of amorphous Ni-like for the Ni₇₀B₃₀ (273 K) while the Ni₇₀B₃₀ (313 K) has amorphous Ni₃B-like structure. In-situ XAFS analysis revealed that the Ni₇₀B₃₀ amorphous alloy prepared at the low temperature of 273 K is directly crystallized into the metallic Ni in a wide temperature range from 498 to 598 K. However, the crystallization of the sample prepared at the high temperature of 313 K is accomplished in two steps: the generation of intermediate product of crystalline Ni₃B starting from 548 K and finishing at about 573 K; the unique formation of crystalline Ni at about 598 K.     

Oxidation behavior of a Zr–Cu–Al–Ni amorphous alloy in air at 300–425 °C

The oxidation behavior of Zr–30Cu–10Al–5Ni bulk metallic glass and its crystalline counterpart was studied over the temperature range of 300–425 °C in dry air. In general, the oxidation kinetics of both amorphous and crystalline alloys followed a two- or three-stage parabolic rate law at T⩾350 °C, while at 300 °C the amorphous alloy oxidized following a linear behavior. The oxidation rate constants for the amorphous alloy are slightly higher than those for the crystalline alloy at 350–400 °C. The scale formed on the amorphous alloy consists of mainly tetragonal-ZrO₂ at 300 °C, while a mixture of monoclinic-ZrO₂ (m-ZrO₂) and tetragonal-ZrO₂ (t-ZrO₂) and some CuO were detected at higher temperatures. The scale formed on the crystalline alloy, on the other hand, consists of mainly Al₂O₃, some tetragonal-ZrO₂, and a slight amount of monoclinic-ZrO₂ at 300 °C. At higher temperatures, the crystalline alloy consists of mainly monoclinic-ZrO₂, some CuO and Cu₂O, and limited tetragonal-ZrO₂. It is suggested that the formation of Al₂O₃ (at 300 °C) and CuO/Cu₂O (at 350-400 °C) on the crystalline alloy is responsible for the reduced oxidation rates as compared with those of amorphous alloy.     

Microstructure and hydrogen permeation of cold rolled and annealed Nb40Ti30Ni30 alloy

The ultimate rolling reduction rate (r_u) of the as-cast Nb–TiNi alloys was evaluated by measuring the thickness changes in cold rolled samples. Furthermore, the effects of cold rolling and subsequent anneal on hardness, microstructure, hydrogen permeability (Φ) and hydrogen flux J of the as-cast Nb₄₀Ti₃₀Ni₃₀ alloy (mol%) were examined by a Vickers hardness tester, a scanning electron microscope (SEM), and a mass flow meter, respectively. The value of Φ for the Nb₄₀Ti₃₀Ni₃₀ alloy was reduced with increasing rolling reduction rate and attained to one third of the original one by 50% rolling reduction, but recovered to the original one by anneal at 1373 K for 605 ks. Hydrogen flux J varied inversely proportional to the membrane thickness at 673 K. J of 12 ccH₂/cm²/min was attained for the sample with the thickness of 120 μm. The present work has demonstrated that rolling and the subsequent anneal are effective and useful for the preparation of the hydrogen permeation Nb–TiNi alloy membrane.     

The influence of volume fraction of amorphous phase on corrosion resistance of Mg67Zn 29Ca 4 alloy

The aim of this study was to investigate the structure and corrosion resistance of amorphous, amorphous‐crystalline, and crystalline Mg₆₇Zn₂₉Ca₄ alloy for biodegradable applications. This paper presents a preparation method and results of the structural characterization and corrosion resistance analysis of the material. Samples were prepared in the form of 3 mm diameter rods. The structure of the alloy was examined with the use of X‐ray diffractometry and scanning electron microscopy. The thermal properties of the samples were examined with differential scanning calorimetry (DSC). Results of DSC analysis were used to determine heat treatment temperatures, allowing to obtain different fractures of crystalline phase in the material. Corrosion resistance of heat‐treated samples was investigated by immersion tests and electrochemical measurements performed in the simulated body fluid. The X‐ray diffraction results confirmed that the prepared Mg₆₇Zn₂₉Ca₄ alloy's structure is fully amorphous. After heat treatment, samples with different fractions of amorphous phase in the structure were obtained. Immersion tests of the samples showed that the structure significantly influenced corrosion resistance in examined materials. It should be pointed out, that certain amounts of crystalline phase in amorphous matrix can greatly improve the corrosion resistance of Mg₆₇Zn₂₉Ca₄ alloy.     

Formation, properties and microstructure of amorphous/crystalline composite Ag20Cu30Ti50 alloy using miscibility gap

The aim of the work was to produce the amorphous/crystalline composite with uniform distribution of fine crystalline soft phase. Silver–copper–titanium Ag₂₀Cu₃₀Ti₅₀ alloy was prepared using 99.95 wt% Ag, 99.95 wt% Cu, 99.95 wt% Ti that were arc-melted in argon atmosphere. Then the alloy was melt spun on a copper wheel with linear velocity of 33 m/s. Investigation of the microstructure for both arc-melt massive sample and melt-spun ribbons was performed with use of scanning electron microscope (SEM) with EDS, light microscope (LM) and X-ray diffraction. The thermal stability was evaluated by differential scanning calorimetry (DSC). The properties such as Young modulus and Vickers hardness number before and after crystallization of the amorphous matrix were measured with use of nanoindenter. The microstructure was investigated by transmission electron microscope (TEM). It was found, that the alloy has a tendency for separation within the liquid state due to the miscibility gap which resulted in segregation into Ti–Cu–Ag matrix and Ag-base spherical particles after arc-melting. During rapid cooling through the melt spinning the Ag₂₀Cu₃₀Ti₅₀ alloy formed an amorphous/crystalline composite of fcc silver-rich spherical particles within the amorphous Ti–Cu–Ag matrix.     

Effects of electrochemical hydrogenation of Zr-based alloys with high glass-forming ability

Zr–(Ti)–Cu–Al–Ni metallic glasses exhibit a high thermal stability corresponding to a wide undercooled liquid region. Depending on their composition, the formation of metastable intermediate phases, e.g. a quasicrystalline phase is possible. The combination of early and late transition metals makes these alloys very interesting regarding their interaction with hydrogen. Amorphous Zr₅₅Cu₃₀Al₁₀Ni₅, Zr₆₅Cu_17.5Al_7.5Ni₁₀ and Zr₅₉Ti₃Cu₂₀Al₁₀Ni₈ ribbons were prepared by melt spinning and their microstructure and thermal behaviour was checked by X-ray diffraction, transmission electron microscopy and differential scanning calorimetry. The cathodic reactivity of alloy samples at different microstructural states and after pre-etching in 1 vol.-% HF was investigated in 0.1 M NaOH by applying potentiodynamic polarisation techniques. Galvanostatically hydrogenated samples were characterised by XRD, DSC, TEM and thermal desorption analysis (TDA). For amorphous Zr₅₉Ti₃Cu₂₀Al₁₀Ni₈ samples an increase in electrochemical surface capacity by two orders of magnitude is observed after pre-etching. Compared to the quasicrystalline and crystalline alloy, the hydrogen reduction takes place at significantly lower overpotentials. Zr-based alloys cathodically absorb hydrogen up to H/M=1.65 while keeping the amorphous structure. Already small amounts of hydrogen cause a significant decrease of the thermal stability and changes in the crystallisation sequence. The hydrogen desorption is a two-stage process: (T<623 K) hydrogen desorption from high interstitial-site energy levels and (T>623 K) zirconium hydride formation and subsequent transformation under hydrogen effusion. Hydrogen suppresses the oxygen-triggered formation of metastable phases upon heating and supports primary copper segregation. At very high H/M ratios, severe zirconium hydride formation causes the crystallisation of new compounds.     

Difference between mechanical alloying and mechanical disordering in the amorphization reaction of Al50Ta50 in a rod mill

Amorphous Al₅₀Ta₆₀ alloy powders have been synthesized by mechanical alloying (MA) from elemental powders of aluminium and tantalum, and mechanical disordering (MD) from crystalline intermetallic compound powders of AlTa respectively using the rod milling technique. The mechanically alloyed and the mechanically disordered alloy powders were characterized by X-ray diffraction, scanning electron microscopy, electron probe microanalysis, transmission electron microscopy, differential thermal analysis, differential scanning calorimetry and chemical analysis. The results have shown that the crystal-to amorphous transformation in the MD process occurs through one stage, while the crystallineto-amorphous formation in the MA process occurs through three stages. At the early and intermediate stages of the MA time, heating the alloy powders to 700 K leads to the formation of an amorphous phase by a solid-state amorphizing reaction. At the final stage of the MA time, the amorphous phase is crystallized through a single sharp exothermic peak. Contrary to this, amorphous alloy powders produced by MD are crystallized through two broad exothermic peaks.