W-2 wt.%Y2O3 composite material with uniform distribution of yttrium element was fabricated through processes of mechanical alloying (MA) and spark plasma sintering (SPS). The relevant productions were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The XRD showed that the W-2 wt.%Y2O3 composite powder, including tungsten matrix and Y2O3 particles, was refined to nanometer sizes during the MA process. The SEM and TEM micrographs showed that the MA produced composite powder presented a lamellar morphology and contained many dislocations and microcracks. The EDS showed that the Y and O elements were uniformly distributed in the W matrix after mechanically alloying for 15 h. The W-2 wt.%Y2O3 composite material with uniform distribution of yttrium was obtained by sintering of the MA produced composite powder.XRD patterns of W-2%Y2O3 composite powder after different MA time, showing evolution of FWHM of tungsten matrix peaks and intensity of Y2O3 peaks (a) Evolution of tungsten matrix peaks; (b) Local XRD patterns highlighting Y2O3 peaks

Addition of yttrium in zirconium causes precipitates of yttrium, which form two types of particles and are oxidized upon heat treatment. One type of particles with sub-micrometer scale sizes has a low population, whereas the other with nano scale sizes has a high population and cluster distribution. Owing to strong affinity of yttrium to hydrogen, the nanoparticles, mostly within the grains of the Zr–Y alloy, attract nucleation of hydrides at the clusters of the nanoparticles and cause preferential distribution of intragranular hydrides. In comparison with that of Zr, additional nanoparticles in the Zr–Y alloy impede further growth of hydride precipitates during hydriding. It is deduced that the impediment of growing hydride precipitates by the nanoparticles is developed during an auto-catalytic nucleation process, which leads to formation of thin and intragranular hydrides, favorable to mitigation of hydride embrittlement.

Helium-containing pure Ti and Ti–Y alloy films synthesized by magnetron sputtering method were investigated using techniques of thermal desorption spectrometry (TDS), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The relevant helium release behavior and microstructure changes were characterized. The mechanical properties of the films were also examined by nanoindentation. It was found that the helium bubbles in the alloy were inclined to be trapped at the interfaces between Y2O3 precipitates and Ti matrix, and there existed a segregation of Y on the surface of the films. Both factors could shift the related TDS peaks to higher temperatures. In addition, the detrimental helium influence on mechanical properties could be suppressed by dispersion of incoherent Y2O3 precipitates in the alloy films, which reduced the sizes of both helium bubbles and matrix grains, and acted as efficient trapping sites for helium bubbles.

Helium-containing titanium films synthesized by magnetron sputtering method were investigated using thermal desorption spectrometry (TDS), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Helium evolution behaviors under thermal treatment from room temperature to 1500 °C were characterized. Four peaks appeared in TDS at around 100, 420, 700, and 1250 °C were identified and attributed to helium desorption from the specimen surface, substitutional helium (helium atom in a vacancy), small HemVn clusters with different helium-to-vacancy ratios, and helium bubbles or voids, respectively. The helium evolution under thermal treatment composed of two coexisting and competing processes, where the faster process dominated in relevant temperature range, i.e. helium diffusion and release at low temperatures, and bubble or void formation at high temperatures. Three characteristic temperatures in TDS were identified in description of the phenomenon.

The permeability and diffusivity of hydrogen in directionally solidified polycrystalline and single crystal nickel foils were measured by gas permeation method. The results showed that both hydrogen diffusivity and permeability were higher in directionally solidified nickel specimen than those in single crystal one at the temperature ranging from 300 to 480 °C, and confirmed the existence of short-circuit diffusion along the grain boundaries (GBs) in the directionally solidified nickel. The results suggested that the rapid diffusion along GBs was more obviously characterized in terms of higher permeability rather than higher diffusivity. The contribution of grain boundary to hydrogen transportation was represented by the differences of diffusivity (and permeability) in single crystal nickel and directionally solidified nickel. By modifying the Fick’s first diffusion law and counting the grain boundary density, the hydrogen diffusivity and permeability of rapid diffusion along GBs were calculated. The results suggested both the diffusivity and permeability fit the Arrhenius relationship well at different temperature.

A porous nickel support was successfully prepared by uniaxial compression of nickel powders. Microstructures and mechanical properties of Nb40Ti30Ni30 membranes fabricated by magnetron sputtering were investigated. Deposited and annealed Nb40Ti30Ni30 membranes consisted of amorphous and crystalline phases, respectively. Higher base temperature was shown to increase the hardness and elastic modulus of the Nb40Ti30Ni30 membrane. Pd/Nb40Ti30Ni30/Pd/porous nickel support composite membranes were then fabricated using a multilayer magnetron sputtering method. The hydrogen permeability of the composite membranes with amorphous and crystallized Nb40Ti30Ni30 metal layer was measured and compared with that of self-supported Nb40Ti30Ni30 and Pd alloys. Solid-state diffusion was shown to be the rate-controlling factor when the thickness of the Nb40Ti30Ni30 layer was about 12 μm or greater, while other factors were in effect for thinner layers (such as 6 μm). The Pd/Nb40Ti30Ni30/Pd/porous nickel support composite membrane exhibited excellent permeation capability and satisfactory mechanical properties. It is a promising new permeation membrane that could replace Pd and PdAg alloys for hydrogen separation and purification.

First-principles calculations based on density functional theory have been performed to investigate the behaviors of He in hcp-type Ti. The most favorable interstitial site for He is not an ordinary octahedral or tetrahedral site, but a novel interstitial site (called FC) with a formation energy as low as 2.67 eV, locating the center of the face shared by two adjacent octahedrons. The origin was further analyzed by composition of formation energy of interstitial He defects and charge density of defect-free hcp Ti. It has also been found that an interstitial He atom can easily migrate along 〈0 0 1〉 direction with an activation energy of 0.34 eV and be trapped by another interstitial He atom with a high binding energy of 0.66 eV. In addition, the small He clusters with/without Ti vacancy have been compared in details and the formation energies of HenV clusters with a pre-existing Ti vacancy are even higher than those of Hen clusters until n ⩾ 3.