We studied the Nb-H system over extended pressure and temperature ranges to establish the highest level of hydrogen abundance we could achieve from the resulting alloy. We probed the Nb-H system with laser heating and x-ray diffraction complemented by numerical density functional theory-based simulations. New quenched double hexagonal close-packed (hcp) NbH2.5 appears under 46 GPa, and above 56 GPa cubic NbH3 is formed as theoretically predicted. Nb atoms are arranged in close-packed lattices which are martensitically transformed in the sequence: face-centered cubic (fcc) → hcp → double hcp (dhcp) → distorted body-centered cubic (bcc) as pressure increases. The appearance of fcc NbH2.5−3 and dhcp NbH2.5 cannot be understood in terms of enthalpic stability, but can be rationalized when finite temperatures are taken into account. The structural and compressional behavior of NbHx>2 is similar to that of NbH. Nevertheless, a direct H-H interaction emerges with hydrogen concentration increases, which manifests itself via a reduction in the lattice expansion induced by hydrogen dissolution

In this paper we show how reliable measurements on porous ceramic films can be made by appropriate nanoindentation experiments and analysis. Room-temperature mechanical properties of the mixedconducting perovskite material La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3−δ (LSCF6428) were investigated by nanoindentation of porous bulk samples and porous films sintered at temperatures from 900-1200 °C. A spherical indenter was used so that the contact area was much greater than the scale of the porous microstructure. The elastic modulus of the bulk samples was found to increase from 33.8-174.3 GPa and hardness from 0.64-5.32 GPa as the porosity decreased from 45-5% after sintering at 900-1200 °C. Densification under the indenter was found to have little influence on the measured elastic modulus. The residual porosity in the "dense" sample was found to account for the discrepancy between the elastic moduli measured by indentation and by impulse excitation. Crack-free LSCF6428 films of acceptable surface roughness for indentation were also prepared by sintering at 900-1200 °C. Reliable measurements of the true properties of the films were obtained by data extrapolation provided that the ratio of indentation depth to film thickness was in the range 0.1 to 0.2. The elastic moduli of the films and bulk materials were approximately equal for a given porosity. The 3D microstructures of films before and after indentation were characterized using FIB/SEM tomography. Finite element modelling of the elastic deformation of the actual microstructures showed excellent agreement with the nanoindentation results.

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High-vinyl polybutadiene rubber (HVBR) and solution-polymerized styrene-butadiene rubber (SSBR) can meet the requirements of high-performance tires due to their excellent wet skid resistance and lower rolling resistance. In this paper, the effects of the vinyl and phenyl groups and their contents on the vulcanization behavior, mechanical strength, fatigue resistance, heat resistance, and wear resistance of HVBR and SSBR were investigated, and the dynamic viscoelasticities of HVBR and SSBR vulcanizates with or without carbon black were explored by dynamic mechanical analysis (DMA). The experimental results showed that the vinyl groups contributed more to the wear resistance and fatigue resistance of vulcanizates than the phenyl groups, but the phenyl groups contributed more to the mechanical strength of the vulcanizates than the vinyl groups. The DMA results showed that the vinyl and phenyl groups could significantly improve the road-gripping capability and wet skid resistance of HVBR and SSBR vulcanizates, but carbon black could slightly weaken the effect of vinyl and phenyl groups on the wet skid resistance of vulcanizates, and the effect of carbon black on vinyl groups was more significant. Despite the presence of carbon black, the phenyl groups contributed more heat buildup to the vulcanizates than the vinyl groups.

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