By using a two-dimensional axisymmetric finite element model, the indentation hardness has been studied with different combinations of material properties at different indentation depths. As the forward problem, the testing hardness is not only a function of material properties (E, σy, and n), indenter geometry (half apex angle, indenter shape), and friction, but also relating to the indentation depth. Based on the previous research on size effect, a model of correlation between several indentation experiment parameters (hardness H, maximum load Pm, and loading curvature C) and material properties has been derived. From simulation results, a better fitting result is obtained by the established model. Furthermore, the characteristic length h∗ in Nix/Gao model has been rewritten and discussed with material properties accordingly.

In this study, thermodynamic properties of BC2N under extreme conditions have been reported by using first-principle calculations and quasi-harmonic Debye model. Isochoric heat capacity (Cv) of BC2N at normal temperature and pressure is 23.15 kJ mol−1 K−1 and it increases with the temperature and decreases with the pressure. In the low temperature region, pressure has no obvious influence on phonons and thus the decrease of Cv is very slow. In the medium temperature region, the decrease of Cv becomes steep. The reason is that high pressure plays an important role in controlling the vibration of atoms. In the high temperature region, the decrease of Cv becomes slow. Debye temperature (θ) decreases with the temperature. However, the tendency is not obvious in the low temperature region but very clear in high temperature. Moreover, θ increases with pressure and the amplitude is larger in higher temperature. Because of the four covalent bonds with different strength and distribution asymmetric thermal expansion along different axes occurs. The value of thermal expansion coefficient along c axis is more than that of along a and b axes.

In this work, mechanical stability, thermodynamic and elastic properties of rhodium (Rh), rhodium monohydride (RhH), and the newly discovered rhodium dihydride (RhH2) under high temperature and pressure are studied by ab initio method together with quasiharmonic Debye model. Mechanical stability test indicates that RhH2 is no longer mechanically stable when pressure is higher than 22.7 GPa, which is quite less than the dynamically stable pressure (90 GPa). The heat capacity at constant volume (Cv) of Rh, RhH, or RhH2 increases proportional to T3 at low temperature, and tends to Dulong–Petit limit (about 241.67, 478.47, and 706.15 J/(kg·K), respectively). The thermal expansion coefficient (α) of Rh, RhH, and RhH2 increases acutely when temperature is not more than 300 K. And then, the increase of α slows down. The α reduces with pressure transiently. H atom's entering in fcc-Rh lattice would greatly change the electron density distribution, which would cause obvious difference in thermodynamic and elastic properties between Rh, RhH, and RhH2.

The corrosion behavior of 2099 Al–Li alloy in NaCl aqueous solutions with different concentrations (1.5, 3.5, and 5.0% in mass fraction) was investigated. Its corrosion resistance was evaluated using electrochemical measurements together with full immersion tests. The results showed that the 2099 Al–Li alloy possessed good corrosion resistance in NaCl aqueous solutions. Its corrosion rate increased with increasing chloride ion concentration. The main form of corrosion failure was pitting corrosion. The impurity containing sulfur leads to surface pitting. The oxide films that formed during the manufacturing process offer a good resistance to corrosion. They are likely to suffer separation, cracking, and drop-off when immersed in aggressive NaCl aqueous solution. The good corrosion susceptibility of the alloy may be attributed to homogeneous coherent nanoscale precipitates.

As a promising reinforcement of aluminum alloy, in situ formed Al3Ti particles have attracted more attention in the fabrication of aluminum matrix composites. In our research, in situ Al3Ti/7075 alloy composites were fabricated by adding K2TiF6 salt powders into molten 7075 alloy at 750 °C via casting method. The formation of in situ Al3Ti particles and their effects on the microstructure and mechanical properties of 7075 alloy, including hardness, ultimate tensile strength (UTS), and yield strength (YS), were investigated. The results showed that in situ formed Al3Ti particles were rod-like in morphology, with the average length and width of 15 µm and 5 µm, respectively. Due to the nucleating effect of Al3Ti particles, α-Al crystals of 7075 alloy transferred from dendritic to equiaxed structure in morphology, the size of which decreased obviously as well. Compared with 7075 alloy, the hardness, UTS, and YS of in situ Al3Ti/7075 alloy were improved by 14.3%, 18.1%, and 25.8%, respectively.

(Cu0.47Zr0.45Al0.08)100–xDyx (x = 0, 1, 2, 3, 4; at.%) metallic glasses with greatly enhanced glass-forming ability (GFA) and plasticity were synthesized based on microalloying technique. The structure, thermal stability, and elastic properties of the BMG samples were studied by x-ray diffraction (XRD), differential scanning calorimetry (DSC), and ultrasonic measurements, respectively. With addition of minor dysprosium (Dy), fully metallic glassy rods with diameters exceeding 20 mm could be successfully fabricated by copper mold casting. In addition, the Cu–Zr–Al–Dy BMGs exhibit good mechanical properties under a compressive deformation mode, i.e., high yield strength of 1735–1906 MPa, Young's modulus of 85–100 GPa, and distinct plastic strain up to 4.02%. The strength and plasticity show remarkable correlations with glass transition temperature and Poisson's ratio, respectively. The role of minor Dy addition in enhancement in GFA and mechanical property of the Cu-rich BMGs is also discussed.

In this study, impurity segregation and solute drag effects on grain boundary (GB) motion were investigated in a binary Al–Ni model system with an inclined Σ5 GB by direct molecular dynamics simulations. By extending the interface random walk method to impure systems, it was found that the GB mobility was significantly influenced by the segregated impurities, which generally decreased as the impurity concentration increased. Moreover, based on simulations at different temperatures and impurity concentrations, we validated that the solute drag effects can be well modeled by the theory proposed by Cahn, Lücke, and Stüwe (CLS model) more than 50 years ago, provided that proper adaptations were made. In particular, we found that in strongly segregated GB system, the boundary mobility was deeply correlated to the impurity diffusivity in the direction perpendicular to the boundary plane in the frame of the moving boundary, instead of the impurity bulk diffusivity assumed in the original CLS model and many past studies.

The thermoelectric properties of Bi2Sr2Co2Ox (BSC-222) bulk materials prepared by three different processing methods, i.e., conventional sintering, hot pressing, or partial melting, were investigated and compared. The electrical current, temperature difference for Seebeck coefficient, and thermal diffusion were measured in the same direction. The hot pressing and partial melting are effective processing methods for improving the electrical transport property in BSC-222 bulk materials due to an improvement of density in hot-pressed samples or by grain growth during partial melting process. For partially melted samples, a decrease in the thermal conductivity is also observed. The highest dimensionless thermoelectric figure of merit (ZT) values have been obtained in the sample prepared by partial melting method, for which ZT has been increased by a factor of 2.7 by comparison with bulk materials prepared by conventional sintering. At 700 °C in air, ZT value reaches 0.27 for partially melted Bi2Sr2Co2Ox bulk materials. This study shows that optimized electrical and thermal transport properties can be achieved in BSC-222 bulk materials possessing microstructures with both large average grain size and appropriate bulk density.

The solid-state phase transitions of bismuth(III) oxide (Bi2O3) nanoparticles were investigated by complementary methods such as differential scanning calorimetry, differential thermal analysis with combined thermogravimetry and mass spectrometry, and high-temperature x-ray diffraction as compacted nanopowder. At room temperature the particles resided in the β-phase, which is usually a metastable high-temperature phase of bulk Bi2O3. The complementary experimental methods were linked and a nanophase (tetragonal β-phase) → bulk-phase (monoclinic α-phase) transition was identified which was preceded by crystal growth and evaporation of O and C containing species. It was also shown that the atmosphere (more precisely its absolute pressure) has an influence on the transition behavior. An interpretation was proposed that successfully explains all observations from this work and from literature: A sudden destabilization takes place around 735 K due to the loss of the stabilizing, carbonized surface. This leads to the observed transformation to the bulk-phase. But if the particles are smaller than a certain, critical size in the nanorange and are not allowed to grow, they remain in the nanophase until they melt.