The influences of (SiN)+ and Eu2+ concentration on the optical properties of BaAl2−xSixO4−xNx:Eu2+ were investigated. The lifetime results show that there are two different cation sites occupied by Eu2+ ions and the energy transfer occurs between them. The Huang–Rhys factor and the Stokes energy shift were determined, and thermal quenching with increasing temperature was observed. Finally, intense yellowish-green light emitting diodes (LED) with the color coordinate of (0.2936, 0.4483) under a forward-bias current of 20 mA was successfully fabricated on the basis of a structure consisting of BaAl2−xSixO4−xNx:Eu2+ phosphor and near-ultraviolet (∼395 nm) GaN chip.

The effects of FePO4 nanoscale coating on PtRu thin films were investigated on the block of Ru crossover. Ru dissolution was examined by the accelerated-potential cycles between 0.4 and 1.05 V. The results showed that Ru dissolution from FePO4-coated PtRu surface was inevitable due to the direct contact between the PtRu surface and aqueous electrolyte. However, the FePO4 coating layer on PtRu thin-film electrodes effectively retained the dissolved Ru species, thus preventing the dissolved Ru species from diffusing into the electrolyte. Moreover, the retained Ru species within the FePO4-coating layer were redeposited onto the PtRu surface during the cycling in the fresh electrolyte.

Mg-Li-Al alloy was prepared by ingot casting and then underwent subsequent reactive ball milling. A Mg-Li-Al-H complex hydride was obtained under a 0.4 MPa hydrogen atmosphere at room temperature, and as high as 10.7 wt% hydrogen storage capacity was achieved, with the peak desorption temperature of the initial step at approximately 65 °C. The evolution of the reaction during milling, as well as the effect of Li/Al ratio in the raw materials on the desorption properties of the hydrides formed, were studied by x-ray diffraction and simultaneous thermogravimetry and differential scanning calorimetry techniques. The results showed that mechanical milling increases the solubility of Li in Mg, leading to the transformation of bcc β(Li) solid solution to hcp α(Mg) solid solution, the latter continues to incorporate Li and Al, which stimulates the formation of Mg-Li-Al-H hydride. A lower Li/Al ratio resulted in faster hydrogen desorption rate and a greater amount of hydrogen released at a low temperature range, but sacrificing total hydrogen storage capacity.

In this study, p-type CuInSe2 (CIS) films were prepared by selenization of one-step electrodeposited Cu-In-2Se (atomic ratio) precursors. To obtain high-quality, dense, and homogeneous CIS films for solar cell application, the effects of substrate temperatures during selenization and precursor compositions on the final microstructures were systematically investigated. The precursor layers evolved in very different ways under different selenization conditions. The final microstructures and phases of the films depended critically on the precursor compositions, selenization temperature, and the selenization thermal process history. Low melting temperature CuxSe phase, which tended to segregate at the film surface, can efficiently assist the CIS grain growth. Large hexagonal CuSe platelets were formed at a temperature as low as 170 °C in Cu-rich precursor, which acted as an element-transport flux agent at higher temperature under high Se vapor and reacted with In-Se selenide to form CIS at temperatures above 500 °C. Good crystalline quality chalcopyrite CIS film was obtained at a selenization temperature of 550 °C.

The poor wettability between ceramics and metals is a main obstacle in obtaining high-performance metal-matrix composites (MMCs) parts using direct metal laser sintering (DMLS). Rare earth (RE) elements, due to their unique physical and chemical properties, have high potential for improving laser processability of MMCs. In this work, a comparative study was performed to investigate the influence of RE–Si–Fe addition on microstructural features and mechanical properties of DMLS processed tungsten carbide (WC) particle reinforced Cu MMCs parts. It showed that by adding 3 wt% RE–Si–Fe, the WC reinforcing particles were refined, the particle dispersion state was homogenized, and the particle/matrix interfacial compatibility was enhanced. The RE–Si–Fe-containing WC/Cu MMCs parts possessed significantly elevated mechanical properties, i.e., densification level of 95.7%, microhardness of 417.6 HV, fracture strength of 201.8 MPa, and friction coefficient of 0.8. The metallurgical functions of the RE–Si–Fe additive for the improvement of DMLS quality of MMCs parts were discussed.

In the present paper, we solidified magnesium-based AZ91D alloys in a superconducting magnetic field when an alternating current flowed through the alloy. As the direction of the magnetic field is perpendicular to that of the alternating current, a periodic electromagnetic force is produced to activate an electromagnetic vibration (EMV) on the alloy during solidification. The microstructure formation and microtexture evolution processed by EMV were examined. A significant difference arises in electrical resistivity between a solid and a liquid in the mushy zone of the alloy, making the solid move faster than the liquid and thus generating uncoupled motion, from which melt flow is initiated. The texture evolution obtained by x-ray diffraction and electron backscatter diffraction (EBSD) mapping reveal a strong dependence of melt flow intensity versus vibration frequency. A further analysis reveals that melt flow is rather weak when the vibration frequency is too low and thus the segmentation of growing crystals cannot be thoroughly completed. At medium vibration frequencies, severe fluid flow occurs, which favors fragmentation and thus results in a refined microstructure and a random microtexture. When the vibration frequency is too high, the relative leading distance covered by the mobile solid is rather short and melt flow once again becomes weak. Meanwhile, the static magnetic field makes the crystals orient to their easy magnetization direction and thus yields highly aligned textures. Experimentally, the present systematic observation indicates that the role of melt flow is of substantial importance in revealing the origin of structure formation when the alloy is solidified at various vibration frequencies.

The grain size of magnesium solid-solution alloys with lithium, indium, and/or zinc has been determined. Lithium, indium, and zinc additions decreased the grain size, D, of magnesium solid-solution alloys cast in a copper mold. The most effective grain refinement was obtained by zinc. In binary Mg–Zn alloys, grain size is related to the growth restriction factor, Q as D = 94 + 312/Q. In Mg–Li and Mg–In binary alloys, grain size versus growth relationships described as D = a + b/Q indicated that these alloys have lower numbers of nucleants but with higher potency than the Mg–Zn binary system. For Mg–Li and especially Mg–In, grain size could be related to growth restriction as D = 383Q−n with higher R2. Ternary and quaternary alloys based on Mg–Zn with Li and/or In additions also follow the D = a + b/Q relationship with the parameters indicating a larger number of lower potency nucleants than the Mg–Zn binary alloys. Electron probe microanalysis showed that Mg–Zn alloys exhibit pronounced and persistent grain-boundary enrichment of Zn, pointing toward Scheil solidification.

Indentation tests involving a constant-loading rate stage followed by a constant-load stage were performed on annealed and 20% cold-worked Au to investigate the effect of indentation depth and initial dislocation density on the indentation deformation process. The indentation strain rate data were analyzed in terms of an obstacle-limited dislocation glide mechanism. The apparent activation energy was of the order of 0.16 μb3 and was neither a function of initial indentation depth nor cold work. The results of Haasen plot activation analysis and direct transmission electron microscopy (TEM) observations indicate that more mechanical work must be applied during the constant-loading rate stage due to the large amount of work hardening compared with the constant-load stage where considerably more dislocation recovery occurs.

The hardness of a material is generally affected by the indentation size effect. The strain gradient plasticity (SGP) theory is largely used to study this load dependence because it links the hardness to the intrinsic properties of the material. However, the characteristic scale-length is linked to the macrohardness, impeding any sound discussion. To find a relevant parameter, we suggest introducing a hardness length-scale factor that only depends on the shear modulus and the Burgers vector of the material and is easily calculable from the relation of the SGP theory. The variation of the hardness length-scale factor is thereafter used to discuss the hardness behavior of a magnetite crystal, the objective being to study the effect of the cumulative plasticity resulting from cyclic indentation. As a main result, the hardness length-scale factor is found to be constant by applying repeated cycles at a constant peak load whereas the macrohardness and the characteristic scale-length are both cycle dependent. When using incremental loads, the hardness length-scale factor monotonically decreases between two limits corresponding to those obtained at high and low loading rates, while the dwell-load duration increases. The physical meaning of such behavior is based on the modification of the dislocation network during the indentation process depending on the deformation rate.

The morphology of the fracture surfaces of a bulk metallic glass (BMG) tested under compression was systematically studied. Experimental results showed that the fracture surface always comprises two kinds of zones, starting with a relatively smooth zone followed by the second zone with vein patterns. It implies strongly that the plastic deformation of BMGs always starts with a cooperative shear. The following catastrophic fracture characterized by the vein patterns may or may not occur, depending on the magnitude of this shear, which is controlled by the sample size and machine stiffness. This phenomenon was interpreted based on the temperature rise resulting from the work done during the cooperative shear. It revealed that for small samples, the shear is so small that the temperature increase is insignificant, accounting for the extensive serrated flow, while the temperature increase in samples beyond a critical size is sufficiently high so that the temperatures are higher than the glass transition temperature or even the melting temperature, leading to catastrophic fracture.

Irreversible or plastic deformation in bone is associated with both permanent plastic strain as well as localized microdamage. Whereas mechanisms at the molecular and mesoscopic level have been proposed to explain aspects of irreversible deformation, a quantitative correlation of mechanical yielding, microstructural deformation, and macroscopic plastic strain does not exist. To address this issue, we developed and applied a two-dimensional image correlation technique to the tensile deformation of bovine fibrolamellar bone, to determine the spatial distribution of strain fields at the length scale of 10 μm to 1 mm in bone during irreversible tensile deformation. We find that tensile deformation is relatively homogeneous in the elastic regime and starts at the yield point, showing regions of locally higher strain. Multiple regions of high deformation can exist at the same time over a length scale of 1 to 10 mm. Macroscopic fracture always occurs at one of the locally highly deformed regions, but the selection of which region cannot be predicted. Locally, strain rates can be enhanced by a factor of 3 to 10 over global strain rates in the highly deformed zones and are lower but always positive in all other regions. Light microscopic imaging shows the onset of structural “banding” in the regions of high deformation, which is most likely correlated to microstructural damage at the inter- and intrafibrillar level.

The structural characteristics of TiMn1.5Vx (x = 0.1–0.5) alloys and the hysteresis phenomenon in the TiMn1.5Vx-H2 system have been studied. The TiMn1.5Vx alloy consists mainly of the C14 Laves phase plus some of the BCC solid solution phase, depending on x. The lattice parameters of the C14 Laves phase increase slightly as x increases from 0.1 to 0.2 but are invariant with a further increase in x up to 0.3–0.5. The pressure-composition isotherms clearly show a pressure hysteresis in the TiMn1.5Vx-H2 system which decreases with an increase in the x value mainly due to the equilibrium pressure change for hydride formation. The free energy loss during hydride formation is related to not only the volume expansion, but also the elastic strain in the TiMn1.5Vx alloy itself, that is, prior to hydrogen absorption.

The evolution of shear bands (SBs) into cracks was observed by using a high-resolution scanning electron microscope in Zr59Cu20Al10Ni8Ti3 metallic glassy samples after a small punch test with different strain rates. As shear strain increased along a radial SB, three distinctive regions of morphologies were found (I) bonded SB, (II) microcrack plus bonded SB, and (III) full crack. In region II with moderate shear strain, some glassy “extrusions” were also observed. Once shear offset increases to a critical value, the SB becomes a full crack. For two different SBs in one specimen, the critical shear offsets maintain approximately the same value, which sheds light on the critical shear failure condition of metallic glass. The critical shear offset was also found to be sensitive to the strain rate and a higher strain rate led to less critical shear offset. It is suggested that the structure evolution and heat evolution within a shearing SB should be responsible for the previous results.

In this study, the mechanical properties of human dental structures have been investigated by using instrumented nanoindentation. Immersion in solutions containing Streptococcus mutans, which is the principal cause of dental caries, was applied to tooth specimens to clarify its effect on the microstructure and mechanical properties of the dental structures. With an extended time of up to 16 h, the pH value of the S. mutans solutions dropped from 7.3 to 5.8. Therefore, after immersion in the S. mutans solutions for 16 h, slight erosions of the dental structures began; after 64 h, severe tooth decay occurred with obviously etched dental features. After 128 h, the elastic modulus of enamel and dentine dropped to 85 and 67%, respectively, of the original values of untreated specimens, and the hardness dropped to 88 and 55%, respectively.

Relaxor ferroelectrics of Pb(Zn1/3Nb2/3)0.5(Zr0.47Ti0.53)0.5O3 (0.5PZN-0.5PZT) were prepared using the conventional oxide mixing method. Both x-ray diffraction analysis and Raman spectroscopy indicate that the amounts of rhombohedral phase are close to tetragonal phase, implying the presence of the morphotropic phase boundary (MPB) in the system of 0.5PZN-0.5PZT, and this result was further confirmed by transmission electron microscopy (TEM) micrographs. At MPB composition, the excellent piezoelectric properties, such as kp (0.66) and d33 (425pC/N), were obtained due to the more possible polarization directions of domains and high dc resistivity of 6.5 × 1010 Ω·cm. Meanwhile, the dielectric studies revealed that the indicator of the degree of diffuseness γ value is 1.73, implying that the relaxor nature of the 0.5PZN-0.5PZT is ceramic. The activation energy related to the dc conductivity was estimated from a linear fitting of the Arrhenius law. The value of 0.09 and 1.04 eV for low and high temperature range corresponds well to the activation energies of migration and first ionization of the oxygen vacancies.

The microstructure in AO-excess SrTiO3 (A = Sr2+, Ca2+, Ba2+) ceramics is strongly affected by the formation of Ruddlesden-Popper fault–rich (RP fault) lamellae, which are coherently intergrown with the matrix of the perovskite grains. We studied the structure and chemistry of RP faults by applying quantitative high-resolution transmission electron microscopy and high-angle annular dark-field scanning transmission electron microscopy analyses. We showed that the Sr2+ and Ca2+ dopant ions form RP faults during the initial stage of sintering. The final microstructure showed preferentially grown RP fault lamellae embedded in the central part of the anisotropic perovskite grains. In contrast, the dopant Ba2+ ions preferably substituted for Sr2+ in the SrTiO3 matrix by forming a BaxSr1−xTiO3 solid solution. The surplus of Sr2+ ions was compensated structurally in the later stages of sintering by the formation of SrO-rich RP faults. The resulting microstructure showed RP fault lamellae located at the surface of equiaxed BaxSr1-xTiO3 perovskite grains.

A set of Bragg peaks consistent with a hexagonal Bravais lattice was observed in the x-ray powder diffraction pattern of cubic pyrochlore rubidium tungstoniobate (RbNbWO6) subjected to high-energy ball milling. The calculated lattice parameters for this hexagonal phase are similar to those of compounds with tungsten bronze structure. In fact, the powder pattern of the hexagonal phase could be refined with a structural model based on the tungsten bronze structure. The hexagonal phase produced by high-energy ball milling of RbNbWO6 transforms back to the pyrochlore structure upon heating to 773 K in air. A similar phase was obtained by ball milling the mixture RbNbWO6 + WO3, but, in this case, the stoichiometric hexagonal tungsten bronze compound thus obtained remained stable up to 1273 K.

Deformation field parameters in plane-strain indentation of a perfectly plastic solid with a punch have been mapped using particle image velocimetry, a correlation-based image analysis technique. Measurements of velocity and strain rate over a large area have shown that the deformation resembles that of the slip line field of Prandtl. A zone of dead metal is found to exist underneath the indenter adjoining which is a transition region of material flow similar to the centered-fan region in the slip line field. Shear bands demarcate the boundaries of these deformation regions. The observations suggest that a representative strain rate may be assigned to the indentation. By integrating the strain rate field along particle trajectories, the strains in the indentation region have been estimated. The strain values are seen to be large, 0.5 to 4, over a region extending to about twice the indenter half-width. A pocket of large strain, ∼4, is found to exist close to the edge of the indenter–specimen contact. Prandtl’s slip line field is modified based on the observations and used to estimate the strain field. The measurements of the deformation parameters are found to compare mostly favorably with the predictions of the slip line field and prior observations of indentation. The implications of these findings for analysis and interpretation of indentation hardness are briefly discussed.

A rate-change instrumented indentation method is introduced to experimentally characterize the strain rate sensitivity of high strength materials, such as metallic glasses and nanocrystalline metals, which generally possess low rate sensitivity at room temperature. This technique has been validated herein, via self-consistency between rate jump and rate drop measurements, as a viable way to characterize rate dependent deformation behavior and thereby the underlying micromechanisms of plastic flow.

The massive spalling of Cu3Sn in the soldering reaction between high-Pb solders and Cu substrates was studied to identify the mechanism behind this rather interesting and frequently observed phenomenon. Four different alloys (99.5 Pb 0.5 Sn, 99 Pb 1S n, 97 Pb 3 Sn, and 95 Pb 5 Sn, in wt%) were soldered at 350 °C for durations ranging from 10 s to 600 min. At low Sn concentration (0.5 or 1 Sn), massive spalling occurred as early as 20 min. However, at high Sn concentration (3 or 5 Sn), massive spalling was not completed even after 600 min. To the best of our knowledge, these results are the most detailed observations ever reported on the sequence of events that occur during massive spalling. The Pb–Sn–Cu phase diagram is used to rationalize the phenomenon.