Mechanical properties of parts constructed with additive manufacturing (AM) technologies are highly influenced by raw material and process characteristics. It is widely assumed that a certain degree of anisotropy should be expected in AM parts due to their layer-upon-layer nature. Present work focuses on the PolyJet process, where each layer is built by selective jetting of photopolymers upon flat surfaces and subsequent UV radiation curing. An extensive experimental program was carried out to find out if the so-constructed parts present viscoelastic behavior and if their mechanical characteristics also depend on part orientation. Both hypotheses have been proven true, so a viscoelastic orthotropic-like behavior shall be expected in PolyJet manufactured part. Nevertheless, a significant improvement on material properties has been found for nearly vertical building orientations. This unexpected behavior is related to a shielding effect upon UV curing caused by support material.

We use transmission electron microscopy (TEM) for in situ studies of electron-beam-induced crystallization behavior in thin films of amorphous transition metal silicon carbides based on Zr (group 4 element) and Nb (group 5). Higher silicon content stabilized the amorphous structure while no effects of carbon were detected. Films with Nb start to crystallize at lower electron doses than the Zr-containing ones. During the crystallization, equiaxed MeC grains are formed in all samples with larger grains for ZrC (∼5 nm) compared to NbC (∼2 nm). The phenomenon of self-terminating crystallization at a dimension of 2–5 nm is explained by segregation of Si that is expelled from growing metal carbide grains into the surrounding amorphous phase matrix, which limits diffusion of the metal and carbon.

The yield behavior of solid polymers may be influenced by the hydrostatic pressure, strain rate, and temperature. In the present work, we focus on evaluating the effect of hydrostatic pressure on the yield strength by instrumented indentation. Using dimensional analysis and finite element analysis, two analytical expressions were derived to relate the indentation data to the plastic properties, and a method for extracting the coefficient of internal friction which reflects the effect of hydrostatic pressure on the yield strength was established. Applications were illustrated on polypropylene (PP), polycarbonate (PC), and unplasticized polyvinyl chloride (UPVC). The coefficient of internal friction determined by this indentation method is 0.20 ± 0.02 for PP, 0.07 ± 0.01 for PC, and 0.10 ± 0.01 for UPVC, which are in good agreement with the values reported in the literature. This demonstrates the proposed indentation method which is useful to evaluate the effect of hydrostatic pressure on the yield strength of solid polymers.

Nitrogen-doped multiwalled carbon nanotube (CNT) bundles exhibiting pine-tree-like morphologies were synthesized on silicon–silicon oxide (Si/SiO2) substrates using a pressure-controlled chemical vapor deposition process. Electron field emission (FE) measurements showed a notable emission improvement at low turn-on voltages for the CNT pine-like morphologies (e.g., 0.59 V/µm) in comparison with standard aligned N-doped CNTs (>1.5 V/µm). We envisage that these pine-tree-like structures could be potentially useful in the fabrication of efficient FE and photonic devices.

Exploiting molecular dynamics simulation, this article investigates the dynamic process of atomic rearrangement in two metallic glasses (MGs), Cu50Zr50 and Fe80P20, which are well known as ductile and brittle MGs under compression, respectively. It was found that the local rearrangements can be identified clearly by the distribution of kinetic energy and atomic strain rate, and that they are always driven by several high-velocity atoms in the core and induce a large shear and tensile strain over a very short duration. The size, kinetic energy, strain rate, and cavitation rate of the clusters in Fe80P20 are markedly larger than those in Cu50Zr50, which explains the distinct strength and brittleness of these two MGs. This study further confirmed that localized rearrangement of atomic structure is the underlying mechanism of plastic deformation in MGs, which governs their macro-scale mechanical performance.

A series of MnOx–CeO2 binary oxide catalysts were synthesized by polyvinylpyrrolidone -assisted supercritical antisolvent precipitation and the effects of the manganese (Mn)/cerium (Ce) molar ratio and calcination temperature on the structure and properties of MnOx–CeO2 were investigated. A solid solution was obtained at each experimental condition and the highest surface area of 107.6 m2/g was obtained at the Mn/Ce molar ratio of 3:5 and the calcination temperature of 400 °C. Low-temperature selective catalytic reduction of emissions of nitrogen oxides, namely NO, NO2, and N2O (deNOx) with ammonia (NH3) to convert them into nitrogen and water, was used as model reaction to evaluate MnOx–CeO2 catalytic performance. It is found that the activity first increased and then decreased with increasing Mn content and decreased with increasing calcination temperature. The highest catalytic activity (93.3% NO conversion and 100% N2 selectivity) was obtained at the Mn/Ce molar ratio of 1/1 and the calcination temperature of 400 °C, which was attributed to the combination of high surface area and high redox performance of the catalyst.

Binary interdiffusion data as function of composition in the Mg–{Ce, Nd, Zn} and Zn–{Ce, Nd} systems were obtained experimentally using solid–solid diffusion couples. For the studied systems, all intermetallic compounds were produced, based on the equilibrium phase diagrams, eliminating the problem of missing compounds in the diffusion couples found in the literature. The composition profiles were obtained using wavelength dispersive spectroscopy line-scans across diffusion couples. The composition-dependent diffusion coefficient at each interface was determined using Boltzmann–Matano analysis. For the available literature data for some of the compounds in the Mg–{Ce, Nd, Zn} systems, the calculated interdiffusion coefficients were in good agreement. No diffusion data regarding Zn–{Ce, Nd} systems could be found in the literature. The activation energy and the preexponential factor of the growth of the Mg–{Ce, Nd, Zn} compounds were determined using Arrhenius equation. The activation energies of the growth of the Mg–Ce compounds showed relatively higher values than those of Mg–Nd and Mg–Zn compounds.

Novel water-soluble titanium complexes coordinated by hydroxycarboxylic acids or amines were developed, and the hydrothermal treatment of the new complexes was carried out to elucidate the formation mechanism of the titania polymorphs including rutile, anatase, and brookite. An empirical relationship among the crystal structure of TiO2, the ligand, and the complex structure was found. Anatase, rutile, or a mixture of both was obtained by the hydrothermal treatment of the complexes coordinated by hydroxycarboxylic acids. The structure of complexes prepared using hydroxycarboxylic acids, which have one hydroxyl and one carboxylic groups, seems to be preferable for the formation of rutile. It was also found that the hydrothermal treatment of titanium complexes coordinated by amine with NAc2 structure resulted in the formation of brookite. Thus, the effect of ligand and complex structure on the crystal structure of TiO2 synthesized by the hydrothermal treatment of the complexes was proposed.

This study was to analyze the microstructure, microhardness, tensile and fatigue performance of the welded joints performed by a fiber laser on 22MnB5 and dual-phase steels (DP590, DP980) in similar and dissimilar combinations. The result shows that the weld zone (WZ) basically consisted of lath martensite. The HAZ in these steels can be divided into 3 parts: quenched, incomplete quenched, and tempered region. The WZ had the highest hardness, and a soft zone existed in the HAZ of all steels. Inside the WZ of the dissimilar welded joints, two hardness subregions were observed due to the difference in the alloying elements of these steels. Tensile specimens of the 22MnB5–22MnB5 and 22MnB5–DP980 welded joints were all broken in HAZ, while the 22MnB5–DP590 welded joints failed in the DP590 base metal (BM). The BM had a higher fatigue life than the welded joints, and the fatigue failure of the 22MnB5 similar and 22MnB5–DP980 dissimilar welded joints respectively occurred in the HAZ and DP980 BM. The fatigue fracture contained 3 parts: crack initiation, crack propagation, and the final fast fracture region.

Isothermal annealing in the temperature range of 300–600 °C, microstructural characterization, and analysis of the grain growth kinetics during annealing were carried out for Cu–5 vol% Al2O3 nanocomposite powder particles produced by high energy mechanical milling. When the annealing temperature was 400 °C or lower, only reduction in dislocation density occurred during annealing. When the annealing temperature was 500 °C or higher, reduction in dislocation density, abnormal grain growth of the nanocrystalline Cu matrix, and coarsening of the Al2O3 nanoparticles occurred. It has been found that the microstructure of the nanocrystalline Cu matrix of the nanocomposite exhibits a far higher thermal stability than that of monolithic nanocrystalline Cu, even though the apparent activation energy of the grain growth of the former is similar to that of the latter over the temperature range of 400–600 °C, showing the dramatic drag effects of finely distributed Al2O3 nanoparticles and Al3+/O2− clusters on the grain boundary motion.

Novel hybrid diblock copolymers consisting of bidentate ligand-functionalized chains have been synthesized via click reaction and RAFT radical polymerization. The chemical structure and molecular weight of the synthesized poly(methacrylate-POSS)-block-poly(4-vinylbenzyl-2-pyridine-1H-1,2,3-triazole) (PMAPOSS-b-PVBPT) were characterized by NMR and GPC. The copolymers had been utilized to construct metal-containing polymer micelle by the metal–ligand coordination and electrostatic interaction in this study. The self-assembly behaviors of PMAPOSS-b-PVBPT in chloroform, a common solvent, under the effect of Zn(OTf)2 and HAuCl4 were investigated by TEM, DLS, and variable temperature NMR. Besides, micellization of this diblock copolymer was achieved in ethylene glycol, a selective solvent for PMAPOSS-b-PVBPT. The experimental results revealed that the incorporation of heterocyclic rings bearing nitrogen atoms in polymer side chains played an important role in the construction of metal-containing copolymer micelles. The prepared metal-containing PMAPOSS-b-PVBPT micelles had good dynamic and thermal stability due to the strong metal–ligand coordination interaction and electrostatic interaction.

A new kind of nontoxic, water-soluble copolymer consisting of isobutylene and maleic anhydride was used to gelcast alumina ceramics at room temperature in air. The polymer acts as both a dispersant and a gelling agent. The influence of the polymer on zeta potential, rheological and gelling behavior of the alumina slurry was studied. Copolymers with a lower molecular weight had greater dispersing ability. Copolymers with a larger molecular weight had greater gelling ability. Alumina slurries with solids loading up to 58 vol% were prepared by adding copolymer (0.3 wt%, relative to the powder) with both short and long molecular chains. Increasing solids loading from 50 to 58 vol% decreased the linear shrinkage from 4.63% to 1.50% after drying, and from 14.51% to 13.18% after sintering, respectively. A solids loading of 56 vol% was associated with the highest flexural strength, as high as 534 MPa.

Tribological behavior of biomedical ultrafine-grained (UFGed) TiNbZrTaFe (TNZTF) composites fabricated by powder metallurgy was investigated under dry wear condition. Results show that compared with two kinds of conventional biomedical Ti–6Al–4V (TAV) and Ti–13Nb–13Zr (TNZ) alloys, the wear loss of the TNZTF samples is only 3.5% and 1% of that of the TAV and TNZ samples, respectively. Unusual tribological behavior is that the wear loss of the TNZTF samples decreases with the increase in sliding speed at the same load. This is attributed to the formation of a large amount of hard Nb2O5 particles on the contact surface of the material during rubbing and more severe plastic deformation in the material layers adjacent to the contact surfaces. The wear mechanism of the three kinds of alloys was also investigated. The outstanding tribological property proves that the UFGed TNZTF alloys should be an excellent candidate material to be used for biomedical application in the future.

In this study, 3 mol% Y2O3-stabilized zirconia (3Y–ZrO2) and commercially pure titanium (cp-Ti) joints were fabricated with an Ag68.8Cu26.7Ti4.5 interlayer (Ticusil) at 900 °C for various brazing periods. After brazing at 900 °C/0.1 h, Ti2Cu, TiCu, Ti3Cu4, and TiCu4 layers were present at the Ti/Ticusil interface, while TiCu and TiO layers were observed at the Ticusil/3Y–ZrO2 interface. In the residual interlayer, clumpy TiCu4 was formed along with the Ag solid phase. After brazing at 900 °C/1 h, Ti3Cu3O and Ti2O layers were formed at the interlayer/ZrO2 interface, while Cu2O was precipitated in the residual interlayer with $\left[ {111} \right]_{{\rm{Cu}}_{\rm{2}} {\rm{O}}} //\left[ {111} \right]_{{\rm{Ag}}}$ and $\left( {20\bar 2} \right)_{{\rm{Cu}}_{\rm{2}} {\rm{O}}} //\left( {20\bar 2} \right){}_{{\rm{Ag}}}$. After brazing at 900 °C/6 h, a two-phase (α-Ti + Ti2Cu) region was observed on the Ti side with $\left[ {2\bar 1\bar 10} \right]_{{\rm{\alpha - Ti}}} //\left[ {100} \right]_{{\rm{Ti}}_{\rm{2}} {\rm{Cu}}}$ and $\left( {0002} \right)_{{\rm{\alpha - Ti}}} //\left( {0\bar 13} \right)_{{\rm{Ti}}_{\rm{2}} {\rm{Cu}}}$, while the TiCu layer grew at the expense of Ti3Cu4 and TiCu4. The bonding mechanisms and diffusion paths were explored with the aid of Ag–Cu–Ti and Ti–Cu–O ternary phase diagrams.

The highly ordered mesoporous chromium–alumina catalysts (denoted as OMCA(x)) with different nAl/nCr ratios of 10 and 20 have been successfully synthesized via an evaporation-induced self-assembly (EISA) pathway associated with thermal treatment and were applied to the liquid phase oxidation of cyclohexane with hydrogen peroxide (H2O2) as an oxidant. For comparison studies, a chromium catalyst with the nAl/nCr ratio of 10 supported on an ordered mesoporous alumina support [denoted as Cr/OMA(10)] was also prepared by an incipient wetness impregnation (IWI) method. Although both kinds of catalysts retained a unidimensionally ordered mesoporous structure, textural properties of the catalysts were significantly affected by the preparation method. The characteristic results from XRD, N2 adsorption, TEM, UV-Vis, 27Al MNS NMR, and H2-TPR showed that the OMCA(x) catalysts exhibited much more highly ordered hexagonal mesostructure, narrower pore-size distribution, higher Brunauer-Emmett-Teller surface area and pore volume, and more homogeneous distribution of Cr species in mesoporous alumina framework in the form of tetrahedrally coordinated hexavalent Cr-oxide moieties than those of Cr/OMA(10) synthesized by an IWI method. In addition, in comparison with Cr/OMA(10), OMCA(x) catalysts showed higher catalytic activity and stability for the liquid phase oxidation of cyclohexane.

In this study, bioactive glass powders were synthesized via an inexpensive hydrothermal chemical route by the use of ultrasonic energy irradiation. Soda lime, calcium nitrate tetrahydrate, and diammonium hydrogen phosphate were used as the precursor materials to synthesize low-sodium bioactive glass materials based on the conventional 45S5 Bioglass®. The morphological properties of the synthesized powders and the microwave-sintered dense compact were investigated. The mechanical properties of the fabricated dense bioactive glasses were characterized and were found to be very good. The ability to form biological apatite under physiological conditions was demonstrated with simulated body fluid (SBF). The material was shown to be highly biocompatible using the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) assay with osteoblast-like MG63 cells. The cell adhesion and proliferation behavior of osteoblast-like MG63 cells were investigated and found to be excellent.

A combined approach of scanning electron microscopy and digital image correlation was used to examine microstructure-scale strain localization and active deformation mechanisms in ultrafine-grained (UFG) high purity (99.99%) aluminum processed by equal-channel angular pressing (ECAP). The results from tensile tests demonstrate a strong relationship between the heterogeneous microstructure and strain localization. The localized deformation was investigated in areas that contain significantly different microstructural features typical of ECAP processed aluminum. It was found that areas of the UFG microstructure containing primarily low angle grain boundaries deformed by dislocation slip and behaved similarly to a coarse-grained material. The greatest strain localization occurred at high angle grain boundaries (HAGBs) separating distinct microstructure regions and with median surface trace angles of approximately 26.6°. In areas of banded microstructure, shear strain localization as high as 30% and shear displacements of up to 500 nm occurred at the HAGBs separating bands, suggesting grain boundary sliding.

The defense mechanism that nacre (mother-of-pearl) uses to protect its living organism against high-speed predatory attack can provide lessons for engineered armor design. However, the underlying physics responsible for nacre's dynamic energy dissipation has hitherto remained a mystery to be uncovered. Here we demonstrate a new energy dissipation mechanism hidden in nacre and activated only upon dynamic loading, where the crack terminates its propagation along nacre's biopolymer interlayers but straightly impinges the aragonite platelets (95 vol%) in a transgranular manner. This intergranular–transgranular transition promotes the fracture energy dissipation, far exceeding that of the currently-used engineered ceramics. The mechanistic origin accounting for the enhancement of fracture energy dissipation is attributed to the unique nanoparticle architectured aragonite platelets. The dynamic manifestation in nacre can inspire a new route to design stronger-and-tougher engineered ceramic armors.

Commonly used techniques for cleaning copper substrates before graphene growth via chemical vapor deposition (CVD), such as rinsing with acetone, nitric, and acetic acid, and high temperature hydrogen annealing still leave residual adventitious carbon on the copper surface. This residual carbon promotes graphene nucleation and leads to higher nucleation density. We find that copper with an oxidized surface can act as a self-cleaning substrate for graphene growth by CVD. Under vacuum conditions, copper oxide thermally decomposes, releasing oxygen from the substrate surface. The released oxygen reacts with the carbon residues on the copper surface and forms volatile carbon monoxide and carbon dioxide, leaving a clean copper surface free of carbon for large-area graphene growth. Using oxidized electropolished copper foil leads to a reduction in graphene nucleation density by over a factor of 1000 when compared to using chemically cleaned oxygen free copper foil.