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A good combination of strength and fracture toughness is required for aerospace applications of laser additively manufactured (LAM) AerMet100 steel. To understand the role of microstructure in the combination of strength and fracture toughness of LAM AerMet100 steel, microstructures, fracture toughness properties and corresponding crack-tip fracture behaviors of the as-deposited specimen and five types of heat-treated specimens were mainly investigated. The results indicate the as-deposited microstructure of LAM AerMet100 steel with a high amount of retained austenite has a high KIC value of ~ 81.7 MPa m1/2. After a short process of cryogenic treatment and subsequent tempering treatment, the KIC value of the steel has the lowest value of ~ 60 MPa m1/2 due to the apparent decrease of austenite and weak cracking resistance, associating with intergranular cracking along the prior austenite columnar grain boundaries and transgranular cracking of intercellular regions. In contrast, the crack-tip fracture mode of the equiaxed-grain tempered martensite microstructure of LAM AerMet100 steel becomes completely transgranular cracking with the main mechanisms of micro-void nucleation and coalescence. Homogenization treatment can apparently decrease the amount and size of large-size alloy carbides and effectively improve the fracture toughness of the steel. Furthermore, proper microstructure modification (including control of large-size carbide, grain refinement and a decrease of retained austenite) by a longer treatment process can prompt tempered LAM AerMet100 steel to achieve a good combination of yield strength (~ 1827 MPa) and fracture toughness (~ 113 MPa m1/2) compared with the wrought one.

Optimizing the coordination/surrounding environments of active metal nanoclusters to promote the catalytic performance during hydrogen evolution reaction (HER) in alkaline media is highly important but extremely challenging. Here, we demonstrate that novel S-coordinated ruthenium (Ru) nanoclusters anchored on N/S-codoped carbon nanosheets (Ru–S/N–C) can be successfully synthesized via the space-confinement pyrolysis of Ru complexes in the framework of polyaniline–ammonia persulfate supermolecules. X-ray absorption fine structure spectroscopy and X-ray photoelectron spectroscopy studies reveal the local coordination structure of Ru–S bonds, the surrounding N/S/C environments of Ru, and the synergistic electronic interactions among N, S, C and Ru atoms. Theoretical calculations further confirm that the coordination/surrounding environments could optimize the adsorption energies of intermediates on Ru through interfacial charge transfer and, thus, accelerate the reaction kinetics of hydrogen evolution. The fabricated Ru–S/N–C exhibits an ultra-small overpotential of 10 mV at 10 mA cm−2 and an extremely high turnover frequency (TOF) of 2.3 H2 s−1 at an overpotential of 50 mV for the HER, as well as a mass catalytic activity about 10 times higher than that of a commercial Pt/C catalyst.

The primary understanding of laser-induced non-isothermal prior β grain growth behaviour of titanium alloys is given by adopting laser quenching on pure titanium. Results indicate that the prior β ...

In our previous research, titanium-based nitride with high conductivity and superior corrosion resistance were developed as an ideal core material for replacing noble metal to form Pt-based core-shell catalysts by pulse electrodeposition. Meanwhile, the smaller sizes of nitride cores would also be available for pulse electrodeposition by dispersing them on carbon nanotubes (CNT). To achieve a better practice on the preparation of the Pt-based core-shell catalysts, in this work, both nitrogen-doped carbon nanotubes (N-CNT) and reduced graphene oxide (N-rGO) were used to support the copper-doped titanium nitride (Ti0.9Cu0.1N) cores. In the course of pulse electrodeposition, their influences as supports on the electronic states of electrodeposited Pt as well as their catalytic activities were compared. The results showed that the Pt preferred to electrodeposit on Ti0.9Cu0.1N cores supported by N-CNT and formed a core-shell structure. While with the same electrodeposition process, the Pt was found to be electrodeposited not only on the Ti0.9Cu0.1N cores supported by N-rGO with heavy aggregations but also on the N-rGO support. Raman spectroscopy analysis indicated that the higher degree of structural defects on N-rGO, as support, might have contributed to such divergence observation.

Exploring advanced electrocatalysts for the sluggish oxygen reduction reaction is extremely important for fuel cell commercialization but still remains a great challenge, especially the durability issue that gains increasing attention. Herein, we demonstrate an extremely durable catalyst prototype that combines structurally ordered intermetallic nanoparticles (NPs) with mesoporous carbon. With ZIF-8 derived mesoporous carbon supported Pt3Co intermetallic NPs (Pt3Co/DMC-F) as an example, we illustrate its synthetic details, electrocatalytic performance and durability enhancement mechanism. The Pt3Co/DMC-F catalyst exhibited significant enhancement in activity and durability. More importantly, its extraordinary performance was observed/verified in a H2/air PEM single cell test. The confinement of mesoporous carbon not only efficiently controls the particle size of Pt3Co and hampers their aggregation during thermal annealing and electrochemical reactions, but also significantly suppresses detachment. Beyond offering an advanced electrocatalyst, this study provides a solution to the durability issue of cathodes that has prevented practical application of proton exchange membrane fuel cells.

Icing/snowing/frosting is ubiquitous in nature and industrial processes, and the accretion of ice mostly leads to catastrophic consequences. The existing understanding of icing is still limited, particularly for aircraft icing, where direct observation of the freezing dynamics is inaccessible. In this work, we investigate experimentally the impact and freezing of a water drop onto the supercooled substrate at extremely low vapor pressure, to mimic an aircraft passing through clouds at a relatively high altitude, engendering icing upon collisions with pendant drops. Special attention is focused on the ice coverage induced by an impinging drop, from the perimeter pointing outward along the radial direction. We observed two freezing regimes: (I) spread-recoil-freeze at the substrate temperature of Ts = −15.4 ± 0.2 °C and (II) spread (incomplete)-freeze at the substrate temperature of Ts = −22.1 ± 0.2 °C. The ice coverage is approximately one order of magnitude larger than the frozen drop itself, and counterintuitively, larger supercooling yields smaller ice coverage in the range of interest. We attribute the variation of ice coverage to the kinetics of vapor diffusion in the two regimes. This fundamental understanding benefits the design of new anti-icing technologies for aircraft.

The prior β grain structure is recognized to be an important factor governing the mechanical properties of laser additive manufacturing (LAM) titanium alloys (ti-alloys) components. Five kinds of ti-alloys plates were fabricated by LAM process aiming to investigate the solidification behavior and grain morphology. Full columnar grains, full equiaxed grains and a special mixed grains structure were observed in LAM TC4, TB6 and TC11 plates, respectively, indicating that the formation tendency and volume fraction of equiaxed grains in LAM ti-alloys plates increase gradually with the increasing alloying content. It was proposed the formation of equiaxed grains is a multifactor functioning result of the constitutional supercooling and the remaining powders in the local melting pool.

Ti-10V-2Fe-3Al alloy specimen has been fabricated by laser melting deposition additive manufacturing technique. Due to the repeated heating and cooling during deposition, complicated and unique phase transformation process take place with forming different microstructures from forging. In this study, a three-dimensional (3D) reconstruction method is used to understand the spatial distribution of α phase in different grains. The results indicated that, in as deposited alloy, α laths has a plate morphology, and they precipitated out from β phase followed a tetrahedral relationship. And the different grain orientation result to the specific different morphology. When the cutting plane parallel to the {100} plane of BCC cell, α laths are perpendicular to each other. If the cutting plane is parallel to the {111} plane, a special morphology with mixture of plate-like and rod-like α phase is founded. Keywords: Laser additive manufacturing, Ti-10V-2Fe-3Al, Titanium alloys, Spatial distribution, Phase transformation

Acid mine drainage (AMD) is a hazardous by-product of coal mining, which may intensify the creep deformation of cemented gangue backfill (CGB) in solid backfill mining. In this study, the long-term stability and creep property of CGB soaked in AMD were quantitatively measured by experimental and theoretical analysis. The uniaxial compressive strength, elastic modulus, and mass of CGB soaked in AMD, with pH of 5.56 and soaking time of 30 to 360 days, were tested. The change trend of compressive strength, elasticity modulus, and mass first increased, then decreased, and finally ended at 94.37%, 96.68%, and 98.00%, respectively. The respective creep processes of CGB soaked in AMD and untreated CGB were similar, initial creep stage lasted only for a short time, and no creep deformation occurred in the steady creep stage. Moreover, the long-term strength of CGB soaked in AMD was 98.6% of the untreated CGB. The creep law of the CGB soaked in AMD was accurately fitted by using the Kelvin model. The theoretical analysis revealed that the final creep deformation of the CGB column soaked in AMD was only 4.4 mm. The results of this paper show the possibility of using CGB in AMD-accumulating goaf.

A new type of Ti-6.5Al-3.5Mo-0.3Si-xZr (x = 1.5, 2.5, 3.5, 4.5 wt%) titanium alloys developed on TC11 alloy (x = 1.5) with different Zr contents were fabricated by laser additive manufacturing process in order to enhance the mechanical properties. Grain morphology and microstructure were systematically investigated. The results demonstrate that the addition of Zr element dramatically refines the grains of the titanium alloys by offering heterogeneous nucleate sites and controlling grain growth during subsequent thermal cycles. And the latter is the main influencing factor. Meanwhile, the addition of Zr element in the alloys does not affect their microstructures, which with similar α lamellar thickness. And the microhardness and compressive strength of the alloys continuously increase with the increase of Zr contents.

In order to evaluate the effects of microstructure characteristics on fatigue crack growth (FCG) resistance of laser additive manufactured (LAM) AerMet100 steel, microstructures and FCG behaviors (in Paris region) of as-deposited specimen and three types of tempered martensite specimens were examined. Results indicate as-deposited specimens of LAM AerMet100 steel have apparent texture characteristics of epitaxy unidirectional growth prior-austenite columnar grains and grain-interior inter-dendritic blocky retained austenite with [001] crystallographic orientation. And poor boundary cracking resistance of these texture characteristics along deposition direction mainly contributes to the FCG rate anisotropy of as-deposited specimens. After post-LAM heat treatments, the FCG resistance of all heat-treated specimens apparently improves with the fracture mode of transgranular cracking. With the increase of yield strength, the value of Paris coefficient C of the steel increases, but the value of Paris exponent m decreases. Compared to the poor dislocation slip resistance of bainite plates in as-deposited specimens, the improved dislocation slip resistance of martensite plates is mainly related to the strong dislocation pinning effect of fine dispersive rod-like coherent M2C carbides, resulting in the stronger FCG resistance of the heat-treated specimens. In the Paris region of low ΔK ( ~ 70 MPa m1/2), higher contents of retained/reverted austenite inversely accelerate the FCG rate of heat-treated LAM AerMet100 steel. In contrast, grain refinement has the little influence on the FCG rate (in most of Paris region) of the heat-treated specimens.

Ultrahigh-strength AerMet100 steel plate was fabricated by laser additive manufacturing process (LAM) followed by subsequent heat treatments. Microstructures and tensile mechanical properties of the steel were examined using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and universal mechanical testing machine. The results indicate that post-LAM heat treatments greatly change alloy carbide characteristics, decrease austenite content and prompt the formation of fine equiaxed prior-austenite grains for LAM AerMet100 steel. Compared to fine short rod-like Nb-rich MC carbides and needle-like M3C carbides in as-deposited specimens, alloy carbides in tempered specimens have the large changes, which include fine spherical Nb-rich MC carbides, fine rod-like M2C carbides, large-size spherical Mo-rich M6C carbides and Cr-rich M23C6 carbides. And the fine rod-like M2C carbides are dispersive distribution and coherency with the martix martensite, resulting in strong coherent strain strengthening. After proper post homogeneity heat treatment processes, tensile mechanical properties of LAM AerMet100 steel have the comprehensive improvement, which are comparable to those of the forged ones. In comparison with low ductility of as-deposited specimen, the higher ductility of tempered specimen is mainly related to its extremely strong strain-strengthening capability achieved by dispersive precipitation of M2C carbides. With the increase of homogenization, the further improved ductility of tempered specimen mainly ascribe to the decreased amount and size of large-size alloy carbides (especially Mo-rich M6C carbide).

Microalloyed coatings were fabricated on a forged TC11 titanium alloy surface by adding different amount of ZrN powders using laser cladding technique. Microstructures of coatings and heat affect zone were systematically investigated with the study of microhardness as well as wear property. Results indicated that all coatings have very uniform equiaxial grains with very fine α + β two-phase microstructure (the thickness of α lamellar is 0.8 μm), and nearly no change of microstructure for coatings was observed with the increase contents of ZrN from 3 wt% to 12 wt%. The changes of microstructure from coating to substrate are: fine α + β two-phase structure, super fine α + β two-phase structure (α lamellar of 0.2 μm), αp + αs + β structure, and α + β (forged). By increasing the contents of Zr and N, the hardness of coatings increased accordingly with no suddenly change at the interfacial region. Due to the strong solid-solution strengthening, coatings maintain high hardness even coarsening their microstructures. The enhanced hardness of coatings largely improves the wear properties of alloys to only more than twice of the TC11 matrix when addition of 12 wt% ZrN.

The severe dissolution of the cathode catalyst, caused by an undesired oxygen reduction reaction at the anode during startup and shutdown, is a fatal challenge to practical applications of polymer electrolyte membrane fuel cells. To address this important issue, according to the distinct structure-sensitivity between the σ-type bond in H2 and the π-type bond in O2, we design a HD-Pt/TiN material by highly dispersing Pt on the TiN surface to inhibit the unwanted oxygen reduction reaction. The highly dispersed Pt/TiN catalyst exhibits excellent selectivity toward hydrogen oxidation and oxygen reduction reactions. With a Pt loading of 0.88 wt %, our catalyst shows excellent hydrogen oxidation reaction activity, close to that of commercial 20 wt % Pt/C catalyst, and much lower oxygen reduction reaction activity than the commercial 20 wt % Pt/C catalyst. The lack of well-ordered Pt facets is responsible for the excellent selectivity of the HD-Pt/TiN materials toward hydrogen oxidation and oxygen reduction reac...

The effect of heat treatments on laser additive manufacturing (LAM) Ti-5Al-2Sn-2Zr-4Mo-4Cr titanium alloy (TC17) was studied aiming to optimize its microstructure and mechanical properties. The as-deposited sample exhibits features of a mixed prior β grain structure consisting of equiaxed and columnar grains, intragranular ultra-fine α laths and numerous continuous grain boundary α (αGB). After being pre-annealed in α+β region (840 °C) and standard solution and aging treated, the continuous αGB becomes coarser and the precipitate free zone (PFZ) nearby the αGB transforms into a zone filled with ultra-fine secondary α (αS) but no primary α (αP). When pre-annealed in single β region (910 °C), all α phases transform into β phase and the alloying elements distribute uniformly near the grain boundary. Discontinuous αGB and uniform mixture of αP and αS near grain boundary form after subsequent solution and aging treatment. The two heat treatments can improve the tensile mechanical properties of LAM TC17 to satisfy the aviation standard for TC17.

In this work, we developed a renewable wood-derived cathode with well-aligned elongated microchannels for high-performance Li–O2 batteries. The cathode was obtained from natural wood following carbonization, activation, and then loading of RuO2 nanoparticles (4.15 wt%) as catalysts (RuO2/WD-C). The cathode has a three-dimensional, high stability carbon matrix, uniformly anchored catalysts, and well-aligned porous microchannels. As a result, the specific areal capacity of the assembled batteries exceeds 8 mA h cm−2 and the charge terminal potential is lower than 3.8 V at 0.1 mA cm−2. The energy efficiency was improved up to 91.9% and exceeded 87.1% after 100 cycles (curtailed capacity of 0.5 mA h cm−2 at 0.2 mA cm−2). Furthermore, the RuO2/WD-C cathode can be fully regenerated from a deep discharge–charge cycle or 100 curtailed-capacity cycles by simply washing with water. The areal capacity of the regenerated RuO2/WD-C cathode is comparable to the performance of the initial cathode. The cut-off voltage was above 2.6 V following 200 cycles. Even when regenerated for the second time, the RuO2/WD-C cathode still demonstrated almost the same high performance as the initial one, indicating its high stability and excellent renewability.

In this study, a novel low-Pt core-shell catalyst is successfully prepared by depositing ultrathin Pt layer on the carbon nanotubes supported titanium nitride nanoparticles (TiN@Pt/CNTs) via a facile pulse electrochemical deposition approach. The catalyst is characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), High-angle annular dark field (HAADF) and energy-dispersive spectrometer (EDS) elemental mapping, X-ray photoelectron spectroscopy (XPS) and electrochemical measurements. The results confirm the core-shell structure of the prepared TiN@Pt/CNTs catalyst. More importantly, the catalyst exhibits superb mass activity and durability for the methanol oxidation reaction (MOR) than that of the commercial JM Pt/C catalyst. Later experiments data demonstrate that the activity and stability of the catalyst can be further enhanced via copper doping, which results from the modified electronic structure of the Pt atoms and the synergistic effects of the core-shell structure.

Direct laser deposition (DLD) is a potential approach to prepare large-scale metal component. This work focuses on understanding microstructural characteristics and mechanical properties along deposition direction of 2A97 Al–Li alloy fabricated by direct laser deposition. As-deposited sample showed coarse equiaxed grains at top and columnar crystals at middle and bottom. Growth texture of as-deposited sample along was relatively obvious, value of which increased first and then decreased from bottom to top. Thermal cycle led to different kinds and distribution of precipitated phases along deposition direction, which affected microhardness and tensile strength. T1 phase and a small amount of T2, TB phase precipitated at top. Effect of thermal cycle from top to bottom gradually increased, resulted in δ′, T2, TB phase coarsened. As a result, microhardness decreased from top (99 HV) to bottom (75HV). The sample in bottom showed an ultimate tensile strength (UTS) of 232.9 ± 4.3 MPa, and elongation of 9.5 ± 1.4%. While, ultimate tensile strength was increased to 268.5 ± 5.2 MPa, and elongation was 12.5 ± 0.9% in middle part, which was close to that of sample at top.

Increasing attention is being paid to the clean and efficient mining and utilization of coal resources. Lignite is a major component of coal; however, its high moisture and volatile contents and low calorific value cause it to have low mining and utilization efficiencies. During the dehydration, upgrading and in-situ heat injection or underground coal gasification of lignite, its pore structure plays an important role in the pyrolysis and product transfer processes. Therefore, it is necessary to systematically study the high-temperature pore structure of lignite. The evolution of pore fissures in gas-pyrolyzed lignite was studied by nuclear magnetic resonance combined with a gas heating reactor and test device. We found that the total connectivity, porosity and permeability of lignite increased between temperatures of 25 °C and 250 °C, then decreased at 350 °C and increased again at 450 °C. At 450 °C, the porosity, effective porosity and permeability of lignite were 18.32%, 30.22% and 856.98 md, respectively. The evolution in the pore structure parameters of lignite with temperature was observed to determine the changes in seepage channels that occur during the processes of lignite mining and utilization.

The oxygen reduction reaction (ORR) takes place on the surface of catalyst, and the precise control of surface component at atomic scale has been an important factor to effectively improve the performance of catalysts. Herein, a highly active and stable catalyst is designed by constructing Pt skin and controllable near-surface atomic distribution of PtNi alloy nanowires (NWs). It is found that the d-band center of Pt-skin down-shifts with Pt ratio in the surface/near-surface of PtNi alloy decreasing, and correspondingly the adsorption energy of atomic oxygen (ΔEO) on PtNi alloys weakens, confirmed by experimental results and theoretical calculations. The optimum PtNi/C-NH3 NWs exhibit the enhanced mass activity (1.02 A mgPt−1) and specific activity (3.86 mA cm−2) for ORR, which are 5.7-fold and 11.4-fold higher than those of commercial Pt/C, respectively. Moreover, the H2/air fuel cell of PtNi/C-NH3 NWs exhibits a current density of 308 mA cm−2 at 0.8 V, which is superior to that of the 2020 target of the U.S. Department of Energy (DOE). Our study provides a new perspective and approach in promoting the electrocatalysis on alloy nanomaterials for ORR.

A class of core–shell structured low-platinum catalysts with well-dispersed inexpensive titanium copper nitride nanoparticles as cores and atomic platinum layers as shells exhibiting high activity and stability for the oxygen reduction reaction is successfully developed. Using nitrided carbon nanotubes (NCNTs) as the support greatly improved the morphology and dispersion of the nitride nanoparticles, resulting in significant enhancement of the performance of the catalyst. The optimized catalyst, Ti0.9Cu0.1N@Pt/NCNTs, has a Pt mass activity 5 times higher than that of commercial Pt/C, comparable to that of core–shell catalysts with precious metal nanoparticles as the core, and much higher than that the latter if we take into account the mass activity of all platinum group metals. Furthermore, only a minimal loss of activity can be observed after 10000 potential cycles, demonstrating the catalyst’s high stability. Atomic-scale elemental mapping confirmed that the core–shell structure of the catalyst remaine...

Nitride nanoparticles based core-shell structured catalysts, TiN@Pt/NCNTs and TiCuN@Pt/NCNTs, were prepared successfully by depositing a ultra thin Pt layer on the surface of nitride nanoparticles with a pulse deposition method. It is found that the catalysts exhibited excellent activity and stability towards the anode oxidation of formic acid. The mass activity of TiN@Pt/NCNTs and TiCuN@Pt/NCNTs could be 3.3 and 4.5 times higher than that of the commercial Pt/C catalyst with the same Pt loadings, and they also exhibited outstanding anti-CO poisoning ability and stability. The addition of Cu in nitride nanoparticles could further enhance the performance of the catalyst significantly. The HAADF/STEM images and EDS mapping measurements revealed the core-shell structure of the catalysts. The enhanced activity of TiCuN@Pt/NCNTs should be attributed to the high dispersion of the Pt atoms and the synergistic effect between the Pt shell and nitride core.

Transition metal nitrides have recently attracted significant interest as electrocatalysts for the oxygen reduction reaction (ORR) owing to their low electrical resistance and good corrosion resistance. In this paper, we describe the preparation of a Nb-based binary nitride material with a porous nanogrid morphology/structure. The catalyst exhibited good catalytic activity and high stability towards oxygen reduction. We also intensively investigated the effect that doping with a second transition metal had on the performance of the catalyst. We found that the ORR activity of NbN could be enhanced significantly by enriching the d electrons of Nb through doping with a second transition metal, and that doping with cobalt resulted in the best improvement. Our optimal catalyst, Nb0.95Co0.05N, had an ORR activity ∼4.6 times that of NbN (current density @ 0.6 V vs. the RHE). XPS results revealed that Co doping increased the proportion of Nb in a low-valence state, which may be one of the most important reasons for the enhanced performance. Another important reason is the high surface area resulting from the porous nanogrid morphology. As transition metal doping is an attractive way to enhance the activity of nitride catalysts, our work may provide an effective pathway to achieve this.

In order to improve the wear resistance of TC11 titanium alloy, a mixture of ZrN (10 wt.%, 20 wt.%, 30 wt.%, and 40 wt.%) and TC11 alloy powders are laser cladded on a forged TC11 substrate. The microstructure and wear property of coatings are systematically analyzed. The results show that the microstructure of sample with 10 wt.% ZrN addition has a very fine &alpha, + &beta, two-phase microstructure, powders of ZrN are fully melted with no new phase appearance. By increasing the amount of ZrN to 20 wt.%, new phases of TiN0.3 precipitate with the dendritic morphology in the coating. A further increase in ZrN to 30 wt.% and 40 wt.% do not significantly change the microstructure of the cladded layer but increase the microhardness significantly, phases of TiN form with further enhancement of coating hardness. At the bottom of the cladded layer, the morphology of TiN0.3 and TiN precipitations changes into a spherical shape with small size. However, the wear performance of the coatings gradually reduces due to the increase of brittleness, and the superior wear properties of the coating are achieved when sample consisted of 20 wt.% ZrN.

Spontaneous combustion of coal is one of the major hazards threatening production safety during longwall mining. Mining-induced voids, which provide passages for air leakage, are the key factor triggering spontaneous combustion of coal in longwall goafs. In this study, a comprehensive method, which combined pressure balance, grouting injection, and filling fissures, was proposed to prevent spontaneous combustion of coal in longwall goafs with complex air leakage. Field engineering practice was carried out in Sitai Coal Mine in China. The results demonstrated that with the application of the proposed method, in the working face, the concentration of CO was decreased from 31ppm to 0 and the air leakage quantity was decreased from 261 to below 80 m3min-1. The gas samples analysis from the gob areas also indicated that concentrations of O2 and CO were successively decreased, indicating that the risk of spontaneous combustion of coal in goafs was eliminated. The above mentioned analysis indicates that, the method proposed in this study is useful and efficient. Successful application of this technology could provide reference for the treatment of other coal mines.

Ultrahigh-strength AerMet100 steel thick plate was fabricated by laser additive manufacturing process. The as-deposited microstructures of the test steel were characterized using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The mechanical properties were then examined using vickers-hardness test and tensile test. Results indicate that the as-deposited microstructures of the steel mainly consist of grain boundary allotriomorphic ferrite (GBA), grain interior irregular proeutectoid ferrite, plate-like upper bainite, needle-like lower bainite and retained austenite, which result in a good strength and some ductility anisotropy. The low deformation compatibility of specimen at the transverse direction (perpendicular to the deposition direction) mainly ascribes to the poor cracking resistance of the prior-austenite columnar grain boundary with coarse GBA phases. Compared to the almost intergranular cracking taken place in the transverse tensile specimen, the fracture mode of the longitudinal tensile specimen is a mixed mode of the predominant transgranular cracking and minor intergranular cracking.

To give a deep insight into the nitrogen transfer mechanism during laser solid-state surface modification on titanium alloy, laser nitridation was conducted on Ti-6.5Al-3.5Mo-1.5Zr-0.3Si titanium alloy (TC11) without melting the metal surface. Microstructure characterizations of nitride layer formed under solid state condition were detailedly explored and the formation process of TiN phase was carefully discussed based on the lattice transformation. Results indicate that the nitride layer forming within a few seconds is composed of TiN phase layer and α phase layer with an orientation relationship: ( 1 1 ¯ 1 )TiN // (0001)α, [011]TiN // [ 2 11 ¯ 0 ]α. Formation of TiN phase experiences fast solid-state transformation from α phase. Phase transformation from α-Ti lattice to TiN lattice experiences orthorhombic lattice transformation due to the shear deformation caused by rapid interstitial solution of nitrogen. After repeated laser nitridation process upon three times, nitride layer was thickened with an improved hardness of 824 HV. Linearly reciprocating ball-on-plane wear tests indicate that wear resistance of laser nitridation samples could be enhanced by a factor of 13.

The high-energy input and thermal history during additive manufacturing lead to complex phase transformations in titanium aluminide alloy. This study mostly focuses on determining the solid-state phase transformation mechanisms during laser deposition and the failure mechanisms of alloys using molecular dynamics simulations. Because of the directional temperature gradient, columnar grains with fully lamellar microstructures are formed first after solidification. A narrow region just below the melting pool is reheated to high temperatures, thus enhancing the precipitation of new equiaxed grains. Multiple thermal cycles in the α + γ phase region promote the formation of massive γ phases (γm) at the grain boundaries. Finally, a nearly lamellar microstructure of alternating columnar and equiaxed grains with γm phases is formed. The deposited titanium aluminide alloy has good room and high-temperature (760 °C) tensile properties of 545 ± 9 and 471 ± 37 MPa, with elongations of 1.50 % ± 0.47 % and 1.50 % ± 0.45 %, respectively. The room and high-temperature samples both fail in the columnar grain region. The molecular dynamics simulations suggest that the interface between α2 and γm is the weakest, especially in the case of semicoherent interfaces (6° angle in the [1–10] direction), which provides good nucleation sites for cracks. Although the equiaxed grain regions contain several γm–α2 interfaces, the samples still fail in the columnar grain regions due to the increase in the cracking distance in the equiaxed regions caused by randomly oriented α2 + γ lamellae and the comparably good plasticity of the γm phases.

Developing cheap and stable electrocatalysts is considered the key factor to achieve the large-scale application of fuel cells. In this paper, three-dimensional (3D) porous Co-doped vanadium nitride (VN) nanosheet-assembled microflowers are prepared with a facile solvothermal approach followed by nitridation at 500 °C in NH3. It is found that the microflower morphology and the Co doping both significantly enhance the oxygen reduction reaction (ORR) performance of the materials. Because the unique 3D porous structure provides higher specific surface area and more active sites as well as enriching the d electrons of V via doping, Co also improves the intrinsic activity of VN. Our optimal V0.95Co0.05N microflowers achieve a half-wave potential for the ORR of up to 0.80 V in 0.1 M KOH solution, which is almost comparable to that of commercial 20% Pt/C. More importantly, the catalysts show superior durability with little current decline (less than 12%) during chronoamperometric evaluation for over 25 000 s. Th...

Laser melting deposition was carried out to deposit a 1Cr12Ni2WMoVNb steel bar on a wrought bar of same material. Room-temperature tensile properties of the hybrid fabricated 1Cr12Ni2WMoVNb steel sample were evaluated, and microstructure, fracture surface morphology, and hardness profile were analyzed by an optical microscope (OM), a scanning electron microscope (SEM), and a hardness tester. Results show that the hybrid fabricated 1Cr12Ni2WMoVNb steel sample consists of laser deposited zone, wrought substrate zone, and heat affected zone (HAZ) of the wrought substrate. The laser deposited zone has coarse columnar prior austenite grains and fine well-aligned dendritic structure, while the HAZ of the wrought substrate has equiaxed prior austenite grains which are notably finer than those in the wrought substrate zone. Besides, austenitic transformation mechanism of the HAZ of the wrought substrate is different from that of the laser deposited zone during the reheating period of the laser deposition, which determines the different prior austenite grain morphologies of the two zones. Microhardness values of both the laser deposited zone and the HAZ of the wrought substrate are higher than that of the wrought substrate zone. Tensile properties of the hybrid fabricated 1Cr12Ni2WMoVNb steel sample are comparable to those of the wrought bar, and fracture occurs in the wrought substrate zone during the tensile test.

Colloidal LiYbF 4 :Er 3+ nanorods were synthesized in an aqueous system which had the ratio of length to diameter of ∼2. These LiYbF 4 :Er 3+ nanorods emitted intense upconversion light under excitation of infrared at 1488 nm. Importantly, the intensities of two- and three-photon anti-Stokes upconversion PL bands were observed which were comparable to that of the Stokes emission under excitation with low power density. The plots of excitation power density versus emission intensity indicated that all the emissions centered at 549, 668, and 978 nm took a two-photon upconversion process. However, it could be simply deduced that the energy of two photons of 1488 nm were inadequate to produce a photon of 668 or 549 nm. For this conflict, the shape and saturation effects in the intermediate energy states were introduced to demonstrate the corresponding upconversion processes.

We propose theoretically a method for designing a narrowband multi-wavelength Solc-type filter based on the linear electro-optic effect in aperiodically poled lithium niobate. As one of its applications we demonstrate a thermally tuned 100 GHz spaced four-wavelength filter, whose working electric field is only 0.219 kV mm − 1 in an 8 cm long crystal. The filter allows four wavelengths to pass simultaneously with a 3 dB bandwidth of 0.26 nm, a passband of 32.5 GHz and a channel isolation of more than 8 dB, which can be tuned by temperature in a wide range at a rate of − 0.69 nm °C − 1. It is found that the domain errors of the aperiodically poled lithium niobate crystal within 25% are beneficial to the performance of the filter. The filter will be useful for dense wavelength division multiplexing optical communication systems.

We theoretically investigate the electro-optic coupling in an optical superlattice of linear chirped-periodically poled lithium niobate. It is found that the electro-optic coupling in such optical superlattice can work in a wide wavelength range. Some of examples, with bandwidths of 20, 40, 80, 120 nm, are demonstrated. The way to determine the electric field for perfect conversion between o- and e-ray and the method using apodized crystals of tanh profile to reduce the ripples are shown. As one of its applications, one kind of broadband Solc-type bandpass filter in optical communication range is proposed.