Phase-field study for effect of chemical composition on pre-precipitation process of γ′ phase in Ni-Al-Ti alloy

The pre-precipitation processes of γ＇ phase in Ni-Al-Ti alloy with different chemical compositions are investigated by microscopic phase-field dynamics model. The simulation results show that the early precipitated phase with L10 structure is formed before the formation of γ＇ phase. With the increase of Al content, the composition of precipitated phase is transformed from the co-existence of γ＇ phase and material phase into single y phase. Furthermore, excessive Al content can stimulate the production of γ＇ phase, and the conversion time from L10 phase to L12 phase will lag behind other samples with lower Al con-tent. By analyzing the occupation probability of Ti, it can be found that the solid solution strengthening effect of Ti is reduced with the increase of Al component.

Acoustical properties of a 3D printed honeycomb structure filled with nanofillers:Experimental analysis and optimization for emerging applications

The novelty of this research lies in the successful fabrication of a 3D-printed honeycomb structure filled with nanofillers for acoustic properties,utilizing an impedance tube setup in accordance with ASTM standard E 1050-12.The Creality Ender-3,a 3D printer,was used for printing the honeycomb structures,and polylactic acid(PLA)material was employed for their construction.The organic,inorganic,and polymeric compounds within the composites were identified using fourier transformation infrared(FTIR)spectroscopy.The structure and homogeneity of the samples were examined using a field emission scanning electron microscope(FESEM).To determine the sound absorption coefficient of the 3D printed honeycomb structure,numerous samples were systematically developed using central composite design(CCD)and analysed using response surface methodology(RSM).The RSM mathematical model was established to predict the optimum values of each factor and noise reduction coefficient(NRC).The optimum values for an NRC of 0.377 were found to be 1.116 wt% carbon black,1.025 wt% aluminium powder,and 3.151 mm distance between parallel edges.Overall,the results demonstrate that a 3Dprinted honeycomb structure filled with nanofillers is an excellent material that can be utilized in various fields,including defence and aviation,where lightweight and acoustic properties are of great importance.

Mechanical properties and acoustic emission characteristics of thick hard roof sandstone in Shendong coal field

The mechanical properties and acoustic emission characteristics of thick hard roof sandstone were investigated. Samples were taken from the 30.87-m thick sandstone roof in a mine in the Shengdong coal field, China. Firstly, the composition and microscopic characteristics were analyzed by XRD and FE-SEM, respectively. Moreover, the indirect tensile test, uniaxial compression test, three axis compression experiment and AE test are carried out by using RMT-150C mechanics experiment system with DSS-8B AE test system. The experiment results indicate that the main framework particles of sandstone are quartz and feldspar, and mainly quartz. Cements are mainly pyrite, kaolinite, chlorite and zeolite cross needle, clinochlore, and clay minerals. The microstructure of sandstone is very dense, with few pores and high cementation degree. The tensile strength, compressive strength and elastic modulus of sandstone are 4.825, 85.313 MPa, 13.814 GPa, respectively, so the sandstone belongs to hard rock. The AE cumulative counts of sandstone can be divided into three phases： relatively flat growth period, rapid growth period and spurt period. The signal strength of AE waveform can be used as a warning signal. In the tensile fracture zone, the warning value is 0.4 mV, and in the compression shear failure zone, it is 4 mV. The numbers of cumulative counts of AE under different stress conditions have obvious difference. Moreover, the growth of cumulative counts of acoustic emission is more obvious when the stress is more than 60% of the peak stress.

The influence of four dual-cure resin cements and surface treatment selection to bond strength of fiber post

In this study, we evaluate the influence of post surface pre-treatments on the bond strength of four different cements to glass fiber posts. Eighty extracted human maxillary central incisors and canines were endodontically treated and standardized post spaces were prepared. Four post pre-treatments were tested： （i） no pre-treatment （NS, control）, （ii） sandblasting （SA）, （iii） silanization （SI） and （iv） sandblasting followed by silanization （SS）. Per pre-treatment, four dual-cure resin cements were used for luting posts： DMG LUXACORE Smartmix Dual, Multilink Automix, RelyX Unicem and Panavia F2.0. All the specimens were subjected to micro push-out test. Two-way analysis of variance and Tukey post hoc tests were performed （α=0.05） to analyze the data. Bond strength was significantly affected by the type of resin cement, and bond strengths of RelyX Unicem and Panavia F2.0 to the fiber posts were significantly higher than the other cement groups. Sandblasting significantly increased the bond strength of DMG group to the fiber posts.

OBSERVATION OF EPITAXIAL OVERLAYER OF METALS AT ATOMIC LEVEL

Observation of epitaxial overlayer of metals at atomic level has been successfully observed in field ion microscope with 5 ns pulsed-laser heating.The condition of superlattice layer growth depends on the surface free energy and the lattice misfit.Many defects,such as vacancies,va- cancy clusters,voids,dislocations and twins are produced during epitaxial growth because of the lattice misfit even though the condition of surface free energy is satisfied.Alloying is ob- served to occur on the surface of the metal during the epitaxial growth.Diffusion is probably via the exchange mechanism.

PRECIPITATION HARDENING OF ELINVAR ALLOY

The microstructural evolution and precipitation hardening of an Elinvar alloy doped with Ti and Al during isothermal aging at 700℃ have been investigated by atom probe field ion microscopy and microhardness measurements.The γ′ precipiates are spherical and coherent with the matrix.The chemical composition of the precipitates are(Ni_(0.53)Fe_(0.47)_3 (Ti_(0.(?))Al_(0.4)). During aging,a Lifshitz-Wagner type dissolution and coarsening reaction of the precipitates has been observed,The hardness of the material varies with the aging time and reaches maxi- mum when the average diameter of the precipitates was about 11 nm.

Microscopic calculation of the magnetic field of neutron stars

Based on the Dirac equation describing an electron moving in a uniform and cylindrically symmetric magnetic field which may be the result of the self-consistent mean field of the electrons themselves in a neutron star, we have obtained the eigen solutions and the orbital magnetic moments of electrons in which each eigen orbital can be calculated. From the eigen energy spectrum we find that the lowest energy level is the highly degenerate orbitals with the quantum numbers pz = 0, n = 0, and m ≥0. At the ground state, the electrons fill the lowest eigen states to form many Landau magnetic cells and each cell is a circular disk with the radius λfree and the thickness λe, where λfree is the electron mean free path determined by Coulomb cross section and electron density and λe is the electron Compton wavelength. The magnetic moment of each cell and the number of cells in the neutron star are calculated, from which the total magnetic moment and magnetic field of the neutron star can be calculated. The results are compared with the observational data and the agreement is reasonable.

Structural and mechanical properties of Al–C–N films deposited at room temperature by plasma focus device

The Al–C–N films are deposited on Si substrates by using a dense plasma focus（DPF） device with aluminum fitted central electrode（anode） and by operating the device with CH_4/N_2 gas admixture ratio of 1：1. XRD results verify the crystalline Al N（111） and Al_3CON（110） phase formation of the films deposited using multiple shots. The elemental compositions as well as chemical states of the deposited Al–C–N films are studied using XPS analysis, which affirm Al–N, C–C, and C–N bonding. The FESEM analysis reveals that the deposited films are composed of nanoparticles and nanoparticle agglomerates. The size of the agglomerates increases at a higher number of focus deposition shots for multiple shot depositions. Nanoindentation results reveal the variation in mechanical properties（nanohardness and elastic modulus）of Al–C–N films deposited with multiple shots. The highest values of nanohardness and elastic modulus are found to be about 11 and 185 GPa, respectively, for the film deposited with 30 focus deposition shots. The mechanical properties of the films deposited using multiple shots are related to the Al content and C–N bonding.

Influence of ash composition on the sintering behavior during pressurized combustion and gasification process

To determine the ash characteristics during fluidized bed combustion and gasification purposes, the investigation of the impacts of chemical composition of Jincheng coal ash on the sintering temperature was conducted. A series of experiments on the sintering behavior at 0.5 MPa was performed using the pressurized pressure-drop technique in the combustion and gasification atmospheres. Meanwhile, the mineral transformations of sintered ash pellets were observed using X-ray diffractometer （XRD） analyzer to better understand the experimental results. In addition, quantitative XRD and field emission scanning electron microscope/energy dispersive X-ray spectrometer （FE-SEM/EDS） analyses of ash samples were used for clarifying the detailed ash melting mechanism. These results show that the addition of Fe203 can obviously reduce the sintering temperatures under gasification atmospheres, and only affect a little the sintering temperature under combustion atmosphere. This may be due to the presence of iron-bearing minerals, which will react with other ash compositions to produce low-melting-point eutectics. The FE-SEM/EDS analyses of ash samples with Fe203 additive show consistent results with the XRD measurements. The CaO and Na20 can reduce the sintering temperatures under both the combustion and gasification atmospheres. This can be also contributed to the formation of low-melting-point eutectics, decreasing the sintering temperature. Moreover, the fluxing minerals, such as magnetite, anhydrite, muscovite, albite and nepheline, contribute mostly to the reduction of the sintering temperature while the feldspar minerals, such as anorthite, gehlenite and sanidine, can react with other minerals to produce low-melting-point eutectics, and thereby reduce the sintering temperatures.

Sub-diffraction-limit cell imaging using a super-resolution microscope with simplified pulse synchronization

Stimulated emission depletion(STED) microscope is one of the most prominent super-resolution bio-imaging instruments, which holds great promise for ultrahigh-resolution imaging of cells. To construct a STED microscope, it is challenging to realize temporal synchronization between the excitation pulses and the depletion pulses. In this study, we present a simple and low-cost method to achieve pulse synchronization by using a condensed fluorescent dye as a depletion indicator. By using this method, almost all the confocal microscopes can be upgraded to a STED system without losing its original functions. After the pulse synchronization,our STED system achieved sub-100-nm resolution for fluorescent nanospheres and single-cell imaging.

Effects of K ions doping on the structure, morphology and optical properties of Cu_2FeSnS_4 thin films prepared by blade-coating process

Quaternary chalcogenide Cu2FeSnS4 （CFTS） nanoparticles, as a kind of potential absorber layer material in thin film solar cells （TFSCs）, were successfully synthesized by using a convenient solvothermal method. Alkali element K is incorporated into CFTS thin films in order to fiLrther improve the surface morphology and the optical properties of related films. X-ray diffraction （XRD）, Raman spectroscopy and field emission scanning electron microscopy （FESEM） were used to characterize the phase purity, morphology and composition of CFTS particles and thin films. The results show that the particle elemental ratios of Cu/（Fe＋Sn） and Fe/Sn are 1.2 and 0.9, respectively, which are close to the characteristics of stoichiometric CFTS. The band gaps of CFTS films before and after doping K ions are estimated to be 1.44 eV and 1.4 eV with an error of ±0.02 eV.