Microstructure of cast γ-TiAl based alloy solidified from β phase region

The microstructures and phase transformation of Ti-43Al-4Nb alloy in as-cast and heat-treated states were investigated by using optical microscopy, scanning and transmission electron microscopy as well as differential scanning calorimetry. The results show that a fine microstructure of the as-cast alloy can be obtained by solidifying through the β phase. γ grains can nucleate directly from the β phase. The coexistence of β phase and γ phase along primary α grain boundaries contributes to the decrease in the grain size of the as-cast alloy. The phase transformation sequence during solidification of the Ti-43Al-4Nb alloy is suggested as L→L＋β→β→α＋β→α＋βr→α＋γ＋βr→lamellae（α2＋γ）＋γ＋βr. The microstructure of the alloy after heat treatment at 1 250 ℃ for 16 h exhibits a certain coarsening compared with that of the as-cast state. The remnant β phase can be removed by the heat treatment process due to the diffusion of Nb and the non-equilibrium state of β phase.

Enhancement of vertical phase separation in sequentially deposited organic photovoltaics through the independent processing of additives

Herein,the impact of the independent control of processing additives on vertical phase separation in sequentially deposited (SD) organic photovoltaics (OPVs) and its subsequent effects on charge carrier kinetics at the electron donor-acceptor interface are investigated.The film morphology exhibits notable variations,significantly depending on the layer to which 1,8-diiodooctane (DIO) was applied.Grazing incidence wide-angle X-ray scattering analysis reveals distinctly separated donor/acceptor phases and vertical crystallinity details in SD films.Time-of-flight secondary ion mass spectrometry analysis is employed to obtain component distributions in diverse vertical phase structures of SD films depending on additive control.In addition,nanosecond transient absorption spectroscopy shows that DIO control significantly affects the dynamics of separated charges in SD films.In SD OPVs,DIO appears to act through distinct mechanisms with minimal restriction,depending on the applied layer.This study emphasizes the significance of morphological optimization in improving device performance and underscores the importance of independent additive control in the advancement of OPV technology.

A Cu-Pd alloy catalyst with partial phase separation for the electrochemical CO_(2) reduction reaction

Cu catalysts can convert CO_(2) through an electrochemical reduction reaction into a variety of useful carbon-based products.However,this capability provides an obstacle to increasing the selectivity for a single product.Herein,we report a simple fabrication method for a Cu-Pd alloy catalyst for use in a membrane electrode assembly(MEA)-based CO_(2) electrolyzer for the electrochemical CO_(2) reduction reaction(ECRR)with high selectivity for CO production.When the composition of the Cu-Pd alloy catalyst was fabricated at 6:4,the selectivity for CO increased and the production of multi-carbon compounds and hydrogen is suppressed.Introducing a Cu-Pd alloy catalyst with 6:4 ratio as the cathode of the MEAbased CO_(2) electrolyzer showed a CO faradaic efficiency of 92.8%at 2.4 V_(cell).We assumed that these results contributed from the crystal planes on the surface of the Cu-Pd alloy.The phases of the Cu-Pd alloy catalyst were partially separated through annealing to fabricate a catalyst with high selectivity for CO at low voltage and C_(2)H_4 at high voltage.The results of CO-stripping testing confirmed that when Cu partially separates from the lattice of the Cu-Pd alloy,the desorption of~*CO is suppressed,suggesting that C-C coupling reaction is favored.

Negative Phase Time Effectin Potential-Well Passing

The properties of phase time taken for particles to pass through a quantum potential well are investigated. It is found in a 1 dimensional quantum mechanical problem that the phase time is negative when the incident energy and the thickness of potential well satisfy certain conditions. Similar results are also found in a 2 dimensional fully relativistic optical analog. It is shown that the expression of the la teral shift of transmitted optical waves is similar to that of the phase time in the 1 dimensional quantum mechanical problem. The phase time in the 2 dimensional optical problem is also shown to be negative under certain conditions.

Effects of initial δ phase(Ni_3Nb) on hot tensile deformation behaviors and material constants of Ni-based superalloy

Effects of initial δ phase（Ni_3Nb） on the hot tensile deformation behaviors and material constants of a Ni-based superalloy were investigated over wide ranges of strain rate and deformation temperature. It is found that the true stress-true strain curves exhibit peak stress at a small strain, and the peak stress increases with the increase of initial δ phase. After the peak stress, initial δ phase promotes the dynamic softening behaviors, resulting in the decreased flow stress. An improved Arrhenius constitutive model is proposed to consider the synthetical effects of initial δ phase, deformation temperature, strain rate, and strain on hot deformation behaviors. In the improved model, material constants are expressed as the functions of the content of initial δ phase and strain. A good agreement between the predicted and measured results indicates that the improved Arrhenius constitutive model can well describe hot deformation behaviors of the studied Ni-based superalloy.

Phase Relations in TiAl+Nb System

The microstructures and phases of ternary TiAl+Nb alloys containing 50-60 at.-%Al, 0-21 at.-%Nb have been studied using transmission electron microscopy (TEM) and X-ray powder diffraction. The phases present in the alloys and their distribution were found to be a sensitive function of composition. The phase relations between γ-TiAl and γ1 (a new ordered ternary intermetallic compound based on γ-TiAl) were determined. Essentially single γ phase was determined for alloys with relativety low Nb content (≤10 at.-%Nb). the γ1 phase was determined to exist in the composition range containing higher Nb contents (15-21 at.-%Nb). Between γ and γ1 phases, with intermediate Nb contents there is a transitional phase γ1 (a superstructure of γ-TiAl). As for the influence of Al concentration on the phase relations. the γ1 phase was inclined to form in the alloys with relatively high Al contents. The ordering transformation of γ, to γ1 is a continuous ordering process and the transition may be second order.

A new method of detecting interferogram in differential phase-contrast imaging system based on special structured x-ray scintillator screen

An x-ray scintillator screen with a special structure, functioning as detector and analyser grating, was proposed for collecting the interferogram of differential phase contrast imaging without absorption grating and difficulty of fabrication by a state of the art technique. On the basis of phase grating diffraction, a detecting model of the scintillator screen was built for analysing the phase and absorption information of objects. According to the analysis, a new method of phase retrievals based on two-images and the optimal structure of screen were presented.

Visibility in differential phase-contrast imaging with partial coherence source

This paper gives theoretical analysis of visibility of fringes, which is influenced by distances, temporal and spatial coherence of source, in hard x-ray differential phase-contrast imaging with microfocus x-ray source. According to the character of longitudinal periodicity of the interferogram, the setup is insensitive to mechanical drift and vibrations. The effect of temporal coherence of x-ray source is investigated and its related bandwidth is derived. Based on the theory of partially coherent light, it shows that the requirement for the spatial coherence of x-ray source is not strict and can be met by the general microfocus x-ray tube for x-ray differential phase-contrast imaging.

Mechanism and Kinetics of Phase Transformation in Two-phase TiAl-based Alloys

The aged and quenched microstructures of both alloys, Ti-42at-%Al and Ti-45at -%Al,homogenized in the disordered single phase field. were investigated And the results show that the quinched microstructure is a supersaturated single phase of ordered 22. When the supersaturated phase is aged in the two phase range at 1273 and 1373 K, it will transform to a lamellar microstructure of γ+α2. with a discontinuous decomposition mechanism in Ti-42at-%Al alloy and a semicontinuous decomposition mechanism in T1-45at-%Al alloy. With the methods of quantitative metallograph examination and X-ray diffraction analysis. the relationship between the amount of γ, phase precipitation and the time of isothermal transformation is agreed

A Uniform Reference Line Based Differential Phase Shifter with Wide Phase Range and Wide Bandwidth

To implement the multi-way phase shifting maintaining the compact size and simplicity in structure,the uniform reference line concept was proposed for the differential phase shifter.However,the performance in bandwidth and phase range deteriorates with the additional requirements considered.To solve this problem,a quarter wavelength coupled line section loaded with open/short stubs is proposed as the basic element to implement the main line and also reference line.According to the theoretical analysis on this basic element,the loading stubs can be used to control the phase shift and also the phase slope of the basic element without affecting the amplitude property.With the predetermined parameters of the uniform reference line,only two parameters are required for the implementation of different differential phase shifts.This demonstrates the high simplicity of the proposed structure.For demonstration,an eight-way differential phase shifter operating at 3.5 GHz was implemented using the vertically installed planar structure.The prototype was further fabricated and measured.Good agreement between simulation and measurement can be observed.The implemented phase shifter can provide a wide range of phase shifting values from 45°to 315°with reference to the uniform reference line over a relative bandwidth of 62.3%.

EFFECT OF INTERSTITIAL IMPURITIES ON THE PHASETRANSFORMATION OF Ti-Al ALLOYS

应用固体与分子经验电子理论的平均晶胞和平均原子模型分析计算了间隙杂质对Ti-Al合金价电子结构和相变的影响。同时根据该理论的键能公式计算了间隙杂质影响下的键能、熔点和液相线的变化。据此解释了Ti-Al合金相变目前尚有争议的主要实验结果。表明，间隙杂质提高了合金元素的原子杂阶，引起键结构呈严重的各向异性，阻碍了β→α相转变，导致中间成分相变的复杂性。间隙杂质也降低了熔点及高温液相线，采用近似处理由该理论可较好地计算其平均降低程度。

Microstructural evolution and phase transformation during partial remelting of in-situ Mg_2Si_p/AM60B composite

The microstructural evolution and phase transformations during partial remelting of in-situ Mg2Sip/AM60B composite modified by SiC and Sr were investigated. The results indicate that SiC and Sr are effective for refining primary α-Mg grains and Mg2Si particles. After being partially remelted, a semisolid microstructure with small and spheroidal primary α-Mg particles can be obtained. The microstructural evolution during partial remelting can be divided into four stages： the initial rapid coarsening, structural separation, spheroidization and final coarsening, which are essentially caused by the phase transformations of β→α, α＋β→L and α→L, α→L, and α→L and L→α, respectively. The Mg2Si particles have not obvious effect on the general microstructural evolution steps, but can slower the evolution progress and change the coarsening mechanism. During partial remelting, Mg2Si particles first become blunt and then become spheroidal because of melting of their edges and corners, and finally are coarsened owing to Ostwald ripening.

Precipitation of α Phase in the Massive and Feathery Structures in TiAl Alloys during Aging in the Single α Field

Precipitation of α-phase in massive and feathery microstructures was studied during aging in the single α field. It was found that the α-phase mainly precipitated along the γ-plate interfaces as laths in the feathery structure, while it nucleated at various sites in the massive structure in the form of particles and dominantly as plates. Precipitation of α-plates in the massive structure occurred by the difFusional ledge mechanism. The γm→α reaction proceeded by the growth of previously nucleated α-precipitates, and chiefly by the development of new α-plates

Spatial heterogeneity in liquid–liquid phase transition

Molecular dynamics simulations are performed to investigate the liquid-liquid phase transition （LLPT） and the spatial heterogeneity in A1-Pb monotectic alloys. The results reveal that homogeneous liquid AI-Pb alloy undergoes an LLPT, separating into Al-rich and Pb-rich domains, which is quite different from the isocompositional liquid water with a transition between low-density liquid （LDL） and high-density liquid （HDL）. With spatial heterogeneity becoming large, LLPT takes place correspondingly. The relationship between the cooling rate, relaxation temperature and percentage of A1 and the spatial heterogeneity is also reported. This study may throw light on the relationship between the structure heterogeneity and LLPT, which provides novel strategies to control the microstructures in the fabrication of the material with high performance.

Semiconductor optical amplifier used as regenerator for degraded differential phase-shift keying signals

Phase and amplitude regeneration are necessary for degraded differential phase-shift keying communication sys- tems. This paper proposes a regenerator based on semiconductor optical amplifier for differential phase-shift keying signals. The key regeneration mechanism is theoretically analysed. The effectiveness of semiconductor optical amplifier based regenerator is demonstrated by comparing the bit error rate and eye diagrams before and after regeneration for 40-Cbit/s differential phase-shift keying 1080-km transmission systems. The results show that regeneration effects are very well. Bit error rate is tess than 10-12 with the regenerator.

A Study on Reflection Phase Time of Particles Passing through a Potential Well

To understand the physical meaning of phase time further more, we discuss the reflection phase time of quantum-particles passing though a potential well It is shown that the reflection phase time is equal to the transmission phase time in value and negative under certain conditions for a square potential well by analyzing While quantum-particles passing through the potential well, we think that this course can be described only with the velocity of energy of quantum mechanics whether or not they are reflected or transmitted eventually

Method for differential phase delay resolution of phase referencing VLBI technique and its experimental verification

The phase referencing Very Long Baseline Interferometry(VLBI)technique is a newly developed tool to measure the angular position of a deep space exploration probe in the plane-of-the-sky.Through alternating observations between the probe and a nearby reference radio source,their accurate relative angular separation can be obtained from the radio images generated by this technique.To meet the requirements of the current orbit determination software,differential delay should be firstly derived from those radio images.A method to resolve the differential phase delay from the phase referencing VLBI technique is proposed in this paper,and as well the mathematical model for differential phase ambiguity resolution is established.This method is verified with practical measurement data from the Chang’E-3 mission.The differential phase delay between the Chang’E-3 lander and rover was derived from the phase referencing VLBI measurements,and was then imported into the Shanghai astronomical observatory Orbit Determination Program(SODP)to calculate the position of the rover relative to the lander on the lunar surface.The results are consistent with those acquired directly from radio images,indicating that the differential phase ambiguity has been correctly resolved.The proposed method can be used to promote applications of the phase referencing VLBI technique in future lunar or deep space explorations,and more accurate orbit determination becomes promising.

Microstructural evolution of a PM TiAl alloy during heat treatment in α+γ phase field

In this study, the effect of temperatures and cooling rates of heat treatment on the microstructure of a powder metallurgy (PM) Ti-46Al-2Cr-2Nb-(B,W) (at.%) alloy was studied. Depending on the cooling rate and temperature, the different structures were obtained from the initial near-γ (NG) microstructures by heat treatment in the α+γ field. The results show that the microstructures of samples after furnace cooling (FC) consist primarily of equiaxed γ and α 2 grains, with a few grains containing lamellae. Duplex microstructures consist mainly of γ grains and lamellar colonies were obtained in the quenching into another furnace at 900°C (QFC) samples. However, further increasing of the cooling rate to air cooling (AC) induces the transformation of α→α_2 and results in a microstructure with equiaxed γ and α_2 grains, and no lamellar colonies are found.

Study on Rare Earth-Containing Phases in TiAl Based Alloys Prepared by Non-Equilibrium Solidification Processing

Microstructure evolution of rare earth rich phase of rapidly-solidified (RS) TiAl based alloys was investigated. The two rapid-solidification techniques employed are melt-spinning technique (MS) and Hammer-and-Anvil technique (HB). MS ribbons and HA foils were obtained in the experiment. The results demonstrate that with the increasing of cooling rates of TiAl based alloys great changes are taken place in the microstructures of rare earth rich phase, from scattering mainly on grain boundaries of as-cast ingot to distributing homogeneously as very fine fibers or powders (nanometer grade) on the matrix. The fine paralleling second phase fibers in the HA foils are considered to be connected with gamma/alpha (2) lamellar colonies. Selected area electronic diffraction (SAED) patterns of the rare earth rich phase is in accordance with that of intermetallic AlCe.

Applications of Wavelet Analysis in Differential Propagation Phase Shift Data De-noising

Using numerical simulation data of the forward differential propagation shift （ΦDP） of polarimetric radar,the principle and performing steps of noise reduction by wavelet analysis are introduced in detail.Profiting from the multiscale analysis,various types of noises can be identified according to their characteristics in different scales,and suppressed in different resolutions by a penalty threshold strategy through which a fixed threshold value is applied,a default threshold strategy through which the threshold value is determined by the noise intensity,or a ΦDP penalty threshold strategy through which a special value is designed for ΦDP de-noising.Then,a hard-or soft-threshold function,depending on the de-noising purpose,is selected to reconstruct the signal.Combining the three noise suppression strategies and the two signal reconstruction functions,and without loss of generality,two schemes are presented to verify the de-noising effect by dbN wavelets：（1） the penalty threshold strategy with the soft threshold function scheme （PSS）; （2） the ΦDP penalty threshold strategy with the soft threshold function scheme （PPSS）.Furthermore,the wavelet de-noising is compared with the mean,median,Kalman,and finite impulse response （FIR） methods with simulation data and two actual cases.The results suggest that both of the two schemes perform well,especially when ΦDP data are simultaneously polluted by various scales and types of noises.A slight difference is that the PSS method can retain more detail,and the PPSS can smooth the signal more successfully.