A two-step transient liquid phase diffusion bonding process of T91 steels

In this study, a two-step heating process is introduced for transient liquid phase （ TLP） diffusion bonding fo r sound joints with T91 heat resistant steels. At first, a short-time higher temperature heating step is addressed to melt the interlayer, followed by the second step to complete isothermal solidification at a low temperature. The most critical feature of our new method is producing a non-planar interface at the T9／ heat resistant steels joint. We propose a transitional liquid phase bonding of T91 heat resistant steels by this approach. Since joint microstructures have been studied, we tested the tensile strength to assess joint mechanical property. The result indicates that the solidified bond may contain a primary solid-solution, similar composition to the parent metal and free from precipitates. Joint tensile strength of the joint is not lower than parent materials. Joint bend＇s strengths are enhanced due to the higher metal-to-metal junction producing a non-planar bond lines. Nevertheless, the traditional transient liquid phase diffusion bonding produces planar ones. Bonding parameters of new process are 1 260 °C for 0. 5 min and 1 230 °C fo r 4 min.

The effect of thermal cycle on joint of Ti/stainless steel phase transformation diffusion bonding

The effects of thermal cycle parameters on the tensile strength and fracture characteristics of phase transformation diffusion bonding(PTDB) joint of titanium and stainless steel (Ti/SS) were studied in this paper. With the maximum cyclic temperature of 1 173～1 223 K , the minimum cyclic temperature of 1 073～1 093 K , the heating velocity of 30～50 K/s , the cooling velocity of 15～20 K/s , the cycle numbers of 15～20 and bonding pressure is 13 MPa , the tensile strength of joint is more than 380 MPa , exceeding 80% of that of Ti.

Phase diffusion of a two-component Bose-Einstein condensates:exact and short-time solutions for arbitrary coherent spin state

We investigate phase diffusion of a two-component Bose--Einstein condensates prepared initially in arbitrary coherent spin state ｜θ0,φ0｜. Analytical expression of the phase-diffusion time is presented for θ0～π/2 case. In comparison with the symmetrical case （i.e., θ0=π/2）, we find that the diffusion process becomes slow due to the reduced atom number variance.

New approach for analysing master equations of generalized phase diffusion models in the entangled state representation

By virtue of the well-behaved properties of the bipartite entangled states representation, this paper analyse and solves some master equations for generalized phase diffusion models, which seems concise and effective. This method can also be applied to solve other master equations.

A study on the two-step transient liquid phase diffusion bonding of K640 superalloy

A new technology, the two-step transient liquid phase diffusion bonding （TLP-DB） technology for cobalt-based K640 superalloy, was investigated. The method consists of a short-time high temperature heating to melt interlayer followed by isothermal solidification of liquid phase at a lower temperature than that of the conventional TLP-DB. The result indicates that the two-step TLP-DB can reliably produce an ideal joint with uniform chemical composition, which is superior to the joint welded by conventional TLP-DB in microstructure and mechanical properties. Bonding parameters of new process are 1 250℃ for 0. 5 h and 1 180℃ for 3 h. The high-temperature tensile strength of the joint by two-step TLP-DB reaches 74% of that of the base material on an equal basis, but the high-temperature tensile strength of the joint by conventional TLP-DB is only 58% of that of the base material.

New Approach for Solving Master Equations in Quantum Optics and Quantum Statistics by Virtue of Thermo-Entangled State Representation

By introducing a fictitious mode to be a counterpart mode of the system mode under review we introduce the entangled state representation （η｜, which can arrange master equations of density operators p（t） in quantum statistics as state-vector evolution equations due to the elegant properties of （η｜. In this way many master equations （respectively describing damping oscillator, laser, phase sensitive, and phase diffusion processes with different initial density operators） can be concisely solved. Specially, for a damping process characteristic of the decay constant k we find that the matrix element of p（t） at time t in 〈η｜ representation is proportional to that of the initial po in the decayed entangled state （ηe^-kt｜ representation, accompanying with a Gaussian damping factor. Thus we have a new insight about the nature of the dissipative process. We also set up the so-called thermo-entangled state representation of density operators, ρ = f（d^2η/π）（η｜ρ〉D（η）, which is different from all the previous known representations.

THE INTERFACIAL BEHAVIORS OF ALUMINUM MATRIX COMPOSITE IN DIFFERENT WELDING METHODS

Non-interlayer liquid phase diffusion welding (China Patent) and laser welding methods for aluminum matrix composite are mainly described in this paper. In the non-interlayer liquid phase diffusion welding, the key processing parameters affecting the strength of joint is welding temperature. When temperature rises beyond solidus temperature, the bonded line vanishes. The strength of joint reaches the maximum and becomes constant when welding temperature is close to liquid phase temperature. Oxide film in the interface is no longer detected by SEM in the welded joint. With this kind of technique, particle reinforced aluminum matrix composite Al2 O3p/6061Al is welded successfully, and the joint strength is about 80% of the strength of composite (as-casted). In the laser welding, results indicate that because of the huge specific surface area of the reinforcement, the interfacial reaction between the matrix and the reinforcement is restrained intensively at certain laser power and pulsed laser beam. The laser pulse frequency directly affects the reinforcement segregation and the reinforcement distribution in the weld, so that the weldability of the composite could be improved by increasing the laser pulse frequency. The maximum strength of the weld can reach 70% of the strength of the parent.

Effect of Electric Current on Diffusion of Aluminum in Ti3AlC2 into Zirconium Alloy

The spark plasma sintering（SPS） method was used to study the mechanism of reaction interface between Zr and Ti3AlC2 with electric current going through it. It was found that electric current greatly reduced the bonding temperature of Zr and Ti3AlC2. By the micro-structure analysis of the interface through SEM/EDS, it was found that Al atoms diffused from the Ti3AlC2 substrate into the Zr side and reacted with Zr to form the Zr-Al compounds at the interface, which is the strengthening mechanism of Ti3AlC2-Zr bonding. The thickness of reaction layers（Zr-Al alloy） was from 0.879 to 13.945 mm depending on different sintering condition. Current direction, heating rate, soaking time, pulse patterns all influenced the diffusion of Al atoms which affected the joining quality of Zr and Ti3AlC2.

Studies of phase transition and impedance behavior of Ba(Zr,Ti)O_(3)ceramics

Ceramic samples of Barium Zirconium Titanate(BaZr_(x)Ti_(1-x)O_(3)(BZT))were synthesized by conventional solid-state reaction method with different concentrations of x(=0.05(BZT1),0.10(BZT2),0.15(BZT3),0.20(BZT4),0.25(BZT5),0.30(BZT6)).Phase confirmation of the samples was done by X-ray diffraction(XRD)technique.All the compositions are in cubic structure.XRD pattern was recorded for samples sintered at different sintering temperatures.Lattice parameters increased with addition of Zr^(+4).Doping with Zr^(+4)into Barium titanate resulted in interesting changes of electrical properties(dielectric,impedance and ferroelectiricity).The strong influence of Zr doping on the phase transition characteristics of the BZT ceramics was studied from the dielectric response of the samples.Diffusivity of phase transition of the BZT ceramic samples increase with Zr^(+4)concentration,indicating changes from normal to diffuse transition to relaxor phase transition behavior.Impedance spectroscopy reveals the presence of temperature-dependent grain,grain boundary effects.Polarization-Electricfield(PE)loop measurements are also done on the samples.

Mass transfer between bubbles and the dense phasein gas fluidized beds

Mass transfer between a bubble and the dense phase in gas fluidized beds of Group A and Group B particles was proposed based on previous experimental results and literature data. The mass transfer coefficient between bubbles and the dense phase was determined by kbe = 0.21 db. A theoretical analysis of the mass transfer coefficient between a bubble and the dense phase using diffusion equations showed that the mass transfer coefficient between a bubble and the dense phase is kbe α εmf√ub/db in both three- and two-dimensional fiuidized beds. An effective diffusion coefficient in gas fluidized beds was introduced and correlated with bubble size as De = 13.3db2.7 for Group A and Group B particles. The mass transfer coefficient kbe can then be expressed as kbe = 0.492εmf√ubdb1.7 for bubbles in a three-dimensional bed and kbe = 0.576εm√ubdb1.7 for bubbles in a two-dimensional bed.

Optical forces on neutral atoms in the presence of fluctuating laser fields:numerical analysis

Doppler cooling of^(88)Sr atoms is studied in the presence of off-resonant red-detuned fluctuating laser fields.Using a semi-classical approach,we show that the relevant physical quantities in the cooling process,such as optical forces,the damping coefficient,Doppler temperature,and atom number in the trap,are strongly affected by the laser amplitude and phase fluctuations.We find that the Doppler cooling limit is higher than the predicted Doppler theory for non-fluctuating lasers.This implies an additional heating mechanism exists due to the laser fluctuations.Furthermore,our numerical analysis shows that the effect of laser power stability on reducing the number of trapped atoms in a magneto-optical trap is more substantial than the effect of laser linewidth.

Glassy behavior study of dysprosium doped barium zirconium titanate relaxor ferroelectric

We report the glassy behavior of dysprosium doped barium zirconium titanate single phase perovskite ceramics with general formula Ba_(1-x)Dy_(2x/3)Zr_(0.25)Ti_(0.75)O_(3)prepared by solid-state reaction method.Temperature and frequency dependent dielectric studies of the ceramics reveal relaxor behavior.A non-Debye relaxation,which is analogous to the magnetic relaxation in spin-glass system,is observed clearly around temperature of dielectric permittivity maximum(Tm).Frequency dependence of Tm governed by production of polar nano-regions is analyzed using Debye relation,Vogel-Fulcher(V-F)relation and power law.A clear change in dynamic behavior is observed by power parameter which is related to growth of interactions between polar nano-regions with different composition.Various parameters like activation energy for relaxation,freezing temperature,relaxation frequency,etc.,are determined after non-linear curve fitting.Temperature dependence of dielectric constant at temperatures much higher and lower than Tm is analyzed by two exponential functions,which gives an idea about the production of polar clusters at high temperature and distribution of freezing temperatures at lower temperature.Various other associated parameters are calculated by non-linear curve fitting and their significance has been explained.

Relaxor ferroelectric behavior of BaBi_(4)Ti_(4)O_(15) aurivillius ceramic

Aurivillius type compound BaBi_(4)Ti_(4)O_(15)(BBT)ceramic was prepared by solid state reaction route and its electrical properties were studied.X-ray diffraction(XRD)pattern showed orthorhombic structure with space group A21am confirming it to be an m=4 member of the Aurivillius oxide.The scanning electron microscope of the sintered pellet showed a plate-like morphology of grains which is a characteristic feature of the Aurivillius compounds.The temperature and frequency dependence dielectric study showed a shifting of transition temperature with frequency indicating relaxor type behavior in the material.The diffuseness parameter(γ)established the relaxor nature and it was attributed to the A-site cationic disorder.The dielectric relaxation obeyed the Vogel
Fulcher(VF)relation and various parameters like activation energy for relaxation,freezing temperature,relaxation frequency were determined after nonlinear curve fitting.The temperature dependence of dielectric constant at temperatures much higher and lower than Tm was analyzed by two exponential functions,which gives an idea about the production of polar clusters at high temperature and the distribution of freezing temperatures at lower temperature.Various other associated parameters were calculated by nonlinear curve fitting and their significance has been explained.

Composition dependence of dielectric properties in Pb(Zn_(1/3)Nb_(2/3))O_(3)–PbTiO_(3)–BaTiO_(3)(PZN–PT–BT)relaxor ferroelectric ceramics

Perovskite solid solution ceramics of PZN–PT–BT with several compositions were synthesized by solid-state reaction method.X-ray diffraction results indicate pure perovskite structures for all samples.Dielectric measurements show that the implicit Ba(Zn_(1/3)Nb_(2/3))O_(3)(BZN)composition could broaden the diffusion phase transition(DPT)peaks and lower the ε_(max) and T_(max) values.The observed dielectric properties may be caused by the increased cation disorder due to the substitution of barium onto the A-site and titanium onto the B-site.

Synergetic migration behavior of La and Ce and related microstructure character of Cr-V-RE co-doped WC-Co alloy

The as-sintered sinter skin and the polished section of WC-11Co-0.4Cr 3 C 2-0.3VC-0.2RE（RE=mischmetal with La/Ce ratio of 0.65） alloy were analyzed.It was shown that the microstructures on the skin and in the inner part of the alloy were all characterized with a WC＋β＋M structure,where β was a cobalt-based binder phase and M represented a RE-containing phase.There existed an inward diffusion of S atoms,which caught and fixed the Ce atoms in the alloy and an outward diffusion of La atoms during the sintering process.Consequently,the M phase was characterized with the decreased La/Ce ratio（0.59） in the inner part and the increased La/Ce ratio（1.01） on the skin.The M phase on the skin was characterized with a γ-Ce 2 S 3 type structure.To suppress the long range migration of rare earth to the skin,S in the sintering atmosphere had to be eliminated.