A one-dimensional incommensurate modulation structure was observed in NiAl3 after 3 keV Ar+ ion etching and studied by image deconvolution in HRTEM. The structure is proposed to be a type of compositional modulations.

The microstructure evolution of the supercooled Ni3Al melt and the kinetic details of the crystalline nucleation in the melt are investigated using the molecular dynamics simulation method. It is indicated that the non-crystal atomic clusters disappear from the melt before the beginning of the nucleation. The crystal nucleus is a random mixture of FCC structures and HCP structures and shows an irregular shape.

Structural changes of a molten Cu cluster containing 55 atoms on cooling have been investigated by employing molecular-dynamics simulations. Through microstructure analysis on pair distribution functions and atom density functions, the simulations show that the structural changes involve in three stages owing to the continuous interchange positions among atoms. In the beginning of the changes, a three-shells structure is formed in this cluster. Then, atoms in this cluster distribute in four shells, and meantime thirteen atoms in the inner part of this cluster form an icosahedron. Finally, the icosahedral structure including fifty-five atoms of this cluster is constructed. In this modeling, the shells are determined by atom density functions.

Based on the concept of the equivalent crack and theories of crack growth, a fatigue-creep life prediction model is presented. The influence of time independent fatigue , time dependent static creep and cyclic creep on the equation of micro crack growth speed is considered. Tomkins micro crack growth model is applied to time independent crack propagation while C* parameter is applied to time dependent crack propagation.1.25Cr0.5Mo steel fatigue creep life with stress control at 540°C is predicted by the model. The predicted results are correlated well with the experimental ones.

The phase field model for predicting second-phase precipitation has been established based on constructing free energy function and considering the effect of grain boundary on the second-phase precipitation process. The numerical simulation of the second-phase precipitation inside the grain and on the grain boundary was carried out in the system with the solute volume fraction less than 2%. The results show that the proportion of second-phase precipitate inside grain and on the grain boundary depends on the item in which ηiand m are orientation variable and exponent relative to the second phase profile, respectively. The proportion of the precipitates inside the grain increases with decreasing m and the size of the second-phase precipatate depends on the gradient energy coefficient κcat the same phase field step. All the precipatates appear on the grain boundary under m=1 or a larger κc value condition.

A two-dimensional (2-D) coupled cellular automaton (CA)-PanEngine model is developed for the simulation of dendritic growth and microsegregation formation in solidification of quaternary alloy system. In the model, the CA approach is employed to describe dendritic growth. The dynamics of dendritic growth is calculated according to the difference between the local equilibrium liquidus temperature and local actual temperature, incorporating with the Gibbs–Thomson effect. Based on the local liquid compositions of three solutes, which are determined by solving the solutal transport equation in the domain, the local equilibrium liquidus temperature and equilibrium solid concentrations of three solutes at the solid/liquid (SL) interface are evaluated with the aid of a thermodynamic phase equilibrium calculation package PanEngine. To reduce computation time, a data tabulation coupling strategy between CA and PanEngine is adopted. The model is validated through the comparisons of simulated results with the predictions of the Scheil model and the equilibrium model for the evolution of solid fraction with the decrease of temperature and for the solid composition profiles as a function of solid fraction in an Al-4.5wt%Cu-0.5wt%Mg-1wt%Si alloy. It is demonstrated that the present model can be used to simulate the evolution of dendritic growth morphology and to quantitatively predict the microsegregation patterns in solidification of quaternary Al-rich alloys.

The uniaxial load flow behavior of granular structure steels is predicted by Eshelby equivalent inclusion theory incorporating the plastic deformation of martensite islands. The result shows that the yield strength and work hardeing ratio of granular structure steels before martensite yielding, increase with increasing the volume fraction of martensite island presenting some nonlinear effects; The morphology of martesite island play a little role in stress-strain curves of homogeneous deformation; the strength of martensite island has little influence on the yield strength of granular structure and martensite island is harder to deform plastically corresponding to lower volume fraction of martensite island.

Dynamic recrystallization action for Nb bearing steel on flexible thin slab rolling has been investigated by Gleeble-2000 thermal/mechanical simulation tester. Considering the effect of Nb content, modelling of dynamic recrystallization have been studied. Research results show that with the increasing of Nb content, (the activation energy of dynamic recrystallization) increase and the value of is higher than that of the traditional hot strip rolling. With the increasing of Nb content, the value of A and n increases linearly, the value of m decreases linearly and the value of B increases. The calculated and experimental results are in good agreement. That is, the modelling of dynamic recrystallization can simulate the dynamic softening action for Nb bearing steel on flexible thin slab rolling and provide the direction for rolling technique.

On the basis of laws of momentum and mass conservation of liquid flux, a mathematical model to represent the liquid friction force in meniscus under non-sinusoidal oscillation was established, and a new liquid friction mechanism was proposed by solving extremum equations of liquid friction force as 2.0 m•min-1 casting speed. The results show that liquid friction force was mainly influenced by the shape of flux channel, depth of molten flux pool and relative motion between oscillating mold and strand and varies with oscillation waveform. Maximum liquid friction force occurs nearby the moment of oscillation velocity equal to casting speed under an ideal state. Surface cracks formed in the positive strip time adjacent to negative strip time, and healed during the negative strip time.

A Mathematical model has been developed to analyze the transient three- dimensional and three–phase flow in an argon gas bottom stirring ladle with one porous plugs. Multiphase Volume of Fluid (VOF) method is used to simulate the slag layer behaviors. Numerical results produce the following transient phenomena: when argon gas is injected into molten steel in a ladle, gas rising passage is formed near the plug, and then bubbles are created in the interior of molten steel; the rising gas bubbles impinge the slag intermittently and breakthrough the slag layer to create the slag eye. Simultaneity, the wave at interface of slag-steel formed and wave frequency increases with the increasing of argon gas flow rate for one off-centered plug case. Parametric studies show that diameter of slag eye changes from 0.43 m to 0.81 m while the argon gas flow rate vary with 100 ~300 Nl/min for a 220 ton ladle. The non-dimensional areas of slag eye vs the modified Froude number is close to experimental data in literature. Significant deformation of slag layer occurs during gas stirring operation, the thickness of slag becomes thin near the slag eye and thick near the ladle wall accordingly. The steel downward flow velocity at the slag eye periphery can be affected significantly by Ar gas flow rate. The higher the velocity, the more slag emulsification can be expected.

ABSTRACT Flow structure and RTD curve in Centrifugal Flow Tundish was predicted by mathematical simulation method, and the results were verified with the measurement data obtained from water model. Simulation results showed that, the molten steel in the rotation chamber rotated in a horizontal pattern due to the effect of electromagnetic force, and the swirling flow will promote the inclusion collision and coalescence. Deflection characteristic of the outflow from the rotation chamber leads to the asymmetrical distribution in the flow structure of distribution chamber, thus a horizontal circumfluence was formed and it will promote the mixture of molten steel and extend the residence time. Compared with the traditional tundish, the fraction of dead volume in the Centrifugal Flow Tundish was reduced, meanwhile the fraction of plug volume and mix volume were increased, and the study on the inclusion behavior also showed that the growth rate due to the collision and floatation rate of inclusions in the Centrifugal Flow Tundish was superior to traditional tundish.

Influence of intermediate annealing temperature on strength of repeat cold -rolled Al-Mg-Sc-Zr alloy was studied. It was found that intermediate annealing at 400℃ has no obvious effect on the strength of the alloy, while it decreases with the rolling times，especially for yield stress, when 450℃ intermediate annealing was applied. High density of dislocations induced by cold rolling will provide fast diffusion channel for Sc and Zr atoms and promot the coarsening of the Al3(Sc, Zr) particles when samples were annealed at 450℃. As a result, Al3(Sc, Zr) particles had weak ability to hinder the movement of dislocations and recovery process of alloy, and the strength of the alloy were decreased.

The effects of B content on the columnar structures of unidirectionally solidified Ti-46Al and Ti-46Al-5Nb alloys were investigated in the paper. The results show that, with B addition, the columnar structures of Ti-46Al and Ti-46Al-5Nb alloys are refined. The effect of B addition on the columnar structure refinement of Ti-46Al-5Nb alloy is greater than that of Ti-46Al alloy. This is resulted from two reasons. (1) The effects of Nb addition on the columnar structure refinement of Ti-46Al alloy. (2) In Ti-46Al alloy the boride fraction is increased because the solubility of B element was decreased with Nb addition.

The effect of a high magnetic field (HMF) on solidification microstructure and magnetic properties of Fe-49%Sn hypermonotectic alloys have been studied. It was showed that the morphologies of Fe-rich dendrites could be changed obviously and then magnetic properties were induced to improve. The morphologies of Fe-rich without HMF were dendrites in random and partially cellular structures. The alignment and preferential growth of Fe-rich dendrites paralleled to the applied field occurred with 10T. The primary dendrite arms of Fe-rich phase could be induced to align along [001] direction. The secondary dendrites were broken to fragments and even disappeared. Microstructure evolution and theoretical analysis were proposed to explain these results, which were in terms of magnetic crystalline anisotropy and preferential growth of dendrites. The aligned structures caused the increased magnetic properties such as the maximum magnetic permeability, remanent magnetization and magnetic crystalline anisotropy energy.

The morphology and distribution of Al3Fe phase in hypereutectic Al-2.89%Fe alloy solidified under high magnetic field was investigated.The effects of cooling rate, magnetic intensity and high gradient magnetic field on the distribution of Al3Fe were studied. The results showed that the primary Al3Fe phase with needle-like morphology was gathered at the bottom of the sample due to the gravity force when the alloy was solidified without the high magnetic field. However, when the high magnetic field of 12T was applied, the primary Al3Fe phase distributed throughout the sample homogeneously because that the magnetic force acted on the primary Al3Fe phase balanced with the gravity force, and the primary Al3Fe phase aligned perpendicularly to the magnetic field direction with a preferred direction [121]. Its orientation extent was not affected by cooling rate, but strengthened with increasing magnetic intensity. When the sample was set at the position with a large positive gradient magnetic field, the magnetic force acted on the primary Al3Fe phase was greater than the gravity force, resulting in their segregation to the upper portion of the sample. Several needle-like primary Al3Fe phases were integrated to form the polymer with a star shape. Furthermore, the mechanism of high magnetic field was discussed.

<110> oriented crystals Tb0.36Dy0.64(Fe0.85Co0.15)2 have been prepared by zone melting directional solidification method. The magnetomechanical coupling factor (k33) was determined by resonance/anti-resonance method in low bias fields. It was found that k33 is sensitive to both the bias field and the compressive pre-stress. Without compressive pre-stress, optimum k33 can be obtained with the value of 0.513 at a bias field of 50.9 kA/m. When applying a compressive pre-stress of 10 MPa, relatively lower k33 was obtained. It was attributed that extra energy of 71° domain wall is induced by the compressive pre-stress, which hinders the movement of magnetic moments or domain walls, decreasing the transition efficiency between the magnetic and mechanical energies.

Antiferromagnetic Fe1-xMnx(x = 0.30, 0.35, 0.40, 0.50, 0.55) alloys have been prepared by induction melting method. A homogenization for 24 h at 1000℃ has been carried out on the samples, followed by furnace cooling to room temperature. The microstructure and magnetostrictive properties of Fe1-xMnx samples were investigated. It was found that when x≤0.40, Fe1-xMnx alloys consisted of fcc γand hcp ε phases with poor magnetostrictive property, and the volume proportion of εphase decreased with the increase of Mn content. When x>0.40, the samples were single fcc γ phase and possessed much better magnetostrictive performance. The magnetostriction of Fe0.50Mn0.50 sample reached 873×10-6 in 1.9T magnetic field. The large magnetostriction in γ-Fe-Mn alloy can be attributed to the magnetic-field-induced fcc→hcp structural transformation.

Titanium dioxide photocatalytic thin films were prepared using method of microarc oxidation. Aimed to improve the photocatalytic activity of the titanium dioxide photocatalytic thin films, the components of the electrolytes were changed in process of the Microarc Oxidation by adding the oxide. The results show that over 10 percent of photocatalytic degradation ratio is improved with using the doped components of V、Ag、Ce, better than that of transition elements, heavy metals and rare earths. The semiconductor doping may obviously improve the photocatalytic activity. As far as the materials of V2O5 or SnO2 are concerned, effect of the concentration on the photocatalytic activity was also investigated. The results show that the photocatalytic degradation ratio was significantly improved as the concentration of V2O5 0.5mmol or SnO2 1.0mmol. The properties and structures were investigated by means of the XRD and SEM. The thickness and surface area of the microarc oxidation coating increase, and microarc channels diameter and particle size of microarc oxidation coating decrease for the Microarc Oxidation process with the treated electrolytes. But crystal lattice structure of titanium dioxide yet remains anatase.

The research is about synthesis process of CaB6 powder by molten salt electrolysis method. The synthesis temperature, electrolysis voltage, electrolysis time is identified. At the same time, under the conditions of different electrolysis time,the phase composition, particle size and shape of cathode products is analysised by X-ray diffraction and scanning electron microscope , experimental results show that synthesis process of CaB6 powder in CaCl2 molten salt system must have the basic conditions: protectiving environment of argon, electrolysis voltage is 3.0V, 900℃ insulation 30h, the range of CaB6 crystal particles size was 2μm～10μm, the morphology of particle is regular with rule cuboid massive crystal. The cathode electrolysis process conducted cyclic voltammetry scan analysis, a preliminary dynamic analysis and calculation to determine that chlorine borate proliferating to the cathode is control step of reaction.

The microstructure, corrosion morphology and corrosion product of AZ91D and AZ91D-1.0La alloy were investigated. With the addition of 1% La in AZ91D, not only rod-like Al11La3 and blocky Al8LaMn4 phase, but also more fine laminar β phase-Mg17Al12 around large β phase particles formed. The fine laminar β phase obviously restrained the further development of corrosion, which greatly improved the corrosion resistance of AZ91D. Al11La3 phase was cathodic phase, but this phase did not accelerate corrosion of α matrix because Al11La3 was rod-like phases, which only offered a small cathodic area. However, blocky Al10Ce2Mn7 phase obviously accelerated corrosion of α matrix because of its large cathadic area. Al11La3 and Al8LaMn4 are corrosion resistant phases, but they could not restrain the development of corrosion because their distribution was not continuous.

Field Activated Sintering (FAS) modeling was made and finite element simulation was done by means of computer aided finite element method. The results show that FAS temperature field was determined by an interaction among Joule heating of electric field, heat released by chemical reaction, and heat transferring characteristics of die-specimen system. Due to overlap of heats by Joule effect and chemical reactions, the highest temperature was in the center of the sample and a radius temperature gradient was established. That significantly took effects to uniformity of microstructure and densification degree. Therefore, it is important to control temperature gradient within the sample of FAS to prepare dense and fine grained bulk materials.

Abstract: The wetting behavior of Pd60-Ni40，PdNi-(3~6)V，PdNi-(7~15)V and PdNi-(16~24)Cr-(6~15)V on Si3N4 was studied by the sessile drop method. The results show that on the condition heating at 1250℃ for 30 min in vacuum, small contact angle and excellent interface are obtained using PdNi-(16~24)Cr-(6~15)V brazing filler. In the interfacial layer with this brazing filler, elements Cr and V preferentially diffused to Si3N4 and resulted in the reaction products of Cr-N phase and V-N phase. A small amount of element Si reacted with elements Cr and V and formed Cr-Si phase and V-Si phase. The matrix of filler metal was composed of Pd-Ni solid solution with some element Si, Pd-Si phase and Ni-Si phase. When the elements Cr and V were added concurrently in the brazing filler, the former diffused to the reaction layer more strongly than the latter.

Three series of ZnO-based varistor materials with different doping levels of antimony and bismuth were prepared, and their mechanical properties were investigated, respectively. Under constant amount of bismuth of 2 at%, with increasing amount of antimony in an appropriate range, the decreasing grain size of ZnO, almost unchanged porosity, and increasing relative density resulted in increase in the modulus, bending strength and fracture toughness. Under constant amount of antimony of 3 at%, with increasing amount of bismuth, the grain size and porosity increased, thus the relative density would decrease although the apparent density might increase. The resultant modulus, bending strength and fracture toughness all decreased. The optimum ZnO-based varistor material in this work had mechanical properties of elastic modulus of 114 GPa, flexure modulus of 115 GPa, bending strength of more than 120 MPa, and fracture toughness of higher than 1.87 MPa.m-1/2.

According to Norton creep constitutive equation and different creep parameters of welding material, heat-affected zone material and parent material, welding residual stress, post weld heat treatment(PWHT) residual stress and creep under inner pressure and PWHT residual stress of the welded joint of P91 steel high temperature piping were analyzed by ABAQUS finite element code. The distribution of welding residual stress and PWHT residual stress was obtained. Creep strain distribution after 100,000 hours and dangerous position of the welded joint were predicted. The results show the higher welding residual stress is in the welded joint for the piping wall thickness and constraints. And the welding residual stress can be reduced effectively by the method of PWHT. But, because of the existence of PWHT residual stress, the creep strain is also influenced by the PWHT residual stress. The stress can not be neglected in the strength design of high temperature piping. And much higher creep strain is in the edge between welding seam and heat-affected zone. The presente work provides a reference for the design and predicting maintenance for high temperature piping.

In this research, Al-Mg-Sc alloy sheets were welded by manual TIG(tungsten inert gas) welding method with Al-Mg-Sc-Zr welding wire as filling material, and the welded joints were processed heat treatment after welding under 350℃for 1h. Mechanical properties and microstructures of welded joints without and with heat treatment were studied comparatively using tensile test, micro-hardness measurement, SEM and TEM analysis methods. The results show that：as the result of 350℃/1h heat treatment, tensile strength and elongation percentage of welded joints increased to 410Mpa and 14.4%from 332 MPa and 5.6% correspondingly, which were that of without heat treatment, and welded joint coefficient reached to 0.98. After heat treatment, micro-hardness of welded zone was raised greatly, and failure position was fusion zone instead of welded zone. On the process of heat treatment, large amounts of Al3(Sc, Zr) particles, which are coherent with matrix, precipitated and deposited uniformly in the welded zone, leading to great improvement of hardness, tensile strength and yield strength of welded zone.