The microstructure and morphology of retained austenite of the austempered high silicon cast steel after various austempering combinations are investigated by TEM, and the volume fraction of retained austenite is also studied by XRD method. The experiments indicate that the retained austenite present at the isothermal transformation temperature has two typical morphologies, film shaped and blocky retained austenite. There are K-S orientation relationship between interface of film shaped retained austenite and bainite ferrite. The film shaped retained austenite is conductive to both high strength and good toughness, while the blocky retained austenite has poor stability and thus is detrimental to the mechanical properties of the steel. It is suggested that the ratio of volume fraction of the film shaped/blocky retained austenite must exceed about 1.0 for optimum mechanical properties.

The interaction between spherical particles and dendrites and the process of microstructure formation including particle distribution for Al-7.0%Si (mass fraction) alloy with additive SiC particles were simulated. Based on heat and solute conservation, solute redistribution, interface curvature and anisotropy were considered. Particle, solid, liquid as well as solid/liquid interface were treated respectively. The numerical models that describe the interaction between single particle/multiple particles and dendrites were established. The engulfment/pushing phenomena between single particle and solidification interface were predicted, and solute concentration and velocity field distribution of the growing dendrites and solid/liquid interface shape close to particle were studied. The interaction process between multiple particles and dendrites and the segregation of particles into the interdendrite regions were recurred. The simulated results show that the interaction between particles and advancing curved solid/liquid interfaces is non-steady state when the particle is pushed, while it can be treated as steady pushing mode when solidification velocity is lower than critical velocity. The simulated results of dendrite microstructure and particle distribution are in good agreement with the experimental.

The atomic cluster models of αandβTi grains, edge dislocation in αgrains and the crack formed with edge dislocation accumulation were set up by computer simulation technique. The electronic structure (Fermi energy level, structure energy, environment sensitive embedding energies etc) of αTi grains, edge dislocation and the crack were calculated by using Recursion method. The effect of alloys element Mo and V on βphase atomic binding energy was calculated and analyzed. The results show that: H prone to gather on the edge dislocation and form H atomic group as the environment sensitive embedding energies is smaller when H is at the edge dislocation. It makes Ti alloys local harden and edge dislocation blocking and forming crack that the edge dislocation fix the H atomic group. As the Fermi energy of the crack tip is higher than that of other area, so the electron run to other area of the crack from the crack tip, which make the electric potential difference between the crack tip and the other area of the crack. The crack tip decomposes as anode under the electrolyte. The tensile force and H air pressure at the crack make the crack cleavage or stretch along grains boundaries, which facilitates the stress corrosion. The alloys element Mo and V can enhance Ti alloys stress corrosion resistance by catalyzingβphase which stops the crack expand in αTi.

Mushy zone properties of AZ6x alloys were characterized and analysed by using cooling curve thermal analysis method and continuous torque measurement technique. The results show that Tn1 (first characteristic temperature of primary crystal nucleation), Tn2 (second characteristic temperature of primary crystal nucleation) and Tch (temperature of dendritic coherency) decrease with the increasing of zinc content, and the temperature difference of (Tn1-Tn2) grows slowly while the temperature difference of (Tn2-Tch) almost remains constant; The results also show that the fs-cc (solid fraction of dendritic coherency) of AZ6x alloys is about 0.27~0.35 while AM60 and AZ66 alloys having higher fs-ch and alloys with 2~5wt% zinc content having lower fs-ch and AZ62 alloy having the lowest fs-ch; The results also show that Tpk (temperature of dendritic packing) decrease with the increasing of zinc content, and the solid fraction at Tpk decreases with the increasing of zinc content, and the mushy zone strength at Tpk increases first and then decreases with the increasing of zinc content while mushy zone strength of alloys with 2~5wt% zinc content having relatively slow increasing speed. the results obtained by cooling curve thermal analysis method and continuous torque measurement technique are accordant to each other.

Molecular dynamics simulations were performed to investigate stress induced crystallization behavior during the indentation process for amorphous Cu. The interaction between atoms in the system adopts the embedded atom method (EAM) reported by Mishin. The Variations of energy, stress and microstructure during the indentation process were studied. The results show that the small grains nucleate at the plastic deformation region, then grow and coalesce with deformation. The local plastic deformation induces the crystal nucleation, grain growth and grain coalescence. The final crystalline phase has an FCC structure which (111) plane is parallel to the shear direction. The nanocrystal grains embedded in the amorphous phase can enhance the rigidity of the sample.

The Au-In-Au low temperature metallic bonding and its application in the structure fabrication of long wavelength vertical cavity surface emitting laser (VCSEL) devices were investigated. The low temperature metallic bonding technic not only improves the thermal characteristic of the bonded devices, but also enhances the reflectivity of the distributed Bragg reflectors (DBR) in the VCSEL structure. The result of Experiments shows that InP based epitaxial VCSEL structure was successfully metallic bonded to the Si substrate at 200 ℃ with high bonding strength, and the bonding quality meets the requirements in the device fabrication of VCSEL. The optical characterization of the bonded samples indicates that the process of low temperature metallic bonding have rarely influence on the optical performance of VCSEL active region and DBR. So this low temperature metallic bonding technic can be used in the structure fabrication of VCSEL devices. And it is expected to be applied in the fabrication of other semiconductor photoelectric devices.

Positron annihilation lifetime and coincidence Doppler broadening measurements have been performed in Ti51Al49 alloy with different amounts of Nb doped. The experimental results indicate that when a low mount of Nb atoms is added into Ti51Al49 alloy, the Nb atoms mainly aggregate at grain boundaries, and then the free electron density increases, which reduces the brittleness of TiAl alloys. In contrast, the density of free electron in grain boundaries and in bulk are both decrease in high Nb doped alloy, due to the formation of the new order structure, which increases the brittleness of TiAl alloys.

Polyaniline films were synthesized on zinc－electroplated steel sheets in sodium salicylate aqueous medium．From the FTIR and XPS values, conclusions can be as follows: (1) Pani layers is doped with some salicylate anions; (2) The doping level is nearly 12~24% for the Pani films.A research is made on the effect of the radialization of electron beam on electropolymerized film of aniline film on zinc-electroplated steel. The obtained results show that the gel content and crosslinking density increase with the dose, get to a maximum at 960kGy, and are independent of dosage quotiety. The corrosion protection capability are improved to a great extent. At the same dose, the corrosion protection capability becomes better with the dosage quotiety becomes lower.

Microstructure and high-frequency magnetic properties were investigated for soft magnetic nanocrystalline (Fe1-xCox78.4)Nb2.6Si9B9Cu1 (x=0.35, 0.5, 0.65) alloys annealed at 490℃for 0.5 hour under vacuum atmosphere (1×10-3Pa). XRD analyzing showed that the α-FeCo(Si) crystallites of about 15 nm were from the amorphous matrix by annealing the samples. With the increasing of Co content, the lattice parameter of α-FeCo(Si) crystallites decreased and the average grain size increased appreciably. Pseudo-Voigt2 function was used to fit the XRD patterns in order to estimate the crystalline volume fraction. The mean composition of the residual amorphous matrix was estimated according to lattice parameter and crystalline volume fraction. Permeability-frequency spectra from 10 kHz to 10 MHz was studied by using an impedance analyzer for nanocrystalline (Fe1-xCox78.4)Nb2.6Si9B9Cu1 alloys. It was shown that with the increasing of Co content, the initial permeability decreased and resonance frequency remarkably increased. The equation of domain wall motion and domain wall pinning mechanism were used to analyze how the high-frequency magnetic property was determined by the Co content for nanocrystalline (Fe1-xCox78.4)Nb2.6Si9B9Cu1 alloys.

A series of Deformation Induced Ferrite Transformation (DIFT) tests are investigated by using Gleeble-3500 hot simulation test machine. The time-stress curve shows that the time of transformation is so short that the diffusion of carbon atoms is not sufficient; the results of EPM (Electron Probe Micro Analyzer) also show that the carbon concentration of DIF (Deformed Induced Ferrite) is far higher than that of conventional ferrite, which combining with the SEM observation indicates that DIF is a kind of transitional phase in quasi-stable state. Therefore, DIF will precipitate the super-saturated carbon from the inner grain and finally transformed to stable ferrite phase during the process of tempering and its hardness will decrease simultaneously.

Based on the microscopic phase-field dynamic model and the microelasticity theory, the morphology evolution of γ′ phase(Ni3Al)and early precipitation mechanism in Ni-Al alloy were studied. Simulation results show that γ′ phase changes from initial circular or irregular shape into the quadrate shape and their orientations become more obvious during precipitation process, in the later stage, the γ′ precipitates present quadrate shape with round corner and regularly align along the [10] and [01] directions. Under the effect of elastic strain energy, the coarsening process follows the rule of preferential election, the particles lying in the elastic soft directions grow and coarsen further; the particles lying out of the elastic soft direction shrink and dissolve, highly preferential selected microstructure is formed in the later precipitation process. The early precipitation mechanism is the non-classical nucleation and growth, the evolution of γ′ phase is in the order: supersaturated solid solution→nonstoicheometric ordered phase→stoicheometric γ′ phase→growth.

The mathematical model of cathodic protection potential distribution on the exterior of tank bottom is established and cathodic polarization performance is described according to the mixed polarization theory. The cathodic protection potential distribution on the exterior of tank bottom under protection of different kinds of anode placement manners is calculated by FLUENT software and the effects of soil resistivity and tank diameter on potential distribution are studied and compared also. The results can provide theoretical guidance for determining cathodic protection effects and choosing anode placement manners.

The problem that the swirling flow in centrifugal flow tundish is not enough is focused. Without the application of external energy and power, it is proposed that the bending nozzle is used to change the height potential of molten steel in ladle into the horizontal outflow kinetics so as to reinforce the swirling flow in rotation chamber. The physical and mathematical models have been developed to understand the effect of bending nozzle on the swirling flow in tundish. Results show that the swirling flow can be reinforced and the increment of maximum velocity exceeds 15% of the original velocity, which is only produced by the magnetic field application.

Internal friction behavior of Fe-Al alloys was examined to understand the motion of Al antisite atoms. A relaxational internal friction peak was observed at about 410℃ that was dependent on the thermal histories of the alloy. The peak height is much higher in the rapidly cooled specimens than in the slowly cooled ones, and similarly, it is much higher in heating than in subsequent cooling for the rapidly cooled specimens. It is therefore suggested that the peak should be related to retained defects due to rapid cooling. In terms of the activation energy of the peak, that is 1.88eV, comparable to the migration energy of the Fe vacancy, it is proposed that the peak originates from the stress-induced movement of Al antisite atoms between Fe vacancies.

Through judiciously using the silicon, manganese and nickel as the alloying elements and effectively controlling the transformation temperature, cooling and tempering parameters for a series of low alloy ultrahigh strength bainitic steels (LUHSBS), the combination of strength and toughness are very excellent and the impact energy absorption (AKV ≥185 J) has been tripled compared to the previously advanced martensitic steel 23MnNiCrMo with the same strength level (＞1500 MPa). The basic reasons giving rise to the enhancement of strength and toughness consist in the increase of carbon content and the refinement of sublaths in the bainitic ferrite (BF) and the very thin films of retained austenite (AR). It is confirmed by the atomicforce microscope (AFM) and scanning tunneling microscope (STM) that there was no any large bulky areas of AR in the structure which is less stable and will reduce the impact toughness of bainitic steels. Not only is the sublaths is significantly refined, but also the average size of subgrains is less than 20 nm and the average thickness of shear units in a BF lath is only about 1.6 nm. The refinement of microstructure, the enrichment of interstitial atom carbon in BF and the increase of both the dislocation density and the volume fraction of AR are some critical factors that affect the ultimate tensile strength, the stability of AR and the impact energy absorption. Furthermore, the physical mechanism on the improvement of the combination of strength and toughness is in depth discussed.

Rate dependent constitutive model is used to simulate the friction stir welding process. The effect of the process parameters on the material deformation on the transverse section of the friction stir weld is investigated. The mixture of the materials on the both sides of the welding line in the nugget zone and thermo-mechanical zone is studied by means of the research on the equivalent plastic strain distributions under different process parameters. The effect of the process parameters on the weld quality is herein judged from the material deformations. Results indicate that mixture of the material can be improved when the angular velocity of the pin is increased or the welding speed is decreased. But flaws may occur when the angular velocity is too high.

An elastoplastic self-stress model for hydrogen diffusion across a metallic tube is established. This model includes the elastic, plastic and residual stresses developed during hydrogen insertion into metallic membranes. It is found that the hydrogen diffusion slows down in the plastic region and local thermodynamic properties of metal-hydrogen system are modified at the same time. The plastic stress can be avoided by using small charging current during hydrogen charging processes.

A three-dimensional heat transfer mathematical model has been developed for the cooling copper plate of the thin – slab continuous casting mold. Alternative boundary conditions are applied for the cooling slots and back plate of mold copper plate cold face. The self -developed computer code is used to calculate the temperature field in visual Fortran language. The temperature distribution temperature in heat face of mold copper plate is cloudy –shaped, and cold face is ice columnar. The influence on mold copper plate temperature fields of operational parameters (casting speed、copper plate thickness、cooling water velocity) are analyzed. Calculated typical positions temperature agrees well with the measured temperature. These results are the important theoretical base for the process control and optimization of mold design.