The oxidation energies of Al₂O₃ and TiO₂ containing different transition metal alloying elements were calculated by using a first_-principles plane_-wave pseudoptential method, the effect of alloying on the relative stabilities of Al₂O₃ and TiO₂ was also analyzed. The results showed that almost all the alloying elements increased the oxidation energies of Al₂O₃ and TiO₂, i.e., destabilized both Al₂O₃ and TiO₂. Comparing the oxidation energies of Al₂O₃ and TiO₂, it was foud that, W, Mo, Re, Nb, etc., decreased significantly the stabilities of Al₂O₃ relative to that of TiO₂, indicating that these alloying elements may hamper efficiently the inner oxidation of Al in the γ-TiAl matrix so as to increase the high_-temperature oxidation resistance of γ-TiAl.

Ni-Fe-Ga-Co is a new ferromagnetic shape memory alloy system, which is promising for magnetically controlled actuators and refrigerators. In order to improve its performance, single crystal or polycrystals with preferred orientation are required. To prepare these crystals, directional solidification is the most effective way. In this work, directionally solidified Ni₅₂Fe₁₇Ga₂₇Co₄ ferromagnetic shape memory alloys were prepared by zone melting liquid metal cooling (ZMLMC) method. The preferred crystal orientation and microstructure in the steady growth zone under three different conditions were studied. It is indicated that under low temperature gradient and high growth velocity, the solidified crystals grew along <100> direction and primary γ phase was formed during the unstable growth; under high temperature gradient and low growth velocities, the coarse columnar crystals had uniform sizes, single martensitic phase and well-developed preferred orientation, i.e. along (222) planes of the martensite. It is deduced that the condition for stable crystal growth is high temperature gradient and low growth velocity. Under this condition, giant martensitic single-variant sets in the oriented columnar crystals were revealed, which is meaningful for potential large magnetic field-induced strain. EBSD results revealed that there was no micro-twin inside the martensitic twins and the twinning plane turned out to be (110) and (110). Additionally, magnetic domains intersecting with martensitic lamellae were observed.

With the increasing consciousness for reducing fuel consumption and improving automobiles safety, the automotive industry is urgent to develop a new-type of steel with high strength and excellent formability. Among many high strength steels, the transformation induced plasticity (TRIP) steel may be a good candidate for automotive applications, as it drastically improves the balance between strength and ductility compared to precipitation hardened and solution hardened steels. While the tensile strength of conventional hot rolled TRIP steels are usually between 500 and 600 MPa, the TRIP steel with higher tensile strength, especially in excess of 750 MPa, is becoming increasingly important for the automotive industry. Thus, many strengthening mechanisms, such as precipitation strengthening, solution strengthening, refinement strengthening and dislocation strengthening, have been employed to improve the strength of the TRIP steel. Among them, microalloying with Nb, V and Ti, may provide effective means for further strengthening via grain refinement and precipitation strengthening. So far, many researches about the Ti--microalloyed high strength low alloy (HSLA) steel have been reported. However, the influences of alloying elements Ti and Mo on the hot rolled TRIP steel, especially the precipitation characteristics and their effects on mechanical properties, were rarely reported. Therefore, in this work the microstructure, retained austenite contents, mechanical properties and precipitation characteristics of the hot rolled TRIP steel containing Ti and Mo after bainitic transformation at different temperatures, were studied by using SEM, XRD and HRTEM. The results show that the bainitic transformation temperature has a significant effect on organizational morphology, retained austenite contents and mechanical properties of the TRIP steel. The optimal bainitic transformation temperature is 400 ℃, in which the retained austenite content and the balance of strength and ductility are 17.13\% and 23.87 GPa·%, respectively. In addition, through HRTEM analysis, it was observed that the larger (Ti, Mo)C carbides over 20 nm in size exhibited the relationship ((100)_{(Ti, Mo)C}//(110)_{α- Fe},[011]_{(Ti, Mo)C}//[111]_{α- Fe}) with ferrite matrix, and the smaller (Ti, Mo)C carbides less than 5 nm in size satisfied the Baker-Nutting orientation relationship: (100)_{(Ti, Mo)C}//(100)_{α- Fe} ,[011]_{(Ti, Mo)C}//[001]_{α- Fe}.

The low－alloyed transformation induced plasticity (TRIP) steels demonstrate an improved combination of strength and ductility, and have became a promising candidate for the application of automotive bodies to reduce the weight without the loss of crash－worthiness. The typical microstructure of TRIP steels consists of the ferrite matrix and a dispersion of bainite, martensite and the retained austenite. The existence of an amount of metastable retained austenite is responsible for the improved mechanical properties, resulted from the enhanced strain hardening capabilities of TRIP steels due to the strain－induced martensitic transformation during straining. The carbon content is considered as an important factor that influences the amount and stability of the retained austenite. In the present work, two cold－rolled C－Mn－Al－Si TRIP steels with different carbon contents, (0.1% and 0.2%, mass fraction) were fabricated by intercritical annealing and isothermal transformation. The microstructures and the mechanical behaviors of the used steels were investigated by OM, XRD and uniaxial tensile tests at room temperature. The results indicated that with the same isothermal transformation time at 400℃,the steels with high carbon content obtained lower fraction of bainite and larger fraction of martensite, and demonstrated higher strength and larger elongation than those of steels with low carbon content. The excellent ductility of steels with high carbon content was mainly attributed to its strong TRIP effect during deformation, resulted from the larger fraction of retained austenite as well as the higher carbon content of retained asutenite in the multiphase microstructure. The value of the product of tensile strength and total elongation, representing the combination of strength and ductility of steels, was increased linearly with the increase of the value of the product of volume fraction and carbon content of retained austenite, which could be used to characterize the TRIP effect. Variation of the formation rate of strain－induced martensite was similar to that of the incremental strain hardening exponent with strain during deformation, further proved the important role of TRIP effect in influencing the strain hardening capabilities of TRIP steels.

The precipitation behavior of the intermetallic phases in a Z3CN20.09M cast austenite stainless steel (CASS) which has been widely used in primary coolant pipes of nuclear power plants has been investigated. The content of the intermetallic phases precipitated in the CASS was calculated by using Image-pro Plus 6.0 software. And then a time-temperature-transformation (TTT) diagram for the intermetallic phases was got. The results showed that the M₂₃C₆ and σ phases were precipitated in the steel during 600-900 ℃ and 600-840 ℃ respectively. The fastest precipitation velocity for the intermetallic phases occurs at 750 ℃. Moreover, the M₂₃C₆ was found to precipitate first at ferrite/austenite phase boundaries,and then σ phase formed in ferrite. The solutionizing temperatures for the M₂₃C₆ and σ phases are 900 and 850 ℃ respectively. The volume fraction of the M₂₃C₆ in the specimen aged at 850 ℃increases with the increase of aging time first and then decreases.

The Ni-Fe based superalloy GH984 with microalloying is fabricated by vacuum induction furnace and hot worked by hot forging and rolling. The effect of B and P microalloying on microstructure and mechanical properties of GH984 alloy was investigated by OM, SEM and TEM after standard heat treatment. The experiment results showed that the addition of B and P has no obvious effects on the microstructure of GH984 alloy which has precipitates of sphericalγ', Ti(C, N), blocky MC as well as discrete M₂₃C₆ distributing along grain boundary. Moreover, the addition of B and P has no obvious influence on the tensile strength at room temperature and 700℃. However, tensile ductility increases greatly at 700 ℃ after B and P doping. It is worth to note that B and P microslloying can improve the stress rupture life of the alloy significantly. For example, the rupture life at the condition of 700 ℃ and 350 MPa increases from initial 115.03 h to 984.15 h. Investigation on the microstucture of the creep samples exhibites that B and P could effectively improve the strength of grain boundary and the fractural model from intergranular fracture to intergranular/transgranular mixed fracture.

According to the present experiment results about the transformation from β－AlFeSi to α－Al(FeMn)Si phase in Al－Mg－Si series alloys, the model and kinetics of phase transformation,and microstructure evolution at 555 ℃ were systematically investigated. The results show that, the homogeneous temperature T can give a significant effect on the transformation kinetics, and with increasing T, the transformation rate increases fast. The nucleus radius of α phase only affects the breakthrough time along the thickness direction of β phase. The distance l between twoα phases mainly has an influence on the dissolving of rim for β phase. The thickness of β phase normally has a greatest influence on the phase transformation β→α,especially for the breakthrough stage of β phase, with increasing the thickness of β phase,the main transformation with longer time in the whole phase transformation process can changes from rim dissolving of β phase to breakthrough along the thickness direction of β phase. The breakthrough time of β phases with the thickness of 0.1, 0.2 and 0.3μm is above 5, 10 and 15 h, respectively, which corresponds with the real experiment results. In addition, if the thickness of β phase is smaller than 0.3μm, the transformation rate f(α) easily reaches above 0.9 after homogeneous heat treatment at 555 ℃ for 16－-24 h. Therefore, the importance of optimizing casting process to make sure the thickness of β phase below 0.3μm, is the same as the homogeneous heat treatment for the better controlling the phase transformation β→α.

Al－Fe alloys have wide potential applications in automobile and aerospace industries due to their high specific strength, high specific stiffness, good stability of microstructure and excellent high temperature strength. However, a wide variety of metastable phases can be formed in Al－Fe binary system, such as Al(Fe) supersaturated solid solution, amorphous and intermetallic phase. In order to better understand the phase formation in Al－Fe alloys, a systematic investigation of microstructure evolution is necessary. In this work, bulk dense Al－5Fe alloys were fabricated by mechanical alloying (MA) and spark plasma sintering (SPS). The phases, microstructures and morphologies of MA powders and the corresponding sintered samples were characterized by XRD, SEM and EDS. Special attention was paid to the effects of different milling times on structural change of phases during MA－SPS process. The results showed that during the MA, the size of alloy powders increased with increasing milling time (0－-10 h), and then decreased with further milling time (10－-20 h). The (111)_Al peaks in XRD spectra of MA powders shifted to higher angles with the increase of milling time, indicating the dissolution of Fe atoms into the Al crystal lattice. Homogeneous Al(Fe) solid solutions were obtained after MA for 20 h. Bulk samples sintered from MA powders of 0 and 10 h contained Al/Al₁₃Fe₄/Al₅Fe₂/Fe layer structure intermetallic phase and tiny Al₁₃Fe₄ phase in the Al matrix. However, bulk sample sintered from MA powders of 20 h contained only relatively small Al₁₃Fe₄ phase in the Al matrix. Based on thermodynamic analysis (effective heat of formation theory) and kinetic analysis (spherical shell model), the primary phase that formed on the interfacial layer of Al/Fe was Al₁₃Fe₄, and then Al₅Fe₂ can be formed by the reaction of residual Fe and Al₁₃Fe₄ for the lower Gibbs free energy of Al₅Fe₂ compared to that of Al₁₃Fe₄, leading to the formation of Al/Al₁₃Fe₄/Al₅Fe₂/Fe layer structure intermetallic phase. The absence of Al₅Fe₂ and Fe phases in sample sintered from MA powders of 20 h were attributed to the complete reaction between relatively small Fe particles and Al melt during SPS process.

Zirconium alloys have low thermal neutron absorption cross-section, good corrosion resistance and adequate mechanical properties. They have been successfully developed as fuel cladding materials in pressurized water reactors. It's well known that the corrosion resistance of Zr-Sn-Nb alloys is significantly superior to that of Zircaloy-4 alloy when corroded in lithiated water. The corrosion resistance of zirconium alloys is controlled by their chemical compositions, characteristics of second phase particles (SPPs) and microstructure evolution of the oxide in them. The corrosion tests of Zr-1Nb-0.7Sn-0.03Fe-xGe (x=0, 0.05, 0.1, 0.2, mass fraction, %) alloys were investigated by means of an autoclave test in lithiated water with 0.01 mol/L LiOH at 360 ℃ under a pressure of 18.6 MPa. The microstructures of the alloys and oxide films on the corroded specimens were examed by using TEM and SEM. The sample for the oxide microstructure observation was prepared by a HELIOS-600I focused ion beam. The results reveal that the corrosion resistance of Zr-1Nb-0.7Sn-0.03Fe-xGe (x=0.05, 0.1, 0.2) alloys was remarkably superior to that of Zr-1Nb-0.7Sn-0.03Fe alloy.The corrosion resistance of Zr-1Nb-0.7Sn-0.03Fe alloys is markedly improved by the addition of (0.05%-0.2%)Ge. In addition to Zr-Nb-Fe-Cr SPPs with the tetragonal crystal structure (tet) and β-Nb SPPs with the bcc crystal structure, the Zr-Nb-Fe-Cr-Ge SPPs with the tet structure and Zr₃Ge SPPs with the tet structure were detected out in Zr-1Nb-0.7Sn-0.03Fe-xGe alloys. The oxidation of SPPs was found to be slower than that of α-Zr matrix. There exist a few micro-cracks and more ZrO₂ columnar grains in the oxide film formed on Zr-1Nb-0.7Sn-0.03Fe-0.1Ge alloys corroded for 190 d. However, more micro-cracks and ZrO₂ equiaxed grains appear in the oxide film formed on Zr-1Nb-0.7Sn-0.03Fe alloys corroded for 130 d. Because the P. B. ratio of Ge is smaller than those of Zr, Nb, Fe and Cr, it is likely that the volume expansion of the oxide on Zr-1Nb-0.7Sn-0.03Fe-xGe (x=0.05, 0.1, 0.2) alloys is smaller than that on Zr-1Nb-0.7Sn-0.03Fe alloy, and the compressive stress can be reduced and the micro-cracks can be effectively decreased in the oxide on Zr-1Nb-0.7Sn-0.03Fe-xGe (x=0.05, 0.1, 0.2) alloys. The addition of Ge can not only delay the developing process of the defects in oxide films to form micro-pores and micro-cracks, but also retard the microstructural evolution from columnar grains to equiaxed grains. Therefore, it is concluded that the addition of Ge can improve the corrosion resistance of alloy.

The aerodynamic levitation process, which possesses the advantages of containerless solidification, easy control and versatility to materials, is a kind of advanced materials processing technology. How to accurately control the cooling rate during aerodynamic levitation is quite important for studying the processing－structure－property relationship of metallic materials. In this study, the characteristics of laser absorption, thermal radiation and heat convection of an aerodynamically levitated sample were analyzed, and a formula for the control of the cooling rate by means of tuning the laser power has been derived, which is described by:ΔT/Δt=-3[σε(T_s⁴-T_f⁴)+h(T_s-T₀)]/cρr+α(6L_s-3kΔt)/8cρπr³. By recording temperature－time curves with cooling rates of 9, 49, 98 and 253 ℃/s for the aerodynamically levitated Al－7.7Ca (mass fraction, %) eutectic alloy, the calculated values of cooling rates agree very well with the experimental data, verifying and validating the formula. Also, the microstructure of the aerodynamically levitated Al－7.7Ca eutectic alloy under different cooling rates was examined using OM and SEM. The metallographic observation shows that, under a low cooling rate of 9℃/s, the solidification structure of Al－7.7Ca alloy during aerodynamic levitation exhibits lamellar regular eutectic. With increasing the cooling rate, the undercooling measured from the recorded temperature－time curves increases, resulting in the refinement of the grain size and interlamellar spacing of regular eutectic. Moreover,  there appears granular anomalous eutectic under higher cooling rates of 49, 98 and 253 ℃/s. The volume fraction of anomalous eutectic is increased with increasing the cooling rate. The anomalous eutectic is attributed to the formation during the rapid solidification stage. By measuring the interlamellar spacing of regular eutectic from Al－7.7Ca metallographs, the fitting data of interlamellar spacing and undercooling are in accordance with the classical JH model, showing that the regular eutectic is formed during slow solidification stage after recalescence.

Immiscible alloys are well suited as functional materials, such as bearings, electrical contacts,switches and superconductors, etc. They usually suffer from heavy segregation under ordinary casting, which is resulted from the decomposition within the miscibility gap of a homogeneous liquid into two immiscible liquids generally with distinct density difference. But this characteristic provides an opportunity to in situ fabricate composites with core-shell morphology. In this study, Al/Sn-Bi core-shelled particles have been successfully prepared by phase separation of Al₇₀Bi₁₁Sn₁₉ alloy. The morphology, microstructure, composition and phase transformation of the core-shelled particles were investigated by means of SEM, EDS and DSC. It reveals that the particle comprises an Al_-rich core with a Sn-Bi hypoeutectic shell, displaying a two-stage melting characteristic. The morphology of particles varies with size. With increasing the particle size from 0.5 mm to 0.9 mm, the core-shell morphology turns from a crescent multi-core type into concentric or eccentric single-core types. Based on the simulation of temperature field of Al₇₀Bi₁₁Sn₁₉ alloy droplets during solidification, the formation mechanism of the core-shell morphology has been discussed in detail, which is attributed to an outcome of the competition among the surface segregation, Marangoni and Stokes motions, Ostwald ripening and cooling rate.

The high temperature titanium alloy with rare earth element Nd addition was prepared by rapidly solidified powder metallurgy (RS－PM) processing. The microstructure of RS－PM high temperature titanium alloy has been investigated systemically. Microstructure study showed that the α' martensite phase in the RS powders initially decomposed at 700 ℃ and vastly at 900 ℃during the hot isostatic pressing (HIP) process. The decomposition products were equiaxed or lamellar α phase as well as grain boundary β phase. The microstructure of the specimen HIPed at the temperature in (α+β) phase field contained equiaxed α phase, lamellar α phase and β phase. The size of equiaxed α phase increased while the aspect ratio of the lamellar α phase decreased when the HIP temperature increased. The microstructure of the specimen HIPed at the temperature in β phase field contained coarsed lamellar α phase, grain boundary α phase and β phase. The microstructure became finer with decreasing the powder particle size. The microstructure of the sample HIPed in the (α+β) phase field and then heat treated in the (α+β) phase field was bi－modal microstructure containing equiaxed α phase and β transformed structure. The microstructure of the sample HIPed in the β phase field and then heat treated in the (α+β) phase field was ternary microstructure containing equiaxed α phase, lamellar α phase and β transformed structure. The microstructure of the sample HIPed in the (α+β) phase field or β phase field and then heat treated in the β phase field was basket－weave structure. The proportion of rich－Nd phases increased with increasing the Nd content,resulting in the reduction of original β grain size.

Eutectic solidification involves many important metals and inorganic non－metallic materials. To date, there still exist a large controversy on the formation mechanism of anomalous eutectic under the nonequilibrium rapid solidification. In this work, adopting glass flux method combined with cyclical superheating, the recalescence behaviors and microstructure evolution in highly undercooled solidification of Ni－30%Sn hypoeutectic alloy were investigated. It is found that, there is not an obvious recalescence process in the alloy melts with the low undercooling. With increasing the melt undercooling, the solidification microstructure experienced a gradual phase evolutions from α－Ni dendrite + (α－Ni+Ni₃Sn) lamellar or feathery eutectic to completely (α－Ni+Ni₃Sn) anomalous eutectic, which led the recalescence process to occur from twice to once in the cooling process. Through analyzing the nucleation behaviors of α－Ni and Ni₃Sn phases and the relationships between their growth velocities and the melt undercoolings, and the variation of their crystalline fraction in rapid recalescence process, the formation mechanism of anomalous eutectic was explained. The formation of anomalous eutectic in highly undercooled Ni－30%Sn hypoeutectic alloy should be attributed to the following two reasons: in the large melt undercooling, the complete coarsening and remelting of the pre－formed refined α－Ni dendrite skeleton occured in the subsequent recalescence process, and then the dendrite fragments were surrounded by the precipitated Ni₃Sn phase, which eventually led to the formation of anomalous eutectic. With the undercooling increased, the primary single－phase dendritic growth will change to the two－phase dendritic growth, the coarsening and remelting of two－phasic dendrites occured in the subsequent larger recalescence process, which also led to the formation of anomalous eutectic.

GH4169 alloy is an important material used for aviation and aerospace engines because of its excellent mechanical properties in the temperature range from -253 ℃ to 650 ℃. In order to improve the safety and reliability of engines, it is crucial to obtain the forging with a uniform and fine microstructure. Generally, theforgings with large size and complex shape, such as turbine disks and engine shafts, are manufactured by multi-stage hot working processes. In addition, the microstructure of the alloy is sensitive to the hot deformation parameters. Therefore, the defects of coarse grain and duplex grain always appear in the forgings. As the δ phase in the alloy can control grain growth through the strong pinning effect, the Delta process (DP) has been developed, which uses an intentional δ phase precipitation cycle and subsequent thermomechanical processing to produce uniform fine grain billet and bar stock. In this work, for the DP of GH4169 alloy, the effect of δ phase on the tensile deformation behavior of GH4169 alloy at high temperature was studied by the tensile tests at 950 ℃. The result indicated that the tensile stress-strain curve of the GH4169 alloy with 8.21% pre-precipitated δ phase was the elastic-uniform plastic curve, and there were two different deformation processes during the uniform plastic deformation stage. The strain hardening exponent in the first deformation process was 0.494, which was higher than 0.101 in the second  process. The fracture mechanism for the pre-precipitated δ phase alloy was microvoid coalescence ductile fracture, and the δ phase and carbide were the nucleuses for the formation of micropores. Thus, the existence of the δ phase made the high-temperature plasticity of GH4169 alloy decrease, and the content of the pre-precipitated δ phase must be controlled in the DP of GH4169 alloy.

The yield strength, corresponding to 0.2% plastic deformation, of superalloy single crystal DD407 with 22 different orientations were measured at 760℃ to investigate the orientation dependence of yield strength for this superalloy. The facets of fractured specimens were observed by scanning electron microscopy and their crystallographic characters were identified with the aid of X-ray diffractometer. The results indicated that specimens near [111] were deformed by cubic slip systems,and the rests were deformed with octahedral slip systems. The orientation dependence of yield strength was established and analyzed by an LCP-model. It showed that the yield strength of DD407 specimens deformed by octahedral slip accorded with LCP-model, whereas those deformed by cubic slip, such as [111] crystals, deviated from LCP-model. A close inspection of the LCP parameters suggests that, in dual-phase γ/γ’ crystals, the effect of γ matrix must be responsible for the positive sign of b₂ term which is negative in mono-phaseγ’ crystals.

Pure and Eu doped ZnO were calculated by first-principles full potential linearized augmented plane wave ultra-soft pseudo-potential method to investigate band structures, density of states (DOS) and optical properties of the structures. The results show that the conduction bands generate conductive carriers introduced by impurity atom of Eu. The electrical conductivity of the system is improved and the Fermi levels shift upward into the conduction band and show n-type conductivity. The absorption coefficient of Eu doped ZnO are higher than that of pure ZnO in low energy region. In the experiment part, pure and Eu doped ZnO powder were prepared through sintering method and the corresponding properties of the samples were investigated by XRD, SEM and photoluminescence (PL) spectra, which show that the lattice constants of ZnO become larger and crystallization turn worse after doping.