Chemical compositions and amounts of equilibrium phases in T/P91 heat resistant steel in the temperature range of 450℃ ~ 1200℃ have been calculated by using thermodynamic software ‘Thermo-Calc’. Concept of elemental partitioning fraction is introduced to study the elemental partitioning characteristics of such main alloying elements as Cr, Mo, Fe, V, Nb, C and N, the stability, the constituents and the evolutional rule of the equilibrium phases at elevated temperatures. The results show that using the elemental partitioning characteristics with the change of temperatures the stability of the equilibrium phases can be easily revealed, and the sub-types of MX and the formation of M and X in MX, and the elemental evolution rule in MX type phases can be reasonably determined, and as well as the effect of carbon content in the matrix phase on the formation of MX phases can be helpfully understood, respectively.

The semi-solid 2024 alloy billets prepared by low superheat pouring were reheated to 625℃ with 7, 15.7 and 31.3℃/min, respectively, and then held isothermally. The effect of heating rate on the microstructure of billets was studied by optical microscope and metallographic image analysis system. The results show that with the prolongation of heating time, the liquid fraction increases gradually, the grains grow up quickly by the coalescence and then spheroidize gradually by the Ostwald ripening. The higher the heating rate is, the quicker the formation rate of liquid phase is and the finer and rounder the grains are. It is found through the analysis of microstructure evolution mechanism that accelerating the formation rate of liquid phase by increasing the heating rate can restrain the coalescence of grains to a certain extent, in which the growth rate of grains is decreased and the spheroidization rate is accelerated.

The microstructure and mechanical properties of Al-Mg-Mn-Zn filler alloys microalloyed by Scandium (Sc), Zirconium (Zr) , Erbium (Er) and Titanium (Ti) were investigated with OM, SEM, SEM and tensile tests. On the basis of the effective grain refinement, the influences of Er element and coexistence of Er and Ti elements on grain boundary morphologies and phase distribution in grain boundaries, as well as their effects on the mechanical properties of experimental alloys, have been emphatically researched. The results indicate that, for the refined Al-Mg alloys by Sc+Zr, adding minor Er element can enhance the grain refinement of alloys, thus improve both the strength and ductility, and ultimately produce Al3Er phase discontinuously distributing in the grain boundaries. The combinational addition of Er and Ti elements can led to the precipitation of (Al,Mg)20Ti2Er intermetallic compound particles with 5~10μm in size and square shape, which distribute in grain boundaries and give some contribution to the improvements in both tensile strength(UTS) and yield strength(0.2YS), but lower the ductility. Coexisting of (Al,Mg)20Ti2Er and Al3Er phases breaks the grain boundary succession, consequently offsets the improvement on the ductility caused by Er grain-refining, and results in the transition of tensile fractographic patterns from the mixed-fracture (intergranular and transcrystalline fractures) to the intergranular fracture.

The uniform、smooth and dense CNx fllms with different nitrogen content were deposited on cemented carbide substrate at different nitrogen flow rate by pulsed bias arc ion plating. The surface morphology、composition、structure、hardness and elastic modulus of CNx films were investigated by Scanning electron microscopy(SEM), Glancing incidence X-ray diffraction(GIXRD), X-ray photoelectron spectroscopy(XPS)、Raman spectra and Nano-indentation, respectively. The result show that the nitrogen content in the CNx films increase linearly and then slowly with the nitrogen flow rate increasing. The X-ray diffraction result indicates that the deposited films were amorphous. The hardness and elastic modulus increase and then decrease with nitrogen content increasing. The hardness and elastic modulus of the films with the nitrogen content of 8.1(at)% has a maximum value of 32.1GPa and 411.8GPa, respectively. The Raman spectra results suggest that the deposited films have the typical characteristic of diamond-like carbon films. The ID/IG ratio decrease and then increase with increasing nitrogen content and the minimum value, which corresponds to the highest sp3 content, was obtained at nitrogen content of 8.1%. The change of sp3 content by adjusting the nitrogen content in the CNx films is the only factor that influence the hardness of the films.

Based on Miedema semi-empirical model and an empirical specific heat equation, the effective heat of formation and its temperature dependence were calculated for Fe-Sn and Ni-Sn systems. Fe-Sn and Ni-Sn nanoparticles were prepared by an arc discharge method and the formed phases were experimentally determined by X-ray diffraction (XRD). Theoretically predicted primary intermetallic compounds were FeSn2 in Fe-Sn system and Ni3Sn4 in Ni-Sn system, which was well consistent with the experimental results of nanoparticles.

Using 3D-phase field theory, spontaneous polarization, hysteresis loop and mechatronic coupling of ferroelectric materials of have been simulated. The results show that the domain switching under applied electric field is carried out through initiating and growing of new domain and/or domain wall motion of the domains along the applied field. 90°domain switching of all kind of domains induces jump in the polarization near the coercive field. A tensile or compressive strain applied perpendicular to the electric field can hinder or promote domain switching.

Method of hybrid machining-tension simulations is proposed and applied to Cu (111) plane nanostructure basing on Molecular dynamics. The results show that atoms at frontage of and under tool deviate from their initial positions and form deformation zone in nanostructure. Dislocations only propagate in surface and subsurface when scratching depths are shallow, and some dislocations form dislocation loops as there exists stress gradient near tool. The number of residual defects increase and Order Degree of crystal structure decrease as scratching depths increase. There exist high residual stress in subsurface, especially near the position where tool withdraw nanostructure. After machining, tensile loads are applied to two ends of nanostructure. The response of initial loaded stage is elastic as a whole, while the stress-strain curves show local decrease as residual stress and defects from machining process result in movement of some atoms and onset of dislocations. The Yang's Modulus and yielding stress decrease as scratching depths increase. The initial plastic deformation of machined nanostructure are determined from dislocations slip and stacking faults, and conjugate slip planes ((1 1) and ( 1) slip planes) are formed at the two side of scratching groove. Dislocation slip results in the decreasing of stress, while pileup of dislocations and the forming of new slip plane result in the increasing of stress. As a result, the stress-strain curves decrease step by step. Order degree of nanostructure for first yielding and strain at 0.8 decreases as scratching depths increase, while Order degree of nanostructure for small scratching depths at the strain of 0.8 increase comparing to that of 0.045.

Mo and Al rolled foils, of which thickness was 20 and 60 m respectively, were diffusion bonded at 873-913 K for 40-240 min. Primary phase of Mo-Al interfacial reaction was Al8Mo3, which nucleated in Mo foils and grew up with breaking the covering Mo layer. With diffusion bonding time increasing, Al8Mo3, Al5Mo and Al12Mo layers presented between Mo and Al, after bonding at 913K for 240 min, Al4Mo appeared between Al8Mo3 and Al5Mo. Kinetic analysis indicated that the incubation period of primary phase decreased from 52 to 34.5min when bonding temperature increased from 873 to 913 K, the pre-exponential factor and diffusion activation energy for an atom of Al in the new phases produced by Mo-Al reaction are 4.6110-2cm2/min and 0.98 eV respectively, correspondingly, those for an atom of Al in Mo foils are 2.0510-2cm2/min and 1.48 eV.

ABSTRACT: Under stressing-controlled cyclic loading, the cyclic accumulation of peak strain and valley strain, denoted as transformation ratcheting, takes place in superelastic NiTi alloy. In this work, the transformation ratcheting behavior of superelastic NiTi alloy and its dependence upon load condition were studied by experiments at room temperature. The evolution rules of peak strain, valley strain, nominal elastic modulus and transition stress under different cyclic loading cases were discussed. It is shown that the alloy presents apparent transformation ratcheting, and the value of transformation ratcheting strain and its evolution rule depend greatly upon the applied stress amplitude, mean stress and loading charts; in the meantime, the nominal elastic modulus of austenite, nominal starting stress for the transformation from austenite to martensite and dissipation energy decrease, while nominal elastic modulus of martensite increases with the increase in the number of cycles, and then reach a steady state after certain cycles. Some significant conclusions are obtained, which are useful to establish a constitutive model describing the transformation ratcheting of the material.

Adopting the molten glass denucleating technology combined with high frequency vacuum melting, and cycle superheating, the main factors affecting purifying of the bulk Fe-rich side Fe-B eutectic alloy melt were investigated. The optimized purification and parameters for high undercooling and hypercooling were given out. The hypercoolings of 324K～460K have been obtained successfully in bulk Fe83B17 eutectic alloy melts, and 485K in Fe80B20 hypereutectic alloy melts. So the primary nucleation undercoolings of (0.3～0.4) Tm were obtained in bulk Fe-B eutectic system alloy melts. The thermodynamic characters of hypercooling rapid solidification were also discussed by analyzing the cooling curves.

By means of pre-compression treatment, the cubic γ′phase in the single crystal nickel-base superalloy is transformed into the P-type rafted structure. An investigation has been into the microstructure evolution of the P-type rafted structure alloy during tensile creep by means of the measurement of creep curve and microstructure observation. Results show that the P-type rafted γ′phase in the alloy is transformed into the N-type structure in the initial stages of the tensile creep. In the role of the tensile stress at high temperature, the change of the elements equilibrium concentration occurs in the γ′/γ phases, which promotes the unhomogeneous coarsening of the γ′phase, and in the further the decomposition of the P-type rafted phase occurs in the alloy to appear the groove structure. It is a main reason of the directional diffusion of the elements and dissolving abruption of the P-type rafted γ′phase up to transformed into the cuboidal-like structure that the enhancement of the chemical potential energy of the solute elements occurs in the groove regions of the P-type γ′rafted structure. And then, the lattice constriction in the horizontal interfaces of the cuboidal-like γ′phase may repel out the Al, Ta atoms with bigger radius due to the role of the shearing stress, the lattice expanding in the side interfaces of the cuboidal-like γ′phase may trap the Al, Ta atoms with the bigger radius in the role of the tension stress, which promotes the directional growing of γ′phase into the N-type rafted structure. Thereinto, the change of the strain energy density in different interfaces of the cuboidal-like γ′phase is thought to be the driving force of the elements diffusion and the γ′phase directional growth.

Abstract: The very high cycle fatigue properties of bearing steel GCr15 prepared by two processing routes are studied in this paper. It is demonstrated that compared with vacuum melting (VM), the specimens prepared by electroslag remelting (ER) have smaller and narrow distribution of the inclusion size. Therefore, the specimens prepared by ER exhibit a better fatigue property. Experimental results and theoretical analysis demonstrate that the stress intensity factor range at the GBF boundary ， ΔKGBF , keeps a constant if the steels are with an identical strength, and it will decrease with the increase of yield strength.

In this article, the turning point in Paris region of lamellar microstructure has been investigated. After testing fatigue crack growth rate of different lamellar structures with various microstructure dimensions, we finally found that β grain size is the most important parameter to affect the position of turning point. The essential reason of turning point appearance was explained through the analyse of micro-stage in fatigue crack growth (FCG) and changing of fracture mode. Fatigue crack growth rate of martensite structure with β grain has been tested, and no turning point exists in Paris region, it reflects that the existence of β grain is not the single reason for the appearance of turning point. The actual dimension of crack tip plastic zone (CTPZ) has also been discussed in constrast to the size of Irwin single CTPZ and Rice cyclical CTPZ.

In order to development an environmental friendly surface coating technology for magnesium, a chrome-free Ce-based process to form a conversion coating on AZ91 magnesium alloy was investigated. Electrochemical impedance spectroscopy (EIS) was chosen to evaluate corrosion resistance due to its low effect on electrochemical test system for getting high reproduction result. The effect of treatment time, temperature of electrolyte, concentration of Ce(NO3)3 and accelerant concentration on corrosion resistance was summarized, while a optimized technology was achieved, 0.02mol/l Ce(NO3)3, 4ml/l accelerant at 35℃ for 35 min. The results indicated that the chemical conversion formed in optimized technology presented yellow and impact surface by naked eye, while took on two layer structure with micro cracks on the outer layer. The content of Ce in inner layer was low than that of outer layer, while it was more impact. Tafel plots indicated that conversion film restrained the anodic and cathodic reaction on the interface, while the corrosion potential shifted anodic 240mV and corrosion current density decreased about 100 times.

A microarc oxidation (MAO) film was prepared on AZ91D magnesium through an alternating current at symmetric voltage in alkaline silicate solution. The corrosion resistance of MAO films were tested by electrochemical impedance spectrum (EIS), potentiodynamic polarization. Scanning electron microscopy (SEM) was used to observe the changing of surface microstructure in experiment. The composition of MAO films and corrosion products were analyzed by X-ray diffraction (XRD). The results showed that circular micron-size pores existed on the surface of MAO film. XRD analysis indicated that the ceramic coating was a spinel phase which was composed of Mg2SiO4 and MgO. The corrosion resistance of magnesium alloy coated with MAO film was improved considerably as verified by electrochemical testing. The corrosion current density decreased nearly thousand while corrosion potential moved to positive about 300mv after surface treatment with MAO. The MAO films prepared in this paper could provide good corrosion resistance of AZ91D magnesium alloy.

The potentiodynamic polarization and electrochemical impendence spectroscopy (EIS) techniques were employed to analyze the effect of salinity on electrochemical characteristics of J55 steel in high salinity CO2 brines. The results show that the CO2 corrosion mechanism of J55 steel is cathode control, corrosion rates increase as brine salinity increases from 12485ppm to 62423ppm, then decreases as the brine salinity increases from 62423ppm to 407997ppm. With increase of brine salinity, the corrosion potential shifts positively and the corrosion mechanism changes from electrochemical steps control to mixed mass transfer – electrochemical steps control. The higher the salinity is, the more obvious the mass transfer control is. The EIS plots present three time constants: capacitance loop in high frequency, inductance and capacitance loops in low frequency. The charge transfer resistance (Rt) decreases with brine salinity up to 62423ppm, then increases above 62423ppm. There are a minimum of Rt and a maximum of corrosion rates at about 62423ppm.

Low density and high strength NiTi shape memory alloys with regular pore shape and large pore size were fabricated by using temporary space-holder, CO(NH2)2, and a conventional sintering process. The pore characteristics can be tailored by adjusting urea particle features and the amount added, and the fabricated porous NiTi alloys show uniform pore size and regular pore shape with pore size and porosity in the ranges of 296-732 µm and 31%-61.6%, respectively. The results manifest that urea particle shape and size have a crucial influence on pore characteristics of porous alloys and show a geometrical heredity effect. The use of urea hardly has any effect on phase constituents of porous NiTi alloys and the martensitic transformation exhibits early. The fabricated porous NiTi alloys show excellent mechanical properties including a steady linear superelasticity.

In view of the high density and low permittivity of the carbonyl iron particles, the light absorbing coatings with broad bandwidth were fabricated by decreasing the mass fraction of carbonyl iron particles and mixing the iron nanofibers with low density and high permittivity into the absorbent. The influences of the mass fraction of the iron nanofibers on the microwave electromagnetic and absorbing properties of the iron nanofibers/carbonyl iron particles composites were investigated. The results showed that the complex permittivity and permeability of the composites increased with the increase of the mass fraction of the iron nanofibers. The absorbing coatings based on the composites consisting of 2.2-4.4 wt% iron nanofibers exhibited a broader bandwidth and lower surface density than that of the absorbing coatings based on carbonyl iron particles, which was attributed to the enhancing of the matching and absorbing properties of the absorbing coatings through the increase of the complex permittivity of the absorbent in an appropriate range. Thereforre, a new method was provided for the preparation of the light absorbing absorbing coatings with broad bandwidth.

A functionally graded Ti-Ti2AlNb alloy, which had continuous compositional gradient and regular outline with a length of ~17 mm, was fabricated by laser solid forming. Phase morphological evolution and microstructure evolution, and microhardness along the compositional gradient direction were analyzed. With the increase of aluminum and niobium contents, a series of phase evolutions along the compositional gradient occurred: α'→α+β→α+α'→α'→α+β→ α+β/B2+α2→ β/B2+α2→ β/B2→ B2+α2+O→ B2, and the compositionally graded material accomplished a transition of α titanium alloy, α+β titanium alloy, β titanium alloy, finally ended with Ti2AlNb-based alloy. In the transition layers, The microhardness increased from 170HV with CP titanium at the bottom to 470HV with Ti2AlNb at the top. Based on the non-equilibrium phase diagram of the Ti-rich corner, the phase morphological evolution during laser solid forming of the graded materials were explained on combining with the analysis of the influence of the Al, Nb on the stability of α，β and α2 phases in titanium alloys.

The effect of the processing parameters on the microstructure during laser solid forming (LSF) of Ti -20wt%Ni alloy was investigated. The microstructure consists of β-Ti dendrite and（β-Ti +Ti2Ni）rod and lamellar eutectic in the inter-dendrite. The characteristic dendritic size F decreased with the decreasing of laser energy density De, resulting from the decreasing of laser power and increasing of scanning velocity, in fact, the characteristic dendritic spacing was decided by. On the other hand, the eutectic spacing also decreased with the increase of scanning velocity. The variation of the characteristic dendritic size and eutectic spacing is roughly in accord with the KGT model and TMK model respectively.

A mathematical model was proposed to study the influences of temperature fluctuation on initial peritectic solidification process in continuous casting. The variation of interface positions and volume fractions of three different phases—delta, gamma and liquid phase—were calculated under different cooling rates, carbon content and temperature fluctuation amplitudes. The results showed that remelting between dendritic structures, unstable variation of interfaces between delta-gamma, and volume fractions variation of different phases happened when there was temperature fluctuation, which lead to uneven growth and stress concentration in the shell. These phenomena are especially serious in the hypo-peritectic steel casting processing. It is considered that the temperature fluctuation is one of the important reasons lead to strong crack sensitivity and difficult casting of the peritectic steels.