Abstract:Accurate evaluation of the elastic modulus of thermal-sprayed coatings is very important to ensure the safety and durability of industrial components, but it seems difficult via conventional technique. Although indentation technique is available to estimate the local modulus of coatings, it does not reflect the effects of porosity or cracks. Impulse excitation technology (IET) is a simple and accurate method to evaluate the elastic modulus of bulk materials. It was used to determine the modulus of thermal-sprayed coatings via relative method in this work. An analytical relationship among the moduli of the coating, the substrate and the coating/substrate system was derived. Thus, the modulus of coatings was obtained via the measured modulus of the samples before and after coating. Experiments on Q235 steels coated with NiCr coatings, were carried out to investigate the effect of atomization gases on the elastic modulus of NiCr coatings. The results indicated that the elastic modulus of NiCr coating prepared by air atomization (NiCr-Air) was higher than that of NiCr coating prepared by N2 gas atomization (NiCr-N2). The reasons for this were the formation of Ni(Cr2O4) reinforced NiCr alloy laminated composite, and the laminated composite structure had a positive influence on the elastic modulus.

Abstract:Al₂O₃ ceramic/Fe-Ni-Co joints are achieved using Ag-Cu-Ti filler alloy in the study to investigate the dependence of the joint microstructure and mechanical performance on the Ti content. Scanning electron microscope (SEM), energy dispersive X-Ray spectrometer (EDS), X-Ray diffractometer (XRD) and electronic universal testing machine are used to characterize the microstructure and mechanical performance of the joints. The results show that the increase of Ti content can obviously intensify the interaction between Al₂O₃ and Ag-Cu-Ti. A layer of Ti-Al and Ti-O products is observed at the interface of Al₂O₃/AgCuTi. The tensile strength of Al₂O₃/AgCuTi/Fe-Ni-Co joint increase as the Ti content increased from 2 wt% to 8 wt.%, and the tensile strength of brazing joint reached the maximum value of 78MPa. Good reaction layer formed by metallurgical reaction at the interface of Al₂O₃/AgCu4Ti, and the typical microstructure is Al₂O₃/TiAl+Ti₃O₅/NiTi+Cu₃Ti+Ag(s,s)/Ag(s,s)+Cu(s,s)+(Cu,Ni)/Fe-Ni-Co brazed at 890_oC for 5 min. Compared with AgCu4Ti filler, the microstructure of the joints change slightly when addition of the active element Ti to 8 wt.% except for the increase of the thickness of reaction layer adjacent to Al₂O₃ ceramic and accompanied the formation of TiO and Ti₃Al in the Al₂O₃/Ag-Cu-Ti interface.

Abstract:The Cu/Al diffusion couples were prepared by solid-liquid bonding method. Interfacial microstructure and phase composition were investigated by scanning electron microscope (SEM), energy dispersive spectrometry (EDS) and X-ray differential (XRD). Moreover, the microstructural evolution of Cu/Al interface was quantitatively analyzed on the basis of diffusion theory and phase diagram. The results reveal that: the interface consists ofⅠ(AlCu+Al2Cu), hypereutectic microstructureⅡ[Al2Cu+(α-Al+Al2Cu)] and hypoeutectic microstructure Ⅲ [α-Al+(α-Al+Al2Cu)] from Cu side to Al side accordingly. Further, there are various morphologies of Al2Cu phase formed with the decreasing of Cu concentration. Additionally, the thickness of three diffusion zones is basically identical with the theoretical prediction.

Abstract:Mullite/ZrB₂-MoSi₂ coating was deposited on carbon/carbon(C/C) composites to protect against ablation by atmospheric plasma spraying (APS). The microstructure and morphology of the coating were characterized by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. The ablation resistance of the coating was investigated at different temperatures with oxypropylene torch. The mass ablation rates of the Mullite/ZrB₂-MoSi₂ coated C/C composites were 3.49×10_-3 g/s and 3.77×10_-3 g/s after ablation at 1700 °C and 1800 °C for 60 s respectively, which exhibited good ablation resistance compared with the single-layer ZrB₂-MoSi₂ coated. The increase of ablation resistance can be attributed to the formation of a silicates glass film, which acted as thermal barrier and self-sealed the defects of the coatings.

Abstract:The development and characterization of new materials is of extreme importance in the design of cryogenic apparatus. Recently a kind of open-cell aluminum foam was used for heat transfer enhancement at cryogenic temperature. Such aluminum foam was tested for cryogenic energy storage with a phase change material of nitrogen. The thermal conductivity of the open cell aluminum foam was studied. The thermal conductivities of the aluminum foam were measured between 50 K and 170 K. The results have shown that the thermal conductivity increases with the temperature decreases. Then the effects of thermal conductivity of open-cell aluminum foams on the performance of aluminum foam phase change material thermal storage unit were investigated. Nitrogen was selected as the phase change material. Temperature variations of the thermal storage unit during cooling and melting processes were tested. Test result has shown that the maximum temperature difference between the up and bottom of the thermal storage unit is less than 0.5 K, much lower than the case without aluminum foam. It was concluded that as the thermal conductivity of thermal storage unit increases, both the container temperature difference and temperature variation of the thermal storage unit decrease. #$NL

Abstract:Abstract: An investigation of dislocation structure and its impact on the mechanical behavior of a ?? strengthened nickel base single crystal alloy under high cycle fatigue (HCF) at 870℃ is studied. The results indicate that HCF lifetime reduced with increase of applied stress amplitude. In the early stages, the fatigue deformation occurs by forced bowing of dislocations through the narrow ? matrix channels on {111} planes. During mid-term fatigue stages, most of the dislocations formed in the matrix are located in the r?/ r"?? interfaces, their intersection and reaction produce new dislocation segments and three-dimensional dislocation networks. The Burgers vectors of the dislocations in the network are 1/2<110>. The interaction of cyclic stress with high temperature induced the precipitation of homogeneous globular r"?? precipitates, that is beneficial to fatigue strength. At the end of fatigue test, the cyclic stress led to the formation of persistent slip bands moving through the r? matrix channels and ?r‘? particles. Dislocation shearing through the r"?? phase was found occasionally. The extrinsic stacking faults was also observed in the present study.

Abstract:In order to improve the corrosion resistance of the sintered NdFeB permanent magnets, Al2O3 ceramic coatings were prepared by a two-step micro-arc oxidation process in an aluminate solution. During the micro-arc oxidation process, the voltage-time curve could be divided into four regions consistent with the valve metals. The coating exhibited a typical micro-arc oxidation porous surface with the thickness of ~5 μm, and was only composed of Al2O3 crystalline phase with some Fe elements and a few Nd and P elements. The surface roughness of coated NdFeB magnets was higher than that of uncoated sample, while the corrosion resistance was enhanced by one order of magnitude. Unfortunately, the magnetic properties (remanence and maximum energy product) of coated NdFeB sample decreased in different degrees.

Abstract:Commercial rolled Mg-3Al-1Zn (AZ31) alloy sheet was used as the experimental material, an Mg-air battery based on its rolling surface (RS) and cross-section surface (CS) were both prepared to study the effect of texture on the performance of Mg-air battery. And the experimental samples had a similar surfaceSroughness to practical application, which was different to the reported studies (the studies about the influence of texture on the electrochemical behavior of Mg alloys). The impedance spectroscopy (EIS) was used to investigate the electrochemical behavior of the samples. The resusts showed that CS surface was more corrosion resistance compared with that of the RS surface. The battery performance was studied by constant current discharge test, the result showed that the Mg-air battery based on the CS surface anode has higher anode efficiency (71.3%) compared with that of the Mg-air battery based on the RS sursace anode (65.7%). The surface morphologies of the magnesium alloy anodes substrate after discharged for 24h were observed by scanning electron microscope. The RS anode exhibited a magnesium alloy anode substrate with more holes and gullies, which may contribute to its lower anode efficiency. Thus, the CS anode dominated by (10-10), (11-20) and (10-11) orientated grains was more suitable to be used on Mg-air battery.

Abstract:ZA27 alloy-based composites reinforced by 10–40 vol. % Ti3AlC2 particles in a step of 10 vol. % were prepared by pressurelessly sintering mechanical alloyed powders at 870 °C for 2.5 h. The effects of Ti3AlC2 content on hardness, density, stretching and bending performance were studied. The results demonstrate that a well bonded interface could be obtained by weak reaction occurred at the interface between Ti3AlC2 and ZA27 alloy during sintering process, and which is beneficial to the mechanical properties of the Ti3AlC2 /ZA27 composites. An increase in Ti3AlC2 content (up to 30 vol. %) leads to enhanced hardness and mechanical strength of the composites due to dispersion strengthening of nano-sized Ti3AlC2 particle. However, with an increase in Ti3AlC2 content to 40 vol. %, the hardness and strength decrease because of the growing number of pores. Comparing the four composites with different Ti3AlC2 contents, the 30Ti3AlC2 /ZA27 composite possesses the best properties of 310 MPa for tensile strength, 528 MPa for bending strength and 1.24 GPa for Vickers hardness. Besides the good interfacial bonding, the improved mechanical properties of the Ti3AlC2 /ZA27 composites are also attributed to the fine-grained microstructure and well dispersed reinforcements.

Abstract:γ-TiAl specimens were coated with an Al₂O₃/Al composite coating using magnetron sputtering. The corrosion resistance of the coated specimens were investigated in molten salt environment of 100 wt.% Na₂SO₄at 850 °C. Al₂O₃/Al composite coating improved the high temperature corrosion resistance of γ-TiAl alloy effectively. This good resistance was attributable to the gradient structure of Al₂O₃/Al composite coating which consist of an Al₂O₃ top-layer, an Al-rich interlayer and a diffusion layer. The results of corrosion test revealed that the Al₂O₃, TiO₂ and TiAl₃ were identified as the main phase structure of the corroded coating surface. Moreover, the sealed coating structure could effectively suppress the erosion of O_2-, S_- and Na₊, while Al₂O₃/Al coating with gradient structure exhibited superior crack and spallation resistance.

Abstract:This paper presents a novel method of preparing stoichiometric titanium carbide (TiC) powders by combining carbothermal reduction and molten salt synthesis (MSS) from raw starting materials of titanium oxide (anatase), C (carbon black), and sodium chloride. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), laser particle size analysis, energy spectrum analysis (EDS), and thermodynamic analysis were used to characterize the powders. The effects of heating temperatures and molar ratios of titania to carbon black on the preparation of TiC are discussed. Results showed that the use of MSS to reduce the synthesis temperatures of both stoichiometric and pure TiC from 1700°C to 1550°C and the time required for synthesis decreased from 10 h for conventional carbothermal reduction of TiO₂ to 3 h. A dissolution-precipitation mechanism of synthesis of TiC by MSS was established based on these observed results.

Abstract:A simple, rapid and eco-friendly technique for the preparation of small-size silver nanoparticles with narrow distribution from 5 nm to 15 nm was developed. In the approach, using silver nitrate as silver precursor, and mulberry leaves extract as both capping and reducing agent, silver nanoparticles were obtained at room temperature, without employing any other reducing and capping agents. The formation of silver nanoparticles was observed by the change of color from pale yellow to brown and the UV-vis absorption spectroscopy. The effect of reaction time, temperature, silver nitrate concentration and mulberry leaves extract amount were studied. The silver nanoparticles were characterized by transmission electron microscopy (TEM), UV-visible spectroscopy (UV-vis), X-ray diffraction (XRD) and fourier-transform infrared spectroscopy (FT-IR). The results demonstrated that the obtained metallic nanoparticles were highly crystalline silver nanoparticles with a spherical shape and capped with extract. A possible formation mechanism was proposed. The method demonstrated in this paper may be extended to synthesize other noble metal nanoparticles by using renewable materials as capping and reducing agents.

Abstract:Phase transformation kinetics of Cu-Be-Co-Zr alloy during aging treatment was investigated in this study. Based on the relationship between electrical conductivity and volume fraction of precipitates, the phase transformation ratio of Cu-Be-Co-Zr alloy aged at 480 degrees Celsius for different holding time (0, 30, 60, 120, 180, 240, 360, 480, and 600 min) were calculated. The kinetics equation of phase transformation and the electrical conductivity equation were derived, respectively. The isothermal transformation kinetics S-curves of Cu-Be-Co-Zr alloy was drawn. By using the integral equation of solid thermal decomposition reaction mechanism, the phase transformation mechanism of Cu-Be-Co-Zr alloy is controlled by three dimensions of diffusion.

Abstract:CrAlN and CrN films were deposited on 304 stainless steel substrate by direct current magnetron sputtering. Effects of Al incorporation on the composition and microstructure for CrN film were investigated by X-ray diffraction (XRD), Scanning electron microscopy (SEM), X-ray photoelectrons spectroscopy (XPS), Atom force microscope (AFM) in the present work, respectively. The tribological behaviors of CrN and CrAlN films were characterized by wear tester against with a diameter of 3 mm Si3N4 ball under different conditions and the wear profiles of film were characterized by Nanomap 500LS. The results showed that the main phases of CrN film were CrN and Cr2N phase and the main phases of CrAlN film were Cr2N and CrAlN phases. The CrAlN film presented a CrAlN (200) preferred orientation and CrN film presented CrN (200) preferred orientation. In terms of CrAlN film, parts of Cr atoms were taken place by Al atoms forming the CrAlN phase which was benefited to refining grain and improving the comprehensive performance of CrAlN film. Therefore, CrAlN film exhibited an excellent wear-resistance performance and lower wear rate than CrN film in all the conditions.

Abstract:The isothermal oxidation behavior of NiTi alloy in H₂-H₂O at the temperature range of 400 °C to 700 °C was studied. The oxidation rate followed cubic laws, and the activation energy for the oxidation of the alloy was determined to be 127.52 kJ/mol. The surface Ni content was significantly reduced by selective oxidation. For the sample oxidized at 400 °C, the morphology was different from that formed at high temperatures. For the samples oxidized at 500 °C, 600 °C,and 700 °C, the oxide scales showed two morphologies, which consisted of cubic grains and oxide whiskers. Cross-section analysis showed that the oxide scales consisted of an outer TiO₂ layer and an inner Ni₃Ti layer. Voids formed near the interface of the two layers.

Abstract:The growth of well-aligned Au/TiO2 nanorods arrays by magnetron sputtering is presented for the first time. The feasibility of preparing Au/TiO2 nanorods was demonstrate via a dc reactive magnetron sputtering at room temperature and heat-treatment at 500 oC in air for 2 h. The heat treatment leads to the formation of Au/TiO2 nanorods with Au nanoparticles embedded in the TiO2 nanorods of anatase phase.These Au/TiO2 nanorods showed lower photoluminescence emission intensity and higher absorption and intensive response to the visible light, compared with traditional TiO2 nanofilms fabricated by similar method. The Au nanoparticles in the TiO2 nanorods suppress the charge recombination.

Abstract:The tensile test of TC4 alloy was carried out in the presence of a high pulsed magnetic field. The effects of magnetic induction intensity (B=0T, 1T, 3T, 5T) on the elongation, phase characteristic, crystal structure and dislocation density were investigated. The results show that the imposed magnetic field has enhanced the elongation. At 3T the elongation arrives at the maximum of 12.41%, which is enhanced by 23.98% compared to that of 0T sample. The 3T parameter is ascertained as a traverse point from increase to decrease tendency. Furthermore, the magnetic field has accelerated the phase transformation from β to α together with the orientation preference of crystal plane along the slipping direction. As for the dislocation density, it exhibits as the first increase followed by the falling tread. At 3T it arrives at the utmost. It is analyzed that the phenomenon is attributed to the enhancement of dislocation strain energy in the presence of magnetic field. Next, the magnetic field promotes the transition from singlet to triplet state. At last the inevitability of optimized 3T parameter is further discussed in the quantum view.

Abstract:Commercial purity zirconium (CP-Zr) was processed by Equal channel angular pressing(ECAP) at room temperature using a die with an internal angle Φ of 90°and an outer curvature angle Ψ of 20°. Advanced characterization and measurement techniques such as transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and so on, were used to analyse microstructural evolution of CP-Zr during one pass ECAP at room temperature. The results showed that the grain of CP-Zr processed by one pass ECAP was refined distinctly. The yield strength and ultimate tensile strength were increased to 397 MPa and 536 MPa (rate of increase up to ~43% and ~53%), respectively. The microhardness value was increased to 1550 MPa. The elongation to failure maintained well. The microstructures of processed CP-Zr observed by TEM proved the existence of elongated bands, dislocations and dislocation cells. The results of XRD indicated that the basal texture and pyramidal texture were transformed to prismatic texture.

Abstract:Aiming at the fact that the oceangoing vessel protective plates is affected by the stormy waves, the tide and the random explosion shock wave, the spallation and cracks are easily caused. By controlling the finite element "life and death" state, the temperature field field dynamic process of pulsed laser remanufacture was simulated. The derivation law of temperature field in forming process was obtained, the forming process of pulse laser remanufacturing was optimized. The analysis and test results show that, the pulsed optimization process parameters are laser power 3KW, the spot diameter is 3mm, the scanning speed is 6mm/s, the pulsed laser pulse width 10ms, the duty cycle is 1:1. The heat affected zone deformation after forming is controlled within 0.02mm, the maximum hardness is 95HV0.1 which appeares in the heat affected zone. The heat affected zone is closely metallurgical bonded with the base metal, the weld is mainly consisted of fine grained structure, the tensile strength is up to 222Mpa.

Abstract:Based on bilinear force displacement law, finite element simulation of shear force test on zirconium-titanium-steel clad plate was carried out by using cohesive zone unit of ABAQUS, then, the effect of cohesive strength and fracture energy on the damage of interface layer was studied. Also the correctness of the prediction formula of shear strength was verified. The results show that cohesive element can simulate the fracture process of clad plate interface layer and agree very well with the results of shear force tests. Shearing displacement and cohesive strength was positively correlated. With the increase of fracture energy, shearing displacement, characteristic displacement and maximum shear force increase. The fitting formula of shear strength can predict shear strength under different heat treatment.

Abstract:_{:The isothermal hot compression test of Cu-1.0%Zr-0.15%Y alloy were carried out by using a Gleeble-1500D thermal simulation machine. The characteristics of true stress-true strain, microstructure evolution and hot deformation mechanism of the alloy were investigated and analyzed at elevated temperature of 550 ℃～900 ℃and at the strain rates of 0.001 s-1～10 s-1. The results show that the typical characteristics of dynamic recovery occurs during the deformation temperature of 550～750℃, while the characteristics of dynamic recrystallization occurs under the deformation temperature of 850～900℃.The deformation temperature and strain rates have significant effects on the microstructure of Cu-1.0%Zr-0.15%Y alloy as hot deformed. Based on the true stress-strain curves, the constitutive equation of the flow stress and strain rates and deformation temperature during isothermal compression deformation is established. The hot deformation activation energy of the alloy is 379.16 kJ/mol, compared with pure copper, the hot deformation activation energy increases by 81% with high Zrcontent. The addition of rare earth element Y not only refines the alloy grains but also promotes the dynamic recrystallization.}

Abstract:Eshelby tensor is not a constant parameter and there is no analytical expression for a non-ellipsoidal particle. To simplify the calculation, non-ellipsoidal particle usually was treated as ellipsoidal in most analysis, while the simplification is need to be verificated for particles in composite are not always ellipsoid actually. To study the error of the simplification, the Eshelby tensor and the average Eshelby tensor of several non-ellipsoidal particles were calculated numerically, and the numerical result is verified by comparing to the finite element method result. Base on the numerical result, the influence of the non-ellipsoidal to equivalent elastic property of the composite is analyzed, and the condition of the simplificating the non-ellipsoidal particle to ellipsoidal particle was obtained. The result indicated that using the numerical method in Eshelby tensor calculation is highly precise. It is acceptable to simplify the non-ellipsoidal particle to ellipsoidal particle when the non-ellipsoidal particle is highly symmetrical. The oblate particle has more important influence on the equivalent elastic property of the composite than other shapes, and hence it cause larger error for simplifying the non-ellipsoidal to ellipsoidal particle than other shapes.

Abstract:Because of the low density, high specific strength and excellent performance at high temperature, γ-TiAl based alloys have become a new generation of materials in the aeronautic field. However, its poor ductility at room temperature leads to its bad performance in the manufacture process, which has set a boundary to its wide applications. In this paper, 16 La and (or) Zr doped γ-TiAl systems (S1, S2, S3, S4, S51~S55, S61~S65, S7 and S8) are constructed and investigated by using the plane wave pseudo potentials method based on the density functional theory and other physical theories. The results of average formation energy show that they possess good energy stabilities. According to the elastic parameters and Born-Huang criteria, it is forecasted that they (except system S61) are in good mechanical stabilities. So, the 15 doped systems can be prepared in experiment and are stable in existence. The comparison of G/B shows that all La and Zr co-doped systems (especially S51, S52, S63 and S64) have better ductile properties than that of pure γ-TiAl systems. The ductility of co-doped systems is not much correlated with comparative position of doping atoms. The calculation results and discussion about population, charge densities indicate that the improvements of ductility and isotropy of co-doped systems come of the decrease of Ti4s→3d, Al3s→3p charge transfer and increase of free electrons number. This change results in the weakening of p-d orbital hybrid, the decreasing number of bonds Al (La, Zr)-Ti and the increasing strength of covalent bond Ti-Ti, and then the chemical bonds Al-Al, Ti-Ti and Al-Ti distinctly tend towards the same strength and become stronger metallic property.

Abstract:The giant magneto-impedance (GMI) properties of FeNiCrSiB/Cu/FeNiCrSiB sandwiched ribbon were studied. The obtained results showed that the sandwiched ribbon had remarkable GMI effects. The maximum values of the longitudinal and transverse GMI ratios were 282% and 408%，respectively，at the frequency of 0.5MHz. Observations indicated the orientation of 180° stripe domains tended to the ribbon axis. Due to the transverse closed magnetic flux loop of sandwiched ribbon, a 10 degrees deflection of stripe domains to the transverse direction is observed.Besides, the relationship between magneto-resistance, magneto-inductance, effective permeability and GMI were analyzed: at the frequency range of 40 Hz~10 MHz, the magneto-inductance played a decisive role.It is attributed to the special sandwiched structure, which reduced energy losses, improved effective permeability significantly and then enhanced magneto-inductance effect.The magneto-inductance effect controlled by effective permeability was the principal features of the GMI.

Abstract:The aim of the paper is to explore the deformation mechanism of particles in cold spray. Focused ion beam/ scanning electronic microscopy (FIB/SEM) system was employed to prepare a TEM specimen of a whole copper particle on aluminum substrate on wipe test. Through analyzing the microstructure of the TEM sample, the result indicates inhomogeneous deformation of Cu particles is due to inhomogeneity of stress field and temperature. During the impact, the kinetic energy of particles transformed to deformation energy and heat, which led to alumina layer broken and the temperature increasing quickly. Because of high temperature and strain rate, re-crystallization has happened in Cu near the interface and intermetallic compound Cu₉Al₄ has been obtained on the interface. The farther the grains were from the interface, the less influence happened on them. Grains had few effect of heat or stress field on the location far away from the interface, especially on the top of particle.

Abstract:In order to study indirect squeeze casting process, we selected ZL101 aluminum alloy with porosity as indicators and analyzed the effect of process parameters of pressure, die temperature and proportionality factor on porosity. Box-Behnken design of experiment have been developed to design response surface experiment and regression model of the relationship between the indirect squeeze casting process parameters and porosity have been established. ANOVA result shows that the fitting effect of the experimental results and the mathematical model is good. The effect of die temperature and pressure on porosity has certain interaction but the effect of die temperature and proportionality factor or the effect of proportionality factor and pressure on porosity does not exist significant interaction by analyzing response surface of interaction of various factors. Due to the applied pressure, the congealed metal shell will happen uneven plastic flow by metallographic testing analysis of the edge of sprue in gating system parts.

Abstract:Fatigue crack growth rates (FCGR) alloy 690 tubes have been obtained in air at room temperature (RT) and 325℃ by using pin-loading tension (PLT) specimen and direct current potential drop (DCPD) method. Testing data has been fitted with Priddle model, thus the threshold stress intensity factor amplitude △K_th and fracture strength K_c were predicted. at higher temperature, fatigue crack growth rates were much faster than that at RT, as a result, the △K_th and K_c decreased in higher temperature. Scanning electron microscopy (SEM) examination of the fatigue fracture surfaces revealed transgranular attack, and the fracture surface were covered with a lot of TiN inclusoins, it’s reasonable to believe that TiN inclusions could enhance fatigue crack initiation and propagation of alloy 690 tubes.

Abstract:Al-Ce and Al-Mg-Ce alloy fuels were prepared by melting method, which the mass fraction of Mg is 15% and the mass fraction of Ce are 0%, 1%, 3%, 5% . The phase composition, oxidation exothermic performance and appearance/element distribution of alloy fuels were characterized by XRD, TG-DTA and SEM/EDX. The reason of differences in oxidation exothermic reaction between alloys with different mass fraction of rare earth Ce and the oxidation behavior of Al-Mg-Ce alloys were analyzed. The results show that the oxidation exothermic performance of Al-Mg-Ce alloys reduces gradually with the increasing of Ce content. The first oxidation reaction temperature of Al-Mg-Ce alloy powders is about 160℃ lower than Al-Mg alloy powders due to the addition of Ce. Al-15Mg-1Ce alloy powders behave better thermal performance with the heat enthalpy of 6413uV?s/mg and weight increasing 90% at 1300℃ among them.

Abstract:The effects of different heat treatment on the tensile properties and microstructure of a 2050 Al-Li alloy sheet were investigated through mechanical testing and TEM. The result indicate that the mainly strengthening precipitates of 2050 Al-Li alloy are T1 and θ′ phases. The aging precipitation characteristic is different upon T6(175℃) and T8(6% pre-deformation+155℃)aging. Compare to T6 aging, the pre-deformation before T8 aging increases the density of T1 and θ′ precipitates, reducing the size and the corresponding strength and elongation are improved. At T8 peak aging state, the σb、σ0.2、δ reached of 531 MPa、488 MPa、11.4%，respectively. The scope of 2% to 10% pre-deformation before T8 aging can promote T1 phase nucleation, the 2% to 6% pre-deformation can promote θ′ phase nucleation. Large deformation (such as 10%) has little effect on further nucleation of θ′ phase, but significantly inhibit the θ′ phase grew up.

Abstract:Electro-spark deposition process was used to prepare the Mo₂FeB₂-based cermet coatings in Ar and air, respectively. Influence of deposition atmosphere on morphology, phase constitute, microhardness and friction and wear performance of the coatings were investigated by SEM, XRD, Vickers microhardness tester and tribometer. The results show that the coatings produced in Ar and in air are dense, metallurgical fusion with the substrate, and no delamination can be observed between the coating and the substrate. However, the coating prepared in air was oxidized severely, and has a more rough surface and non-uniform thickness. They are composed of amorphous phase and martensitic phase while more amorphous phase is involved in the coating produced in Ar. The peak microhardness of the coatings produced in Ar and air are 1286.2HV_0.05 and 1012.9HV_0.05, respectively. The coating prepared in Ar is of better wear resistance, its wear mass is about 1/7 that of the coating produced in air. The abrasion mechanism of the coatings is fatigue wear and abrasive wear, and the coating produced in air is mainly fatigue wear, whereas the coating prepared in air is primarily abrasive wear.

Abstract:_{:The effect of flux-cored ingredients and welding parameters on porosity sensitivity of ENiCrMo3T0-4 flux-cored wires were investigated by stereomicroscope and optimum design software. It was found that porosity sensitivity was reduced with the ratio of SiO2/ZrO2,TiO2/ZrO2,and (TiO2+ZrO2+SiO2)/MnO decreased in flux-cored ingredients. The shielding gas flow rate had little influence on number ofneedle holeson weld surface. Big wormhole in weld surface would be formedif flow rate was too low.The number of needle holes and porosity sensitivity of weld metal were the lowest when welding voltage was 25 V, welding current 160 A and wire extension 20 mm.Porosity sensitivity of weld metal can be reduced by enlarging solid-liquid phase temperature and hydrogen solubility in high temperature slag.}

Abstract:This study aims to evaluate the static and dynamic mechanical properties of 20Zr-70Ti-6Al-4V alloy. The XRD, DSC, OM and SEM were used to test and analyze the phase transition and microstructural evolution of the 20Zr alloys subjected to different heat treatments. Dynamic compression tests were conducted by the SHPB(split Hopkinson pressure bar) to study the dynamic mechanical properties. The results showed that all 20Zr alloys were comprised of α and β phase and presented typical basketweave microstructures. At static conditions, the tensile strength was up to 1301 MPa., the plastic strain up to 14.9%, while the compressive strength was up to 1386 MPa. Under dynamic compression experiments, the dynamic compressive strength increased as the strain rate increased from 1000s-1 to 3000s-1, which reflected the strain hardening effect. In addition, the dynamic compressive strength and the plastic strain of 20Zr alloys undergoing the solid solution and aging treatment exceeded the anneal treated alloys. Besides, the failure of alloys resulted from the adiabatic shear bands.

Abstract:_{:The WC-12Co composite powder was synthesized by reduction and carburization reactions. With adding various contents of combined grain growth inhibitors (GGI) VC and Cr3C2 into theWC-12Co compositepowder, the effects of the GGI addition on the phase constitution, microstructure and mechanical properties of the coating havebeen investigated by X-ray diffraction (XRD)and scanning electron microscopy (SEM)respectively. The result shows thatthat with the content of GGI increasing in the composite powder, the abnormal grain growth disappears and homogeneous ultrafine grain structure forms, the coefficient of friction of the coating reduces. When the total amount of inhibitor is added in combination 1.0wt.%, the maximum hardness of WC-12Co coating is 1367 HV0.3, and the wear rate of the coating isthe lowest.Further increasing the content of inhibitor, the wear rate of the coating increases, the hardness and the wear resistanceof the coatingdecreases.}

Abstract:Effect of Morphology and quantity for the primary α phase for TC4-DT titanium alloy on fracture toughness is discussed in this paper. Different α phase contents were obtained by heat treated below phase transition point. The result shows that contents of primary α phase drop with solution temperature increasing, and the size of grains change little. The content of secondary alpha phase increases, and length-width radio increases with solution temperature increasing, which leads to fracture toughness to increase. Sizes of primary α phase increase under furnace cooling than under air cooling, the thickness of lamellar α increase, fracture toughness of the alloy increases obviously, and the growth mechanism is analyzed through fracture.

Abstract:The effects of prerecovery ( 250℃×24h + 300℃×6h + 400℃×6h ) to aluminum alloy Al-10.78Zn-2.78Mg-2.59Cu-0.22Zr-0.047Sr on microstructure and properties was researched by analysis of EBSD、XRD and test of hardness、conductivity、tensile、intergranular corrosion、exfoliation corrosion. The results show that, prerecovery treatment can refine grain size with average size reduces from 7.30 μm to 5.57 μm and increase the proportion of low angle grain boundary from 0.588 to 0.623. The effect of prerecovery on hardness and conductivity of the alloy is small, but the strength of the alloy is obviously improved by the prerecovery. The yield strength of alloy at peak aging(120℃×48h) processed by prerecovery is 633.2 MPa. Compared with the alloy without prerecovery treatment, the yield strength increased by 35 MPa. The intergranular corrosion and exfoliation corrosion of alloy after prerecovery treatment are improved from rank 4 to rank 3 and rank EA to rank PB respectively.

Abstract:The mechanical properties, microstructural evolution and deformation mechanisms of room-temperature compressive deformation of Ti–26 titanium alloy were investigated using the single pass compression experiment at strain rates of 0.001~0.1 S–1 and height reductions of 20%~60%. The results show that discontinuous yielding appears at a strain rate of 0.1 S–1 and the yield strength are more sensitive to the changes of the compression rate in the same height reductions. With increasing strain rates and height reductions, the initially equiaxial grains evolve into fibrous grains and the larger the height reductions and strain rates are, the more significant the elongation of the beta grains are. Small deformation condition, the microstructure of Ti-26 alloy has obvious slip and a small amount of twinning, and dislocation slip and twinning mutual coordinate and promote the alloy deformation at room temperature. Large deformation condition, The slip occupy more the single β grain and expand around the β grain, a small amount of twins can be completely engulfed, dislocation slip only coordinated deformation mechanism.

Abstract:In this paper, electron beam physical vapor deposition technique was taken to prepare double structure thermal barrier coatings on Ni-based single crystal substrate. Then, a Nd: YAG laser was used to modify the surface of the as-deposited samples to obtain a thermal barrier coatings with a composite structure. The oxidation resistance and corrosion resistance of EB-PVD deposited as well as laser-modified coatings were investigated by isothermal oxidation treatment at 1100℃. The microstructure and phase composition of the coatings were characterized by scanning electron microscopy (SEM) and X-ray diffractometry (XRD). The results revealed that the surface of the coating formed a dense layer after the laser modifing, which structure was together with the original columnar crystals YSZ layer, deposited by EB-PVD, to a composite ceramic coating. Consequently, the diffusion behavior of harmful element was slowed down by composite ceramic coating into the substrate, and the oxidation resistance and corrosion resistance of the samples were improved.

Abstract:The transformation of phase structure and microstructure for solution treated Ti-1300 alloy during isothermal aging between 350～700℃ were investigated using optical microscopy, scanning electron microscopy, X-ray diffraction and transmission electron microscopy analyses. Results show that the fine ellipsoidal ω phase formed in the Ti-1300 alloy at 350℃ firstly, then with the disappearing of ω phase, acicular α phase precipitates formed in the β matrix. The decomposition mechanism of this process was β→ω+β→α+β. The glabol β′ phase separated from the β matrix at 400℃ after 1h. With the increasing of holding time, the β′ phase could be served as the nucleation sites for α phase precipitates, thus leading to acicular α microstructure. And the decomposition mechanism was β→β′+β→α+β. After aging at 500℃~700℃, the decomposition mechanism of metastable β phase became as β→α+β. The nucleation site of the secondary α phase was mainly in the prior β grain boundaries and the internal nucleation of the prior β grain, and the grain boundary α phase with same orientation grew into α cluster gradually. Increasing the aging temperature, the thickness of α plate-like phase increased.

Abstract:The effects of ruthenium (Ru) additions on the microstructures of Ni-based single crystal superalloys in as-cast, post-heat treated and long term aging (at 1100 °C) are investigated by using optical microscope (OP), scanning electron microscope (SEM) and transmission electron microscope (TEM). The results show that Ru additions promote the increasing of eutectic and primary dendritic arm spacing. Because Ru additions lead more refractory elements segregating (e.g. Re and W et al.) to the dendrite arm, the solution heat treatment of the 3Ru alloy is more difficult. The stacking fault energy of the g matrix is obviously decreased after Ru additions. The extend dislocations in the g matrix may impede the movement of the following dislocations during plastic deformation and improve the mechanical properties significantly. During long term aging at 1100 °C, Ru additions has no significant effects on the rafting process, and the type of topologically close-packed (TCP) phase is not changed after Ru additions (mainly P phase). However, the precipitation process of TCP phase is suppressed after Ru additions. As the aging time prolong, the suppression effects is weakening (over 500 h).

Abstract:Thermal oxidation (TO) treatments were conducted on Ti6Al4V under 973 K for 10 h, 20 h ,30 h, 40 h and 50 h,. Microstructural characteristics of the TO layers were analyzed using X-ray diffraction (XRD), glow discharge optical emission spectrometer analysis (GDOES) and scanning electron microscope (SEM). Effect of TO duration on microstructure and properties of Ti6Al4V were estimated on microhardness tester, MFT-R4000 reciprocating friction-wear testing machine and electrochemical workstation. The results showed that the obtained TO layers were uniform and continuous. TO duration had certain impacts on the formation, surface hardness, wear and corrosion resistance on TO layers. The TO layer produced at 973 K-30 h exhibited more promising characteristics indicating by thickness value, surface hardness, wear and corrosion resistance in comparison with other TO layers.

Abstract:The cast samples of low-alloy bainite wear-resistant cast steel of 20MnCrNi2Mo with anthanum-cerium mischmetal were tempered at 200, 250, 300, 350, 400, 450, 500, 550, 600 and 650 ℃ respectively for 1 h. The microstructure was observed by QUANTA-400 environmental scanning electron microscope and JEM-2100 transmission electron microscope, the precipitation was qualitatively and quantitatively analyzed by using physicochemical phase analysis, and the retained austenite after different temperature tempering was measured quantitatively by D8 ADVANCE X ray diffracmeter. The microstructure evolution during the tempering was investigated. The results show that the microstructure of the tested steel as cast is granular bainite. The precipitated equilibrium-phase carbide during the tempering is alloying cementite with trace amount of solid-solution rare earth. The recovery has not been found during tempering at 500 ℃. The subgrains are found become distinctly and the recovery is observed clearly during tempering at 650 ℃. The M/A islands do not decompose tempered at 200 ℃, with the increase of the tempering temperature, the M/A islands gradually decompose, and the amount of the M/A islands decreases so obviously that it can not be detected when the tempering temperature is up to 450 ℃.

Abstract:The vacuum gas pressure infiltration was performed by 3D five-directional and 3D orthogonal braided performs woven by M40 graphite fiber composite (3D-Cf/Al) with the volume fraction of 51% and the density higher than 97%. After analyzing the morphology and formation mechanism of micro defects and control measures, and comparing the effects of braiding structures on micro defect formation, the results showed that the defects in the composite were micron grade micro defects, of which the main defects included pores within the fiber beam and partial fiber reunited, cold shut, microscopy shrinkage cavity and small inclusion in the substrate concentration. Of note the pores between the fiber beam and pores within the fiber beam of 3D orthogonal composite were less than 3D five-directional composite, while the fiber reunited phenomenon of 3D orthogonal composite was more serious than 3D five-directional composite. The main reason for the different defects was braided structure distinctions. By increasing the fiber preheat temperature could effectively reduce the internal pores defect and partial fiber reunited phenomenon.

Abstract:The volt-ampere characteristics of gas discharge was introduced into the glow-arc discharge transitional section using adjustable pulse power control mode and deposited TiN films under different target current density conditions.The influence of target current density on the microstructure, hardness and bonding strength of the films was studied by means of XRD, SEM, TEM, nano indentation tester and coating adhesion automatic scratch tester. The results showed that plating material particles leave-target mechanism transformed form collide leave-target in sputtering condition to collide enhance heat emission leave-target and the deposition particles had a higher density, high ionization and high energy with the increase of target current density. The films have better surface quality and density degree, and the hardness and membrane-binding strength were upgraded from 13.4GPa、10.5N to 24.7GPa、16.8N respectively.

Abstract:The mineralization and sintering behaviors of SiO₂ gels were investigated. After calcined at 500 °C, the decomposition of Si-OH in the amorphous gels accomplished. As the temperature continued rising, crystallinity of the products strengthened grdually. After calcined at 1400 °C, cristobalite was separated out from amorphous SiO₂. As sintering temperature increased, relative density, elastic modulus and hardness of SiO₂ ceramics were all increased gradually. Three-dimensional aluminosilicate fiber-reinforced silica matrix composites were fabricated by sol-gel process. Effects of sintering temperature on the density, microstructure and mechanical properties of the composites were investigated. The composites prepared at 900 °C displayed the highest mechanical properties. The average flexural strength, interlaminar shear strength and fracture toughness of those composites, with the density of 1.97 g/cm₃, were 119.7 ± 7.5 (MPa)、10.8 ± 0.7 (MPa) and 4.0 ± 0.4 (MPa.m_1/2), respectively. Moreover, as sintering temperature increased, the pullout fiber shortened gradually and eventually disappear at the composite fracture surface.

Abstract:The carbon-coated MnO/C micro-nano composites were fabricated via precipitation, followed by thermal treatment, with Mn(CHCOO)2?H2O, Ethylene glycol and Oxalic acid dehydrate as the reactants, PVP, C6H12O6 and C6H4(OH)2 as carbon. The structure, Morphology and electrochemical properties of the MnO/C materials were characterized with X-ray diffraction, scanning electro microscope, transmission electro microscope and electrochemical experiments. The results indicate that the MnO/C composite with a 3nm carbon-coated layer may be a good anode material for lithium-ion battery. It shows an excellent cycling stability of 586.1mAh/g after 50 cycles and excellent structural stability after several high-current charge and discharge courses.

Abstract:The influence of different extrusion ratios and extrusion temperatures(Holder temperature) on grain size and mechanical properties of AZ63M magnesium alloy were investigated and then the optimal aging treatment parameters and heat processing parameters of as-extruded AZ63M were studied. The extrusion experiments were undertaken with extrusion ratio of 9, 32, 41, 81 and extrusion temperature of 200℃, 250℃, 300℃. T5 and T6 heat treatment were used to develop mechanical properties and the heat processing map were depicted at temperature ranging from 300℃ to 450℃ with strain rate from 5×10-2s-1 to 5×10-4s-1. The results reveal that with the decreasing extrusion temperature from 300℃ to 200℃, the grain size decreased from 31μm to 14μm, the ultimate tensile strength and the elongation increased from 277MPa to 368MPa, 13.6% to 17.3% respectively. With the increasing extrusion ratio from 9 to 81, the average grain size refined from 24μm to 8μm, the UTS and the elongation increased from 277MPa to 376MPa was 376MPa, from 15.3% to 16.1% respectively. Subjected to T6 treatment, the UTS of as-extruded AZ63M increased by 18%, up to 390MPa and the elongation decreased by 6% compared with the as-extruded alloy (extrusion ratio: 32, extrusion temperature: 250℃) and the optimum heat processing parameters of as-extruded AZ63M were at temperature 400℃～450℃ and strain rate 5×10_-4 s_-1～1.5×10_-3s_-1.

Abstract:Zn1-xCoxAl2O4 (x=0, 0.20, 0.40 and 0.60) nanocrystals were successfully prepared via hydrothermal method using CTAB as surface active agent. The crystal structure, morphology, chemical composition, valence state and optical properties of the sample were investigated. The experimental results show that the samples are single phase spinel structure with good crystallization. According to the XRD data, the value of the crystal cell parameters, lattice spacing dhkl and grain size D were calculated, which show the decrease trend with the increase of doping concentration of Co ions. The XPS result clearly shows that the Co ions mainly occupied the tetrahedral site and a small amount of Co ions occupied octahedral center position. With the increasing of Co ions concentration, the ultraviolet absorption intensity is gradually increased.

Abstract:The effects of single-stage homogenization technology without pre-precipitation treatment and two-stage homogenization technology treatment with pre-precipitation treatment on microstructure and mechanical properties of Al-4.3Zn-1.7Mg (wt.%) alloy ingot casting and plate were investigated contrastively by optical microscopy (OM), scanning electron microcopy (SEM), transmission electron microcopy (TEM) and uniaxial tension(TS) test. The results show that the trace elements Mn, Cr and Zr recombined in the alloy after semicontinuous casting quenching are retained in the matrix in the form of solid solution,and the pre-precipitated phase particle Al₆Mn、Al₇Cr and Al₃Zr are precipitated in the process of homogenization treatment for supersaturation solid solution. The pre-precipitated phase in the matrix is big and there is uneven distribution under the conditions of 470°C×24h single-stage homogenization technology without pre-precipitation treatment. The precipitation behavior of the precipitated phase can be improved significantly in the process of homogenization by the low temperature pre-precipitation treatment. The fine pre-precipitated phase with dispersion distribution is obtained, meanwhile, non-equilibrium eutectic organization of grain boundary also can be eliminated. The best homogenization effect can be achieved for alloy ingot casting. The precipitated phase particles has good thermal stability, and it cannot be markly coarsened in the process of hot rolling and subsequent solid solution aging heat treatment. So the migration of grain boundary and dislocation movement can be inhibited significantly, and the performance of alloy plate can be improved.

Abstract:By adding SiC micro-particles with different sizes to the electrolyte, micro-arc oxidation (MAO) technique was employed to fabricate oxide ceramic layer of Ti-6Al-4V alloys reinforced by SiC micro-particles. Scanning electron microscope, X-ray diffractometer and ball-on-disk sliding tester were used to analyze surface topography, phase composition and tribological properties of the prepared samples, respectively. The result showed that SiC micro-particles have significant effects on the surface topography and tribological properties of the reinforced layer. SiC particles with smaller sizes would reduce the porosity and improve the density and tribological property of Ti-6Al-4V alloys dramatically, especially for SiC particles with the diameter of 1~2μm. By contrast, larger SiC particle can not go through the pores in the oxide layer for its larger size, so that the wear resistance property of the oxidation layer was improved slightly.

Abstract:Solidification microstructure and properties of aluminum alloy impeller produced by centrifugal counter-gravity casting has been investigated. For comparison, vacuum suction casting has also been used. Applying centrifugal force during centrifugal counter-gravity casting was found to have a significant effect on α-Al dendrites, which was fragmented into smaller spherical particles. Furthermore, applying centrifugal force at the early stage of centrifugal counter-gravity casting also improves the filling and feeding capacity during solidification and thereby reduces the formation of defects such as shrinkage porosity and shrinkage cavity. This investigation demonstrates that centrifugal counter-gravity casting is very promising to produce high quality complex thin-walled castings.