Abstract:Nickel ferrite and related materials have recently received considerable attention as potential anode in lithium-ion batteries for their high theoretical specific capacities. To overcome the problem of low intrinsic electronic conductivity and large volume expansion during the Li insertion/extraction process, in this work, nano-NiFe₂O₄ pinning on the surface of the graphite composite is prepared by hydrothermal method. As the superior anode material, the as-obtained nano-NiFe₂O₄/graphite composite demonstrates high capacity and excellent cycle stability. An initial specific discharge capacity of approximately 1478 mAh g_-1 and a reversible specific capacity of approximately 1109 mAh g_-1 after 50 cycles at a current density of 100 mA g_-1 are reached. When the charging current is increased to 1000 mA g_-1, it also delivers a charge capacity of 750 mAh g_-1. The excellent performances are attributed to the special structure of NiFe₂O₄ nanoparticles pinning on the surface of the graphite, especially the enhanced electronic conductivity and area specific capacitance during the cycling process.

Abstract:The performance of the cathode always has a close relationship with the electro-deoxidation process and its current efficiency. In this paper, the effect of sintering temperature on the electrical resistivity of an ilmenite concentrate cathode was measured. The results showed that the sintering temperature had a significant effect on the electrical conductivity of the cathode. The electrical resistivity of ilmenite concentrate cathode decreased with increasing of the sintering temperature and increasing of the contact area. Besides, the influence of the cathode porosity on electrochemical process during preparation of Ti-Fe alloy in molten salt was studied. The results also revealed that the porosity of ilmenite concentrate cathode had a direct effect on the reduction process. The increasing of porosity was beneficial to the formation of intermediate product (CaTiO3) and improvement of the current efficiency.

Abstract:12% Cr alloy based on iron is usually used for advanced electric rotor shaft which requires very good mechanical property and fine inclusions, as the large-sized inclusions in the alloy usually can cause performance deterioration. In this work, quenching process was adopted after slow cooling experiment in order to retain the inclusions precipitated during melt cooling and solidification of 12% Cr alloy. The morphology and the composition of the inclusions were detected by scanning electronic microscopy (SEM) and energy dispersive spectrometry (EDS), respectively. The results show that except various shapes of oxide, typical TiN inclusion is found in the sample. However, there is no Ti added in metallurgical process. Thermodynamic calculation was executed to interpret the inclusion precipitation during solidification and the calculation results indicate that TiN inclusion precipitates at the terminal stage of solidification. Even a trace amount of Ti drawn from raw materials would induce the precipitation of TiN, which would grow into large size and be harmful to alloy property, while the formation of Al₂O₃ inclusion occurred in liquid alloy. Suggestions for the control of Ti and O are given based on the calculation results, which would be helpful to the production of 12% alloy. The precipitation potential of Ti₂O₃ inclusion in the experiment has also been discussed by studying the competition of element concentration between Ti and Al.

Abstract:NiCrAlY coating was deposited on 3Cr13 stainless steel substrates by arc ion plating technique. This paper is to explore the feasibility of using NiCrAlY coating for the damping application and characterize the method that may be used in defining the vibration features of the coatings. The phases of the NiCrAlY coating were determined by X-ray diffraction (XRD) technique. The surface morphology and chemical composition of the NiCrAlY coating were analyzed by scanning electron microscope (SEM) and Energy Dispersive Spectrometer (EDS), respectively. The damping properties were characterized by DMA and sine sweeps. The damping properties of the substrate were considerably improved by the NiCrAlY coating.

Abstract:Ti/Al/Ti laminates were prepared by explosive cladding method. Then hot pressing was employed to further process the laminates. The results indicated that both linear and wavy bonding interfaces coexisted and element diffusion occurred in the interfacial zone between the titanium and aluminum layers after explosive cladding. After 25 h heat treatment and 2.5 h hot pressing, the aluminum layer was consumed completely. The reaction layer consisted of Al₃Ti and Ti₂Al₅ phase.

Abstract:High velocity oxy-fuel (HVOF) spray technique has been utilized to fabricate WC-17Co cermet coatings. To achieve a high performance of mechanical properties and abrasive wear resistance, four types of WC-17Co powders with different feedstock particle size were investigated. The results show that the feedstock powder with finer particle size had higher velocity and temperature during spraying process, resulting in a denser coating and a stronger splat-splat bonding. It was found that the micro-hardness of WC-17Co coating increased with the decreasing of feedstock size. The coating deposited by finer feedstock powder had superior abrasive wear resistance, attributing to the smaller porosity and boundary flaws on coating. However, coating fracture toughness could be affected by feedstock size if it is too small. Among all those investigated, the one with medium particle size and narrow size distribution exhibited both excellent mechanical properties and wear resistance.

Abstract:A ceramic coating was formed on AZ91D magnesium alloy by micro arc oxidation technology in aqueous solution containing silicate and phosphate. The phase compositions, surface, cross-sectional and wear track morphologies of coatings were analyzed by XRD, SEM and Laser Scanning Confocal Microscope (LSCM) respectively. Using the UMT-3 High Temperature Tribometer to study the friction and wear behaviors of coatings within 150 ℃. The results showed that the coatings’ mean friction coefficient firstly increased with temperature, when ambient temperature exceed 100 ℃ it began to reduce. While the coatings’ wear rate was much lower than that of magnesium alloy substrate and it reduced as temperature went up. The results indicated that micro arc oxidation coating had excellent wear resistance particularly at high temperature. Through the analysis of grinding cracks’ micro-structure at the load of 2N, the main wear mechanism of these coatings at different temperatures was all abrasive wear.

Abstract:An important concern in forming is whether the desired deformation can be accomplished without cracking or fracture of the work material. In this research, based on the cracking specimens obtained from hot compression experiment, the fracture behavior of as-cast highly β stabilized Ti40 alloy was investigated at the deformation temperatures of 1123-1373K, strain rates of 0.01-10s-1 and height reduction of 70%. The main fracture modes consisted of 45o shear fracture and longitudinal cracking occurred on free-surface, as well as inner cracking occurred at the triple boundary junctions. Moreover, the influence of deformation parameters on fracture mechanism was analyzed emphatically in terms of SEM. At low temperature of 1123K the transgranular cleavage brittle fracture was observed, at 1273K the ductile fracture occurs, at high temperature of 1373K a large number of small dimples on the fracture interface are examined. Furthermore, the effect of strain rate on the fracture behavior of as-cast Ti40 alloy is significant. At 0.01s-1, the fracture did not occur. At the strain rates of 0.1 and 1s-1, the fracture surface is covered with a large amount of dimples indicating that the fracture mode is ductile fracture, while at high strain rate of 10s-1, the fracture surface appears brittle fracture feature. Finally, the damage mechanism and fracture reason were discussed and fracture principle diagram was drawn for the as-cast Ti40 titanium alloy.

Abstract:The hydrostatic extrusion process of magnesium alloy AZ80 tube with different mandrel angles (90°,120°,150°) was simulated by the DEFORM-3D software with different extrusion speeds and initial billet temperature. The simulated results show that the peak load of the extrusion process with big mandrel angle is obviously higher than that of the small angle and the inhomogeneity of billet velocity field is intensified with the increase of the mandrel angle.

Abstract:Metal nitride hard coatings, such as TiN and TiAlN, were widely used to protect materials because of their higher hardness and wearing properties. However, these coatings always contain a high degree of internal stress which could arouse adhesion problems. It’s hard to synthesize monolayer TiN or TiAlN coatings thicker than 10μm by PVD method. The multilayer composite structure, offering an efficient way of controlling residual stress, is an effective way to synthesize thicker hard coatings. In this study, a series of multilayer composite Ti/TiN coatings with different composite periods were synthesized by plasma enhanced ion plating and how the multilayered structure affects the coating’s mechanical properties was studied in detail. The result shows that the coating’s mechanical properties are strengthened as increasing the periods of composite Ti/TiN layer. The micro hardness can reach to about 2750HV0.25 albeit possessing better toughness and higher thickness (i.e.>50?m). The coating’s toughness is almost direct proportional to hardness. And also the coating’s tribological performance is improved with a lower dry friction coefficient (about 0.35) and higher wearing resistance by alternating 48 periods of Ti/TiN layer. However, the coating’s bonding strength is weakened as increasing the period of Ti/TiN layer blindly due to the weak interface of coating and substrate.

Abstract:Titanium-zirconium-molybdenum (TZM) alloy and rare earth lanthanum doped La-TZM alloy were fabricated using powder metallurgy and rolling technique. Their electrochemical corrosion behavior was studied quantitatively using potentiodynamic polarization, scanning electron microscope and energy spectrum techniques. The corrosion behavior of the TZM alloy and doped La-TZM alloy was investigated in neutral, acidic and alkaline medium, while keeping the Cl- concentrations invariant. The results show that the corrosion resistance of the tested TZM alloy is better than that of the La-TZM alloy in neutral and alkaline media, while in an acidic medium, the La-TZM alloy is better. It was also found that the alloys are more corrosion-resistant in an acidic medium than in a neutral medium, and are the least corrosion-resistant in an alkaline medium. Finally, we found that Cl- effectively destroys the corrosion formed on the surface passivation film, OH- and Cl- double erosion promoted these two types of alloy intergranular corrosion increased.

Abstract:The Pd/Al2O3 close-coupled catalysts supported on modified alumina were prepared by the impregnation method, and characterized by means of H2-temperature programmed reduction (H2-TPR), CO chemisorption, and X-ray photoelectron spectroscopy (XPS). Both total catalytic activity and single reactions in related to C3H8 conversion were tested in simulated exhaust gas. The results show that the amount of active PdOx decreases and negative metallic Pd0 generates during aging treatment. The light-off temperature (T50) and complete conversion temperature (T90) increase by 76 oC and 64 oC after aging treatment, signifying that the low-temperature activity decreases more obviously than high temperature property. The results of comparison among single reactions indicate that the light-off activity of reactions which occur in atmosphere with the participation of NO but without H2O injection decrease dramatically after the aging treatment. The inhibitive effect of NO on light-off activity and the positive effect of H2O on high temperature property become obviously during the aging treatment.

Abstract:Annealing behavior of AlCoCrFeNiTi0.5 high entropy alloy coatings prepared by laser cladding was investigated in this paper. The specimens were annealed at 900℃ for five hours. The microstructure and wear resistance property of the as-annealed and as-cast specimens were investigated in this study. The XRD results indicated that the as-annealed AlCoCrFeNiTi0.5 high entropy alloy coating was composed of Al80Cr13Co7, Co3Ti, and AlFe solid solution phase. The SEM results and EDS data showed that a typical spinodal decomposition structure with uniform composition formed after annealing treatment. The average Vickers micro-hardness of the as-annealed coatings could reach 989HV0.5 which was increased about 73.5% compared with that of the as-cast coatings. The abrasion resistance testing showed that the abrasion loss of the as-annealed coatings was reduced about 92.5% and the wear width was reduced about 50% compared with the values of as-cast coatings.

Abstract:WO3 nanoplates are synthesized by a hydrothermal method. Morphology and structure of the WO3 nanoplates are analyzed by SEM and XRD. Gas sensing properties of the as-prepared WO3 sensor are investigated by a static gas-sensing system. The results show the WO3 nanoplates demonstrate good crystallinity with mean edge length of 200-300 nm and wall thickness of about 50 nm. The optimal operating temperature of the WO3 sensors is 300?C. At this operating temperature, the WO3 sensor exhibits ultra-fast response (2-4 s) and fast recovery time (4-16 s) for ethanol detection, and high selectivity to other gases such as methanol, benzene, dichloromethane and hexane, which indicates its excellent potential application as a gas sensor for ethanol detection.

Abstract:The effects of withdrawal rate on the microstructure and segregation behavior of a nickel-base single crystal superalloy were investigated. The results indicate that, by increasing the withdrawal rate, the primary dendrite arm spacing (λ₁), the secondary dendrite arm spacing (λ₂) and the size of γ" precipitates decrease gradually. Moreover, the shape of γ" precipitates is more regular at higher withdraw velocities. Also, the size of γ/γ" eutectic are smaller while the total volume fraction increased. Considering the composition segregation is determined by diffusion time of the constituent elements, when withdrawal rate was elevated, diffusion time of solutes decreased, the effects of segregation were raised.

Abstract:Cu-Al₂O₃ composite sheets were prepared by the internal oxidation of Cu-0.50 wt.%Al alloy sheets at 900 ℃ for 25 hours. Enrichment extraction method was used to extract Al₂O₃ phase in Cu-Al₂O₃ composites. The type, distribution, relationship with the Cu substrate interface of Al₂O₃ phase in the Cu-Al₂O₃ sheets were studied by TEM. The extracted powder was studied by X-ray diffraction (XRD) and TEM. The results show that theSprecipitated phases of Cu-Al₂O₃ composites by the internal oxidation of Cu-Al alloy sheets are mainly γ-Al₂O₃, and a few of α-Al₂O₃ and θ-Al₂O₃ were precipitated. The Al₂O₃ particles wereSdistributedSin theSCu matrix and completely coherent with the Cu matrix. From the surface to the deep of 0.5 mm,the size of Al₂O₃ particles is reduced from 14 to 5 nm and the spacing of Al₂O₃ particles is reduced from 10 to 15 nm.

Abstract:In this paper, AA5083-H112 aluminium alloy and T2 pure copper were LFW welded with no obvious defect under different forging pressures. The microstructure and mechanical properties were investigated by SEM, hardness and tensile tests. The results showed that “friction effect” would increase with the decrease of the forging pressure so that more Cu particles infiltrated into the Al base metal, while with the increase of the forging pressure, the tensile property dropped significantly because rising of the forging pressure could supply more heat input so that layered Al₂CuMg phase came out which was harmful to the tensile strength of the welds.

Abstract:In order to research the effects of Al₂O₃ micro powder additive amount on characteristics of micro-arc oxidation coating formed on AZ31A magnesium alloy, it was treated by using micro-arc oxidation in different concentration of Al₂O₃ micro powder electrolyte. Surface morphologies, Ca, Mg, O and Al elements distribution, phase composition of micro-arc oxidation coating were analyzed by SEM, EDS and XRD. Thickness and hardness of micro-arc oxidation coating and surface charge of Al₂O₃ micro powder in electrolyte were measured. The doping modification mechanism was discussed in this paper. The results show that the oxidation voltage was raised firstly and then declined gradually while Al₂O₃ micro powder amount increasing. The numbers and sizes of hole and distribution of Ca element on oxidation coating surface and formation efficiency decreased, compactness of coating, and the hardness of surface porosity coating increased. Oxidation coating was mainly composed by MgO and MgO₄ phase.

Abstract:The atmospheric heat dispersion of magnesium alloys AZ80、AZ31、ZK60 and aluminum alloys AA6082 were measured. It was apparently that the thermal dispersion curves of the columnar model can be exponential fitted as T=T0+ΔT0·exp(-t/A0). The result shows that the solution treatment can make the thermal conductivity of the magnesium alloys decrease. However, the solutionizing plus aging treatment can make the thermal conductivity increase. The relationship between ΔT/T and the heat dispersion rate was also studied. The heat dispersion rate of high columns (60mm) is about two times that of low columns (20mm) in the condition of forced air convection, while there is no obvious difference in the condition of natural convection. Moreover, the dispersion properties of these alloys can be evidently dived into two regions by ΔT/T in natural convection. There was no much difference among AZ80、AZ31、AA6082 alloys when 0.05<ΔT/T<0.25 (20~120℃), while the AZ80 and AZ31 exhibited more preferential performance than AA6082 alloys when 0.25<ΔT/T<0.45 (120~220℃).

Abstract:In this paper, a near beta titanium alloys reinforced with different weight fraction of SiCp were prepared by vacuum induction melting technology.The addition of SiCp was 0wt.%,0.1 wt.%,0.4wt.%,1.0wt.% respectively. Effect of SiCp addition on microstructure and mechanical properties of near beta titanium alloys was systematically investigated by XRD,SEM ,Vicker’s micro- hardness tester and Instron universal testing machine.The XRD patterns of the composite materials were α-Ti,β-Ti and TiC phase.The addition of SiCp refined prior β grain size obviously and the grain size in the alloy decreased from 639 to 323 μm with the addition of SiCp range from 0 to 1wt.%.Moreover, the Vicker hardness and compression strength were higher but worse plasticity compared with unreinforced titanium alloy. These composites utilize the strengthening effects of both particulate reinforcements of TiC and Si elements through solid solution hardening, fine grain hardening.

Abstract:The very-high-cycle fatigue test and fatigue reliability life for Ti-6Al-4V were investigated based on the self-bulit ultrasonic fatigue test system and MTS fatigue system at both 20KHz and 20Hz. Fracture morphology of the specimen was analysed with scanning electron microscopy. The distribution of fatigue life was determined. Single side allowance factor was proposed to calculate the reliability fatigue life with both reliability and confidence level. The results indicated that fatigue life continuous increases with the decrease of the stress amplitude and there is no fatigue limit in the very high cycle regime. The specimens fracture from defects at specimen surface at short fatigue life region and the location of crack initiation tends to subsurface with the fatigue life increase. The specimen fracture surface tested at 20KHz is smooth than that of 20Hz and dark rough aeras are observed around the dark facet. The fatigue data tested at different frequency corresponds with each other which imply that distinct frequency effect is not found on the ultra-high fatigue properties of Ti-6Al-4V. Reliability fatigue life reduces more when the reliability increases than when confidence level does to the same degree. A new fatigue model (p-γ-S-N curve) is also established to predict the reliability fatigue life.

Abstract:Anodic oxide films on TA2 commercially pure titanium surface were prepared with sodium tartrate environmental solution by potentiostatic method at the concentrations of 1, 5, 15, 30 and 50 g/L. The microstructure of the films was analyzed by atomic force microscope, the Tafel polarization curves and electrochemical impedance spectra of the samples at low potential of 3.5% NaCl were analyzed by electrochemical workstation, and the influence of microstructure on corrosion resistance wsa discussed. The results show that when the concentration is about 15 g/L, the oxide film has a good micro morphology, broad passivation area, maximum polarization resistance value, smaller passivation current and self corrosion current, is the best process conditions.

Abstract:High strength and high conductivity Cu-Nb microcomoposites were fabricated by Accumulative Bundling and Drawing (ABD) process. The microstructure of composite and interface diffusion were observed during the four times compositing process by SEM and EDS. Crystal orientation evolution of Nb filaments and Cu matrix were characterized by XRD at extrusion and drawing conditions of different compositing process. The interface structure and crystal orientation were analyzed by HRTEM and IFFT. It is shown that the diffusion between Cu/Nb interfaces had taken place during the 3rd compositing. The texture of Nb fibers is <110> orientation while for Cu matrix is <111> orientation after the severe plastic deformation. And atomic planes (111)Cu are parallel to that of (110)Nb with a angular deviation of 18.7?, which means that a crystal mismatch dislocation appears at interval of every six Cu (111) crystal planes.

Abstract:Graphene-based LaF₃ (GN/LaF₃)nanocomposite materials were prepared by the melthod of Liquid-phase Ultrasonic Exfoliation. The morphologies of GN/LaF₃nanocomposite materials were charactered by means of SEM, TEM. Its tribological properties as water additive were investigated using an multi-functional reciprocating friction and wear tester. The lubrication mechanism was discussed based on the results of analysises of SEM, XPS. The results showed that the LaF₃nanoparticles, at the size of 5-50nm, were densely and randomly deposited on the surface of multilayer graphene sheets. The GN/LaF₃nanocomposite materials express good friction-reducing and antiwear performance. Compared with pure water, it can reduce the friction coefficient at 34.35% and the wear mass fall at 52.40% with the load 10N and concentration 0.01wt%. The prosperity is attributed to the effection of the adsorption membrane and tribochemistry reaction films which inhibit the oxidation of Fe and reduce the wear.

Abstract:Modified titanium materials, including TiO₂ and TiO₂-HA bioceramic coatings, were prepared by micro-arc oxidation and micro-arc oxidation-hydro-thermal methods. Determination of the hemocompatibility of the coatings through a hemolysis experiment, dynamic clotting time test, and platelet adhesion experiment was also performed. The results demonstrated that: Hemolysis rates of all samples were less than 5%, no hemolysis was observed. Compared with titanium and TiO₂ bioceramic coating of titanium, TiO₂-HA bioceramic coating of titanium exhibited lower hemolysis rate, slower change in dynamic clotting time and less platelet adherence. The proposed TiO₂-HA bioceramic coating further showed a lower degree of deformation, better inhibition of platelet aggregation and deformation, and excellent hemocompatibility.

Abstract:La_0.6Pr_0.4Fe_11.4Si_1.6B_0.2 alloy of kilogram grade was produced by induction melting method with industrial raw materials, then the annealed alloy was hydrogenated to increase its Curie temperature to around room temperature. The microstructure of the alloy was examined after annealing at 1373-1473 K for different times. The Curie temperature of the alloy annealed at 1473 K for 30 h is 202 K and the maximum magnetic entropy changes are 8.1-8.6 J/kg.K under a magnetic change of 1.5 T. The Curie temperature of the alloy was increased to 320 K by hydrogenating at 553 K and 0.13 MPa H₂ pressure for 5 h, and the maximum magnetic entropy changes of 7.7-8.0 J/kg.K were also obtained.

Abstract:In this paper,the effect of RE elements on microstructure of Al-10Sr master alloy and the application in Al-20Si alloy casting was investigated. The experimental results revealed that: 1) the microstructure of Al-10Sr master alloy mainly containedα(Al) matrix and Al₄Sr phase; 2) The morphology of the Al₄Sr phase on Al-10Sr master alloy changed from acicular shape to small blocks with the addition of RE to 4.0wt %; 3) The grain size of primary silicon on Al-20Si alloy was refined into a range of 13.81-37.61μm, and the average grain size was 24.58μm with a homogeneous distribution during modification by using the Al-10Sr-4RE master alloy; 4) It was found that after adding RE, the Al₄Sr phase distribution became more homogeneous, and it exhibited better modification effect on Al-20Si alloy.

Abstract:In order to explore the transport and coupling properties of multiferroic interfaces, a multiferroic/paramagnetic-composition thin film was investigated by successively growing La2/3Sr1/3MnO3 (LSMO) and BiFeO3 (BFO) multilayer-structure. Laser molecular beam epitaxy (LMBE) method was employed to prepare an idea structure of the composition thin film. Analysis of the leakage current demonstrates that the space-charge-limited current dominates the leakage current mechanism. Magnetic measurements show that the ferromagnetism of the composition thin film originates from BFO layer and the net magnetic moments could be responsible for the enhanced magnetoelectric coupling. The interface exhibits robust magnetodielectric effects at temperature points of 160K and 170K for zero field cooling (ZFC) and field cooling (FC), respectively. Furthermore, there exists a split in the loss tangent-temperature curves over temperature range of 150-170K between different cooling conditions, which is related to phase transition in the BFO layer.

Abstract:Abstract: Hot compression tests were conducted on TC4 titanium alloy at different temperatures in a range of 800-950℃ and at different strain rates in the range of 0.001-10s-1. Flow softening behavior of this alloy was investigated. The flow softening degree increased with increasing strain rate and decreasing temperature. Meanwhile, softening was mainly attributed to flow instability at temperatures of 800℃and 850℃, strain rates of 1 s?1 and 10 s?1. Conversly, softening was dominated by globularization of lamellar alpha at temperatures of 900℃and 950℃, strain rates of 0.001 s?1 , 0.01 s?1 and 0.1 s?1. In addition, the effect of strain was incorporated in the Arrhenius equation by considering the effects of strain on material constants including α、n、A and Q. The calculated flow stresses were compared with the experimental results. Results show that this model gives a precise estimate for the flow stress, especially at 800-850℃and 10s-1, 900-950℃ and 0.1s-1. The average deformation activation energy is about 403kJ/mol and the average strain rate sensitivity exponent of TC4 alloy is 0.26.

Abstract:The high-cycle fatigue properties and crack initiation and propagation behavior of 2397-T87 Al-Li alloy were investigated. The results show that when the stress ratio R is 0.1, the fatigue limit of smooth specimens of 2397-T87 Al-Li alloy in the L orientation, LT orientation and ST orientation are about 192 MPa, 243 MPa and 151 MPa respectively. The fatigue limit of notch specimens in the L orientation, LT orientation and ST orientation are about 72 MPa, 78 MPa and 70 MPa respectively. Fatigue crack initiation of this alloy mainly occurred on the sample surface, with initiation from the defects caused by the oxides and inclusions, the Al(CuMnFe) secondary phases. Persistent slip bands (PSB) and grain orientation have important influence on fatigue crack propagation at early stage.

Abstract:A numerical model of flow and heat transfer for micro-droplet deposition forming was established on 7075 aluminum alloy by adopting semi-implicit pressure-linked equation algorithm (SIMPLE), and the volume of fluid (VOF) method with Piecewise Linear Interface Construction (PLIC) was employed to reconstruct the free surface. The influence of process parameters including impacting velocity, relative distances between two successive molten droplets, the temperature of the substrate and droplet size on end-shapes morphology is simulated during fabricating 7075 aluminum alloy by micro-droplets, and the numerical models are validated with experimental results. The results show that the determination of reasonable impact velocity and droplet relative distances is the key to obtain a good precision and quality, and under the condition of 100μm diameter molten 7075 aluminum alloy droplet on a stainless steel surface at temperature 350K with velocity 1.5m/s, the distance between two successive droplets is 200μm, can obtain better forming effect. The simulation results agree well with the experimental results, better reflects the actual process of droplet impacting, spreading and solidification behavior, provides a reference for the practical application of the process.

Abstract:A 3D thermal elastic-plastic finite element model was developed to predict welding residual stresses induced by full-penetration electron beam welding of Ti2AlNb alloy. Rotary-Gauss body heat source model was modified and improved to reflect the full-penetration weld. The results showed that the cross section profiles of the weld seam simulated with the modified heat source model agreed well with the experimental results. The residual stress distribution also had a good agreement between the numerical and experimental results, which proved the validity of the finite element model. The longitudinal tensile stresses played a major role in the welded joint of Ti2AlNb alloy and the region of residual stresses distribution was very narrow that extended a distance 3 mm away from the weld centerline. Compressive transverse stress was observed on the top and bottom surfaces while tensile transverse stress at the center of the weld, and the discrepancy was ascribed to the longitudinal and normal contracting of the weld. In addition, the phenomenon of local three dimensions residual tensile stresses appeared in the plate center.

Abstract:The PEO ceramic coatings included ZrO₂-Al₂O₃-SiO₂ three phases were prepared on Al-12.5%Si alloy in the electrolyte solutions containing ZrO₂ nano-particles.The microstructures and phases of the coatings were analysed by SEM and XRD,and the heat insulation performances and the thermal shock resistances were also investigated.The results show that the ZrO₂ nano-particles can increase the density and binding performance of the coatings significantly,and effectivly weaken the inhibition of Si element on PEO process and then improve the growth rate of PEO coatings; the PEO ceramic coatings included three phases are mainly composed of SiO₂ and steady phases such asα-Al₂O₃ and c-ZrO₂,and it is the special microstructure and composition makes the ceramic coatings formed in solutions with ZrO₂ nano-particles posses good heat insulation performances and thermal shock resistances.

Abstract:To study the effect of solder process parameters and thermal shock on Sn2.5Ag0.7Cu0.1RE0.05Ni/Cu of soldered joints, the interface intermetallic compounds and strength of the joints were observed and analyzed with the help of SEM, EDS, XRD. The results showed that adding 0.05 wt% Ni can refine the primary β-Sn phase and eutectic of the Sn2.5Ag0.7Cu0.1RE solder alloy. The maximum shear strength was 26.9MPa, which obtained from the joint under the soldering temperature of 270℃ and soldering time of 240s. The maximum shear strength increased 8.9% than Sn2.5Ag0.7Cu0.1RE/Cu joint. The interface roughness, the average thickness of the Sn2.5Ag0.7Cu0.1RE0.05Ni/Cu joint rased with the increasing of temperature and time. The shear strength of the joints increased and then decreased. The interface IMC of the solder joints irregular growth with the rasing of thermal shock cycle. At the same time, the strength of the joint was decreasing. The added 0.05 wt% Ni can inhibite the quick decrease of the reliability of soldered joint in the process of the thermal shock.

Abstract:Al-6.3Cu alloy straight wall samples were produced using AC-GTAW process. The influence of heat input, environmental atmosphere, and wire feed speed on porosity characteristics of deposition samples were investigated. It is observed that heat input is the most important factor affecting the porosity defect. Gas pore counts and its diameter can be reduced with proper heat input. With lower heat input, the gas pores can be further reduced in argon environment and lower wire feed speed. The experimental results show that, in argon environment, with travel speed of 0.30m/min and wire feed speed of 2.0m/min, the gas pores can be controlled effectively.

Abstract:Ultra-fine grained commercial purity titanium (UFG CP Ti) was fabricated by combined refining process (Equal channel angular pressing (ECAP), cold rolling and rotary swaging) at room temperature. The grain average size of UFG CP Ti was about 180 nm, and ultimate tensile strength of UFG CP Ti was over 870 MPa. The nanoindention creep tests of UFG CP Ti were carried out by the nanoindenter with the constant loading rate/load at room temperature. The creep strain rate sensitivity m was determined by using depth and micro-hardness during the holding load stage. The results show that due to the obvious grain refinement, increase of the amount and the length of grain boundaries and the dislocation multiplication, UFG CP Ti shows good resistance to creep at room temperature and its major creep mechanism is the dislocation creep. The values of indentation creep rate sensivities are independent of loading conditions, but are close related to the microstructure of the materials.

Abstract:Fabrication of TiAl strengthened Ti-based alloy by hot-pressed sintering of mixed powders of TiAl and Ti was studied at 1473 K under a pressure of 30 MPa for 1.5 h. The effects of composition ratio on the phase constitute and microstructures of hot-pressed sintering products were subsequently analyzed by XRD and SEM. Large difference exists in the phase distribution for the sintering products with different composition rations occurred. The feasibility of TiAl reinforced Ti-based alloy was confirmed with TiAl/Ti volume ratio of 7:3. Element Fe was examined to be concentrated in Ti2Al and Ti3Al. TiAl, Ti2Al(Fe), Ti3Al(Fe) and Ti-based phases were mainly formed in the sintering product. Different types of diffusion reactions occurred within the sintered body during hot-pressed sintering, finally leading to the formation of fine graded microstructures, Ti/Ti3Al(Fe)//Ti2Al(Fe)/TiAl.

Abstract:The microstructure and mechanical property of the Ti-22Al-25Nb is investigated and the effects of the forging, solution and aging temperature on the mechanical properties are introduced. As the isothermal forging temperature increases, the strength and ductility of the alloy increases at first and then decreases. When solution conducted in O+B2 region, as the solution temperature increases, the increasing B2 volume and decreasing particle are the main reason for high ductility of the alloy. When solution conducted in α2+B2+O region, the decrease of lamellar thickness is beneficial for the strength while the large B2 grain size and fine lamella are harmful for the ductility. The phase volume, morphology and size have significant influence on the mechanical properties of the alloy. A basic principle to improve the tensile property of the alloy is isothermal forging nearby the B2-transus in order to control the amount of the particle and the B2 grain size, and followed by low temperature aging to obtain fine lamella.

Abstract:Commercial pure titanium was selected to be a model material. Commercial pure titanium plates having different types of dislocation boundaries were prepared by multi-pass cold rolling. As-impacted titanium samples were obtained by the split Hopkinson pressure bar, and the evolution of dislocation boundary was characterized through transmission electron microscopy analysis. Through these, The high-speed deformation response of dislocation boundaries in commercial pure titanium was launched. It was demonstrated that the initial dislocation boundary became a major obstacle to dislocation slipping under high-speed compression at the strain rate of 1000/s. Plates distributed with geometrically necessary boundaries at the spacing of 0.5um can generate new dislocation boundaries intersected with the initial ones after high-speed deformation. When the spacing of geometrically necessary boundaries was about 0.3um, the dislocation groups formed among them. As the spacing of geometrically necessary boundaries reduced to 0.1um or below, the localized microstructure mode was bending of initial boundary and dislocation groups. There were only dislocation groups and sub-grain in the highly localized zone.

Abstract:_{: Ti-(8~20)Mo alloys from elemental powders were fabricated by powder metallurgy technique. The effects of sintering temperature and Mo content on the microstructure and mechanical properties were studied. The results show that the Ti-Mo alloys with high-density and uniform microstructure can be produce atsintering temperature range of 1400℃~1500℃. The lowest densification sinteringStemperatureSgradually increase with the rise of Mo content. Ti-(8~16)Mo alloys shows typical widmanstatten structure, whereas the Ti-20Mo alloy consists of single β grains. TheIn the range of 8%~16%,increasing Mo content can result in the decrease of β grains, and corespondingly the α lamellars become less and thinner.The as-PMed Ti-(8~20)Mo alloys obtained show good mechanical performence, and possess lower elastic modulus of 59~68 GPa.In comparison, the Ti-14Mo alloy sintered at 1450℃exhibits the superior mechanical properties with hardness of 35.7HRC, compressive strength of 2227 MPa, compression rate of 29.1%, and elastic modulus of 62.2 GPa.}

Abstract:Ti-Mo-(0~9) Fe alloys were processed by mechanical alloying and subsequent spark plasma sintering (SPS) from elemental powders, and the influences of preparation parameters on the performance of milled powders and sintered alloys were studied. The results show that at the Fe content range of 3~9wt.% titanium based alloys with high density and ultra-fine grain structure can be produced by SPS at 900℃ from the powders milled for 10h. The microstructure of the titanium alloys mainly consists of β-Ti phase matrix and FCC-Ti particles, and the average grain size is in the range of 130~490nm. It is the first time that titanium based alloys with face-centered cubic structure are produced. During mechanical alloying process, the addition of Fe element greatly improves the glass forming ability of the alloy system, and the ability and the volume fraction of amorphous phase in the powders are obviously enhanced as increasing Fe content. After high-energy ball-milling for 10h, amorphous/nanocrystalline Ti-Mo-Fe composite powders are found to exhibit favorable thermostability.

Abstract:The rhenium coatings were prepared by cold-wall chemical vapor deposition approach on the molybdenum matrix using ReCl₅ heat decomposition reaction. The effect of deposition temperature to phase composition, deposition rule, surface morphology, density and hardness were studied. The results show that all of as-parpered coatings have a strong preferential growth orientation of (002). With the increasement of deposition temperature, the deposition rate and efficiency rapidly increase. Meanwhile, the topography of CVD Re coatings change from complicated polyhedron to hexagonal pyramid. All the coatings are quite dense and the relative density can reach up to 99.9%. Vickers hardness increase with the deposition temperature and it can be up to 610.

Abstract:Ceramic phase increased NiCr-Cr3C2 coatings were prepared by HEPJet supersonic plasma spaying (SPS). The friction coefficients and wear loss for NiCr-Cr3C2 coating and Q235 steel pairs under dry and salt spray one week corrosion were measured using the UMT-3 friction and wear tester by line-contact reciprocating sliding. The morphology and element distribution of worn surfaces were examed and analyzed by using SEM, EDS respectively. The effects of salt spray corrosion environment on tribological properties of coatings were discussed. The result showed that, the wear mechanism of NiCr-Cr3C2 coatings was abrasive and adhesive wear, whereas under salt spray corrosion conditions, it became corrosion wear. The friction coefficient under salt spray corrosion conditions significantly reduced by 1/5, but the wear losses under salt spray corrosion conditions were more than that under dry friction conditions about 5 times, which demonstrates that the salt spray corrosion environment accelerated the deterioration of coating’s tribological properties and the corrosion resistance of coating remains to be further improved.

Abstract:The effects of rolling reduction and rolling velocity on microstructure and mechanical properties of AZ31 Mg sheets were investigated in this paper. The grain size was significantly refined and the mechanical properties were raised after hot rolling. When the rolling velocity was 5m/min and the rolling reduction was 50%, the average grain size was refined to 9μm, and the tensile strength, yield strength and elongation were enhanced above 280MPa, 180MPa and 30%, respectively. The relationship between grain size and yield strength was studied. Based on the literatures on AZ31 rolling and experiments in this paper, the comparisons on mechanical properties of AZ31 Mg sheets were carried out. The results reveals that the rolling parameters used in this research can significantly enhance the mechanical properties of AZ31 Mg sheets, and the anisotropy in transverse direction and rolling direction was not obvious.

Abstract:The low ionization rate of magnetron sputtering ion plating and the micron-size droplet splash of multi-arc ion plating restrict the development of ion plating technique for a long time. According to the Joule heating effect which result in that the electron goes through the defect area with a relatively higher resistance value will increase the temperature of the defect area, and the thermionic emission from the metal surface with a high temperature, a new type of micro-arc ion plating technology based on the target material escaping from the target by the ion collisions and thermal emission is established. The temperature of target surface rose rapidly by the bombardment of Ar₊ and Joule heating effect, the kinetic energy of the target electrons and atoms increased to overcome surface work function to escape from the target surface. The increasing of atoms and electrons in the plasma improved the collision ionization rate of the target atoms, and the target surface did not appear obvious arc and avoided the melt splashing of target material, therefore the target atoms of the micro-arc ion plating could obtain a high ionization rate and a high density. The results showed that the TiN film deposited by micro-arc ion plating has dense microstructure, fine surface quality, high hardness, well film adhesion and strong corrosion resistance.

Abstract:The Al2O3 reinforced 7055 aluminum matrix composite was subjected to pulsed magnetic field treatment with different induced intensity (B). The dislocation density in composites increases when the B rises from 0,1T, 3T to 5T. It is attributed to the enhancement of strain energy of dislocation and the transition from S to T for the radicals between the dislocation and pinning center. Meanwhile, the orientation tendency of intragranular precipitates is lowered, together with the increase of amount and size. For the precipitates at grain boundary, the morphology has transformed from continuous to disconnected states. The precipitation amount has been decreased while the size increased. It is highlighted that the precipitation free zone can be found. It is analyzed that the magnetic field accelerate the diffusion of solute atoms and vacancies. The increased distortion energy and internal stress facilitate the precipitating and growing process. As for the mechanical properties, the trend displays as the first rise followed by falling. When B equals to 3T, the tensile strength, elongation and micro hardness arrived at 548.04MPa, 17.235% and 122.4HV, which are increased by 10.3%, 16.2% and 20.7% separately compared to the initial sample without any magnetic field treatment. The strengthening mechanisms are attributed to the dislocation strengthening and second phase strengthening.

Abstract:The effects of substrate roughness on wettability of non-reactive wetting and compound forming wetting systems are investigated by the sessile drop technique at high temperature. The AgCu28/copper system is selected in the presented study. It is found that the existence of roughness promotes wetting and spreading significantly. With the increase of roughness (R_a), the contact angle decreases sharply first and then approaches to a constant value, while the drop base radius increase linearly with R_a. Spreading of the liquid alloy on rough surface combined two modes: on top of the rough surface and inside the capillary grooves. The wetting kinetics for both modes follow the power law relationship. The driving force of flowing on the top of the rough surface follows the basic Young’s equation, while an additional driving force of capillary force exists when flow inside the micro v-grooves, leading to a decrease in final contact angle and consequently a better wettability.

Abstract:The previous researches show that appropriate power modulation methods can increase the weld penetration and decrease the drawbacks of splatters and pores in laser welding for the high reflectivity materials such as magnesium alloy, aluminium alloy and copper alloy. This paper conducts tentative explorations to the underlying physical mechanism of this phenomenon. The sine modulated laser welding test of AZ31 is developed based on ternary quadratic regression design and the influence of average power (AP), modulation amplitude (A) and frequency (F) on welding joint cross-sectional fusion zone area (FZA) are studied. The results show: power modulation can obviously improve energy coupling in the lower AP welding process, while this improvement will be weakened and even disappeared with AP increasing. Both “Small amplitude + high frequency” and “large amplitude low frequency” can increase the cross-sectional FZA when welding in the case of lower AP. The longitudinal-sectional morphology of “stainless steel (reflectivity: 60%) Mg alloy (reflectivity: 80%) ” bimetallic specimen welded joint obtained in the sine modulated welding of 8Hz is achieved and compared, which demonstrate when power begin to decrease from the peak value, the weld depth in lower reflectivity materials 2205 is decreasing synchronously, but the decreasing moment of weld depth in high reflectivity materials AZ31 delays about 0.036s(about 30% of a sine period).The reason for this phenomenon may be that a deeper keyhole could be formed by the instantaneous peak power value, which increase the number of reflection of laser beam in keyhole. Then, in spite of the declining of transient laser power, the high aspect ratio keyhole will be maintained for about 1/3 of a sine period due to the enhanced energy coupling efficiency. It is the key point for power modulation to improve the energy coupling efficiency of high reflectivity materials that the high aspect ratio keyhole can be existed and maintained for a long time.

Abstract:Dense cerium conversion coating was prepared on the surface of Mg-9.95Li alloy by immersing Mg-9.95Li alloy in cerium nitrate solution which added H2O2 and citric acid. The chemical composition and morphologies of conversion coatings were characterized by X-ray photoelectron spectroscopy(XPS) and scanning electron microscopy(SEM). Electrochemical measurements(electrochemical impedance spectroscopy, polarization curves, open circuit potential) were used to analyze the anticorrosion properties of the conversion coatings. The results indicate that the conversion coating mainly composed of CeO2 and Ce(OH)4 cross-linked by citric acid, then make the conversion coating more dense and uniform. The dense cerium conversion coatings have better anticorrosion properties to Mg-9.95Li alloy. The electrochemical impedance was reached 104 Ω?cm2, and the corrosion current density was only 8.86×10-6 A?cm-2, which reduce two orders than that of Mg-9.95Li alloy.

Abstract:Since the discovery of superconductivity at 39 K in MgB₂, it has been considered as one of the most promising candidates for engineering applications due to its low material cost and relativity high critical transition temperature. However, the realization of large-scale application for MgB₂ based superconducting technology essentially relies on the improvement of superconducting properties of MgB₂. Some techniques have been developed to improve the critical current density, such as chemical doping, high-energy ball milling and various processing techniques. We introduce some research progress of MgB₂ superconducting materials prepared by high-energy ball milling. The investigation showed high-energy ball milling is effective to obtain high density and fine grain size MgB₂with high J_c performance. We also introduce that high J_c MgB₂ was synthesized by two-step reaction method and high-energy ball milling. High-energy ball milling may be a good choice for reducing the void percentage and enhancing the average density in MgB₂ long wires.