Abstract:Cu-Nb alloys with Nb concentration ranging from 0-30wt% were prepared by mechanical alloying (MA) at room temperature. The effects of Nb content on the crystalline refinement process and mechanical property of the immiscible Cu-Nb system have been investigated by X-ray diffraction, scanning electron microscopy with energy-dispersive X-ray detection, optical microscopy, transmission electron microscopy and microhardness measurement. It is found that the completed dissolution of Nb in Cu can be achieved in the samples with Nb content less than ~11wt% after 100 h milling, although the equilibrium solubility level is nearly zero. The grain size refinement capability of MA-ed Cu-Nb powders enhances with increasing Nb content up to 30wt%. This is because the susceptibility to recovery process becomes reduced, when the amount of Nb solutes segregated into the dislocation of Cu phase is increased. For the 100 h milled Cu-30wt%Nb powders, the average Cu grain size is only ~6nm. The microhardness of the samples shows an enhancement with increasing Nb concentration. The main strengthening mechanisms of the MA-ed Cu-Nb alloys are linked to the grain size reduction and the dissolution of Nb into Cu matrix.

Abstract:In this work, the penetration process of Ti-Al3Ti metal-intermetallic laminate composites impacted by a projectile was numerically investigated. The ballistic performance, stress distribution, failure and energy absorbing mechanisms of Ti-Al3Ti metal-intermetallic laminate composites under high-speed impact were examined in detail. The results shown that Ti-Al3Ti metal-intermetallic laminate composites under high-speed impact was mostly under tensile stress, since the compressive wave was reflected back as a tensile wave. During projectile penetration, transverse, inclined, and vertical cracks formed in the Al3Ti phase, which can dramatically absorb the kinetic energy of projectile.

Abstract:The stray grain was observed in electron beam welded (EBW) joint of single crystal molybdenum (Mo). Finite element (FE) method, combining the theoretical analysis, is used for evaluating the stray grain formation. Temperature-dependent thermal properties of molybdenum are incorporated in the model and a 3D volumetric moving double-ellipsoid heat source is applied. The relationship between parameter Φ, describing the degree of stray grain formation, and the thermal gradient G and the growth velocity V is used. Temperature and thermal gradient data of the model are extracted from simulation results under different operating conditions, and Φ is calculated. The effects of the welding parameters, including welding power Q and welding speed S on the formation of the weld stray grain are obtained.

Abstract:Ultrafine W-20wt.%Cu(W-20Cu) powders doped with 0-0.8 wt.% rare earth oxides Ce_0.8Sm_0.2O_1.9, (SDC) were synthesized by the EDTA-citrate method using ammonium meta-tungstate and copper nitrate as raw materials, and the resultant powders were pressed and sintered at 1250°C in H₂ atmosphere for 2h to obtain SDC/W-20Cu composites. Morphology of the SDC/W-20Cu powders and microstructure of the sintered SDC/W-20Cu composites were observed by SEM, and density, physical and mechanical property of sintered SDC/W-20Cu composites were also tested to investigate the influence of rare earth addition. The results show that the SDC/W-20Cu powders have irregular shape with particle size ranging from 100 to 200 nm. The addition of SDC has slight influence on the electrical conductivity, but obviously refines the grain size and improves the mechanical properties of the W-20Cu composites. The sintered SDC/W-20Cu samples have relative density above 97%. Bending strength and micro-hardness of the SDC/W-20Cu specimens are 1128MPa and 318HV with the addition of 0.6wt.% SDC, respectively, and the highest tensile strength reaches 580MPa and 258MPa at room temperature and 600°C, respectively..

Abstract:The evolution of microstructure in Al-Mn alloy with a low ratio of Fe/Si produced by twin-roll casting (TRC) during various homogenization treatments has been investigated. The grain structure near the surface transforms from fibrous to coarse elongated recrystallized grain structure during homogenization at 550℃ for 4h. The grain in the interior tends to be equiaxed with the temperature. The primary particles are broken up after homogenization at 450℃ and 500℃ for 4h, respectively, and coarsened when temperature increases to 550℃. The evolution of dispersoids is controlled by nucleation and growth mechanisms at 450℃ and 500℃ for 4h, respectively, whereas the coarsening and dissolution are predominant mechanisms during homogenization at 550℃ for 4h. Many small size Zr-bearing dispersoids are obtained during homogenization at 500℃ for 4h.

Abstract:A nano-crystal layer of weld joints surface was generated after the UIT (Ultrasonic impact treatment) and A-UIT (Aging and ultrasonic impact compound treatment) treating 7A52 aluminum alloy welded joints. Results indicate that the grain size of weld joints is finer and the surface hardness of the weld joints increases more significantly after A-UIT. Compared with the UIT, which the surface hardening mechanism of 7A52 aluminum alloy welded joints is fine grained strengthening, the surface hardening of 7A52 aluminum alloy welded joints obviously improved with the common effect of fine strengthening and precipitated phase strengthening after the A-UIT.

Abstract:Sn is a kind of low melting point metal and can be used as a liquid coolant due to its higher thermal conductivity. Compared with the currently used sodium liquid coolant, Sn is more chemical stable and unfeasible to fire or explore when contacting with air or water. In this paper we examined the chemical reactions between Sn and 304 stainless steel, which is widely used as primary circuit pipeline materials in fast reactor, and discussed the effect of temperature on the corrosion behavior between 304 stainless steel and liquid Sn. The results showed that pitting happened when the temperature was lower than 823K, and dissolution happened when the temperature was higher than 823K.

Abstract:Nano tin oxide (SnO2) was synthesized by a novel, fast and facile approach through applying electric current of high density to a line-type joint specimen consisting of a high tin-content alloy between two pieces of conductor (copper or nickel). The fabricated SnO2 shows various morphologies, such as branch-like, pine-leaf-like, grass-like and batting-like, and has the tetragonal rutile structure confirmed by scanning electron microscopy, energy dispersive X-ray spectroscope and Raman spectrum. The present work has not only offered a facile and novel method for fabricating SnO2 of various morphologies, but also provided an inspiriting yet practical idea as well as technical possibilities for preparation of other functional oxide materials.

Abstract:The CoCrAlSiY alloy coating with a Si mass concentration of 0, 2% and 5% was prepared in this work. The effect of Si element on the structure and properties of the alloy powder and coating was analyzed. In addition, the function of Si element on the high temperature performance of the coating was also discussed. The results show that the Si element is mainly distributed in the β phase, whose volume content and distribution have a great influence on the high temperature performance of the coatings. Furthermore, the Si element promotes the change from internal oxidation to external oxidation of alloy and the formation of the protective oxide film. However, the higher Si addition results in a higher PBR value of oxide film, which will increase the oxide film stress. This is not connected to the improvement of the coating thermal shock resistance at high temperatures.

Abstract:For development of low-Ag lead free solder alloys for microelectronic packaging, the correlation of creep properties with microstructure of novel Sn-0.3Ag-0.7Cu-0.5Ga (SAC-Ga) solder alloys bearing Pr has been investigated using nanoindentation. The results show that the creep deformation of SAC-Ga, SAC-Ga-0.06Pr, SAC-Ga-0.5Pr is 1717 nm, 1144 nm,1472 nm, respectively, which indicates that Pr addition could significantly enhance the creep resistance of SAC-Ga solders due to the refinement and more uniform distribution of Cu₆Sn₅ intermetallic compounds (IMCs). However, compared with the SAC-Ga-0.06Pr solder alloy, the SAC-Ga-0.5Pr alloy shows lower creep resistance which is mainly attributable to the surface oxidation of excess rare earth Pr. In addition, Dorn model has been used to describe the creep behavior and to obtain stress exponents of the SAC-Ga solder alloys bearing Pr. It is proposed that strengthening mechanism of creep resistance in SAC-Ga solder alloys bearing Pr is that when encountering refined and well-distributed Cu₆Sn₅ IMCs, a dislocation line cannot climb through the IMCs but bypass the IMCs, leading to a decrease in the creep deformation of the solder alloys bearing Pr.

Abstract:Surface modification of implant substrate is very important to obtain a biocompatible or functional interface. In this work, MgO film was sol-gel prepared on titanium substrate by sintering at 400 ?C. Microstructure, bioactivity, cytotoxicity and antibacterial property of the obtained film were investigated. It was found that MgO converted to Mg(OH)2 after ageing in air. The film was crack free observed by scanning electron microscopy. It was bioactive in the simulated body fluid test, biocompatible with osteoblast cells and slightly antibacterial against E. Coli. The MgO film would have potential application in surface modification of biomedical titanium implants.

Abstract:A new composite thermal interface material (TIM) was synthesized by combining AlN with liquid metal (LM, Ga68.5In21.5Sn10) and polydimethylsiloxane (PDMS), one of the most commonly used silicone oils, to enhance the interfacial heat transfer. The microstructure and chemical composition of the material were measured using scanning electron microscopy (SEM) with an energy dispersive spectrometer (EDS) to investigate its principle of heat dissipation. The thermal conductivity (κ) of the AlN liquid metal thermal grease (ALTG) was found to be 5.014 W/m·K, higher than that of a liquid metal/PDMS composite (LMTG) and higher than that of one of the best existing thermal grease products (X23-7762) by approximately 5% and 20%, respectively. Meanwhile, the thermal contact resistance (R) was reduced by 20% and 50%, respectively, and the viscosity remained in an appropriate range, reducing the risks of overflow during usage. An actual test on a CPU showed that ALTG could significantly reduce the operating temperature. The thermal mechanism of ALTG was studied, and a synergistic effect was suggested for the heat transfer process. The results prove the ideal heat dissipation properties of TIMs and their wide application prospects in industry.

Abstract:U-Zr alloys cladded with Zircaloy-4 alloy are being developed as metallic fuels for water-cooled reactors. The fuel-cladding compatibility is key to the safe operation of the reactors, however, there are few studies on the interfacial reaction and diffusion of U-Zr alloys and Zircaloy-4 alloy. To investigate the compatibility and the diffusion behavior between U-Zr alloys and Zr-4 alloys, solid-to-solid U-10wt.%Zr/Zr-4 diffusion couples were assembled by vacuum hot pressing and then vacuum annealed at the temperatures range from 580 ℃ to 1100 ℃ for various time. Both scanning and transmission electron microscopy were employed for analysis of the microstructures and composition profiles at the interfaces of the couples. The compatibilities between the two alloys were systematically investigated. δ-UZr₂ and ~20nm-thin U-rich layers existed in vacuum hot pressed samples. The interdiffusion coefficient constant and the activation energy were measured, which are 4.23(±0.63)×10^-6 m²/s and 160.73(±1.67) kJ/mol, respectively. The interdiffusion coefficients of U-10wt.%Zr/Zr-4 alloys couples are higher than that of U-Zr alloys, especially for low temperature.

Abstract:The effects of particle size of precursor powder on microstructure and superconducting of Bi-2223 tape were investigated. Three kinds of precursor powders with different particle size (8μm, 2μm, <1μm) were prepared by spray pyrolysis method via adjusting the concentration of metal nitrates solution and ball milling. All powders were composed of Bi-2212, (Sr,Ca)_xCu_yO_d (AEC) and CuO phase after heat treatment. It was showed that AEC phase dimension and content increased with decreasing of particle size of precursor powders. However, the powder with average particle size of 2um had the minimal dimension and content of CuO phase. For 37-filaments Bi-2223 tapes fabricated by three kinds of precursor powders, the highest critical current (I_c) was achieved for powder with average particle size of 2um, which had highest (Bi,Pb)₃Sr₂Ca₂CuO_x(Pb-3221) and lowest AEC phase compared to other tapes. The results showed that particle size of precursor powders mainly affected dimension and content of AEC and CuO phase, which further caused difference of I_c and non-superconducting phases in Bi-2223 tape.

Abstract:The basic properties, heats of formation, energies of formation, equilibrium concentration of point defects, elastic properties, and electronic structures for point defect structures of B2-NiAl crystal are detailed analyzed by the density functional theory. Compared with B2-NiAl and other B2 intermetallic compounds, purity NiAl has the better ductility and bonding strength. According to the calculated heats of formation, energies of formation, and equilibrium concentration of point defects, the Ni antisite and Ni vacancy are primary defects in B2-NiAl crystal. The calculated G/B0 and Cauchy pressure parameters C12–C44 values confirm that Ni vacancy, Ni antisite, and Al antisite can promote the brittleness of B2-NiAl, and in which Ni vacancy is the primary defect, while Al vacancy with a low concentration can improve ductility of B2-NiAl. The density of state confirms that B2-NiAl intermetallic compounds are conductors, and point defects can promote the stability of the system expect Ni antisite defect.

Abstract:Non-equilibrium solidified Cu100-xZrx(x=5, 30, 50) alloys with different compositions were prepared by vacuum induction melting and spray casting method. The microstructure evolution including grain morphology, element distribution and phase components of non-equilibrium solidified alloy was presented by optical microscope, scanning electron microscope, energy spectrum analysis and X ray diffraction technique. The solidification process of the alloys was studied by differential scanning calorimetry. The results show that the volume fraction of primary phase increases continuously with the increase of Zr content and reveals a transition from non-faceted to faceted and finally non-faceted phase. Affected by the fast cooling effect of copper mould, both the peritectic transformation in Cu70Zr30 alloy and eutectoid transformation in Cu50Zr50 alloy are suppressed, which are further verified by the thermal analysis curve under slow cooling condition. Consequently, the formation regularity of non-equilibrium microstructure of spray casted Cu-Zr alloy can be well explained.

Abstract:This paper studies the doping of Mg2Si by alloying elements Bi from the kinetic point of view. the occupancy. The occupancy, structural stability, elastic properties and electronic structure of alloying element Bi-doped Mg2Si phase were discussed by the first principle calculations, which based on density functional theory in CASTEP program.The calculated results show that Mg2Si,Mg7Si4Bi and Mg8Si3Bi can be stable and the interstitial solid solution Mg8Si4Bi is unstable in the system, the Bi atoms preferentially occupy the Si atoms in the Mg2Si crystal; Mg2Si, Mg7Si4Bi, Mg8Si3Bi are all brittle phase. The ductility, alloying ability and electrical conductivity of Mg2Si can be improved by doping alloying elemen; The essence to the bonding of Mg2Si is a combination of metal bonds, covalent bonds and ionic bonds, Bi-Si and Bi-Mg bonds are formed in Mg2Si phase by doping Bi atoms, which are beneficial to improve the stability of the system.

Abstract:Hot compression tests were carried out on TC17 titanium alloy by using thermal simulation testing machines, and the influence of different deformation parameters on the morphology and structure of TC17 titanium alloy with widmanstatten microstructure was characterized by Electron Back Scattered Diffraction (EBSD) techniques. The results show that adiabatic shear bend (ASB) occurs in the TC17 alloy with widmanstatten microstructure while the hot compression deformation temperature is over 700℃, and the central region of ASB is mainly composed of equiaxed β-phase grains formed by dynamic re-crystallization and a small amount of α-phase. The residual α phase and also the β-phase grain size increase with increasing of the hot compression temperature. Different deformation parameters have little effect on the orientation distribution of β-phase in the central region of ASB, and Goss texture mainly forms in β-phase. Furthermore, the research shows that the TC17 titanium alloy with widmanstatten microstructure has good adiabatic shear sensitivity, and it increases gradually with the increase of the hot compression deformation temperature.

Abstract:This article researched the microstructure evolution of ω and α phase in the solution treatment and ageing process of β-CEZ alloy, which is a kind of typical near-β titanium alloy. The results show that ultrafine athermal ω precipitates (about 1~2 nm) were formed in β-CEZ alloy by quenching from above the β transus temperature. Needle-like α precipitates, about 100nm in length, were formed when solution treated β-CEZ alloy samples were aged at 350℃. The scale of ω assisted α increased to about 200nm in length while increasing ageing temperature to 500℃. The scale of α precipitates grown to about 300nm in length and ω disappeared when the ageing temperature increased to 550℃. Long strip shape α were formed at grain boundaries and the scale of intragranular α increased to several microns when the β-CEZ alloy samples were aged above 650℃.

Abstract:The oxidation behavior in air of Al₂O₃/Ti₂AlN composite at temperature of 900 ℃ 1 000 ℃ and 1 100 ℃ in 20 hours were studied by oxidation weight experiment, back scanning electron imaging(BSE) and energy dispersive spectrometer (EDS). The results show the oxidation behavior of composite obeys a parabolic law from 900 ℃ to 1 100 ℃. The oxidation weight gain respectively is 2.78×10_-2 kg/m₂、10.4 ×10_-2 kg/m₂、21.9 ×10_-2 kg/m₂. The parabolic rate constant corresponding to 1.08×10_-8 kg₂/m₄s、1.44×10_-7 kg₂/m₄s、6.56×10_-7 kg₂/m₄s. the oxide activated energy is 274 kJ/mol. The composed of oxide layer are TiO₂ and Al₂O₃. The good oxidation resistance of Al₂O₃/Ti₂AlN composite is coming from the continuous outer Al₂O₃ layer. The structure changes of oxide layer is due to The temperature effect the diffusion rate of Ti₄₊, Al₃₊ ions outward and O_2- inward, it also effect the nucleation and growth rate of TiO₂ and Al₂O₃. Those are the reason of the changes of oxide layer structure at different temperature. To control the interface between the matrix and oxidizing atmosphere is the key to improve the Al₂O₃/Ti₂AlN composite oxidation resistance

Abstract:In this paper, electro-less Ni-P-ZrO2 composite plating was preformed on Zr-8Al alloy. The microstructure, microhardness, wear resistance and corrosion resistance in 3.5 wt% NaCl solution of electro-less composite platings for different ZrO2 addition were investigated. The results show that the microhardness of electro-less Ni-P-ZrO₂ composite plating was improved compared with that of electro-less Ni-P plating. The microhardness and wear resistance of electroless Ni-P-ZrO2 composite plating for 4g/L ZrO2 addition is super. The corrosion resistance of the electroless Ni-P-ZrO2 composite plating is a bit lower than that of electro-less Ni-P plating, yet the composite plating after corrosion is still complete. So the corrosion resistance of the electroless Ni-P-ZrO2 composite plating for 4g/L ZrO2 addition is still better. The Ni-P-ZrO2 plating on Zr-8Al alloy is potential to applied for moving parts in space which require excellent wear resistance and good corrosion resistance.

Abstract:A density functional theory method has been employed to investigate the crystal structures, band structures and photoelectric properties of oxygen-deficient rutile TiO_2-x(x=0~0.5). Defected states composed of Ti 3d and O 2p appear in the band gap owing to the introduction of oxygen vacancies. These defected states reduce the energy for electrons jumping from valence bands to conduction bands, so the absorption edge of TiO_2-x has a red shift, and the absorption intensity of visible light is enhanced, which is beneficial to the photocatalytic activity under visible light. The band gap first decreases and then increases with the increasing of oxygen vacancy concentration (θ) from 1.39% to 25%. When θ=6.25%, the band gap is the smallest which is 1.46 eV. Moreover, according to the UV-vis absorption spectra, it could be confirmed that θ=6.25% is the best oxygen vacancy concentration to improve the photocatalytic activity of TiO₂ because of the large electron mobility and the highest absorption ability of visible light.

Abstract:The microstructure of as-cast AZ91-3Ca magnesium alloy before and after annealing treatment and the corrosion behavior under different annealing conditions were studied by scanning electron microscopy (SEM), X-ray diffractometer (XRD), electrochemical test and weight loss method. The results show that the as cast AZ91-3Ca alloy is mainly composed of matrix a -Mg phase and a network eutectic phase along the grain boundaries. The eutectic phase contains a -Mg phase, a solid block β-Mg17Al12 phase and a Mg (Al) 2Ca phase. The microstructures of the alloys annealed at 300 ℃ and 400 ℃ have no obvious change. After annealing at 500 ℃ for 2.0 h, the solution of β-Mg17Al12 phase promotes the precipitation of Mg, Al, Zn and Ca new phase. After annealing at 500 ℃ for 16.0 h, the content of Al in the matrix is the most, and the distribution is uniform and the corrosion resistance is the best, in NaCl aqueous solution the corrosion potential was -1330 mV, the current density was 1.222 × 10-4 A / cm2, and the corrosion rate was 0.11 mg / cm2h.

Abstract:The oxidation behaviors of FeCrNiAl high entropy alloy at high temperature were investigated in this paper, and the oxidation kinetics model was constructed. The phase structure, morphology and composition were characterized by XRD, SEM and EDS, and the oxidation mechanisms were analyzed. The results show that the alloy are all oxidation-resistant at 800-1000℃, the average oxidation rate in unite area in 100h increases with increasing temperature at first, then decrease and the average oxidation rate at 1000℃ is smaller than at 800℃.The relationship between weight increment in unite area and oxidation time for all temperatures meets parabola function, and the oxidation active energy was calculated to be 167.507KJ/mol. The oxidation products in dendrite at 800℃ are bar-shape TiO2 with rutile structure, while the interdendritic products are Cr2O3 and TiO2 which show plate shape. The oxidation products at 900℃ are TiO2, Cr2O3 and Fe2O3, while TiO2 and α-Al2O3 are observed at 950℃. Only tight α-Al2O3 film are gotten on the surface at 1000℃, which results in the more excellent oxidation-resistant property.

Abstract:Helium was introduced into ZrCo and Zr_0.7Hf_0.3Co alloys by mixed energy ion implantation. The evolution of helium bubble morphology with storage time was observed by Transmission Electron Microscope (TEM). Results showed that the average size of helium bubbles in Zr_0.7Hf_0.3Co alloy was smaller than that of ZrCo and both of them were observed in the coalescence and growth of helium bubbles with storage time increasing. The effect of storage time on the thermal helium desorption behavior was investigated by Thermal Desorption Spectroscopy (TDS). Results showed that in ZrCo alloy the helium release fraction at lower temperature range decreased sharply and the total helium desorption capacity decreased with the storage time reaching 105 days. While in the case of Zr_0.7Hf_0.3Co, the helium release fraction at lower temperature range gradually increased and the total desorption capacity of helium was almost constant during the storage period of 175 days. This indicated that Zr_0.7Hf_0.3Co alloy had more superior ability to contain helium than ZrCo alloy.

Abstract:To control the O content and further improve the glass forming ability and mechanical properties of Zr(-Ti)-Cu-Ni-Al metallic glasses, Y, Gd, La and Ce are added into the alloys based on the mechanism of strong interaction between O and rare earth elements. Metallic glasses are prepared by the copper mold casting method. The glass forming ability and microstructure of the alloys are studied by Differential Scanning Calorimetry (DSC), X-ray Diffraction (XRD) and Transmission Electron Microscopy (TEM), and the mechanical properties and corresponding fracture modes are investigated by quasi-static compressive tests and Scanning Electron Microscope (SEM). The results show that the addition of Y improves the glass forming ability greatly. Bulk metallic glasses with the diameter over 10 mm can be prepared under relatively low vacuum. The compressive strength is up to 1900 MPa.

Abstract:The corrosion behavior of Zr-Nb-Cu alloys in 500 ℃/10.3 MPa superheated steam were investigated in the present work. Severe non-uniform corrosion was occured in Zr-Nb-Cu alloys with low content of Nb or Cu elements, while Zr-0.2Nb-0.2Cu and Zr-0.2Nb-1.0Cu alloys demonstrated relative good corrosion resistance. It was found that the non-uniform corrosion behavior has been fully inhibited in Zr-0.2Nb-0.2Cu alloy, and further increase of amount of Cu element showed slight effect on the corrosion resistant behavior. The microstructure of zirconium alloys (especially the micro-pores, micro-cracks) is strongly related to the oxidation of alloying elements and precipitates. The presence of Nb in zirconium alloys would delay the oxidation of Zr₂Cu phase and the corresponding diffusion of the oxidation products. Moreover, Nb element could also inhabit the formation of the cracks in the oxide film and the delay the transformation from columnar to equiaxed crystal morphology. Therefore, the addition of Nb element could improve the corrosion resistance of the zirconium alloys containing Cu elements.

Abstract:A NiCoCrAlY coating has been prepared on Hastelloy N substrate by the powder-feeding laser cladding technique. The corrosion behaviors in molten LiF-NaF-KF salt at 900oC for 100h are studied for both the substrate and the coating. The corrosion resistance in molten FLiNaK salt is evaluated by the corrosion weight loss method, while the microanalysis on phase constitution, morphologies and compositions are carried out by XRD, SEM and EDS. The results show that, the corrosion rate of the NiCoCrAlY coating is merely two thirds that of the Hastelloy N substrate. The substrate is characterized by intergranular corrosion and the element Cr was selectively corroded along the grain boundary. The origin Hastelloy N is consisted of γ-Ni and Mo, and a new Cr1.12Ni2.88 phase is precipitated after the corrosion test. The NiCoCrAlY coating exhibits a homogeneous corrosion feature, in which the element Al diffuses outwards and the corresponding Al-rich corrosion products act as the barrier and thus protect the substrate by impeding the diffusion of other elements. The laser-cladded coating is consisted of γ-Ni, AlNi3 and Al0.983Cr0.017, and only γ-Ni retains after the corrosion test. The corrosion resistance of Hastelloy N in molten FLiNaK salt is greatly improved by the laser-cladded NiCoCrAlY coating.

Abstract:To exam the carbothermic reduction behaviors of the (1-x)FeTiO₃?xFe₂O₃ solid solutions with various x value, the solid solutions were artificially synthesized successfully and then subjected to non-isothermal carbothermic reduction. The results show that the solid solutions synthesized in laboratory were uniform texture and high purity. Meanwhile, lattice distortion degree of FeTiO₃ was greater with increasing the value of x, and the initial reduction temperature and reduction rate which is the increasing rate of reduction degree α were also improved. The reduction could be improved for FeTiO₃ as Fe₂O₃ dissolving, and the Fe₂TiO₄ as well as Fe₃Ti₃O₁₀ were existed as the transition phase in the reduction process. FeO, Fe₂TiO₄ and TiO₂ were firstly generated in the interface of solid - graphite, and then reduced to Fe and Ti₂O₃. It is concluded that the apparent activation energy of 295.54 kJ/mol from the calculation and analysis of the non-isothermal kinetics for the carbon thermal reduction process.

Abstract:In this paper, the Co_1.2Mn_0.8B compound was prepared by ball milling and solid state reaction. The crystal structure, magnetic properties and magnetocaloric effect of Co_1.2Mn_0.8B compound have been investigated. The results show that the phase structure of the compound is Co₂B single phase with the CuAl₂-type tetragonal crystal structure, space group of I14/mcm. The Co_1.2Mn_0.8B compound undergone second-order magnetic phase transitions from ferromagnetic (FM) state to paramagnetic (PM) state in the vicinity of Curie temperature of 175K, and the thermal hysteresis is about 0.7 K. The maximal magnetic-entropy change (ΔS_M) of the compound reaches to 1.17 J/kg.K in an external magnetic field of 0~5.0 T. and the temperature corresponding to ΔS_Mdoes not change with the variation of the external field. The material has a potential value in the field of magnetic refrigeration and magnetic heat sensor.

Abstract:Titanium and its alloys have been extensively used in numerous application fields. However, both their low ductility and their lack of work-hardening when compared with steels or Co-Cr alloys, limit their use in advanced applications where superior combinations of strength and ductility are required. Therefore, inspired from the superior mechanical properties of TRIP/TWIP steels (TRIP for Transformation Induced Plasticity and TWIP for Twinning Induced Plasticity), we proposed a new type of metastable β Ti-alloys showing combined TRIP/TWIP effects through controlling the β stability of Ti-alloys. The alloys were designed based on the “d-electron alloy design method” and controlling of electron/atom ratio (e/a). The results show that so-designed alloys display excellent combination of high strength (ultimate tensile strength ≈1020MPa), high ductility (uniform elongation 43%) and improved work-hardening behavior. The detailed microstructural analysis indicates that the superior performances arise from the synergic effects between α? phase transformation induced plasticity (TRIP) and {332}<113> twinning induced plasticity (TWIP).

Abstract:Hot deformation behavior of Ti-22Al-24Nb alloy was investigated in the temperature range of 900~1110 ℃ and strain rate range of 0.01~10 s-1 employing Gleeble-3500 thermo-mechanical simulator. Characteristics of flow stress curve at elevated temperature and hot deformation activation energy in different phase regions were analyzed, and hot forming parameters of the alloy were optimized by processing maps under instability criterion of Prasad and Murty and corresponding organizational characteristics. The results show that the flow stress of the alloy is sensitive to the hot forming parameters. By the calculation of Arrhenius power function equation, the deformation activation of the alloy is 406.25 kJ/mol in B2 single-phase region that can be a large difference between with (α2+B2) two-phase region(603.56 kJ/mol), which indicates that there may be different deformation mechanisms between different phases regions. According to the comparison of two kinds of processing maps and the microstructure observation, processing map of the alloy based on the Prasad instability criterion is more reasonable. The corresponding main instability zones are 900~990 ℃、0.2~10 s-1 and 1035~1095 ℃、1~10 s-1, and the adiabatic shear bands and the local plastic instability in the microstructure were predicted by the instability zones. However, the dynamic recrystallization and the microstructure of the cellular substructure are easy to appear in the η peak regions, indicating that the better thermodynamic parameter range are 990~1035 ℃、0.01~0.03 s-1, 1040~1090 ℃、0.02~1 s-1 and 1090~1110 ℃、0.01~0.18 s-1.

Abstract:Abstract: The Sn2.5Ag0.7Cu0.1RE0.05Ni/Cu solder joints were fabricated by the ultrasionc wave (USW) and the electric field (E) assisted soldering technique. The microstructure and mechanical properties of solder joints were analyzed by the scanning electron microscope (SEM), the energy dispersive spectrometer (EDS) and the X-ray diffraction (XRD). The Results showed that the USW or the USW-E have great influence on the microstructure of the solder joints. The USW or the USW-E assisted soldering technique not only can refine microstructure of the Sn2.5Ag0.7Cu0.1RE0.05Ni/Cu solder joints and promote the proportion of eutectic structure, but also can reduce the average thickness, the roughness and the grain size of interfacial IMC. The shear strength of the Sn2.5Ag0.7Cu0.1RE0.05Ni/Cu soldering joints under the USW-E assisted soldering is closely related to the roughness of interfacial IMC layer. The USW played an important role in the decrease of the roughness of the interfacial IMC during the USW-E assited soldering. Compared with shear strength of the traditional soldering joints, a 24.1% increase of shear strength of the soldering joints was achieved with the USW-E assisted soldering. With applying the USW or the USW-E, the fracture path of the Sn2.5Ag0.7Cu0.1RE0.05Ni/Cu soldering joints was transferred from the interfacial transitional region composed of soldering seam and interfacial IMC layer to the side of soldering seam. The fracture mechanism of the soldering joints obtained by the USW or the USW-E assisted soldering was brittle-ductile mixed fracture with the cleavage of interfacial (Cu, Ni)6Sn5 IMC and the cleavage-dimple of soldering seam, which increased the proportion of ductile fracture zone and the shear strength of soldering joints.

Abstract:An interesting and simple strategy to prepare Pt nanoparticle arrays with different morphologies on a substrate was developed by using monolayer colloidal crystal as a template, followed by depositing a layer of Pt film and annealing at different temperatures. Hat-shaped, cup-shaped, rice-shaped and sphere-shaped Pt nanoparticle array were obtained after annealing the PS template with Pt shell at 300℃, 500℃, 700℃ and 900℃, respectively. Their extinction spectra presented two obvious peaks, assigning to transverse and longitudinal localized surface plasmon resonances of the Pt nanoparticles. The transverse and longitudinal localized surface plasmon resonances peaks both blue shifted when geometrical morphology changed from hat-shaped to cup-shaped, and then to rice-shaped due to increasing annealing temperature. The transverse localized surface plasmon resonances peaks blue shifted from 487 nm to 453 nm, and longitudinal localized surface plasmon resonances peaks blue shifted from 1201 nm to 898 nm. With strong absorption in near infrared, the hat-shaped, cup-shaped and rice-shaped Pt nanoparticles array may be suitable for thermotherapy application. However, in the curves of extinction spectra of the hat-shaped, cup-shaped and rice-shaped Pt nanoparticle arrays, the Bragg diffraction peaks were not very obvious. This may be attributed to overlap of their localized surface plasmon resonance peaks and diffraction peaks or absorbance of Pt nanoparticles is too high, resulting in diffraction peak too weak to be detected. Compared with hat-shaped, cup-shaped and rice-shaped Pt nanoparticle array, in the curve of extinction spectra of sphere-shaped Pt nanoparticle array, there was only one localized surface plasmon resonance peak because of its symmetrical nanostructure. But it presented a peak at 635 nm, which is assigned to Bragg diffraction of the highly ordered structure of the Pt nanosphere array. In a word, this controlling annealing temperature strategy is simple and could be potentially extended to prepare novel anisotropic nanostructures for other materials, which is difficult to be synthesized via conventional wet chemical method. And this method would promote more research efforts in developing new methods to fabricate asymmetrical nanostructures. Additionally, these novel properties originating from the anisotropic nanostructures may open up new applications in many fields.

Abstract:In present work, a semi-solid ZCuSn10P1 copper alloy was used as the research object. A four-piece extrusion mold was independent designed. The semi-solid squeeze casting experiments were carried out. The effects of forming specific pressure and extrusion rate on microstructure and mechanical property of semi-solid ZCuSn10P1 copper alloy squeeze casting parts were investigated. The results show that with the specific pressure increase from 180 MPa to 250 MPa, the average diameter of the solid phase of semi-solid copper alloy decreases gradually from 89.25 μm to 77.96 μm, and the liquid fraction decreases from 36.7% to 22.3%, tensile strength increases from 318 MPa to 387 MPa, an increase amplitude of 21.70%, the elongation decreases from 4.2% to 2.8%. When the extrusion rate increases from 11mm /s to 15mm /s, the roundness of the solid phase is reduced from 1.54 to 1.32, the tensile strength increases from 368 MPa to 387 MPa, increased by 5.16%, the elongation decreases from 3.3% to 2.8%.

Abstract:The mechanism of fatigue crack propagation of γ-TiAl alloy under different strain ratios is studied using the molecular dynamics method. The results show that fatigue crack propagates in the manner of cleavage firstly, and then propagates through disordered region by driving force. Finally, it changes into sub-main crack mechanisms. The difference is that the change in the mode of crack propagation occurs at different times under different strain ratios. At the stage of plastic deformation, dislocations emit at different times and glide at different planes due to different strain ratios. Defects, such as vacancies, divacancies, trivacancies, etc are generated during dislocation gliding. Meanwhile stacking faults are generated along the different close-packed planes under different strain ratios.

Abstract:In order to investigate the effect of annealing treatment on microstructures and mechanical properties of CrCuFeMnTi high entropy alloy, the as-cast CrCuFeMnTi alloy ingot was prepared by vacuum arc melting under the argon protection, and then the microstructures observation and mechanical properties testing of alloy samples under annealing treatment at different temperatures were performed. The results show that the as-cast CrCuFeMnTi alloy is composed of a hexagonal close packed and a face centered cubic solid solutions, and typical microstructures with dendrite and interdendrite phases are observed. The element diffusion and morphologies homogenization mainly proceed when the annealing temperature is under 750℃, and the hexagonal close packed phase would transforms into body centered phase after alloy annealed at 900℃. This phase transition is caused and controlled by the element diffusion. The hardness and strength of alloy are all improved when alloy is annealed at below 750℃, meanwhile, the alloys all show the brittle fracture character.

Abstract:The purpose of this paper is to explore the effects of equal-channel angular pressed (ECAP) process on the microstructure and corrosion behavior of biomedical Mg-Zn-Ca Alloy. As-cast Mg-3Zn-0.2Ca alloy was extruded for 1-4 passes by ECAP using route A process. The influences of ECAP process on the microstructure, texture and corrosion behavior of Mg-3Zn-0.2Ca alloy were investigated by optical microstructure observation, X-ray reflection and electrochemical methods. Particularly, the effects of ECAP process on the microstructure evolution and electrochemical corrosion behavior in simulated body fluid on the different cross-section of ECAPed alloy. The results indicated that with increasing ECAP passes, grain size of Mg-3Zn-0.2Ca alloy gradually refined, and (0002) basal texture emerged after ECAP 4 passes. With increasing ECAP passes, the corrosion resistance of Mg-3Zn-0.2Ca alloy increased firstly and then decreased. The influence of ECAP process on corrosion resistance of Mg-3Zn-0.2Ca was the combined action of grain size, crystal defect and texture. The corrosion resistance of ED, TD and ND cross-section of ECAPed alloy were different, and the corrosion resistance of TD section is superior to the other two directions.

Abstract:In order to study the isothermal oxidation performance of CoCrAlY coatings prepared by EB-PVD after high energy compound shot peening process with different intensity, the CoCrAlY coatings were surface shot peened with strength of 0.3N, 0.3N+0.1N and 0.3N+0.2N. The surface morphology of coatings were observed before and after shot peening; The surface roughness, surface residual stress, thickness and cross-sectional hardness of the coatings were measured after shot peening; The phases change and performance of isothermal oxidation of CoCrAlY coatings were analysised after shot peening. The investigation results show that: the performance of isothermal oxidation of CoCrAlY coating prepared by EB-PVD with compound shot peening is improved more than common shot peening, and the compound shot peening with strength of 0.3N+0.1N show the best performance of isothermal oxidation. Compared with common shot peening, compound shot peening process can reduce the surface roughness of CoCrAlY coating prepared by EB-PVD, increase the density of the coating, change the phases structure, and lead to the improvement of isothermal oxidation performance of CoCrAlY coating. When the shot peening intensity is greater than or equal to 0.3N, scales formed on the surface of CoCrAlY coating. And result in preferential growth of TGO in the place. Because of TGO film rupture by stress concentration here, the service life of coating is degraded. Meanwhile, the compound shot peening can remove the scales.

Abstract:With H2C2O4?2H2O as precipitant and NiSO4?6H2O as Ni source, NiCO4 precursor was prepared through coprecipitation method in the first step. Afterwards, highly regular sub-micron spherical Ni powders were calcined and reduced under H2 atmosphere at middle temperature in the second step. Scanning electronic microscopy, X-ray diffraction and laser particle size analyzer were used to characterize the morphology and microstructure of Ni powder. The results show that the purity of Ni powder is very well. The secondary particle of Ni powder is about 40μm agglomerated with a lot of 0.5μm dispersed and uniform primary particles, which guarantees the excellent forming property and sintering activity. The crystallinity of Ni powder increases with the sintering temperature. The optimal preparing parameters are 0.7mol.L-1 Ni2+ concentration, 40℃ reactive temperature and 500℃ sintering temparature. Grain growth activation energy of Ni powder can be calculated as 26.9 kJ?mol-1 according to the relationship between grain size and sintering temperature and Ni powder’s growing mechanism is interfacial diffusion controlling mechanism.

Abstract:The precursor Ni_0.5Co_0.2Mn_0.3(OH)₂ is synthesized by hydroxide co-precipitation method, further high temperature solid state method is used to obtain the LiNi_0.5Co_0.2Mn_0.3O₂ by mixing with lithium source. The quality change of the precursor and lithium source during the high temperature calcination process and the effect of calcination process on the structure and properties of materials are discussed. Thermal gravimetric analysis (TGA) shows that there is little change in the material quality during the calcination process after 750℃. X-ray diffraction (XRD) indicates that all samples, which are synthesized from 750℃ to 900℃, have good α-NaFeO₂ layered structure and small cation mixing degree. Scanning electron microscope shows that the material has a smooth surface and a uniform distribution of spherical structure. The material, calcined at 850℃, shows a initial discharge capacity of 193.7mA.h.g_-1 in the voltage range of 2.5?4.6V at 25℃ and 0.2C, with the capacity retention rate of 94.2% after 30 cycles, which delivers the best electrochemical properties, including the rate capability.

Abstract:In this work, the permanent magnetic field was applied to prepare gold alloy and the influences of permanent magnetic field on secondary dendrite arm spacing and precipitate of gold alloy was also discussed. The results show that the rotating magnetic field remarkably refined the microstructure and reduced secondary dendrite arm space of gold alloy. However, a too high rotating speed can increase the skin effect of the molten metal and lower the magnetic flux density of the centre, thereby increasing secondary dendrite arm space. The area fractions of α2 can be increased by rotating magnetic field. At 300r/min, the gold alloy had the highest area fractions of α2, which was 59.4% higher than without permanent magnetic field.

Abstract:Optical microscope(OM), electron back scattering diffraction(EBSD) and uniaxial tension and compression tests were carried out to investigate the effect of Y content (1，5 wt.%), extrusion temperature(ET) and extrusion ratio(ER) on the microstructure and tension-compression deformation behavior of extruded Mg-Y alloy bars. Results show that the grain change from typical bimodal structure to small ,homogeneous and fully dynamic recrystallized grains with increasing Y content from 1% to 5%(ET=300℃, ER=9). The average grain size of cross section (ED plane) and longitudinal section (TD plane) of two alloy bars are close and approximately 14.1±1.9μm~16.5±1.6μm. As a result of dramatically weakened basal plane fiber texture and decreasing texture intensity (~53%), the room temperature tensile yield strength (TYS) decreases from 173±3MPa to 125±6MPa while fracture strain remarkably raises from 11.0±2.1% to 31.0±1.2%. Furthermore, the tension-compression asymmetry changes from common (CYS/TYS=0.8) to inverse (CYS/TYS=1.10) with increasing of Y content. With the increasing extrusion ratio from 9 to 32 (ET=300℃),the TYS of Mg-1Y alloy bars drastically increases to 242±1MPa (~40%), which may be closely related to fully dynamic recrystallization, finer grain size (~10.1±1.4μm) and obviously weakened basal plane fiber texture (~75%). The increasing extrusion temperature (300~400℃) has little effect on grain size and tension mechanical properties of Mg-1Y alloy bars (ER=32) while compression yield strength (CYS) raises to 236±9MPa (~15%), the value of CYS/TYS changes from 0.85 to 1.02 which means alloy exhibit tension-compression symmetry. Y content has an obvious influence on the deformation behavior of extruded Mg-Y alloy bars. All of the extruded Mg-1Y alloy bars show sigmoid compression stress-strain curve while no similar phenomenon in Mg-5Y alloy bar is observed. Observation of microstructure after compression suggests that this phenomenon is closely related to twining dominant deformation mechanism.

Abstract:Effects of isothermal heat treatment temperature near the phase transition temperature and holding time on the microstructures of Mg97Zn1Y2 alloys with LPSO structure were studied. Meanwhile, the evolution mechanism was discussed. The main results shows that the long - period structure has a tendency of growing with the increase of time，when the temperature of solid-solution treatment is 500℃. It is found that the dendrite structure of Mg97Zn1Y2 alloy can be transformed into spherical crystal by isothermal heat treatment. When the insulation temperature range of the alloy is from 540℃ to 600℃, the size of microstructures changes in the order of large-small-large, in other words, it is coarsened, separated and spheroidized, and finally coarsened. The trend of microstructure evolution is from dendritic to irregular spherical and massive, and finally spherical at the isothermal heat treatment temperature of 575 ℃. When the holding time is of 15min, its microstructures are rounded spherical crystal.

Abstract:This work has developed a low-cost method to render 5A02 Al alloy substrate superior anti-corrosion property with the acid etching, passivation treatment and fluoroalkyl-silane modification. The micro-nano structures were constructed with the micro-scale porous terraces and nano-scale flocculent layer by optimizing the hydrochloric acid etching and potassium permanganate passivation conditions. After the fluoroalkyl-silane modification of the fabricated aluminum surface, a superhydrophobic surface was attained with a water contact angle of 156.1°and a contact angle hysteresis of 1.5°. Meanwhile, the electrochemical tests showed that the fabricated micro- and nano-scale hierarchical structures could inhibit the anode and cathode reaction of the electrochemical corrosion and impede the contact between the substrate and the corrosion medium. As a result, the anti-corrosion property of the fabricated surface was finally improved, which can broaden the application fields of aluminum with important engineering significance.

Abstract:The dynamic spreading experiment of active solder on the surface of the porous graphite had been completed by the ultrasonic-assisted spreading technology. In this paper, the spreading process of an active solder droplet was captured by a high-speed camera. And the external characteristics of spreading under the action of the ultrasonic were analyzed. The spreading behavior and mechanism of active solder droplets on the surface of the graphite were studied under the action of ultrasonic wave .The results showed that ultrasonic amplitude was been decayed quickly in the surface of graphite, which makes it impossible for acoustic spreading on the surface of graphite. However, as these holes on the surface of the graphite were filled with solder, amplitude attenuation was decreased, acoustic spreading function was strengthen gradually. In the case of ultrasonic power is large enough, the liquid solder can spread on the graphite surface. Solder surface oxidation film is the key factors that hinder the solder spreading. The surface oxidation film of solder can be removed by ultrasonic vibration.

Abstract:Raw material powder has a significant effect on the sintering of spark plasma sintering (SPS). Two kinds of WTi mixtures were used as the raw materials, one was the mixed powders of W (unmilled or milled) and Ti (or TiH2), and the other mixture was the mechanically alloyed W-Ti powders. The W-10Ti alloys were then prepared by SPS at 1400℃ for 10min. XRD, SEM and nano indentation were used to investigate the effect of raw material powders on the microstructures and properties of W-10Ti alloys. The results show that WTi alloy prepared by using milled W powders has no pure Ti phase, the content of Ti-rich phase is decreased by 44% and the nanohardness is improved by 55.7%, when WTi mixed powders are used as the raw materials. Meanwhile, TiH2 powders with fine particles is help to obtain the WTi alloy with less Ti-rich phase which is also fine and uniformly distributed in the microstructure. The obtained alloy has a relative density of 100% and its electrical conductivity, nanohardness and eastic modulus are improved by 7%, 46% and 34%, respectively, compared with those of the alloy prepared by using Ti powders. For the WTi alloy preared using the mechanically alloyed WTi powders, the content of tiny stripped Ti-rich phase is higher and the alloy has better ductility but a lower density of 96.8% and nanohardness of 2.8GPa compared with those of the alloy prepared with WTi mixed powders. Proper raw powders are a key factor to obtain excellent WTi alloy by SPS.

Abstract:In order to investigate the hot deformation behavior of TC17 titanium alloy, isothermal compression tests on a Gleeble 3500D simulator were carried out in a temperature range of 973-1223 K, the strain rate range of 0.001-10s_-1 and strain of 0.9. The results indicated that the flow stress was sensitive with deformation temperature and strain rate. Meanwhile, discontinuous yielding phenomenon was found at the strain rate of 10s_-1 with temperature of 1123K, 1183K and 1223K. Based on multiple regression, a constitutive model was put forward to describe the role of the flow stress as the Zener-Holloman parameter. Thereafter, the processing map on the basis of dynamic materials model was established, and the validity of the developed processing map was verified by using the microstructure of compressed TC17 titanium alloy.

Abstract:BN_f/BN, BN_f/SiBN and BN_f/Si₃N₄ mini-composites were fabricated by Low pressure chemical vapor deposition/infiltration (LPCVD/CVI) process. The microstructure, tensile property and dielectric property of BN fiber bundle and these three mini-composites were investigated. Results indicated that BN fiber composed of h-BN with low crystallinity, phase structure of which unchanged after heat treatment at 650 _oC and 800 _oC. Amounts of micro pores with size of 50-500nm exist on the surface of BN fiber. Mean tensile strength of BN fiber bundle heat treated at 800 _oC is 94 MPa. Average tensile strength of BN_f/BN, BN_f/SiBN and BN_f/Si₃N₄ mini-composites were 68.8 MPa, 30.6 MPa and 26.2 MPa, respectively. Three mini-composites all exhibited brittle fracture behavior, owing to the modulus mismatch between fiber and matrix and strong interphase bond strength. Cracks cannot be effectively deflected and fibers cannot bear the load effectively. Real part of dielectric constant and dielectric loss were lower than 3 and 0.04, respectively, indicating good Electromagnetic wave transmitting property. BN_f/BN possessed the best comprehensive performance.

Abstract:The ultrahigh-temperature Nb-Silicide-based composites have been extensively studies as candidate materials for the high-pressure turbine blade and oriented blade of the high thrust-weight ratio aero-engine due to its attractive mechanical and physical properties. This essay talks about the research status of the ultrahigh-temperature Nb-Silicide-based composites. The main research of multiphase refractory Nb–Si in situ composite is to make room temperature fracture toughness, high elevated-temperature strength and resistance to oxidation to have a better match through alloying and the improvement of preparation technology. And hoping to lay a basis for further research.