Structural,Dielectric,and Magnetic Studies on Electrospun Magnesium Ferrite-Polyvinylidene Fluoride Core–Shell Composite Fibers

The sub-micron(of the order of 150 nm) thick core–shell composite fibers of magnesium ferrite-polyvinylidene fluoride are prepared by electrospinning.The loading of magnesium ferrite is varied from 1 to 10 wt%.The study results by X-ray diffraction,scanning electron microscope,and infra-red spectroscopy indicate the formation of core–shell structure and an enhancement in the amount of b-phase compared to a-phase in the polyvinylidene fluoride.The particle size of the magnesium ferrite in the fiber is evaluated to be 30 nm.The low frequency dielectric studies indicate that the addition of the magnesium ferrite increases the polarization resulting in the increase in the dielectric constant but decreases the dielectric loss.The magnetization measurements indicate an increased value of coercivity compared to bulk due to the nano-size of the magnesium ferrite.The microwave absorption at the ferromagnetic resonance increases with the increase in the concentration of magnesium ferrite.The resonance field is found to vary with the loading of MFO.     

Bioleaching of low-grade copper sulphides

The bioleaching behavior of low-grade copper sulphides under the condition of preferential solution flow was investigated through experiments. ,The experiment of bioleaching was conducted within the multifunction autocontrol bioleaching apparatus. The results show that the concentrations of Cu^2＋ and total Fe increase slowly at the beginning. The recovery rate decreases with the increase of depth of dump. The preferential solution happens within the fine region when the application rate is low, and the recovery rate of the fine region is higher than that of the coarse region. The content of fine ore particles within both fine and coarse regions increases during the leaching period, and the preferential solution flow shifts from fine region to coarse region. The surface of the ores at the top of dump is attacked seriously, and the ores in the middle is attacked slightly. There are plenty of crackles on the surface of bottom ores because of the precipitation layer on the surface.     

Microstructure of fast tool servo machining on copper alloy

The development of the fast tool servo (FTS) for precision machining was investigated.The micron machining performance of a piezoelectric-assisted FTS on copper alloy was evaluated.The results indicate that the quality of the microstructure depends mainly on two important factors:the cutting speed (or spindle speed) and the driving frequency of the FTS.The excessive driving frequency increases the formation of burrs.The effect of the clearance angle of the diamond tool on the microstructure machining precision was also investigated.     

Mathematic model of solid fraction during rheo-casting by the cooling sloping plate process

A mathematic model of the solid fraction during rheo-casting by the cooling sloping plate process was established, and the effects of the process parameters on the solid fraction were analyzed. The calculation results show that the experimental result is approximately agreed with the calculation value. The effect of the casting temperature on the change rate of the solid fraction is not obvious. But the beginning solidification length is greatly influenced by the casting temperature. The beginning solidification length increases with the increment of the casting temperature. The effect of the sloping angle on the solid fraction becomes obvious with the increment of the sloping plate length. The solid fraction increases sharply with the decrease of the initial thickness of the melt. The melt initial thickness between 15 and 20 mm is suggested.     

Study of the Laser-MIG Hybrid Welded Al-Mg Alloy

The technology of laser-MIG hybrid welding is hotspot in welding researched field at present.It can improve the velocity of the welding,reduce the distortion of the welding,optimize the structure of the welding joint and etc..The 5052 aluminum alloy of the 10mm thick was welded by the laser-MIG hybrid welding.The structure,the alloy elements profile and the mechanical property of the welded joint are researched by the optical microscope,SEM,sclerometer and etc..The results showed:The medium thick Al alloy was welded in high speed by the laser-MIG hybrid welding.The appearance of the welding joint is well.The weld joint and the weld interface are fine.The intenerate region in the welding joint is small.The tensile strength in welding joint has achieved 94.4% of that in base metal.     

Platinum and Iridium Coatings Obtained by Double Glow Plasma Technology

Pt and Ir coatings were produced by double glow plasma technology on the surface of Ti alloy substrates. The chemical compositions of the coatings were determined by X-ray diffraction and X-ray photoelectron spectroscopy. The microstructure and morphology of the coatings were observed by scanning electron microscopy. The hardness and elastic modulus of the coatings were estimated by nanoindentation. The measurements of adhesive forces of the coatings were performed with scratch tester. The results indicated that the Pt and Ir coatings displayed the preferred (220) orientation due to the initial nuclei with preferred growth on the surface of the substrates. The interface between the Pt coating and substrate exhibited no evidence of delamination. The Ir coating was composed of irregular columnar grains with many nanovoids at the interface between the coating and substrate. The mean values of hardness for Pt and Ir coatings were 0.9 GPa and 9 GPa, respectively. The elastic modulus of Pt and Ir coatings were 178 GPa and 339 GPa, respectively. The adhesive forces of the Pt and Ir coatings were about 66.4 N and 55 N, respectively. The Pt and Ir coatings adhered well to the Ti alloy substrates.     

Reaction mechanism between oxide film on surface of Al-Li alloy and CsF-AlF3 flux

The composition of the oxide fill on the surface of Al-Li alloy was measured after accelerated oxidation at 500 and 540℃ , and the reaction mechanism between CsF-AlF3 flux and the oxide film on the surface of Al-Li alloy was also discussed. The results show that the oxide fill on the surface of Al-Li alloy is mostly composed of Li2CO3 and amorphous Al2O3. The brazing technology for Al-Li alloy is accomplished using the improved CsF-AlF3 flux. The improved flux CsF-AlF3 can effectively remove the oxide film by the way of reacting and/or dissolving the oxide film, of which CsF compound plays an important role in the course of removing the oxide fill. The key step is the generation of HF, which induces and accelerates the reaction of removing oxide fill. The generation of H2O also accelerates the reaction.     

Study on dynamic optimization of the double railway suspended vehicle for automatic transportation in the welding shop

The 2DOF dynamic equations of the doable railway suspended vehicle for automatic transportation in the welding shop are established. The sensitivities are analyzed. The parameter design is researched in ADAMS in terms of the inner railway radius, wheelbase, gauge, girder length of the doable railway suspended vehicle for automatic transportation in the welding product line. The mutual-restriction among the design variables is discussed and the selective ranges of the variables are confirmed. The result shows that the stability of the doable railway suspended vehicle for automatic transportation in the welding product line depends on parameters of the inner railway radius, wheelbase, gauge, girder length. The optimal results of the optimal objective and design variables have research significance for the virtual prototype of the doable suspension railway automation vehicle. The optimal results are input into the simulation model iteratively and the simulation results are fed back to the physical prototype. The veracity and reliability of peoformance forecast are improved so that the manufacture cost of the doable suspension railway automation vehicle is reduced significantly.     

Friction stir butt welding of A5052-O aluminum alloy plates

Friction stir butt welding (FSW) between A5052-O aluminum alloy plates with a thickness of 2 mm was performed.The rotation speeds of the welding tool were 2000 and 3000 r/min,respectively.The traverse speed was ranged from 100 mm/min to 900 mm/min.The defect-free welds with the very smooth surface morphology were successfully obtained,except for at the welding condition of 3000 r/min and 100 mm/min.The onion ring structure was observed in the friction-stir-welded zone (SZ) at the condition of 2000 r/min and 100 mm/min.For all the welding conditions,the grain size of the SZ was smaller than that of the base metal,and was decreased with the decrease of the tool rotation speed and with the increase of the tool traverse speed.The stir zone exhibited higher average hardness than the base metal.The decrease of the tool rotation speed and the increase of the tool traverse speed resulted in the increase in the average hardness of the SZ.The tensile strength of the FSWed plates was similar to that of the base metal,except for at the welding condition of 3000 r/min and 100 mm/min.The total elongation of the FSWed plates was lower than that of the base metal.     

Effects of induction heating on properties of X80 longitudinal submerged-arc welding line pipe

The local induction heating process and the whole induction heating process were adopted to develop the X80 φ1219 mm×22 mm induction bends in this paper. After the tempering of the bends, the effect of induction heating on the properties of X80 longitudinal submerged-arc welding line pipe was studied. The results show that for the X80 bend manufactured via the local induction heating, both the tensile strength and yield ratio of unquenched straight tangents are higher than those of the quenched bend area. The toughness of straight tangents is lower than that of the bend area. The strength and toughness of straight tangents do not match perfectly that of the bend area. The induction heating can improve effectively the toughness of weld pipe, reduce the tensile strength and yield ratio to some extent. The whole induction heating makes the match of properties between the straight tangents and the bend area reasonable, thus it is an optimum process for the manufacturing of X80 induction bend.     

Effect of solidification parameters on the microstructures of a single crystal Ni-based superalloy AM3

A single crystal Ni-based superalloy AM3 was processed at withdraw rates of 3.5, 10, 50, 100, 200, and 500 μm·s-1, respectively.The as-cast microstructures and solidification segregation ratio were characterized with various withdraw rates.The shape and size of carbide microstructures were determined.As expected, the primary and secondary dendrite arm spacings (PDAS and SDAS) decrease with the increase of withdraw rate.The highest volume fraction of eutectic γ/γ' is observed at the 100 μm·s-1 withdraw rate.The volume fraction of eutectic γ/γ' does not appear to be a strong function of the withdraw rate.With increasing withdraw rate, interface morphologies change in the sequence of planar, cellular, and dendrite.There is a general refinement of the microstructure as the withdraw rate increases.EPMA analysis showed that withdraw rate does not have obvious influence on the segregation of elements.     

重燃叶片定向凝固宏/微观数值模拟及实验研究

通过模拟和实验的方法对比研究了重燃叶片定向凝固过程宏观温度场及微观组织的变化规律。建立了非均匀网格的求解模型,提高了计算效率。基于温度场的模拟结果分析了糊状区的演化规律。采用线性插值算法结合元胞自动机有限差分(cellular automaton finite difference,CAFD)模型模拟了叶片的微观组织,并和实验进行了对比,模拟和实验结果吻合良好。讨论了几种常见晶粒缺陷产生的原因,提出了预防措施。采用电子背散射衍射(electron backscattered diffraction,EBSD)技术进一步探讨了晶粒的竞争生长行为。建立了枝晶臂间距的计算模型,模拟了叶片的枝晶臂间距分布,并进行实验观察,分析了枝晶臂间距的变化规律。从宏、微观的角度解释了叶片的凝固特征,为实际生产提供帮助。     

Dependency of microstructure and microhardness on withdrawal rate of Ti-43Al-2Cr-2Nb alloy prepared by electromagnetic cold crucible directional solidification

The intermetallic Ti-43Al-2Cr-2Nb(at.%) alloy was directionally solidified in an electromagnetic cold crucible with different withdrawal rates(V) ranging from 0.2 to 1.0 mm·min~(-1), at a constant temperature gradients(G=18 K·mm~(-1)). Macrostructures of the alloy were observed by optical microscopy. Microstructures of the alloy were characterized by scanning electron microscopy(SEM) in back-scattered electron mode and transmission electron microscopy. Results showed that morphologies of macrostructure depend greatly on the applied withdrawal rate. Continuous columnar grains can be obtained under slow withdrawal rates ranging from 0.2 to 0.6 mm·min~(-1). The microstructure of the alloy was composed of α_2/γ lamellar structures and a small number of mixtures of B2 phases and blocky γ phases. The columnar grain size(d) and interlamellar spacing(λ) decrease with an increasing withdrawal rate. The effect of withdrawal rate on microhardness was also investigated. The microhardness of the directional y solidified Ti-43Al-2Cr-2Nb alloy increases with an increase in withdrawal rate. This is mainly attributed to the increase of B2 and α_2 phases as well as the refinement of lamellae.     

高温合金单晶叶片定向凝固过程的宏微观数值模拟

基于有限元和Panda热动力学数据库建立了单晶叶片真空熔模铸造定向凝固过程的数理模型,对不同工艺下单晶叶片试样凝固过程中的温度场、糊状区演变及枝晶二次臂间距进行了仿真,研究了缺陷形成机理和规律。计算结果与实验吻合良好。计算结果显示,拉速大时二次臂细小,但杂晶产生的趋势加大;拉速小时杂晶不易形成,但二次臂增粗。对实际空心薄壁复杂单晶叶片定向凝固过程的模拟研究表明,二次臂间距在叶身部分分布比较均一, 3.5 mm/min抽拉时有可能在缘板处产生杂晶。采用变拉速工艺,不仅可避免杂晶缺陷,还能保证工件大部分枝晶细小,提高生产效率和成品率     

Prediction of Primary Dendrite Arm Spacing in Pulsed Laser Surface Melted Single Crystal Superalloy

Primary dendritic arm spacing(PDAS) is an important microstructure feature of the nickel-base single crystal superalloys.In this paper,a numerical model predicting the PDAS evolution with additive manufacturing parameters using pulsed laser is established,which combines the theoretical PDAS models with the temperature field calculation model during pulsed laser process.Based on this model,processing maps that related process parameters to the evolution of PDAS are generated.To obtain more accurate prediction model,the parameters of different solidification conditions,■ and ■,are selected to calculate PDAS.The simulation results show that the PDAS increases as the arise of P and t.The processmgPDAS map can accurately predict the evolution of PDAS with pulsed laser process parameters,which is well in accordance with the experimental results.Additionally,the PDAS values calculated by the ■ are more in line with the experimental results than those calculated by the ■.     

Study on primary carbides precipitation in H13 tool steel regarding cooling rate during solidification

This study aims to investigate the primary carbides precipitation in H13 steel solidified at relatively high cooling rates, ranging from 300 to 6,000 ℃·min~(-1), based on in situ observations with a high temperature confocal laser scanning microscope. In the cooling rate range investigated, the solidification microstructure becomes more refined as cooling rate increases and the relationship between the secondary dendrite arm spacing(SDAS), λ_2, and cooling rate,.T, can be expressed as λ_2=128.45.T~(-0.124). Regardless of cooling rates, two kinds of primary carbides, i.e., the Mo-Cr-rich and V-rich carbides, are precipitated along the interdendritic region and most of them are the Mo-Cr-rich carbides. The morphology of Mo-Cr-rich carbide is not obviously influenced by the cooling rate, but that of V-rich carbide is obviously affected. The increasing cooling rate markedly refines the primary carbides and reduces their volume fractions, but their precipitations cannot be inhibited even when the cooling rate is increased to 6,000 ℃·min~(-1). Besides, the segregation ratios(SRs) of the carbides forming elements are not obviously affected by the cooling rate. However, compared with the conventionally cast ingot, the SDAS and primary carbides in the steel solidified at the investigated cooling rates are much finer, morphologies of the carbides have changed significantly, and SRs of the carbides forming elements are markedly greater. The variation of primary carbide characteristics with cooling rate is mainly due to the change in SDAS.     

Effect of cooling rate on morphology and type of vanadium-containing phases in Al-10V master alloy

Effects of cooling rates on the morphology, sizes and species of primary vanadium-containing phases in Al-10 V master alloys were investigated. The results show that the primary vanadium-containing phases with different morphologies and compositions present in Al-10 V master alloys at different cooling rates with the pouring temperature of 1,170 °C. When the Al-10 V master alloy is solidified in the refractory mold at a cooling rate of 2 °C·s~(-1), the vanadium-containing phases are mainly plate-like Al_(10)V phases, with the average size of 100.0 μm in the center and 93.2 μm at the edge of the ingot. When the master alloy is solidified in the graphite mold at a cooling rate of 24.3 °C·s~(-1), the primary vanadium-containing phases are dendritic Al_3V phases, with the average length of 297.0 μm for the first dendrite in the center and 275.0 μm at the edge of the ingot. The secondary dendrite arm spacing(SDAS) is 9.5 μm in the center and 9.3 μm at the edge of the ingot, respectively. When the solidification is carried out in the copper mould at a cooling rate of 45.7 °C·s~(-1), the primary vanadium-containing phases are also Al3 V phases but with smaller size, compared with that prepared at the cooling rate of 24.3 °C·s~(-1). As a result, the average length is 190.0 μm for the first dendrite in the center and 150.0 μm at the edge of the ingot. The SDAS is 9.8 μm in the center and 4.4 μm at the edge of the ingot, respectively.     

Microstructure and fractal characteristics of the solid-liquid interface forming during directional solidification of Inconel 718

The solidification microstructure and fractal characteristics of the solid-liquid interfaces of Inconel718, under different cooling rates during directional solidification, ware investigated by using SEM. Results showed that 5 μm/s was the cellular-dendrite transient rate. The prime dendrite arm spacing (PDAS) was measured by Image Tool and it decreased with the cooling rate increased. The fractal dimension of the interfaces was calculated and it changes from 1.204310 to 1.517265 with the withdrawal rate ranging from 10 to 100 μm/s. The physical significance of the fractal dimension was analyzed by using fractal theory. It was found that the fractal dimension of the dendrites can be used to describe the solidification microstructure and parameters at low cooling rate, but both the fractal dimension and the dendrite arm spacing are needed in order to integrally describe the evaluation of the solidification microstructure completely.     

一种镍基单晶高温合金的高温度梯度定向凝固组织及枝晶偏析

采用双区加热和液态金属冷却法 (LMC) 相结合, 对一种含4%Re (质量分数) 的镍基单晶高温合金进行了高温度梯度定向凝固. 结果表明: 与传统的“ 高速凝固法 (HRS) ” (温度梯度G=20-40 K/cm, 抽拉速率V=50-100 μm/s, 一次枝晶间距 λ₁=200-400 μm)相比, 该技术可以显著提高凝固界面前沿的温度梯度 (G=238 K/cm) 和抽拉速率 (V=500 μm/s). 随着抽拉速率的提高, 凝固界面形态呈现出平面、胞状、粗大枝晶和细枝晶形态, 一次枝晶间距不断减小, 通过固态相变析出的γ' 强化相也被显著细化, 当G=238 K/cm, V=500 μm/s时, λ₁和枝晶干γ' 相平均尺寸分别减小到61.3和0.04 μm. 电子探针测定表明, 随着抽拉速率的提高, 枝晶偏析呈现先增大后减小的趋势. 这是高温度梯度条件下, 固相反扩散作用强烈影响元素在枝晶中分布的结果.     

氯法拉滨注射液在白血病患者中的单剂量及多剂量临床药代动力学研究

目的: 研究氯法拉滨注射液单剂量及多剂量静脉滴注的人体药动学过程。方法: 4例白血病患者单剂量恒速静脉滴注氯法拉滨注射液 52 mg·m^-2·d^-1 ,单剂量试验结束后进入多剂量给药试验, 52 mg·m^-2·d^-1 ,连续给药 5 d。采用高效液相色谱串联质谱法测定血浆及尿液中氯法拉滨的浓度,并采用DAS药动学软件对试验数据进行处理,求算有关药动学参数。结果: 4例受试者单剂量静脉滴注氯法拉滨注射液后,主要药动学参数分别为C_max(414±205) μg/L,t_max(3.0±1.4) h,t_1/2z(4.4±2.0) h,AUC_0-t(2475±659) μg·h·L^-1,AUC_0-∞(2566±606) μg·h·L^-1,CLz(21.2±5.1) L·h^-1·m^-2,V_z(142±97) L/m²,MRT_(0-t) (6.3±2.2) h,Zeta(0.18±0.07) h^-1,24 h 平均尿液累积排泄率为(39.53±20.98)%。52 mg·m^-2·d^-1静脉滴注氯法拉滨注射液,连续给药5 d,第5日达稳态,主要药动学参数为C_max(581±126) μg/L,t_max(2.0±0.8) h,t_1/2z(6.4±3.1) h,AUC_0-t(2451±349) μg·h·L^-1,AUC_0-∞(2603±409) μg·h·L^-1,CLz(20.4±3.7) L·h^-1·m^-2,V_z(187±80) L/m,Zeta(0.13±0.05) h^-1,MRT_(0-t) (5.1±1.8) h,C_ss(102.14±14.53) μg/L,蓄积因子R(1.04±0.28),血药浓度波动度DF(576.26±226.89)%。结论: 氯法拉滨注射液静脉滴注给药 52 mg·m^-2·d^-1 ,连续给药 5 d,药物在体内无蓄积,安全性好。