B4Cp/6061Al复合材料动态再结晶临界条件

通过等温热压缩实验对25vol.% B₄C_p/6061Al复合材料的热变形行为和动态再结晶临界条件进行了研究,采用的温度范围为350℃-500℃,应变速率范围为0.001s_-1-1s_-1。应力-应变曲线显示动态再结晶是复合材料热变形过程中主要的软化机制,并利用峰值应力构建了基于Arrhenius形式的本构方程。基于加工硬化率曲线,求解了表示动态再结晶发生的临界应变与临界应力值。结果表明,临界应力与峰值应力存在线性关系：σ_c=0.8374σ_p-0.33708。此外,引入Zener-Hollomon 参数描述变形条件对临界条件的影响,得到临界应变与Z参数的关系：ε_c=2.39×10_-4Z_0.11022。最后,通过θ-ε曲线得到了复合材料完成动态再结晶时的稳态应变,并绘制了动态再结晶图。     

25vol%B_4Cp/2009Al复合材料热变形本构模型（英文）

对25vol%B_4Cp/2009Al复合材料进行等温压缩实验,采用的温度范围为300~500℃,应变速率范围为0.001~1 s~(-1)。结果表明,B_4Cp/2009Al复合材料的高温流变应力随着变形温度的升高和应变速率的减小而下降。对流变曲线进行了摩擦修正,修正后的流变应力值低于实验结果。摩擦力的影响随着温度的降低和应变速率的增大而更明显。随后构建了基于Arrhenius形式的本构方程,求解了不同应变量下的材料常数(α,n,Q和A)。与实验结果进行对比,利用构建的本构方程计算得到的流变应力值具有很高的计算精度,相关系数达到0.992。研究发现,较高的温度和较低的应变速率有助于B_4Cp/2009Al复合材料的高温热变形。     

新型钛合金Ti-555热变形行为及热加工图研究

本文通过高温热压缩试验研究Ti-555钛合金热变形过程中变形温度、应变速率对流变应力的影响,采用Arrhenius双曲正弦函数模型推导出Ti-555本构方程,并依据动态材料模型建立了ε=0.6时的热加工图。结果表明,Ti-555钛合金流变应力对应变速率和变形温度较为敏感,热变形时随变形温度升高或应变速率降低,流变应力下降。根据热加工图确定了两个热加工安全区参数为(1)变形温度为850～950 ℃、应变速率为0.6～10 s_^-1;(2)变形温度为950～1150 ℃、应变速率为0.36～0.9 s_^-1。     

纳米SiCp/Al复合材料的热变形行为

在Gleeble-1500D热模拟机上对纳米SiCp/Al复合材料试样进行了单向热压缩试验,研究其在变形温度为460～520℃、应变速率为0.1～5 s~(-1)条件下的高温变形行为。根据实验数据绘制出纳米SiCp/Al复合材料的真应力-真应变曲线,利用双曲正弦函数模型构建纳米SiCp/Al复合材料的应变补偿本构方程,并通过误差分析对该应变补偿本构方程的准确性进行验证。结果表明:纳米SiCp/Al复合材料的流变应力曲线均呈现出先升高至峰值随后缓慢下降的趋势,流变应力随着变形温度的升高和应变速率的降低而减小;在本文试验条件下纳米SiCp/Al热变形激活能的平均值为278.79 kJ/mol;通过应变补偿本构方程得到的流变应力预测值与试验值的线性相关系数为0.991,平均相对误差为2.05%。     

粉末TC4钛合金热压缩动态软化行为分析

通过热模拟压缩实验获得的应力应变曲线表明粉末TC4钛合金在温度为850~950℃,应变速率为0.1~10s_^-1范围内变形时具有加工硬化和连续的动态软化特性,建立了材料本构方程,很好的描述了粉末TC4钛合金的流变行为。进一步对动态软化行为进行了分析,并计算了各种因素对软化的影响程度。结果表明：变形温度越低,应变速率越小,流动软化程度越大;在应变速率为1s_^-1和10s_^-1时,主要是变形热导致流动软化;当应变速率为0.1s_^-1,温度为850℃和900℃时,有变形热、动态相变和α相形态演化三种软化因素,且温度越低,α相形态演化导致的软化占比越大,温度增加,动态相变软化所占比例增加;当应变速率为0.1s_^-1,变形温度为950℃时,有变形热和动态相变两种软化因素,变形量增加,动态相变软化所占比例增大。     

GH2907合金热变形行为及热加工图

通过热模拟压缩实验研究了GH2907合金在变形温度为950~1100℃、应变速率为0.01~10s_^-1、变形量为60%条件下的热变形行为,流变应力随着变形温度的升高或应变速率的降低而显著降低；根据Arrhenius方程和Zener-Hollomon参数,计算了热变形激活能Q,建立了GH2907合金的热变形本构方程；根据动态材料模型,确定了GH2907合金在不同应变下的功率耗散图,功率耗散效率η较高的区域位于温度为1050~1100℃,应变速率为0.01~0.03s_^-1范围,在该变形区域内组织发生了明显的动态再结晶现象；基于Preased失稳判据,绘制了GH2907合金在不同应变下的热加工图,流变失稳区位于高温高应变速率区域,即温度为970~1100℃,应变速率为0.6~10s_^-1范围,在该变形区域内动态再结晶晶粒沿着绝热剪切带和局部流动分布。根据GH2907合金热加工图及微观组织分析得到适宜的加工区域是温度为1050~1100℃,应变速率为0.01~0.03s_^-1范围。     

基于加工图的两种TC4-xFe合金的热变形行为研究

利用Gleeble 3800热模拟试验机对两种TC4-xFe合金在应变速率范围为1~10 s_-1,变形温度介于800~950℃之间,工程应变量为60%条件下的热变形行为进行研究。通过对应力应变曲线的分析研究,建立了以变形温度、应变速率和真应变为参数的本构方程。TC4-0.18Fe和TC4-0.55Fe合金计算得到的变形激活能分别为550.77kJ/mol和420.57kJ/mol。基于动态材料学模型,构造出合金在真应变为0.92下各自的加工图,借此来评估合金的流变失稳区并优化相应的工艺参数。结果表明：这两种合金的理想加工条件为950℃/5~10s_-1,功率耗散效率分别为0.52和0.47。     

低成本Ti-Al-V-Fe-O钛合金热变形行为及热加工图

通过真空非自耗熔炼炉制备了低成本Ti-6Al-2.5V-1.5Fe-0.15O合金,利用Gleeble-1500D热模拟机,研究了其热加工参数为：变形温度875℃-1100℃、应变速率0.001s_-1-1s_-1,变形量为70%时的热变形行为,建立了Ti-6Al-2.5V-1.5Fe-0.15O合金考虑应变量的Arrhenius本构方程,基于动态材料模型建立热加工图。研究结果表明：变形温度升高,应变速率降低,流变应力降低。通过本构方程计算可得两相区平均热激活能为398.824KJ/mol,远大于纯钛自激活能,表明热变形软化机制与动态再结晶有关。单相区热激活能为210.93KJ/mol,略大于纯钛自激活能,以动态回复为主。通过热加工图确定两个失稳区,中等变形温度(950℃-1070℃)高应变速率(0.31-0.1s_-1)易发生绝热剪切,结合热加工图确定适合的加工区间：应变速率为0.001-0.01s_-1,变形温度为875℃-925℃。     

一种新型Ni-Cr-Co基合金的热变形行为及其组织演变研究

采用Gleeble-3800热压缩实验机研究了新型Ni-Cr-Co基合金在1050~1250 ℃、0.001~1 s_^-1条件下的热变形行为,并利用EBSD探讨了变形温度和应变速率对合金组织演变和动态再结晶形核机制的影响。结果表明,流变应力随变形温度的升高而降低,而随应变速率的增大而增加。基于流变应力曲线,建立合金的Arrhenius本构方程和热加工图,得到热变形激活能为520.03 kJ/mol,最佳热加工区间为1175~1250 ℃、0.006~1 s_^-1,该区域最大功率耗散效率为45％。动态再结晶分数随变形温度的升高和应变速率的降低而增加,且动态再结晶过程形成均匀细小的等轴晶粒以及∑3孪晶界。动态再结晶形核主要以晶界“弓出”为特征的不连续动态再结晶机制主导。低温高应变速率下,持续亚晶转动诱导的连续动态再结晶作为辅助形核机制发挥作用。     

DEFORMATION BEHAVIOR AND CONSTITUTIVE EQUATION FOR Zr55Cu30Al10Ni5 BULK METALLIC GLASS IN SUPERCOOLED LIQUID REGION

Zr₅₅Cu₃₀Al₁₀Ni₅块体非晶合金(BMG)在过冷液态区内的单向压缩实验表明: 材料在过冷液态区内的形变行为强烈依赖于温度和变形速率. 随着应变速率的增加, 材料的流变特征由Newtonian流变转变为非Newtonian流变.利用扩展指数本构方程模型建立了非晶合金的流变应力、应变速率和温度的关系.     

改进型镁扩散法制备高临界电流密度MgB2超导体性能研究

本文采用一种改进型镁扩散法成功制备出密度达到1.95g/cm₃的MgB₂超导块材。论文研究了不同的热处理条件对MgB₂块材的超导转变温度(T_c)和临界电流密度(J_c)性能的影响。采用最佳热处理条件制备的MgB₂超导体T_c和J_c分别达到了38.1K和0.53MA/cm₂(10K,自场)。为了改进镁扩散法MgB₂超导体中弱的高场磁通钉扎性能,本文还研究了nano-Pr₆O₁₁和C掺杂对MgB₂超导体的临界电流密度和不可逆场(H_irr)的影响。结果表明C掺杂的MgB₂超导体临界电流密度在10K,6T下达到了10₄A/cm₂,该结果比未掺杂MgB₂超导体在同样条件下性能提高了两个量级,甚至比固态反应法制备的nano-C掺杂MgB₂超导体性能更好。利用该方法制备的nano-Pr₆O₁₁掺杂的MgB₂超导体在10K,2T下也比未掺杂样品J_c提高达9.4倍。根据大量的实验结果和理论分析我们提出基于改进型镁扩散法和化学掺杂,包括纳米粒子和C掺杂,很有可能是一种制备高性能MgB₂超导体非常有效的途径。     

废旧锂离子电池中Li, Fe和V的回收及xLiFePO4-yLi3V2(PO4)3的制备

由于LiFePO_4和Li_3V_2(PO_4)_3材料的特征相近,制备方法类似,提供了一种从废旧LiFePO_4和Li_3V_2(PO_4)_3混合电池中回收Li、Fe和V,再制备xLiFePO_4-yLi_3V_2(PO_4)_3的方法。在空气气氛中600℃热处理1h后,去除粘结剂PVDF使活性物质与集流体分离。调节Li、Fe、V和P摩尔比,球磨、锻烧,配制不同比例的xLiFePO_4-yLi_3V_2(PO_4)_3(x:y=5:1,7:1,9:1)复合电极材料。表征了其形貌、结构和电化学性能,结果表明,回收制备的复合材料将同时具备LiFePO_4和Li_3V_2(PO_4)_3两种材料的电化学性能,能显著改善LiFePO_4的倍率性能。     

Effects of K2O-Li2O doping on surface and catalytic properties of Fe2O3/Cr2O3 system

The effects of K₂O and Li₂O-doping (0.5, 0.75 and 1.5 mol%) of Fe₂O₃/Cr₂O₃ system on its surface and the catalytic properties were investigated. Pure and differently doped solids were calcined in air at 400-600 °C. The formula of the un-doped calcined solid was 0.85Fe₂O₃:0.15Cr₂O₃. The techniques employed were TGA, DTA, XRD, N₂ adsorption at −196 °C and catalytic oxidation of CO oxidation by O₂ at 200-300 °C. The results revealed that DTA curves of pure mixed solids consisted of one endothermic peak and two exothermic peaks. Pure and doped mixed solids calcined at 400 °C are amorphous in nature and turned to α-Fe₂O₃ upon heating at 500 and 600 °C. K₂O and Li₂O doping conducted at 500 or 600 °C modified the degree of crystallinity and crystallite size of all phases present which consisted of a mixture of nanocrystalline α- and γ-Fe₂O₃ together with K₂FeO₄ and LiFe₅O₈ phases. However, the heavily Li₂O-doped sample consisted only of LiFe₅O₈ phase. The specific surface area of the system investigated decreased to an extent proportional to the amount of K₂O and Li₂O added. On the other hand, the catalytic activity was found to increase by increasing the amount of K₂O and Li₂O added. The maximum increase in the catalytic activity, expressed as the reaction rate constant (k) measured at 200 °C, attained 30.8% and 26.5% for K₂O and Li₂O doping, respectively. The doping process did not modify the activation energy of the catalyzed reaction but rather increased the concentration of the active sites without changing their energetic nature.     

Improved capacity and rate capability of Ru-doped and carbon-coated Li4Ti5O12 anode material

Pure Li₄Ti₅O₁₂, modified Li₄Ti₅O₁₂/C, Li₄Ru_0.01Ti_4.99O₁₂ and Li₄Ru_0.01Ti_4.99O₁₂/C were successfully prepared by a modified solid-state method and its electrochemical properties were investigated. From the XRD patterns, the added sugar or doped Ru did not affect the spinel structure. The results of electrochemical properties revealed that Li₄Ru_0.01Ti_4.99O₁₂/C showed 120 and 110 mAh/g at 5 and 10 C rate after 100 charge/discharge cycles. Li₄Ru_0.01Ti_4.99O₁₂/C exhibited the best rate capability and the highest capacity at 5 and 10 C charge/discharge rate owing to the increase of electronic conductivity and the reduction of interface resistance between particles of Li₄Ti₅O₁₂.It is expected that the Li₄Ru_0.01Ti_4.99O₁₂/C will be a promising anode material to be used in high-rate lithium ion battery.     

Preparation and characteristic of spherical Li3V2(PO4)3

Spherical Li₃V₂(PO₄)₃ was synthesized by using N₂H₄ as reducer. The products were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that single-phase, spherical and well-dispersed Li₃V₂(PO₄)₃ has been successfully synthesized in our experimental process. Electrochemical behaviors have been characterized by charge/discharge measurements. The initial discharge capacities of Li₃V₂(PO₄)₃ were 123 mAh g⁻¹ in the voltage range of 3.0–4.3 V and 132 mAh g⁻¹ in the voltage range of 3.0–4.8 V.     

The high-temperature corrosion behavior of Nb-Al alloys in a H2/H2S/H2O gas mixture

The corrosion behavior of pure Nb and three Nb Al alloys containing 12.5, 25, and 75 at.% Al was studied over the temperature range of 800–1000°C in a H₂/H₂S/H₂O gas mixture. Except for the Nb-12.5Al alloy consisting of a two phase structure of -Nb and Nb₃Al, other alloys studied were single phase. The corrosion kinetics followed the parabolic rate law in all cases, regardless of temperature and alloy composition. The parabolic rate constants increased with increasing temperature, but fluctuated with increasing Al content. The Nb-75Al alloy exhibited the best corrosion resistance among all alloys studied, whose corrosion rates are 1.6–2.2 orders of magnitude lower than those of pure-Nb (depending on temperature). An exclusive NbO₂ layer was formed on pure Nb, while heterophasic scales were observed on Nb-Al alloys whose compositions and amounts strongly depended on Al content and temperature. The scales formed on Nb-12.5Al consisted of mostly NbO₂ and minor amounts of Nb₂O₅, NbS2, and -Al₂O₃, while the scales formed on Nb-25Al consisted of mostly Nb₂O₅ and some -Al₂O₃. The scales formed on Nb-75Al consisted of mostly -Al₂O₃ and Nb₃S₄ atT 900°C, and mostly -Al₂O₃ , Nb₃S₄ and some AlNbO₄ at 1000°C. The formation of -Al₂O₃ and Nb₃S₄ resulted in a significant reduction of the corrosion rates.     

Synthesis of lanthanum carbonate nanoparticles via sonochemical method for preparation of lanthanum hydroxide and lanthanum oxide nanoparticles

Lanthanum carbonate nanoparticles were synthesized from the reaction of lanthanum acetate and Na₂CO₃ under sonication via sonochemical method. Lanthanum hydroxide nanoparticles were prepared by facial hydrothermal processing from the resulted product at 110 °C for 24 h. The role of surfactant, calcination temperature and sonication time were investigated on the morphology and particle size of the products. Products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectrum (XPS), and Fourier transform infrared (FT-IR) spectra. La₂O₃ nanoparticles were obtained by calcinations of the nanoparticles of lanthanum carbonate at 600 °C.     

Alloyed W–(Co,Ni,Fe)–C phases for reaction sintering of hardmetals

It has been shown that W–Co–C phases could dissolve a substantial amount of metals such as V, Cr and Ta, which are known to positively influence the microstructure of hardmetals with respect to uniform grain size distribution and fine grain size. This offers a tool to circumvent the conventional doping of hardmetals with individual carbides. In the present study we used double- and triple-alloyed κ-W₉Co₃C₄ (i.e. κ-(W,V,Cr)₉Co₃C₄ and κ-(W,V,Cr,Ta)₉Co₃C₄) and applied a variety of sintering experiments to obtain WC–Co, WC–(Ti,Ta,Nb)C–Co and WC–(Ti,Ta,Nb)(C,N)–Co hardmetals. We also prepared κ-W₉Fe₃C₄, alloyed κ-W₉Ni₃C₄, and κ-W₉(Fe/Ni)₃C₄, and used the latter for sintering.     

The high-temperature corrosion behavior of Co-Nb alloys in mixed-gas atmospheres

The corrosion of Co-Nb alloys containing up to 30 wt.% Nb in H₂-H₂S-H₂O gas mixtures was studied over the temperature range of 600–800°C. The gas composition falls in the stability region of cobalt sulfide and Nb₂O₅ in the phase diagrams of the Co-O-S and Nb-O-S systems at all temperatures studied. Duplex scales, consisting of an outer layer of cobalt sulfide and a complex, heterophasic inner layer, were formed at all temperatures studied. In addition to cobalt sulfide and CoNb₃S₆, a small amount of NbO₂ was found in the inner layer. The reason for the formation of NbO₂ over that of Nb₂O₅ in the scale is that the outer sulfide scale lowers the oxygen activity within the scale into the NbO₂-stability region. Two-stage kinetics were observed for all alloys, including an initial irregular stage usually followed by a steady-state parabolic stage. The steady-state parabolic rate constants decreased with increasing amounts of Nb, except for Co-20Nb corroded at 700°C. Nearly identical kinetics were observed for Co-20Nb corroded at 600°C and 700°C. The presence of NbO₂ particles leads only to a limited decrease of the available cross-section area for the outward-diffusing metal ions. The activation energies for all alloys are similar and are in agreement with those obtained in a study of the sulfidation of the same alloys. The primary corrosion mechanism involves an outward Co transport.     

定-转子反应器制备LiFe1-xMxPO4 (M= Mn, Ni)粉体及其性能研究

采用具有高效传质和微观混合性能的定-转子反应器制备了LiFe_1-xMn_xPO₄ (x=0.0, 0.1, 0.2, 0.3)和LiFe_1-xNi_xPO₄ (x=0.00, 0.03, 0.05, 0.07)粉体,分别用作正极材料制成电池后,采用电池测试系统测定了电池的电化学性能随温度的变化规律。结果表明,粉体颗粒呈类球形,尺寸分布均匀,粒径范围为5~10 μm,Mn和Ni的掺杂没有改变粉体的晶体结构。以LiFe_0.8Mn_0.2PO₄和LiFe_0.95Ni_0.05PO₄两种组成的粉体性能最好,在倍率0.1 C下,所得电池的首次充放电比容量在室温和50 _oC时,分别为153.2和155.7 mAh/g,及156.4和160.4 mAh/g;100次充放电循环后电池的容量保持率分别为95.4和96.5%,及93.8和95.0%。借助具有过程强化作用的定-转子反应器制备的Mn和Ni掺杂LiFePO₄正极材料的电性能得到显著提高。原因是定-转子反应器一方面可以制备颗粒尺寸均匀的粉体,另一方面又可使掺杂的Mn和Ni在粉体颗粒中均匀分布,两者同时提高了电池中Li₊的扩散速率,进而提高了锂离子电池的电化学性能和高温电性能。