电化学射流加工SiC_p/Al复合材料的试验研究

对SiC_p/Al复合材料进行了电化学射流加工试验,探讨材料去除机理,分析加工电压、加工时间对加工形貌及材料去除率的影响。研究发现,材料的去除过程主要包括铝基体的阳极溶解与SiC颗粒的冲刷脱落,SiC颗粒脱落在加工表面形成微凹坑,微凹坑的几何尺寸及数量对加工表面粗糙度具有较大影响;材料去除速率随加工电压的增加而增大,这与电化学射流加工单一金属材料相似。     

基于二维切削的SiCp/Al复合材料表面损伤形成机制研究

目的 研究SiCp/Al复合材料切削过程中的表面损伤形成机制。方法 以SiCp/Al复合材料为研究对象,展开基于二维切削的仿真和实验研究,建立了包含铝合金2A14、SiC增强颗粒以及界面特性的SiCp/Al切削仿真模型,对作用于不同Si C颗粒部位的材料表面缺陷进行分析;接着利用高速直线电机搭建能映射二维切削条件的实验平台,在不同材料去除条件下,利用扫描电子显微镜和白光干涉仪对切削表面形貌进行测试,分析和验证切削表面损伤形成条件。结果 SiCp/Al复合材料切削表面损伤机理取决于SiC颗粒相对刀具切削路径的位置：当刀尖作用在Si C颗粒的顶部时,表面损伤主要为基体撕裂、颗粒破碎;当刀尖作用在Si C颗粒的中部时,表面损伤为颗粒破碎导致的裂纹和凹坑;当刀尖作用在Si C颗粒的底部时,表面损伤为颗粒拔出导致的凹坑。随着切削深度的增大,凹坑逐渐增多,表面粗糙度随之增大。结论 利用二维切削模型仿真方法和高速直线电机实验,可以有效研究复合材料切削损伤形成机制。Si C颗粒相对刀具切削路径的位置不同会导致切削损伤不同;SiCp/Al复合材料表面质量会随着切削速度的提升而有所提高。     

单晶硅超精密切削的刀具磨损试验研究

针对单晶硅超精密切削过程中金刚石刀具磨损问题,对单晶硅进行超精密车削试验。通过观察金刚石刀具磨损演变过程,分析刀具的磨损过程对表面加工质量的影响,得到刀具磨损机理。结果表明,在超精密切削单晶硅过程中,随着切削距离的增加,刀具磨损面积逐渐增加,加工过程中产生的碳化硅及类似金刚石碳颗粒与刀具后刀面发生划擦造成磨粒磨损;同时,由于交变载荷作用导致的应力疲劳现象,进而伴有解理断裂产生。当切削路程小于4km时,加工表面的粗糙度Ra值在200nm以内,切削路程大于8km时,表面粗糙度Ra值在350nm~400nm之间。     

Research Progress of Diamond Tool Machining Technology for Ferrous MetalsEI北大核心CSCD

金刚石刀具是超精密加工最理想的刀具之一,但在黑色金属超精密加工领域“石墨化”导致刀具快速磨损,其应用极大地受到了限制。首先,针对金刚石刀具的磨损机理进行介绍。然后,综述金刚石刀具切削黑色金属的几种常见方法,如刀具表面改性、工件表面改性、低温辅助切削、超声振动辅助切削等,通过研究实例来分析各方法的应用效果和存在问题,并从技术层面分析影响金刚石刀具在黑色金属加工领域发展的关键因素。最后,对金刚石刀具切削黑色金属未来的发展趋势进行探讨。总结金刚石刀具在黑色金属领域的加工方法,分析加工黑色金属时抑制金刚石刀具磨损的核心技术,对黑色金属的精密超精密加工具有重要的引领和推动作用。     

SiC颗粒对SiC_p/2009Al复合材料疲劳短裂纹扩展的影响

采用粉末冶金法制备15%(体积分数)SiC_p/2009Al复合材料,研究该材料的微观组织、力学性能、高周疲劳性能以及疲劳断口形貌.结果表明:在SiC_p/2009Al复合材料的疲劳短裂纹扩展阶段,SiC颗粒及其表面包覆的2009Al薄层在裂纹扩展面上形成"丘陵"状形貌,使疲劳断口的粗糙度增大,裂纹的闭合效应也随之增大:同时"丘陵"状形貌可以引发疲劳裂纹扩展路径偏析,使裂纹扩展的有效驱动力减小并使裂纹扩展路径增加;上述裂纹迟滞效应使SiC_p/2009Al复合材料在短裂纹扩展阶段具有较高的疲劳裂纹扩展抗力.     

电镀金刚石线锯切割光伏多晶硅的表面特性与锯丝磨损分析

电镀金刚石线锯切割的光伏多晶硅切片表面特性,影响其断裂强度和后续的制绒工艺;为探究线锯锯切工艺参数对多晶硅切片表面特性的影响规律,揭示电镀金刚石锯丝的磨损机理,开展了光伏多晶硅的电镀金刚石线锯切片试验。研究结果表明:锯切的多晶硅表面存在由金刚石磨粒的塑性剪切、微切削去除形成的塑性浅划痕与较深的沟槽,及材料脆性去除留下的表面破碎微凹坑;切片表面材料的塑性去除和脆性去除相对比例随工艺参数组合变化而变化,增大晶片进给速度,降低走丝速度,切片表面粗糙度增大,表面形貌逐渐由塑性沟槽为主转变为以破碎微凹坑为主;使用表面镀镍(金属化)的金刚石颗粒制备的电镀金刚石锯丝的磨损形态在稳定阶段主要是磨粒磨平,使用后期主要是磨粒脱落和镀层磨损。      

SiCp/Al复合材料高速切削去除机理及表面质量研究

目的 探究高速加工下SiC_p/2024Al复合材料切屑形成机理及加工表面质量情况,为改善该材料加工性能提供理论依据。方法 设计高速正交铣削实验,对SiC_p/2024Al复合材料进行不同切削速度下的高速加工,并通过对切屑形态、切削力、切削能耗、加工表面形貌及加工硬化情况进行分析,探明高速加工下材料去除机理及加工表面质量变化。结果 在较低速度下复合材料的切屑形成过程为第一变形区的剪切变形和SiC颗粒破碎,切屑形态为锯齿状;切削速度在300～800 m/min时,随着速度的提高复合材料切屑连续性下降,切削速度在1 000 m/min时,复合材料韧脆性能发生转变,切屑呈现崩碎状;切削力在切削速度300～1 000 m/min时,随速度提高明显减小,主切削力由300 m/min时的320 N左右下降至1 000 m/min时的180 N左右,切削能耗显著降低;失效的SiC颗粒破坏加工表面质量,而高速加工对表面质量有一定改善,切削速度由300 m/min提高到1 000 m/min时,表面粗糙度由0.68μm下降至0.47μm,加工硬化深度也随切削速度提...     

超声辅助磨削SiCf/SiC陶瓷基复合材料

针对碳化硅纤维增强陶瓷基复合材料(SiC_f/SiC)存在加工质量差、刀具磨损严重等问题,开展金刚石砂轮端面超声辅助磨削SiC_f/SiC复合材料试验,对比研究超声辅助磨削和普通磨削SiC_f/SiC过程中的磨削力、表面形貌及表面粗糙度,并分析其材料去除机理。结果表明:超声辅助磨削可有效降低磨削力;超声作用能促使SiC纤维断裂,形成较短纤维而被去除,减少了纤维的折断和剥落,提高了其表面加工质量;在纵向振动端面磨削条件下,超声振幅在一定范围内有助于改善其表面加工质量,振幅过大则会导致表面冲击作用过强而使其表面质量降低。      

高体积分数SiCp/Al复合材料超声辅助划切微观去除机理

目的 揭示高体积分数SiC_p/Al复合材料在超声辅助加工条件下的材料去除机理。方法 采用SiC_p/Al复合材料的超声辅助划切试验,探究划切参数变化对超声振幅、划切力及摩擦因数的影响规律,并通过扫描电子显微镜和激光共聚焦显微镜对划痕表面微观形貌进行观察,分析单点金刚石磨粒工具超声辅助划切材料去除的特点。结果 随着划切深度从0.01 mm增加到0.05 mm,电流值逐渐降低,电流值变化量从12 mA增加到25m A,超声振幅逐渐衰减,金刚石压头的轴向冲击作用减弱。划切深度和划切速度的增加使切向挤压切削作用增强,划切力和摩擦因数增大。在材料去除过程中,碳化硅颗粒存在破碎成小颗粒、剪切断裂破碎和拔出等多种去除形式,铝基体出现明显的塑性流动和涂覆现象,并形成切削沟槽外侧堆积。结论 当切削深度和进给速度较小时,材料去除主要是在轴向的高频振动冲击作用下完成,材料表面加工质量较好;当切削深度和进给速度逐渐增大时,材料去除是在轴向冲击破碎和切向挤压切削共同作用下完成,材料表面加工质量逐渐降低。     

车削45%SiCp/Al复合材料刀具寿命及磨损机制研究

为探索金刚石刀具(PCD)和涂层硬质合金刀具加工45%SiCp/Al复合材料时的刀具磨损、切削力、表面粗糙度的变化规律,对45%SiCp/Al复合材料进行了切削试验。分别使用三向测力仪对切削力进行测量,光学显微镜对刀具磨损进行了观察和测量。分析了PCD和涂层硬质合金刀具磨损的演变过程及刀具磨损对切削力、表面粗糙度的影响规律。研究结果表明,对于PCD刀具,前刀面磨损形式依次为晶粒脱落、磨粒磨损、粘结磨损并存在崩刃。后刀面的主要磨损形式为磨粒磨损,并伴有积屑瘤的产生。硬质合金刀具前刀面磨损形式依次为涂层脱落、磨粒磨损,后刀面出现严重磨粒磨损并且出现粘附现象,用PCD刀具切削45%SiCp/Al复合材料,切削力随积屑瘤增长或脱落呈周期性变化。用涂层硬质合金刀具切削时,主切削力是PCD刀具的两倍。对于PCD刀具,表面粗糙度也随积屑瘤呈周期性变化。涂层硬质合金刀具切削45%SiCp/Al复合材料的表面粗糙度大于PCD刀具,并且随切削距离增加急剧增长。     

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.     

Fe3O4/SiO2/Bi2WO6磁性复合光催化剂的制备及其光催化性能

钨酸铋(Bi₂WO₆),结构最简单的Aurivillius相化合物,是近期受到研究者关注的新型光催化材料。然而,光催化剂粉末在反应介质中难被回收,工业化应用成本较高。本文用三步方法合成了可回收的Fe₃O₄/SiO₂/Bi₂WO₆磁性复合光催化剂,通过溶剂热法合成具有磁性的Fe₃O₄,用溶胶凝胶法在Fe₃O₄表面覆盖SiO₂层,后将磁性颗粒与Bi₂WO₆纳米片相结合。光催化剂的形貌结构及性能通过XRD、SEM、PL、UV-vis进行表征测试。结果表明,直径约500 nm的Fe₃O₄微球附着在边长约500 nm的Bi₂WO₆纳米片的表面,SiO₂在两者之间起到了粘连作用。光催化剂Fe₃O₄/SiO₂/Bi₂WO₆对于罗丹明B的光降解活性较好,且有一定磁性,可以通过外加磁场将其从溶液中分离,有较大的应用潜力。     

钕的添加对V2O5-MoO3/TiO2平板式脱硝催化剂性能的影响

本研究制备了一系列不同Nd含量的V₂O₅-MoO₃-Nd₂O₃/TiO₂平板式脱硝催化剂。采用XRD、N2-吸附脱附、XPS、H2-TPR、拉曼光谱、NH3-TPD和红外光谱等表征手段对催化剂进行分析。结果表明:适量的Nd2O3(0.25%、0.5%,质量分数)可以增强V₂O₅-MoO₃/TiO₂催化剂的还原性能,增加了催化剂的Oα/(Oα+Oβ)比率,从而提升了催化剂的脱硝活性。然而,过量Nd₂O₃(0.75%、1%)的添加,会导致催化剂酸性性能的显著降低,造成催化剂脱硝性能的下降。此外,过量Nd的添加还会对催化剂的耐磨性能有负面影响。各催化剂中,VMoN d(0.5%)/Ti催化剂显示了最佳的脱硝活性。并且,该催化剂还显示了优良的抗SO₂、H₂O性能。     

国外多孔基体氧化铝/氧化铝复合材料工程应用进展

氧化铝/氧化铝复合材料(Al2O3/Al2O3)是20世纪90年代兴起的一类连续陶瓷纤维增强陶瓷基复合材料,已经发展为与SiC/SiC、C/SiC等非氧化物陶瓷基复合材料并列的一类陶瓷基复合材料。与非氧化物陶瓷基复合材料相比,Al2O3/Al2O3具有长时抗氧化、高温耐腐蚀、低成本等独特优势,已经在航空发动机、地面燃气轮机等军民两用热结构材料领域展现出广阔的应用前景。本文从材料应用的角度出发,系统分析阐述了目前在Al2O3/Al2O3占主导地位的多孔基体Al2O3/Al2O3(P-Al2O3/Al2O3)的增韧机制、成型工艺和性能特点,重点归纳了国外近年来P-Al2O3/Al2O3的工程化应用进展及前景,最后指出了P-Al2O3/Al2O3存在的局限性并展望了未来发展方向,旨在为国内Al2O3/Al2O3体系发展提供借鉴和参考。     

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。     

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.     

Sol-gel synthesis of Bi3.25La0.75Ti3O12 nanotubes

Ferroelectric Bi_3.25La_0.75Ti₃O₁₂ (BLT) nanotubes were synthesized by sol-gel technique using nanochannel porous anodic aluminum oxide (AAO) templates, and were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM). BLT nanotubes with diameter of around 240 nm and the wall thickness of about 25 nm exhibited a single orthorhombic perovskite structure and highly preferential crystal growth along the [1 1 7] orientation, which have smooth wall morphologies and well-defined diameters corresponding to the diameter of the applied template. The formation mechanism of BLT nanotubes was discussed.     

Sinterability and dielectric properties of Ba0.55Sr0.4Ca0.05TiO3-CaTiSiO5-Mg2TiO4 composite ceramics

The composite ceramics of Ba_0.55Sr_0.4Ca_0.05TiO₃-CaTiSiO₅-Mg₂TiO₄ (BSCT-CTS-MT) were prepared by the conventional solid-state route. The sintering performance, phase structures, morphologies, and dielectric properties of the composite ceramics were investigated. The BSCT-CTS-MT ceramics were sintered at 1100 °C and possessed dense microstructure. The dielectric constant was tailored from 1196 to 141 as the amount of Mg₂TiO₄ increased from 0 to 50 wt%. The dielectric constant and dielectric loss of 40 wt% Ba_0.55Sr_0.4Ca_0.05TiO₃-10 wt% CaTiSiO₅-50 wt% Mg₂TiO₄ was 141 and 0.0020, respectively, and the tunability was 8.64% under a DC electric field of 8.0 kV/cm. The Curie peaks were broadened and depressed after the addition of CaTiSiO₅. The optimistic dielectric properties made it a promising candidate for the application of tunable capacitors and phase shifters.     

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.     

Low temperature sintering and microwave dielectric properties of (Mg0.7Zn0.3)0.95Co0.05TiO3 ceramics with BaCu(B2O5) additions

The effects of BaCu(B₂O₅) additives on the sintering temperature and microwave dielectric properties of (Mg_0.7Zn_0.3)_0.95Co_0.05TiO₃ ceramics were investigated. The (Mg_0.7Zn_0.3)_0.95Co_0.05TiO₃ ceramics were not able to be sintered below 1000 °C. However, when BaCu(B₂O₅) were added, they were sintered below 1000 °C and had the good microwave dielectric properties. It was suggested that a liquid phase with the composition of BaCu(B₂O₅) was formed during the sintering and assisted the densification of the (Mg_0.7Zn_0.3)_0.95Co_0.05TiO₃ ceramics at low temperature. BaCu(B₂O₅) powders were produced and used to reduce the sintering temperature of the (Mg_0.7Zn_0.3)_0.95Co_0.05TiO₃ ceramics. Good microwave dielectric properties of Q × f = 35,000 GHz, ?_r = 18.5.0 and τ_f = −51 ppm/°C were obtained for the (Mg_0.7Zn_0.3)_0.95Co_0.05TiO₃ ceramics containing 7 wt.% mol% BaCu(B₂O₅) sintered at 950 °C for 4 h.