ZA22/Al2O3复合材料切削加工表面质量的研究

采用硬质合金刀具研究了挤压铸造Al₂O₃短纤维强化ZA22合金复合材料的切削加工表面质量。发现在相同切削条件下,该复合材料表面质量优于ZA22合金。高的切削速度、低的进给量及低的切削深度有利于提高该复合材料的切削加工表面质量。随Al₂O₃纤维体积分数增大,复合材料切削加工表面粗糙度降低。     

亚微米Al2O3P/Al-Mg-Si复合材料时效行为

为了研究亚微米级Al₂O₃颗粒对基体合金时效过程的影响规律,在 6061 铝合金基础上调整Mg、Si含量,采用压力浸渗法,制备了Al₂O₃体积分数为30%的亚微米级Al₂O_3P/Al-2.26Mg-0.63Si复合材料。通过硬度试验、SEM和TEM等手段,研究了复合材料及其基体合金的时效行为。结果表明,Al-2. 26Mg-0.63Si 合金的时效过程比较明显,随时效温度的提高峰时效时间提前,190℃时出现时效软化现象。亚微米Al₂O₃颗粒的加入强烈抑制复合材料的时效过程,时效曲线未出现明显时效峰。分析认为,由于大部分Mg 元素被消耗在界面形成MgAl₂O_4,且基体中位错稀少,不利于溶质原子扩散,因此复合材料中沉淀相在过时效阶段仍停留在GP区状态,没有充分长大,时效析出受到抑制。     

20wt% SiO2/Al-Mg复合材料的界面反应及其微结构

采用粉末冶金法制备了20wt% SiO₂/Al-Mg复合材料。研究了SiO₂和基体元素Al,Mg反应机制,研究表明:在原SiO₂颗粒内,形成MgAl₂O₄,MgO,Mg₂Si和少量Al和Si。MgAl₂O₄呈不规则形状,而且MgAl₂O₄往往和Al相邻;MgO和Mg₂Si形成片层状共析体;经620℃烧结30min,SiO₂被完全反应掉。反应生成物Si多数被排到Al基体中;原Al-Mg基体中主要物相为:Al,Mg₂Si和Si,Mg₂Si颗粒的尺寸小于0.2μm。原Al-Mg基体中,单质Mg已不存在,Mg反应形成Mg₂Si。     

ZA22/Al2O3f复合材料机械性能的神经网络模拟研究

采用人工神经网络的典型模型即B-P算法对ZA22/Al₂O_3f复合材料的机械性能进行分析和预测,结果表明:B-P模型不仅适用于单变量输出非线性系统的拟合与预测,同时还适用于多变量输出的非线性系统;B-P模型对研究复合材料ZA22/Al₂O_3f的机械性能有良好容错性.     

原位生成TiB2/ZA27复合材料的制备与性能

以Al熔液为载体,采用原位反应生成形状规则、尺寸细小的TiB₂颗粒相,再将TiB₂颗粒传递到ZA27合金中,形成TiB₂颗粒增强的ZA27复合材料。采用合理的熔炼工艺促进了TiB₂颗粒在基体中的均匀分布。实验结果显示,TiB₂颗粒在ZA27复合材料中,分布均匀,平均直径在3 μm以下。TiB₂颗粒的加入使得复合材料的晶粒明显细化,并随着TiB₂颗粒含量增加,复合材料的抗拉强度、硬度明显提高,2.1%TiB₂/ZA27复合材料与基体合金相比室温抗拉强度提高13%、布氏硬度提高21%,弹性模量也有所提高,在强度、硬度及弹性模量提高的同时,材料的塑性并未恶化,延伸率略有提高,另外,材料的热膨胀系数随着TiB₂颗粒的加入有所降低。     

硅酸铝短纤维增强AZ91D复合材料的界面微观结构及力学性能

以晶化的硅酸铝短纤维（Al₂O₃-SiO₂ ）_sf为增强体、用磷酸铝为预制体粘结剂,通过挤压浸渗工艺制备了（Al₂O₃-SiO₂ ）_sf /AZ91D镁基复合材料。通过光学显微镜、TEM和HREM分析研究了复合材料的界面微观结构和界面反应产物。结果表明：用挤压浸渗法制备的硅酸铝短纤维增强AZ91D镁基复合材料的界面厚度约为100 nm,界面上除有一定数量的MgO颗粒和少量的MgAl₂O₄和Mg₂Si颗粒外, 还有少量的MgP₄等反应产物存在;硅酸铝增强纤维与镁合金基体之间形成了较强界面结合,界面微观结构比较理想。力学性能测试表明,与AZ91D基体合金相比,复合材料的室温抗拉强度提高了约18%,弹性模量提高了约58%。     

Al2O3-SiO2纤维增强ZL108合金复合材料的强度特性

用低成本的Al₂O₃-SiO₂系纤维作为增强相,通过加压铸造法制作ZL108合金复合材料,并对该复合材料和ZL108合金进行不同温度下的时效处理和压缩试验。通过DSC、EPMA和TEM分析认为:经488K、0.5h时效处理(T6处理)的V_f 20%的复合材料在573K以下的压缩屈服强度低于ZL108合金,是由于基体中的Mg与Al₂O₃-SiO₂纤维在加压铸造过程中起化学反应而生成MgAl₂O₄,损耗了基体中的大量Mg,导致基体铝合金时效硬化效果很差,所以压缩屈服强度低下。623K、720h保温后的V_f 20%的复合材料的压缩屈服强度比ZL108合金要高得多,是由于在这种温度环境下对ZL108合金来说是过时效,所以纤维的增强怍用显得明显。在高温(673K)下V_f 20%的复合材料的屈服强度比ZL108台金高一倍左右。不论在什么温度场合下V_f5%的复合材料的屈服强度比V_f 20%的复合材料都低。     

α-Al2O3 P/Al复合材料无压渗透制备反应加工机制的探讨

本工作利用无压渗透法制备刚玉颗粒(α-Al₂O_3p)增强AlMg10合金复合材料,采用扫描电镜和EDS分析显微组织,并对无压渗透过程热力学研究,提出其反应加工机制:刚玉颗粒间隙内有限容积气氛(21%O₂,79%N₂),同熔融合金中铝(Al)镁(Mg)元素反应,形成固相,造成某种真空度,为无压渗透的驱动力。高温长时间条件下熔融基体AlMg10合金同刚玉颗粒和附加物的残留物发生化学反应。     

SiO2玻璃原位反应合成Al/Al2O3复合材料

利用SiO₂玻璃具有易近成型、致密及各向同性的特点,通过SiO₂玻璃与铝熔体间的反应合成了Al/Al₂O₃复合材料,克服长期以来在合成Al/Al₂O₃复合材料时均采用颗粒反应物的局限。反应产物是一种组织均匀致密的Al 与Al₂O₃互为网络的Al/Al₂O₃陶瓷基复合材料。反应温度升高,整个反应产物中的Al的体积分数上升。Al/Al₂O₃复合组织在三维空间的真实形态中存在着Al相被Al₂O₃完全包围的形态,证明了网络状Al₂O₃组织形成的烧结机理。与合成Al/Al₂O₃的其它工艺相比,本工艺可在1000℃的较低温度进行,并具有反应速度快、断裂韧性和抗弯强度值高的特点。     

原始SiC颗粒表面及SiCP/Al复合材料界面化学状态的研究

本文采用X射线光电子谱(XPS)和俄歇能谱技术(AES)对原始SiC颗粒表面和粉末冶金法制备的SiC_P/Al复合材料界面的化学状态进行了研究.结果表明:原始SiC颗粒表面主要存在SiC、SiO₂、游离C、吸附氧、Fe₂O₃等;SiC_P/Al复合材料界面存在Mg偏聚和氧元素.由热力学分析可知,Mg元素能够向界面偏聚,并可能与界面处的氧反应生成MgO.     

Fabrication of (TiB/Ti)-TiAl composites with a controlled laminated architecture and enhanced mechanical properties

The(TiB/Ti)-TiAl composites with a laminated structure composing of alternating TiB/Ti composite layers,α₂-Ti₃Al interfacial reaction layers of andγ-TiAl layers were successfully pre pared by spark plasma sintering of alternately stacked Tib₂/Ti powder layers and TiAl powder layers.And the influence of thickness ratio of Tib₂/Ti powder layers to TiAl powder layers on microstructure evolution and mechanical properties of the re sulting(TiB/Ti)-TiAl laminated composites were investigated systemically.The results showed that the thickening ofα₂-Ti₃Al layers which originated from the reaction of Ti and TiAl was significantly hindered by introducing Tib₂particles into starting Ti powders.As the thickness ratio of Tib₂/Ti powder layers to TiAl powder layers increased,the bending fracture strength and fracture toughness at room temperature of the final(TiB/Ti)-TiAl laminated composites were remarkably improved,especially for the(TiB/Ti)-TiAl composites prepared by Tib₂/Ti powder layers with thickness of 800μm and TiAl powder layers with thickness of 400μm,whose fracture toughness and bending strength were up to 51.2 MPa·m^1/2and 1456 MPa,respectively,293%and 108%higher than that of the monolithic TiAl alloys in the present work.This was attributed to the addition of high-performance network TiB/Ti composite layers.Moreover,it was noteworthy that the ultimate tensile strength at 700℃of(TiB/Ti)-TiAl composites fabricated by 400μm thick Tib₂/Ti powder layers and 400μm thick TiAl powder layers was as high as that at 550℃of network TiB/Ti composites.This means the service temperature of(TiB/Ti)-TiAl laminated composites was likely raised by 150℃,meanwhile a good combination of high strength and high toughness at ambient tempe rature could be maintained.Finally,the fracture mechanism of(TiB/Ti)-TiAl laminated composites was proposed.     

亥姆霍兹上喷嘴出口结构对射流振荡特性的影响

应用FLUENT软件对二维的亥姆霍兹喷嘴自振射流进行了模拟,并以此为基础研究了上喷嘴出口凸出部深入振荡腔对亥姆霍兹喷嘴自激振荡特性的影响。结果表明,上喷嘴的出口凸出部长度和喷嘴壁厚度都对自激振荡特性产生显著的影响。长度为0～0.15D_1时,自振射流的脉动幅值可以提高20%～80%,提升幅度在射流速度较低时更大;凸出部长度为0.15～0.25D_1时,射流振幅的提升逐渐降低;长度0.25～0.3D_1时,射流振幅比普通喷嘴更低,稳定性下降;长度超过0.3D_1时自振射流会完全消失。凸出部分喷嘴壁厚度在0δ0.1D_1范围内对射流性能几乎没有影响,但随着厚度δ的不断增大,性能会减弱,δ0.15D_1时无法形成自振射流。总之,上喷嘴出口凸出可改善射流振荡性能,但长度和厚度需在一定范围内,否则无法产生自振射流。     

铸渗法制备颗粒增强钢基复合材料的研究

通过对负压铸渗理论的分析, 得出了影响负压铸渗深度的因素及其影响规律(见式(9) ) ;用碳化钨、镍包氧化铝及不同粒度氧化铝为陶瓷颗粒、耐热钢为基体进行了负压铸渗实验, 得到了颗粒分布均匀的复合材料, 揭示和证实了颗粒与金属液间的湿润特性及颗粒粒度对铸渗的影响规律。      

原位反应法制备Cf/SiC复合材料MoSi2-SiC-Si涂层

以C_f/SiC复合材料为基体, 采用原位反应法制备了MoSi₂-SiC-Si涂层, 借助XRD、扫描电镜及能谱对涂层的结构及组成进行了分析研究, 并考查了其高温抗氧化性能. 结果表明, 涂层总厚度约120μm, 主要由MoSi₂、SiC和Si组成. MoSi₂-SiC-Si涂层具有优异的高温抗氧化性能, 在1500℃静态空气中氧化96h, 涂层试样失重仅1.8%. 涂层试样失重的主要原因是由于氧气通过涂层中的贯穿性裂纹与C_f/SiC复合材料基体发生了反应.     

以氧化石墨烯为氧化介质制备石墨烯/聚苯胺导电复合材料

采用超声辅助Hummers法制得厚度约为1 nm的氧化石墨烯, 以其为氧化介质与苯胺反应合成了石墨烯/聚苯胺(RGO/PANI)导电复合材料。利用AFM、SEM、XRD和FTIR对反应所得产物进行了表征。结果表明: 苯胺在略高于室温的酸性水溶液中可以对氧化石墨烯(GO)进行还原, 而苯胺自身则被氧化石墨烯中大量的含氧基团氧化并发生聚合反应, 最终生成RGO/PANI导电复合材料, 当苯胺用量为1 mL, 氧化石墨烯用量为0.1 g, 在水浴温度为70 ℃下剧烈搅拌24 h时, 获得的RGO/PANI复合材料导电性最佳, 约为10 S/cm。     

Experimental study on impact-initiated characters of W/Zr energetic fragments

Fragments of energetic materials have stronger damage effect than traditional inert fragments due to additional energy released by simultaneous chemical reaction. In order to characterize the effect of the properties of energetic materials on the chemical reaction, a vented chamber is used to measure the released energy of energetic fragments under impact conditions, a method developed by Ames. Two energetic fragments, W/Zr-based alloy composites and W/Zr-based metallic glass composites, are also used. They are driven by a 12.7 mm ballistic gun, with various levels of velocity, to impact the sealed chamber containing plates with different material and thickness. High-speed videos of energetic fragments of impact-initiated reaction are recorded through an observational window. The pressure in the chamber is measured by strain pressure sensors. According to one-dimensional shock wave theory, the critical energy generated from the impact-initiated chemical reaction by W/Zr-based alloy composites energetic fragments are calculated, using the data collected from the experiment. The effects on impact-initiated chemical reaction, of types of energetic fragments used in the experiment, as well as target material and thickness are discussed and analyzed.     

Synthesis of core–shell FeCo@SiO<Subscript>2</Subscript> particles coated with the reduced graphene oxide as an efficient broadband electromagnetic wave absorber

The FeCo@SiO₂@RGO composites were prepared by combining liquid-phase reduction reaction in Argon atmosphere with hydrothermal reaction. The crystal structure, chemical composition and morphology of the as-prepared composites have been investigated in detail. SEM and TEM results illustrate that the FeCo@SiO₂ composites are of core–shell structure with a diameter of about 150–200 nm. Compared with FeCo@SiO₂ and FeCo@RGO composites, the as-prepared FeCo@SiO₂@RGO composites exhibit excellent electromagnetic (EM) wave absorption properties. As an EM wave absorber, the maximum R_L reaches ?52.9 dB at 9.12 GHz with a thickness of 3.0 mm, and the absorption bandwidth with the reflection loss below ?10 dB was up to 5.36 GHz (from 8.8 to 14.16 GHz) with a thickness of 2.5 mm. It is believed that the FeCo@SiO₂@RGO composites can serve as an excellent microwave absorbent and can be widely used in the microwave absorbing area.     

主梁式TBM关键结构参数对其动力学特性的影响规律

全断面岩石隧道掘进机(TBM)在掘进过程中,承受不断变化的大推力、大扭矩、倾覆力矩等随机载荷,引起主机较大的振动。为了减少主机系统各部件的疲劳失效,提高掘进效率,基于动力学仿真软件建立了主梁式TBM主机系统动力学模型,研究主机系统的动力学特性及主梁结构参数对其动力学特性的影响规律。研究结果表明:主梁1长度增加会导致主梁1振动变大,主梁2和鞍架的振动减小。主梁1板厚增加会导致主梁1振动减小,主梁2的振动缓慢增大,鞍架的振动先增加后减小,在上、下腹板厚度50 mm,侧板厚度40 mm,前、后法兰厚度105 mm时,振动达到最大值;刀盘掘进方向的加速度有效值为1.1 g,主梁加速度有效值为0.21 g,随着向后传递振动逐渐减弱,振动频率主要集中在0~50 Hz;依据仿真结果确定了主梁的相关参数,该TBM在某引水工程中经过2年的应用,工程已顺利贯通;现场测试结果表明,三向振动测试数据与仿真结果的误差基本低于20%。     

Effects of PyC shell thickness on the microstructure,ablation resistance of SiCnws/PyC-C/C-ZrC-SiC composites

SiC nanowires/pyrocarbon (SiCnws/PyC) core-shell structure toughened C/C-ZrC-SiC composites were fabricated by CLVD process,and the influences of PyC shell thickness on the microstructure and ablation resistance of the composites were researched.The results presented that SiCnws/PyC core-shell structure had a linear shape,and the composites became dense with the increasing PyC thickness.When the thickness of PyC shell increased from 0 to 2.4 μm,the density and thermal conductivity of the composites was improved gradually,but the coefficient of thermal expansion (CTE) decreased firstly and then increased.After the ablation test for 90 s,the ablation rates of the composites decreased continuously as the PyC thickness increased from 0 to 1.4 μm,but increased when the PyC thickness was up to 2.4 μm.Especially when the PyC thickness was 1.4 μm,the linear and mass ablation rates of the composites were 71.25 ％ and 63.01 ％ lower than those of the composites without PyC shell.The reasons behind the remarkable improvement of anti-ablation property were that the proper PyC thickness could alleviate the CTE mismatch to promote the formation of complete oxide coating,improve the thermal conductivity to reduce heat corrosion and enhance the capability to limit the mechanical erosion.     

Interfacial control of uni-directional SiCf/SiC composites based on electrophoretic deposition and their mechanical properties

Interfacial control of uni-directional SiC_f/SiC composites were performed by EPD, and their mechanical properties at room temperature were evaluated. The effect of the thickness of carbon interphase on SiC fibers by EPD on mechanical properties of uni-directional SiC_f/SiC composites was also investigated. The average thickness of carbon coating on SiC fibers increased from 42 nm to 164 nm with an increase in the concentration of colloidal graphite suspension for EPD. Dense SiC_f/SiC composites were achieved and their fiber volume fraction was 47–51%. The SiC_f/SiC composites had a bending strength of 210–240 MPa. As the thickness of carbon coating was below 100 nm, the SiC_f/SiC composites (SC01 and SC02) fractured in almost brittle manner. In contrast, the SiC_f/SiC composites (SC03) showed a pseudo-ductile fracture behavior with a large number of fiber pullout as the thickness of carbon coating was above 100 nm. The fracture energy of SC03 was 3–4 times as high as those of SC01 and SC02 and the value was about 1.7 kJ/m². In consideration of the results of mechanical properties, the thickness of carbon coating on SiC fibers should be at least 100 nm to obtain high-performance SiC_f/SiC composites. The fabrication process based on EPD method is expected to be an effective way to control the interfaces of SiC_f/SiC composites and to obtain high-performance SiC_f/SiC composites.