反应等离子喷涂 Al2O3-TiB2-Al 复相涂层的反应机理

目的在铝合金表面制备Al2O3-TiB2-Al复合涂层,研究Al,TiO2,B2O3在等离子喷涂中的反应机理。方法采用反应等离子喷涂技术在铝合金表面制备复合涂层,应用扫描电镜与X射线衍射技术测试复合涂层的物相组成和显微组织,并通过燃烧波淬熄试验分析等离子喷涂产物。结果机械球磨可以有效降低粉末发生反应的活化能,等离子喷涂最佳飞行距离范围为150~200 mm。结论喷涂粉末在飞行过程中发生反应,经历了预热、熔化、分解、团聚等过程,验证了最终引燃发生燃烧化学反应的机理。     

Compressive behavior of SiCp/AlSi9Mg composite foams

Closed-cell AlSi₉Mg foams and SiC_p/AlSi₉Mg composite foams with different SiC_p volume fractions were prepared successfully by means of direct foaming of melt using CaCO₃ blowing agent in this paper. The compressive behaviors of these foams were studied. In comparison with the compressive stress–strain curve of AlSi₉Mg foams that of SiC_p/AlSi₉Mg composite foams is not smooth and exhibits some serrations. At the same relative density of composite foams, the yield stress and collapse stress of the composite foams increase with increasing SiC_p volume fraction. The relationship of yield stress, relative density and SiC_p volume fraction of SiC_p/AlSi₉Mg composite foams with a given particle size was obtained.     

Fabrication and performance of La0.8Sr0.2MnO3/YSZ graded composite cathodes for SOFC

The performance of multi-layer (1 − x) La_0.8Sr_0.2MnO₃/x YSZ graded composite cathodes was studied as electrode materials for intermediate solid oxide fuel cells (SOFC). The thermal expansion coefficient, electrical conductivity, and electrochemical performance of multi-layer composite cathodes were investigated. The thermal expansion coefficient and electrical conductivity decreased with the increase in YSZ content. The (1 -x)La_0.8Sr_0.2MnO₃/x YSZ composite cathode greatly increased the length of the active triple phase boundary line (TPBL) among electrode, electrolyte, and gas phase, leading to a decrease in polarization resistance and an increase in polarization current density. The polarization current density of the triple-layer graded composite cathode (0.77 A/cm²) was the highest and that of the monolayer cathode (0.13 A/cm²) was the lowest. The polarization resistance (R_p) of the triple-layer graded composite cathode was only 0.182 ω·cm² and that of the monolayer composite cathode was 0.323 ω·cm². The power density of the triple-layer graded composite cathode was the highest and that of the monolayer composite cathode was the lowest. The triple-layer graded composite cathode had superior performance.     

Preparation of nanostructured Ni/Al2O3 composite coatings in high magnetic field

Ni/Al₂O₃ composite coatings were prepared by a novel method from a modified Watt's type electrolyte containing nano-Al₂O₃ particles, where a high magnetic field was imposed in the direction parallel to an electrolytic current instead of mechanical agitation. Effects of magnetic field on the content of particles, surface morphology, microhardness and wear resistance of plating layer were investigated. It was found that the high magnetic field played an important role in the formation of composite coatings. The amounts of nano-Al₂O₃ particles in the composite coating increased with increasing of magnetic flux density and reached a maximum value at 8 T, then reduced slightly. The microhardness and wear resistance of the nanocomposite coatings also enhanced with increasing of magnetic flux density as compared to that of pure Ni coating fabricated in the absence of magnetic field. That was because the co-deposited nano-Al₂O₃ particles were uniformly distributed in the Ni matrix and contributed to greatly increase the microhardness and wear resistance of the composite coatings. Moreover, the mechanism of action of high magnetic field was discussed preliminarily.     

Characterization and properties of the MgF2/ZrO2 composite coatings on magnesium prepared by micro-arc oxidation

Through micro-arc oxidation, the MgF₂/ZrO₂ composite coatings were prepared on magnesium at the different applied voltages (in the range of 400-550 V) in a zirconate electrolytic solution. The morphologies, phase components, microhardness, bond strengths, and corrosion resistances of the composite coatings were investigated. The effect of the applied voltages on the characteristics and properties of the composite coatings and the basic formation mechanism of the coatings were also discussed. The results indicate that the composite coatings are relatively dense and uniform in thickness, and predominantly composed of MgF₂, tetragonal ZrO₂ (t-ZrO₂) and monoclinic ZrO₂ (m-ZrO₂). The composite coatings exhibit a gradient distribution in phase component from the surface to the inner part. It is found that the applied voltage plays an important role in the characteristics and properties of the composite coatings. With the increase of the applied voltage, the thickness and the t-ZrO₂ content of the composite coatings increase, while the m-ZrO₂ content decreases and no significant variation is observed in the MgF₂ content. Moreover, the surface microhardness and bond strength of the coatings increases with the applied voltage increasing. The microhardness values display a gradient distribution in the cross sections of the coatings, and the maximum microhardness value and its corresponding position in the cross sections are related to the applied voltage. In addition, the corrosion resistances of the composite coatings on magnesium surface are obviously superior to the magnesium substrate in the NaCl solutions, and the effect is more remarkable at higher voltage.     

Fabrication and characterization of Al356/SiCp semisolid composites by injecting SiCp containing composite powders

Al356/5 vol.% SiC_p cast composites were fabricated by the injection of reinforcement particles into the melt in three different forms, i.e. as untreated SiC_p, milled particulate Al-SiC_p composite powder, and milled Al-SiC_p-Mg composite powder. The resultant composite slurries were then cast in the semisolid temperature range of the alloy, upon which the effects of the type of injected powder on the distribution and incorporation of the reinforcement particles, along with the hardness of the cast composites, were investigated. Injection of milled composite powders resulted in considerable improvement in SiC_p wetting as well as the incorporation and distribution of SiC_p in the Al356 matrix alloy. Al356/5 vol.% SiC_p composite with well dispersed reinforcement particles of less than 3 μm average diameter was successfully produced by injecting Al-SiC_p-Mg composite powder into the melt. The best microstructural characteristics in terms of the reinforcement incorporation and distribution, and the highest hardness value of the cast composites, were achieved when magnesium was added through the injected composite powder and not directly into the melt.     

C_f/SiC复合材料与钛合金Ag-Cu-Ti-C_f复合钎焊

采用Ag-Cu-Ti-Cf(Cf:碳纤维)复合钎料作中间层,在适当的工艺参数下真空钎焊Cf/SiC复合材料与钛合金,利用SEM,EDS和XRD分析接头微观组织结构,利用剪切试验检测接头力学性能.结果表明,钎焊时复合钎料中的钛与Cf/SiC复合材料反应,在Cf/SiC复合材料与连接层界面形成Ti3SiC2,Ti5Si3和少量TiC化合物的混合反应层.复合钎料中的铜与钛合金中的钛发生互扩散,在连接层与钛合金界面形成不同成分的Cu-Ti化合物过渡层.钎焊后,形成碳纤维强化的致密复合连接层.碳纤维的加入缓解了接头的残余热应力,Cf/SiC/Ag-Cu-Ti-Cf/TC4接头抗剪强度明显高于Cf/SiC/Ag-Cu-Ti/TC4接头.     

Effect of medium temperature on the dispersion of WC/ZrO2/VC composite powders

This article proposed a novel method to disperse WC/ZrO₂/VC composite powders so as to attain a perfectly uniform suspension. Besides using conventional dispersing means such as adding dispersant (PEG, polyethylene glycol), mechanical stirring, ultrasonic vibration and ball milling, the temperature adjustment of dispersing-medium distilled water had also been employed. The agglomerating and dispersing mechanisms were analyzed by means of TEM observation of WC/ZrO₂/VC composite powders dispersed under five different temperatures, with the results showing that the most uniform dispersion was obtained under the temperature of 100 °C based on the criterion for conglomeration number per unit. The dispersed WC/ZrO₂/VC composite powders were dried and consequently sintered by hot-press sintering in nitrogen atmosphere at 1580 °C with pressure of 30 MPa. The testing results of mechanical properties such as relative density, hardness, bending strength and fracture toughness show that the optimal properties are obtained by using the WC/ZrO₂/VC composite powders dispersed under 100 °C. The surface crack morphologies of sintered samples are investigated and the results show that crack extended in a more tortuous path for the sample sintered from well-dispersed composite powders.     

HfB2/SiC as a protective coating for 2D Cf/SiC composites: Effect of high temperature oxidation on mechanical properties

In the field of thermal shielding for aerospace applications C_f/SiC composites are raising great interest, provided that they are protected from oxidation by suitable coatings. Conversely, ultra high temperature ceramics, and in particular HfB₂, are among the best oxidation resistant materials known. A coating made of a HfB₂/SiC composite (20% weight SiC) was tested as an oxidation protection on a C_f/SiC composite. The composite was produced by Polymer Impregnation Pyrolysis (PIP), which is a simple and low cost method; the coating was applied by painting a slurry on the surface of the composite and by heat treating. The thermal behaviour was studied by thermo-gravimetric analysis, and mechanical tests were conducted before and after oxidation. The HfB₂/SiC composite seems to effectively protect the underlying C_f/SiC composite, with a mechanical strength reduction of only 20% after 30 min at 1600 °C, even if some weight loss due to partial carbon fibre damage is observed. A first analysis of thermal cycling in oxidizing environment suggested that the HfB₂/SiC coating reduces continual damage thanks to the sealing effect of the glassy surface layer.     

喷射电沉积技术制备Co-Cr_3C_2复合镀层的工艺优化

为提高微米级硬质陶瓷颗粒在金属基复合镀层的含量,制备性能优异的防护性镀层,采用喷射电沉积的方法在直流电压下制备了Co-Cr_3C_2复合镀层,利用控制变量法探讨了电流密度、固体颗粒用量、镀液流量以及喷枪移动速度等对镀层中颗粒含量及镀层性能的影响,并分析了各因素的影响机理。同时,分别采用能谱仪、显微硬度计和摩擦磨损试验机对复合镀层的成分、硬度和摩擦因数进行分析,最终确定了制备该复合镀层的较优工艺参数。结果显示:喷头移动速度对颗粒复合量的影响最为显著;颗粒复合量越大,复合镀层硬度越高、摩擦因数越低;在较优工艺参数下制备的Co-Cr_3C_2复合镀层的Cr_3C_2颗粒含量高达23.6%。     

纳米稀土CeO2掺杂对Ni-Fe-Co-P合金镀层性能的影响

利用喷射电沉积技术制备了Ni-Fe-Co-P-CeO_2复合镀层。通过SEM、XRD、EDS等测试了复合镀层的表面形貌、截面形貌、物相结构和组成成分,同时,表征了复合镀层的硬度、耐磨和耐蚀性能,探究和分析了纳米稀土CeO_2颗粒浓度对镀层性能的影响。结果表明:该多元复合镀层为非晶态结构;随着镀液中CeO_2颗粒浓度的增加,复合镀层的显微硬度、耐磨性和耐蚀性均呈先增强后减弱的趋势;镀液中CeO_2颗粒浓度为1 g/L时,复合镀层的表面均匀致密,其HV_(0.1)显微硬度达到最大值5982 MPa,且具有最优的耐磨和耐蚀性能。     

PREPARATION OF MICROARC OXIDATION COATING ON (Al2O3-SiO2)sf/AZ91D MAGNESIUM MATRIX COMPOSITE AND ITS ELECTROCHEMICAL IMPEDANCE SPECTROSCOPIC ANALYSIS\par

在硅酸盐电解液体系中, 采用交流微弧氧化方法在增强体体积分数为33%的 (Al₂O₃-SiO₂)_sf/AZ91D镁基复合材料表面制备出完整的保护性氧化膜. 利用SEM, EDS和XRD分析了氧化膜的形貌、成分和相组成, 测量了膜层的显微硬度分布. 采用电化学阻抗谱(EIS)评价了微弧氧化表面处理前后复合材料的电化学腐蚀性能, 确立了不同浸泡时间对应的等效电路. 结果表明, 微弧氧化膜主要由MgO和Mg₂SiO₄相组成, 最大硬度达到1017 HV. 氧化膜电化学阻抗模值|Z|与镁合金基体相比大幅度提高, 耐腐蚀性能明显高于基体. 在3.5%NaCl溶液里浸泡96 h后, EIS出现感抗弧, 显示膜内部开始出现点蚀破坏. 氧化膜耐蚀性由膜内致密层特性所决定.     

304不锈钢表面Ni-Al2O3复合镀层制备及性能研究

采用复合电沉积法在304奥氏体不锈钢表面制备Ni-Al₂O₃纳米镀层. 研究了Al₂O₃颗粒在复合镀层中的分布情况, 确定了镀液中颗粒的最佳加入量、最佳电流强度和最佳搅拌速度. 用扫描电镜和能谱仪、X射线衍射仪等设备鉴定镀层显微组织与组成. 结果表明, Ni-Al₂O₃纳米复合镀层均匀、致密、晶粒细小; 复合镀层结合强度、耐腐蚀性能优良, 抗高温氧化性能优于纯镍镀层.     

BN/Al2O3 复合粉末及其聚合物基复合材料的制备与导热性能

采用固-液相共混法制备了多种BN/Al₂O₃复合粉末,通过冻融法和表面修饰法对BN进行了改性处理,改变表面修饰剂类型和摩尔比得到了前驱体和烧结态BN/Al₂O₃复合粉末,并利用机械混合法制备了聚合物基BN/Al₂O₃复合材料,并测试分析了其导热性能。结果表明,经冻融处理的BN分散性和界面相容性明显优于未经冻融处理的BN。多巴胺对BN的改性效果优于聚乙二醇。采用多巴胺作为表面修饰剂且BN与Al(NO₃)₃的摩尔比为1:1时,能够得到纳米Al₂O₃均匀包覆的微米BN粉末,即BN/Al₂O₃微纳复合粉末,其聚合物基复合材料的导热系数可达0.62 W·m^-1·K^-1,是纯聚合物导热系数的3倍,是采用纯微米BN粉末制备的聚合物基复合材料导热系数的1.5倍。在BN表面附着的Al₂O₃可以形成层状热传导通道,能够有效提高聚合物基BN/Al₂O₃复合材料的热导率。     

Comparison of thermal and ablation behaviors of C/SiC composites and C/ZrB2-SiC composites

A comparison was presented of the thermal and ablation behaviors of two carbon fiber reinforced ceramic-matrix composites (one with a SiC matrix and the other with a ZrB₂-SiC matrix). The C/SiC composite possessed a lower thermal conductivity (TC) and a higher emissivity in comparison to the C/ZrB₂-SiC composite. The two composites exhibited the good ablation-resistive properties with no obvious erosion rate after the arc-heated wind tunnel ablation tests. The surface of the C/SiC composite appeared to be coarse and had many rounded protrusions while a denser and more homogeneous glass oxide scale was formed for the C/ZrB₂-SiC composite. The maximum surface and back side temperatures of the C/ZrB₂-SiC composite were about 50 °C lower than those of the C/SiC composite, respectively, which was mainly attributed to the evaporation of the B₂O₃ as well as its higher TC.     

Investigation on the corrosion and oxidation resistance of Ni-Al2O3 nano-composite coatings prepared by sediment co-deposition

Ni-Al₂O₃ composite coatings were prepared by using sediment co-deposition (SCD) technique from a Watt's type electrolyte containing nano-Al₂O₃ particles. The corrosion resistance and high temperature oxidation resistance of resulting composite coatings were investigated. It was found that the incorporation of nano-Al₂O₃ particles in Ni matrix refined the Ni crystal and changed the preferential orientation of composite coatings. Meanwhile, the corrosion and oxidation resistance were improved after the incorporation of nano-Al₂O₃ particles into Ni matrix. The nano-Al₂O₃ content in deposits plays an important role for improving the corrosion and oxidation protection. The corrosion and oxidation resistance of Ni-Al₂O₃ nano-composite coatings produced via SCD technique are superior to that of CEP technique. Compared to pure Ni and Ni-Al₂O₃ composite coatings fabricated using CEP technique, the Ni-7.58 wt.% Al₂O₃ composite coating obtained by SCD technique exhibits better corrosion resistance and enhanced high temperature oxidation resistance. Moreover, the mechanism of corrosion and high temperature oxidation resistance of Ni-Al₂O₃ nano-composite coatings are discussed.     

镶嵌结构Na0.5Bi0.5TiO3-CoFe2O4复相多铁性陶瓷的制备与界面阻抗特性

使用溶胶-凝胶法原位制备了具有镶嵌结构的0-3型Na_0.5Bi_0.5TiO₃-CoFe₂O₄(NBT-CFO)复相多铁性陶瓷,并研究了其电、磁性能。通过TG-DTA、XRD等表征手段研究了干凝胶的结晶过程,利用CFO与NBT的差异化结晶温度设计了分步煅烧结晶工艺并得到粒径45 nm的NBT-CFO纳米粉体,并烧结得到具有镶嵌结构0.9NBT-0.1CFO复相陶瓷,陶瓷中CFO晶粒均匀分布在NBT晶粒内部。与使用机械混合法制备的复相陶瓷相比,具有镶嵌结构的0.9NBT-0.1CFO复相陶瓷在250-1M Hz频率范围内的室温介电损耗均更低,250 Hz时其损耗只有前者的30%。介电温谱、阻抗谱与模谱分析表明具有镶嵌结构的复相陶瓷在350-650 ^_oC温区内表现出由铁电-铁磁相界面极化造成的介电弛豫行为,其激活能为0.77 eV。镶嵌结构使复相陶瓷在室温下具有更大的剩余极化和更高的抗击穿场强,提高了其铁电性能。     

Fabrication and characterization of AI/TINI shape memory composites

Metal matrix composites reinforced with shape memory alloys induce compressive residual stress in the matrices resulting in improved tensile properties in the composite. In the present study, Al/TiNi shape memory composites were fabricated by squeeze casting and powder metallurgy the so-called Plasma Activated Sintering (PAS). Fairly good matrix/reinforcement bonding was observed in the Al/TiNi composites. The effects of the residual stress caused by the shape recovery force were compared as a function of reinforcement volume fraction, prestrain, matrix strength and reinforcement shape. Strengthening effect due to TiNi reinforcement as well as the compressive residual stress were investigated. It was found that the yield strength of the composites increased the volume fraction of TiNi reinforcement increased and the amount of prestrain applied to the composite. Moreover, the percentage of strength increment of the pure continuous fiber Al/TiNi (Al/TiNi_cf) composite caused by prestrain was higher than that of the AC4A Al/TiNi_cfcomposite. The percentage of strength increment of the Al/TiNi_cf composite was higher than that of the particulate Al/TiNi (Al/TiNi_p) composite.     

Improvement in the properties of nickel by nano-Cr2O3 incorporation

Nano-ceramic composite coatings were prepared by the electrodeposition method using sulphamate electrolyte. Nickel was chosen as the metal matrix and nano-Cr₂O₃ particles were chosen as the reinforcement. The surface morphology and the particle distribution in the coating were analysed using field emission scanning electron microscope (FESEM). The particle content was obtained using energy dispersive X-ray analysis (EDAX). A change in the surface morphology of Ni was seen on the incorporation of Cr₂O₃ particles. The coatings were characterized for their structure and no change in the diffraction pattern was seen between plain Ni and Ni-Cr₂O₃ composite. The mechanical property like microhardness and tribological behaviour of the nano-composite coatings was studied and it was observed that the incorporation of Cr₂O₃ particles enhanced the mechanical properties of Ni matrix. The nano-composites were analysed for their thermal stability and corrosion resistance. An improvement in thermal stability was observed but no change in the corrosion behaviour of Ni was seen on the incorporation of nano chromium oxide particles.     

Effects of CeO2 additive on the microstructure and mechanical properties of in situ TiB2/Al composite

In this paper, CeO₂ was investigated as an additive for in situ preparation of TiB₂/Al composite using an exothermic reaction process via K₂TiF₆ and KBF₄ salts. Experimental results indicated that when 0.5 wt.% CeO₂ additive was added, the dispersion of TiB₂ particles was improved significantly. Meanwhile, α-Al matrix grain was further refined. Compared with the composite without CeO₂, the ultimate tensile strength, yield strength, elastic modulus and tensile elongation increased by 8%, 7%, 26% and 14%, respectively in as-cast condition, and the tensile fracture behavior of the composite with CeO₂ belonged to a typical ductile fracture with microvoid coalescence.