Surfactant-decorated graphite nanoplatelets (GNPs) reinforced aluminum nanocomposites: sintering effects on hardness and wear

The exceptional properties of graphene make it ideal as a reinforcement to enhance the properties of aluminum matrices and this critically depends on uniform dispersion. In this study, the dispersion issue was addressed by sonication and non-covalent surface functionalization of graphite nanoplatelets (GNPs) using two types of surfactant: anionic (sodium dodecyl benzene sulfate (SDBS)) and non-ionic polymeric (ethyl cellulose (EC)). After colloidal mixing with Al powder, consolidation was performed at two sintering temperatures (550 and 620℃). The structure, density, mechanical and wear properties of the nanocomposite samples were investigated and compared with a pure Al and a pure GNPs/Al nanocomposite sample. Noticeably, EC-based 0.5wt% GNPs/Al samples showed the highest increment of 31% increase in hardness with reduced wear rate of 98.25% at 620℃, while a 22% increase in hardness with reduced wear rate of 96.98% at 550℃ was observed, as compared to pure Al. Microstructural analysis and the overall results validate the use of EC-based GNPs/Al nanocomposites as they performed better than pure Al and pure GNPs/Al nanocomposite at both sintering temperatures.     

Mechanical properties of graphene nanoplatelets reinforced 7075 aluminum alloy composite fabricated by spark plasma sintering

A 0.3 wt% graphene nanoplatelets(GNPs) reinforced 7075 aluminum alloy matrix(7075 Al) composite was fabricated by spark plasma sintering and its strength and wear resistance were investigated. The microstructures of the internal structure, the friction surface, and the wear debris were characterized by scanning electron microscopy, X-ray diffraction, and Raman spectroscopy. Compared with the original 7075 aluminum alloy, the hardness and elastic modulus of the 7075 Al/GNPs composite were found to have increased by 29% and 36%, respectively. The results of tribological experiments indicated that the composite also exhibited a lower wear rate than the original 7075 aluminum alloy.     

Investigation on microstructural, mechanical and electrochemical properties of aluminum composites reinforced with graphene nanoplatelets

In present study, the microstructure, mechanical and electrochemical properties of aluminum–graphene nanoplatelets (GNPs) composites were investigated before and after extrusion. The contents of graphene nanoplatelets (GNPs) were varied from 0.25 to 1.0 wt.% in aluminum matrix. The composites were fabricated thorough powder metallurgy method, and the experimental results revealed that Al-0.25%GNPs composite showed better mechanical properties compared with pure Al, Al-0.50%GNPs and Al-0.1.0%GNPs composites. Before extrusion, the Al-0.25%GNPs composite showed ~13.5% improvement in ultimate tensile strength (UTS) and ~50% enhancement in failure strain over monolithic matrix. On the other hand, Al-0.50%GNPs and Al-0.1.0%GNPs composites showed the tensile strength lower than monolithic matrix. No significant change was observed in 0.2% yield strength (YS) of the composites. However, the extruded materials showed different trends. The 0.2%YS of composites increased with increase in GNPs filler weight fractions. Surprisingly, UTS of composites with 0.25 and 0.50% GNPs was lower than monolithic matrix. The failure strain of the baseline matrix was enhanced by ~46% with 0.25% graphene nanoplatelets. The superior mechanical properties (in terms of failure strain) of the Al-0.25%GNPs composite maybe attributed to 2-D structure, high surface area and curled nature of graphene. In addition, the corrosion resistance of pure Al and its composites reinforced with 0.5 and 1.0 wt% GNPs was also investigated. It was found that the corrosion rate increased considerably by the presence of GNPs.     

Effects of sintering temperature on the microstructural evolution and wear behavior of WCp reinforced Ni-based coatings

This article focuses on the microstructural evolution and wear behavior of 50wt%WC reinforced Ni-based composites prepared onto 304 stainless steel substrates by vacuum sintering at different sintering temperatures. The microstructure and chemical composition of the coatings were investigated by X-ray diffraction (XRD), differential thermal analysis (DTA), scanning and transmission electron microscopy (SEM and TEM) equipped with energy-dispersive X-ray spectroscopy (EDS). The wear resistance of the coatings was tested by thrust washer testing. The mechanisms of the decomposition, dissolution, and precipitation of primary carbides, and their influences on the wear resistance have been discussed. The results indicate that the coating sintered at 1175°C is composed of fine WC particles, coarse M₆C (M=Ni, Fe, Co, etc.) carbides, and discrete borides dispersed in solid solution. Upon increasing the sintering temperature to 1225°C, the microstructure reveals few incompletely dissolved WC particles trapped in larger M₆C, Cr-rich lamellar M₂₃C₆, and M₃C₂ in the austenite matrix. M₂₃C₆ and M₃C₂ precipitates are formed in both the γ/M₆C grain boundary and the matrix. These large-sized and lamellar brittle phases tend to weaken the wear resistance of the composite coatings. The wear behavior is controlled simultaneously by both abrasive wear and adhesive wear. Among them, abrasive wear plays a major role in the wear process of the coating sintered at 1175°C, while the effect of adhesive wear is predominant in the coating sintered at 1225°C.     

原位合成TiC颗粒增强铝基复合材料及其磨损性能

利用原位合成的方法在几种锻铝基体中合成了TiC颗粒.X射线衍射谱表明,在复合材料的显微组织中TiC是惟一反应生成物.与基体材料相比,引入TiC后材料的耐磨性能有很大幅度的提高,且磨损性能与基体材料的强度之间没有必然的联系.对磨损试样表面的sEM观察显示,在磨损过程中TiC颗粒凸起于基体,在表面起支撑载荷的作用,同时使摩擦副(滚轮)与基体表面之间形成一个储存润滑油的间隙,从而改善了磨损过程中的润滑条件,减小了试样的磨损量.     

Microstructural evolution of hybrid aluminum matrix composites reinforced with SiC nanoparticles and graphene/graphite prepared by powder metallurgy

The dispersion of ceramic nanoparticles is of significance to the microstructure and properties of particulate reinforced metal matrix composites.In this study,two hybrid enhancers,SiC-graphite and SiC-graphene nanosheets(GNSs),were incorporated into aluminum matrix composites using powder metallurgy.The dispersion of the reinforcements and microstructural evolution of the composites were characterized by using Scanning Electron Microscopy,X-Ray Diffraction,Transmission Electron Microscopy,and Raman spectroscopy.The results show that thin GNSs accelerated the deformation of the aluminum particles,and defects were introduced into the carbonaceous phases during the ball milling process.Al_4 C_3 needles generated during hot pressing,and were observed to bridge the aluminum grains.Compared with graphite,GNSs were more uniformly dispersed throughout the composite,which in turn restrained grain growth.As a result,a nanostructured composite(57.7 nm) was successfully produced upon the addition of SiC-GNSs.     

石墨、铝电极低压脉冲电解含油废水效果对比

对铝、石墨电极-低压脉冲电解含油废水影响因素:时间、电压、频率、占空比、电解质进行了对比试验.结果表明:石墨电极和铝电极电解效果与支持电解质Na2SO4用量有较为明显的关系,当Na2SO4用量小于0.7%时,石墨电极的油去除率高于铝电极;大于0.7%时,铝电极的油去除率高于石墨电极.在支持电解质Na2SO4用量较高的条件下,石墨电极油去除率受电压、占空比、频率因素影响较大,随频率增加而增加,随电压、占空比增加油去除率先增加而后下降;当电压大于6 V,频率高于500 Hz,占空比大于30%时,改变参数对铝电极的油去除率影响不显著.     

连续配筋混凝土路面性能参数影响的试验

在对连续配筋混凝土路面(CRCP)病害调查的基础上,选定冲断和密集裂缝作为CRCP性能评价指标,修筑了11个CRCP试验段,通过改变混凝土组成、基层类型、钢筋防护、纵横向钢筋的夹角、纵向钢筋的埋置深度和主动控制裂缝间距等因素,测试了混凝土的抗压强度、抗拉强度、抗弯拉强度、抗压模量和抗弯拉模量;调查了各试验段裂缝发展状况,进行了落锤式弯沉仪(FWD)测试,并对比分析了各因素对CRCP性能的影响。结果表明,混凝土材料、纵横向钢筋的夹角和基层类型对密集裂缝的影响大于混凝土面板和基层之间夹层的影响,1~5 m的主动控制裂缝间距可以有效防止自然裂缝的产生。     

Cu-Zn-Al2O3 nanocomposites: study of microstructure,corrosion, and wear properties

Alumina nanoparticles were added to a Cu-Zn alloy to investigate their effect on the microstructural, tribological, and corrosion properties of the prepared alloys. Alloying was performed using a mixture of copper and zinc powders with 0vol% and 5vol% of α-Al nanopowder in a satellite ball mill. The results showed that the Cu-Zn solid solution formed after 18 h of mechanical alloying. The mechan-ically alloyed powder was compacted followed by sintering of the obtained green compacts at 750℃ for 30 min. Alumina nanoparticles were uniformly distributed in the matrix of the Cu-Zn alloy. The tribological properties were evaluated by pin-on-disk wear tests, which revealed that, upon the addition of alumina nanoparticles, the coefficient of friction and the wear rate were reduced to 20% and 40%, respectively. The corrosion properties of the samples exposed to a 3.5wt% NaCl solution were studied using the immersion and potentiodynamic polarization methods, which revealed that the addition of alumina nanoparticles reduced the corrosion current of the nanocomposite by 90%.     

烧结气氛对氮化铝陶瓷结构与性能的影响

以高温自蔓延法合成的氮化铝(AlN)粉末为原料,加入5%Y2O3作为烧结助剂,注射成形后分别在氮气和还原性氮气氛中1850℃常压烧结成AlN陶瓷,研究烧结气氛对AlN陶瓷结构与性能的影响.研究表明,不同气氛中烧结的AlN陶瓷的密度、第二相和热扩散系数有所不同,氮气中烧结的AlN陶瓷的密度、第二相和热扩散系数分别为3.20g·cm-3、钇铝酸盐(Y3Al5O12和Y4Al2O9)和0.559cm2·s-1;还原性氮气氛中烧结的AlN陶瓷的密度、第二相和热扩散系数为3.00g·cm-3、氮化钇(YN)和0.581cm2·s-1.扫描电镜(SEM)分析显示氮气氛中烧结的AlN陶瓷结构均一,而还原性氮气氛中烧结的AlN陶瓷内外结构不一致,容易产生变形.     

Cu-Zn-Al_2O_3 nanocomposites:study of microstructure,corrosion,and wear properties

Alumina nanoparticles were added to a Cu-Zn alloy to investigate their effect on the microstructural,tribological,and corrosion properties of the prepared alloys. Alloying was performed using a mixture of copper and zinc powders with 0vol% and 5vol% of α-Al nanopowder in a satellite ball mill. The results showed that the Cu-Zn solid solution formed after 18 h of mechanical alloying. The mechanically alloyed powder was compacted followed by sintering of the obtained green compacts at 750°C for 30 min. Alumina nanoparticles were uniformly distributed in the matrix of the Cu-Zn alloy. The tribological properties were evaluated by pin-on-disk wear tests,which revealed that,upon the addition of alumina nanoparticles,the coefficient of friction and the wear rate were reduced to 20% and 40%,respectively. The corrosion properties of the samples exposed to a 3.5wt% Na Cl solution were studied using the immersion and potentiodynamic polarization methods,which revealed that the addition of alumina nanoparticles reduced the corrosion current of the nanocomposite by 90%.     

成型和烧结工艺对高纯氧化铝磨球性能的影响

为研究成型和烧结工艺对高纯氧化铝磨球性能的影响,采用团粒法制备形状良好的球坯,利用常压烧结方法制备高纯氧化铝磨球。结果表明,成型机转速和旋转时间对磨球粒径分布有较大的影响。随着烧结温度的提高以及保温时间的延长,高纯氧化铝磨球的质量密度逐渐增加,磨损率逐渐减小。在1 500℃保温210 min制得高纯氧化铝磨球的质量密度为3.15 g/cm3,磨损率为0.63%。     

Effect of feeding ratios on the structure and electrochemical performance of graphite oxide/polypyrrole nanocomposites

Graphite oxide (GO)/polypyrrole (PPy) nanocomposites (GPYs) were synthesized using in situ polymerization.The effect of the feeding ratios of pyrrole and GO on the structure and electrochemical performances of GPYs was investigated.The structure was characterized via Fourier-transform infrared spectroscopy,scanning electron microscopy,transmission electron microscopy and X-ray diffraction.The electrochemical performance was characterized via cyclic voltammetry,galvanostatic charge-discharge and electrochemical impedance spectroscopy.The results indicate that the more pyrrole is added to GO (with GO concentrations of 20% and 50%),the more agglomeration of both PPy and GO layers occurs.This is detrimental to the capacitance utilization of PPy.When the feeding ratio of GO:pyrrole is 80:20,PPys with nanofibrils are dispersed homogenously in/on the exfoliated layer of GO and the conductivity is enhanced.The capacitance utilization of PPy in a composite with a GO concentration of 80% (383 F/g) is higher than that of pure PPy (201 F/g),which indicates the presence of a synergistic effect between GO and PPy.     

Influence of sintering temperature on the thermoelectric properties of Ba_8Ga_(16)Si_(30) clathrate treated by spark plasma sintering

A series of Ba_8Ga_(16)Si_(30) clathrate samples were prepared by arc melting,ball milling,acid washing,and spark plasma sintering(SPS).X-ray diffraction analysis revealed that the lattice of the Ba_8Ga_(16)Si_(30) samples expanded as the SPS temperature was increased from400 to 750℃.Lattice contraction recurred when the SPS temperature was further increased in the range of 750-1000℃.This phenomenon can be explained by the variation of Ga content in the lattice.The thermoelectric figure of the merit ZT value of clathrates increased with the increase in SPS temperature and reached a maximum when the sample was subjected to SPS at 800℃.A further increase in SPS temperature did not contribute to the improvement of ZT.The variation of the lattice parameter a vs.SPS temperature T was similar to the variation observed in the ZT-T curve.     

添加等量铝粉和石墨对低碳镁碳砖性能的影响

随着冶金行业的发展,低碳镁碳砖已成为镁碳砖研究的一个重要发展方向.本文以＜5～3 mm,＜3～1mm,＜1～0.074 mm,＜0.074 mm的电熔镁砂和＜0.172 mm的鳞片状石墨为原料,热固性酚醛树脂为结合剂,金属Al粉为抗氧化剂,研究了加入石墨的质量分数对低碳镁碳砖性能的影响.实验结果表明：随着石墨质量分数的增加,低碳镁碳砖的常温强度、体积质量和显气孔率均随之减小,高温抗折强度和抗氧化性随之提高;综合分析当加入石墨的质量分数在2％时所得低碳镁碳砖的综合性能最优.     

放电等离子烧结及热处理制备的Fe/316L/430–Ti(C,N)复合材料的滑动磨损行为

A series of novel steel–Ti(C,N) composites was fabricated by spark plasma sintering (SPS) and subsequent heat treatment. The hardness, indentation fracture resistance, and wear behaviour of the steel–Ti(C,N) composites were compared with those of the unreinforced samples, and their potentials were assessed by comparison with traditional cermet/hardmetal systems. The results showed that with the addition of 20wt% Ti(C,N), the wear rates of the newly examined composites reduced by a factor of about 2 to 4 and were comparable to those of cermets and hardmetals. The martensitic transformation of the steel matrix and the formation of in situ carbides induced by heat treatment enhanced the wear resistance. Although the presence of excessive in situ carbides improved the hardness, the low indentation fracture resistance (IFR) value resulted in brittle fracture, which in turn resulted in poor wear property. Moreover, the operative wear mechanisms were investigated. This study provides a practical and cost-effective approach to prepare steel–Ti(C,N) composites as potential wear-resistant materials.     

Effect of sintering temperature on phase evolution of Al_(86)Ni_6Y_(4.5)Co_2La_(1.5) bulk amorphous composites synthesized via mechanical alloying and spark plasma sintering

Al_(86)Ni_6Y_(4.5)Co_2La_(1.5) amorphous powders were synthesized by mechanical alloying for 200 h. Subsequent consolidation was performed via spark plasma sintering in the temperature range of 250 ℃ to 500 ℃ at the pressure of 500 MPa. The role of viscous flow on densification was investigated by studying the viscosity change of the amorphous phase at different consolidation temperatures. The decrease in viscosity at higher sintering temperatures resulted in better particle bonding and densification of consolidated samples. The formation of only FCC Al was observed in the consolidated samples at sintering temperatures ≤ 300 ℃ and the intermetallic phases formed at temperatures ≥ 400 ℃. The mechanical properties of the bulk samples were measured by Vickers microhardness and nanoindentation tests. The testing results showed that the average values of microhardness, nanohardness and elastic modulus of the sample consolidated at 500 ℃ were 3.06 ± 0.14 GPa,4.85 ± 1.14 GPa and 89.53 ± 9.25 GPa, respectively. The increase in hardness and elastic modulus of the higher temperature consolidated samples is attributed to the improvement in particle bonding, densification and distribution of various hard intermetallic phases in the amorphous matrix.     

Studies on the effects of pre-firing and sintering temperature on NSDC nanocomposite electrolytes

Solid oxide fuel cells (SOFCs) technology, with fuel flexibility, is one of the most promising power generation technology. However, the high operating temperature of SOFCs has hindered their commercial applications. As a crucial requirement to enhance its performance, SOFCs electrolytes should operate at a low temperature. Carbonate/ceria composites are developed as electrolytes for low operating temperature SOFCs, and a better understanding of the mechanism of its ionic conductivity serves this purpose. In this work, ceria-carbonate composite electrolyte, Na₂CO₃/samarium doped ceria (NSDC) were synthesized by the co-precipitation method. The synthesized electrolytes were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and UV–Vis spectroscopy. The XRD and SEM results showed that the sintered NSDC nanocomposite comprised a single-phase dense electrolyte structure. The crystallite size of the NSDC nanocomposite was greatly affected by the different pre-firing temperatures and different sintering temperatures. Also, the ionic conductivity of the prepared NSDC nanocomposite electrolytes was strongly dependent on the pre-firing and sintering temperatures. The NSDC nanocomposite electrolytes were pre-fired at 950 ?°C and 650 ?°C and sintered at 1200 ?°C and 900 ?°C respectively, had ionic conductivity in H₂ and air high as 0.36 ?S/cm and 0.3 ?S/cm.     

保温时间对铝厂废渣研制的氧化铝磨介微观结构及性能影响

以铝型材厂废渣为主要原料,通过添加少量粘土,滑石及碳酸钡复合助烧剂研制刚玉耐磨瓷球.探讨不同保温时间对瓷球微观结构及各项性能指标的影响.采用XRD和SEM等测试手段探讨其晶相结构和显微结构并测试抗弯强度、硬度、磨损率和气孔率等性能指标.结果表明:最佳保温时间为3 h,此时样品由4种晶相组成,其中刚玉为主晶相,含量约75%,其各项性能分别为:吸水率为0.032%,气孔率为0.105%,体积密度为3.289 g/cm3,抗弯强度为136 MPa,显微硬度为8.25 GPa,磨损率为0.044 1%/h.