Fabrication of an electrolyte-supported protonic ceramic fuel cell with nano-sized powders of Ni-composite anode

Composite anodes of nano-sized Ni and Ba(Zr_0.85Y_0.15)O_3-δ (BZY) were fabricated by infiltrating a single precursor solution of BZY and Ni into the BZY scaffold, and decreasing the calcination temperature to 1173 K. This decrease in the fabrication temperature of the Ni-cermet anode prevents the chemical reaction between the electrolyte and nickel, thus preventing a reduction in the conductivity of the electrolyte. By optimizing the amount of Ni in the Ni-cermet and infiltrating additional catalysts such as CeO₂ and Pd, the non-ohmic ASR of the Ni-cermet anode could be optimized. This resulted in a smaller non-ohmic ASR of anode than one that was fabricated by the conventional co-sintering method. Consequently, a high power density of 790 mW/cm² at 973 K can be obtained from electrolyte-supported cells.     

Wet abrasive wear behavior of WC-based cermet coatings prepared by HVOF spraying

In this study, three kinds of WC-based cermet coatings including WC–CoCr coating, WC–Ni coating and WC–Cr₃C₂–Ni coating were prepared by the high-velocity oxygen-fuel (HVOF) spraying process. Scanning electron microscopy (SEM), energy disperse spectroscopy (EDS) and Vickers hardness tester were used to analyze the microstructure and mechanical properties of these coatings. The WC–CoCr coating presented the highest average microhardness of 1205 HV_0.3, and then followed by the WC–Cr₃C₂–Ni coating (1188 HV_0.3) and the WC–Ni coating (1105 HV_0.3). The abrasive wear behavior of the WC-based coatings under the conditions of different applied loads and sediment concentrations were studied by a wet sand-rubber wheel tester. The results indicated that the abrasive wear loss rates of all the coatings increased with the increment of applied load or sediment concentration. In addition, the coatings with higher microhardness appeared to have higher abrasive wear resistance. The abrasive wear resistance of the WC-based coatings was 4–90 times higher than that of AISI 304 stainless steel under the same testing condition. The abrasive wear mechanism of the WC-based coatings was deduced to be the extrusion and removal of binder phases, as well as the fragmentation and peel-off of hard phases.     

Effect of MQL and nanofluid on the machinability aspects of hardened alloy steel

Abstract

The current research comprises of various machinability aspects of 4340 hardened alloy steel which are scrutinized with in context of improvements in main cutting force, tool flank wear, crater wear, surface roughness, micro-hardness, machined surface morphology, chip morphology, chip reduction coefficient and apparent coefficient of friction under three different cutting fluid applications i.e. compressed air, water soluble coolant and nanofluid (using eco-friendly radiator coolant as the base fluid and Al₂O₃ as the nanoparticle) using uncoated cermet cutting inserts and a comparative assessment was performed to select which fluid performed better in terms of various machining attributes among three cutting fluids. The minimum quantity lubrication technique (MQL) was used in which a smaller volume of coolant sprinkled at high pressure. This method is found as the most effective alternative to minimize health risks and machining costs, which is quite high in other setups. The test specimen was machined at three different cutting speeds i.e. 100, 120 and 140?m/min along with two machining parameters i.e. feed and depth of cut were kept constant respectively at 0.2?mm/rev and 0.4?mm. Outcomes made a conclusion that Al₂O₃ enriched ecofriendly nanocoolant outperformed both compressed air and water soluble coolant in terms of every machinability aspects.     

Process development for the laser powder bed fusion of WC-Ni Cermets using sintered-agglomerated powder

Although ceramic particle-metal matrix materials (i.e., cermets) can offer superior performance, manufacturing these materials via conventional means is difficult compared to the manufacturing of metal alloys. This study leverages the laser powder bed fusion (LPBF) process to additively manufacture dense tungsten carbide (WC)-17 wt.% nickel (Ni) composite specimens using novel spherical, sintered-agglomerated composite powder. A range of processing parameters yielding high-density specimens was discovered using a sequential series of experiments comprised of single bead, multi-layer, and cylindrical builds. Cylinders with a relative density >99% were fabricated and characterized in terms of microstructure, chemical composition, and hardness. Scanning electron microscopy images show favorable wetting between the Ni binder and carbide particles without any phase segregation and laser processing increased the average carbide particle size. Energy dispersive X-ray and X-ray diffraction analyses detected traces of secondary products after laser processing. For samples processed at high energy densities, complex carbides and carbon agglomerate phases were detected. The maximum hardness of 60.38 Rockwell C is achieved in the printed samples. The successful builds in this study open the way for LPBF of dense WC-Ni parts with a large workable laser power-laser velocity processing window.     

基于线性回归和神经网络的金属陶瓷激光熔覆层形貌预测

目的研究激光熔覆关键工艺参数(激光功率、扫描速度、送粉速率)与单道熔覆层宏观形貌(宽度、高度、熔池深度)之间的数量关系,以实现对WC-Co50复合熔覆层形貌的预测,从而为牙轮钻头的修复提供参考。方法设计不同的实验参数,利用4k W光纤激光器在牙轮钻头钢15MnNi4Mo表面熔覆单道WC-Co50复合涂层。采用工业显微镜观察单道熔覆层的横截面宏观形貌,并测量其三维尺寸。在上述形貌参数的基础上,分别运用多元线性回归分析和人工神经网络方法,建立关键工艺参数与熔覆层宏观形貌之间的关系模型,并将实验结果与模型预测结果进行对比。结果总体来讲,神经网络对熔覆层形貌的预测结果更为精确,平均相对误差为5.3187%;多元线性回归分析预测的平均相对误差为6.0028%。分析表明,对熔覆层宽度的预测结果最精确,两种方法的平均相对误差仅为1.2999%;对高度及熔池深度的预测结果稍差,平均相对误差分别为8.0586%和7.6237%。结论两种预测方法都具有较高的精度,但神经网络法函数关系不明确,运算过程复杂,需要通过进一步的算法优化来提高预测精度。     

Purified high‐sulfur coal as a fuel for direct carbon solid oxide fuel cells

The use of low‐rank coal in a clean and efficient manner is a major challenge facing the current coal technology. A high‐sulfur coal with 4.5 wt% sulfur is chosen to examine the compatibility of the pristine coal and the purified contrast with a solid oxide fuel cell (SOFC) with nickel cermet anodes. Desulfurization of the pristine coal is performed by molten caustic leaching method with a removal ratio of 80%. Analyses of the physicochemical properties of coal samples indicate that the purified coal has a more favorable structure and higher Boudouard reactivity, which is suitable as a fuel for fuel cells. The assessment of electrochemical performance reveals that the purification treatment not only makes the peak power density of SOFCs improve from 115 to 221 mW cm^?2 at 900°C but also extends their durability from 1.7 to 11.2 hours under a current density of 50 mA cm^?2 at 850°C with a fuel availability increasing from 6.25% to 40%. The postmortem analyses show that far less deposited carbon and nickel sulfide are observed on the anode surface. The fuel‐based investigation reveals that the purified coal is a promising fuel for direct carbon fuel cells.     

Cracking induced tribological behavior changes for the HVOF WC-12Co cermet coatings

HVOF sprayed WC based cermet coatings have been widely used in industries as barriers against wear and hydrodynamic cavitation due to their high hardness and relatively high toughness. However, cracking of the coatings can occur during coating production or in service, which can reduce operational performances. It can be difficult to assess the performance impact due to cracks within the coating and as to whether the cracked coatings should be resprayed or removed from service. In this work, artificial cracks of different widths were introduced to liquid fuel HVOF sprayed WC-12Co coating through uniaxial tension of the coated steel substrate to assess the implications of such cracking. Tribological performances of the cracked coatings were examined using rubber wheel dry abrasion, ‘ball on disc’ sliding wear, and ultrasonic cavitation erosion. The results show that the crack deteriorates the abrasive wear resistance of the coating at the initial stage due to preferable mass loss at the cracks. However, after 30?min of abrasion, all the cracked coatings showed the same wear rate as compared to the non-cracked coating, with the abrasive wear resistance acting independent to the crack characteristics. Because the cracks could store wear debris and thus minimize the debris induced abrasion to the coating surface during sliding wear test, both improvement in wear resistance and reduction in coefficient of friction (COF) were detected in the cracked coatings. During the cavitation test, it was found that the mass loss of the specimen increased significantly (up to 75%)with crack width and density suggesting that the crack presence greatly deteriorated the cavitation resistance of the cermet coatings.     

Electromagnetic coupling field strengthening of WC-TiC-Co cermet tools

This work proposes the application of pulsed electromagnetic coupling field processing (EMCFP) to enhance the lifetime and cutting performance of WC-15TiC-6Co cermet tool for the first time. Firstly, the developed electromagnetic field coupling equipment is introduced, the treatment process is analyzed, and the magnetization characteristics of WC-15TiC-6Co cermet tool are evaluated. Secondly, the strengthening effect of the EMCFP treatment is demonstrated by mechanical properties testing and cutting experiments, which reveal that the optimally treated tools exhibit a fracture toughness increased by 18%, an average cutting temperature decreased by 10%, and a friction coefficient for the rank face decreased by 7.9%. Collectively, these enhancements result in a tool lifetime increased by a factor of 1.92 relative to the lifetime of untreated tools. In addition, the results of simulation demonstrate that the simultaneously pulsed magnetic and electric fields contribute toward greater magnetic flux density and current density on the surface of the WC-15TiC-6Co cermet tool than would be obtained from the magnetic and electric fields alone.     

Structural and optical behavior of electrodeposited black chrome‐graphite encapsulated FeCo nanoparticles composite coatings

Black chrome‐graphite encapsulated FeCo nanoparticles (BC‐GEFeCo NPs) composite coatings were electrodeposited on substrates such as stainless steel, Cu, and Ni‐coated Cu. The major content of the deposited film is contributed by Cr, Fe‐Cr, Fe₂AlCr, and FeCr_0.29Ni_0.16C_0.06 as deduced from X‐ray diffraction. The root‐mean‐square roughness value of black chrome on Ni‐coated Cu employing PbSb anode is measured by atomic force microscopy (nanoindentation) studies as 57.176 nm, which is in satisfactory agreement with the literature value of 53.83 nm. With the addition of GEFeCo Nps, the root‐mean‐square roughness value for BC‐GEFeCo composite coatings on Ni‐coated Cu increases approximately 6.1 times that of black chrome surface. Copyright © 2016 John Wiley & Sons, Ltd.     

Ti(C,N)基金属陶瓷的芯-壳显微结构与性能研究

以TiC、TiN为原料,Ni、Co为粘结剂,WC、Mo2C、TaC、C、Cr3C2为添加剂,采用真空热压烧结工艺制备Ti(C,N)基金属陶瓷材料。借助于SEM、EDS和XRD分别分析其显微结构、组成和物相,并测试其性能。结果表明:按配方(质量分数,%):TiC:41.2,TiN:10,Ni:7,Co:7,Mo2C:12,WC:15,TaC:6,Cr2C3:0.8,C:1配料,在1450℃,30MPa热压制得的试样晶粒细小,具有完整的芯-壳显微结构。其主要性能为:相对密度99.12%,维氏硬度22.74GPa,断裂韧性10.1MPa·m1/2,抗弯强度1192.83MPa。