热障陶瓷涂层厚度对活塞的影响

利用喷涂稳定的氧化镁氧化锆等离子体陶瓷涂覆在铝活塞顶部来改善活塞铝基体的温度,同时提高柴油机性能,探讨了涂层厚度对活塞温度场和热应力分布的影响,并且与无陶瓷涂层活塞进行了比较,分析了0.2mm、0.4mm、0.6mm、0.8mm、1.0mm厚度涂层的温度场和热应力。结果发现,涂层活塞的表面温度明显高于无涂层的活塞,并且涂层表面的温度随着涂层厚度的增加而增加,和无涂层的活塞相比,1.0mm涂层厚度活塞的铝基体温度下降了25.47%。随着涂层厚度的增加,最大等效热应力随之减少,热应力最大的地方出现在过渡层第一层的下表面,这个值是铝合金基体的3~4倍,并且可以发现陶瓷层、过渡层以及基体的最大等效应力近乎是涂层厚度的函数。     

基体条件对等离子喷涂Sm_2Zr_2O_7热障涂层热冲击性能的影响

采用有限元分析软件ANSYS对等离子喷涂Sm2Zr2O7热障涂层在金属基体材质类型、厚度、半径变化时涂层的冲击热应力进行了分析。结果表明,涂层表面及表面层/金属粘结层界面处热应力及其应力梯度随着金属基体热膨胀系数增加而增大。当基体厚度超过20mm后,其对冲击热应力的影响基本可以忽略。当基体半径达到28mm后,涂层最大径向冲击热应力趋于稳定,最大轴向热应力随基体半径增加逐渐减小,最大剪切应力不受基体半径的影响。     

单层厚度对Sm2Zr2O7/8YSZ热障涂层残余热应力的影响

采用有限单元法研究了金属粘结层厚度、热生长氧化层厚度及陶瓷层厚度对Sm2Zr2O7/8YSZ双陶瓷层热障涂层残余热应力的影响。结果表明,金属粘结层厚度为0.1mm时,涂层径向应力最小。涂层径向应力随热生长氧化层的厚度的增加而减小。当YSZ厚度在0.1～0.5mm之间时,径向热应力随YSZ厚度增加而增大,超过0.5mm后应力基本不再变化。陶瓷层最佳厚度组合是0.1mmYSZ+0.9mmSm2Zr2O7。     

汽车活塞用WS_2/Sb_2O_3涂料涂层摩擦性能及仿真

为提高汽车发动机活塞摩擦磨损性能,设计了WS_2/Sb_2O_3混合涂料配方,采用悬浮液喷涂法在活塞表面制备一层减摩涂层。利用RETC多功能摩擦磨损试验机对涂层试件和未喷涂涂层试件进行摩擦系数测试。利用有限元分析,对喷涂减摩涂层和未进行喷涂的活塞进行最大等效应力、变形和疲劳寿命对比和分析。结果表明:有涂层活塞摩擦系数为0.06,无涂层活塞的摩擦系数为0.15;有涂层活塞最大等效应力比无涂层活塞减少30.54 MPa;有涂层活塞最大变形为0.013 545 mm,无涂层活塞最大变形为0.015 627 mm;有涂层活塞最低寿命为35 261次,无涂层活塞寿命为20 036次。WS_2/Sb_2O_3涂层能有效地降低活塞摩擦系数,提高活塞工作性能和寿命。     

等离子喷涂Sm_2Zr_2O_7热障涂层残余热应力

采用有限元分析软件ANSYS对等离子喷涂Sm2Zr2O7热障涂层在金属基体材质类型、厚度、半径变化时涂层的残余热应力进行了分析。结果表明,金属基体的热膨胀系数对Sm2Zr2O7热障涂层的残余热应力有着显著影响,金属粘结层与表面陶瓷层界面处的残余应力及其应力梯度随着金属基体热膨胀系数增加而增大。金属基体厚度和半径不是影响Sm2Zr2O7热障涂层残余应力的主要因素。     

基体条件对Sm2Zr2O7/YSZ双陶瓷层热障涂层界面残余热应力的影响

采用有限元分析软件ANSYS对等离子喷涂Sm2Zr2O7/YSZ双陶瓷层热障涂层界面残余热应力分布进行了数值仿真。结果表明:基体厚度不同时,涂层界面Sm2Zr2O7/YSZ及界面YSZ/NiCoCrAlY对应应力及应力梯度基本不变,表明应力及应力梯度与基体厚度无关;但基体材质热膨胀系数对涂层系统界面的径向、轴向及剪切应力梯度有决定性的影响,且各应力梯度随金属基体的热膨胀系数差异增加而增大,表明基体材质是影响涂层界面径向残余热应力及应力梯度的根本原因。采用多层陶瓷结构并合理选择各层材质的热膨胀系数将更加有利于降低涂层应力梯度,进而改善涂层性能,延长涂层寿命。     

陶瓷材料预压应力加工的力学模型

基于弹性力学和压痕断裂力学,建立了陶瓷材料预压应力下的加工力学模型,分析了预压应力及载荷比对材料内部第一主应力及最大剪应力的影响.随着预压应力的增大,第一主应力由拉应力逐步转变为压应力,最大剪应力先减小而后随之增大.若施加合适的预压应力,则能降低材料内部的最大剪应力,改变材料内部裂纹的扩展方向,从而有效降低陶瓷加工过程中的损伤.随着载荷比增大,第一主应力在压头后方迅速变为拉应力,最大剪应力也随之增大,但压头正下方的应力状态不受载荷比的影响.最后对碳化硅陶瓷进行预压应力划痕实验,验证了上述分析结果,进一步表明陶瓷材料预压应力加工是可行的.     

基于流热固耦合的熔盐泵转子动力特性分析

用ANSYS软件模拟了熔盐泵转子的应力与变形,研究了不同介质流量下非定常流动对转子部件的影响,考察了泵转子结构的模态性能. 结果表明,转子温度自叶轮部件沿泵轴向轴承逐渐降低,不同介质流量下叶轮内的最大等效应力均出现在叶片进口边与前盖板的结合处,泵轴与轴承的配合处出现了明显的应力集中,转子部件的最大变形出现在叶轮边缘,且最大等效应力和变形量均随介质流量增大而减小,设计流量下转子部件最大等效应力和总变形量的变化幅度最小,添加预应力后转子部件前6阶固有频率增加,但振幅变化不大,流量对转子部件模态性能的影响较小.     

内压圆筒斜接管的强度研究与应力评定

以内压圆筒斜接管为研究对象,借助ANSYS有限元分析软件,通过改变筒体内径、接管内径、筒体厚度、接管厚度、接管与筒体夹角5个参数,考察其对圆筒轴向斜接管开孔接管区最大等效应力的影响,并对其进行应力安全评定。结果表明,随着接管内径、筒体内径的增大,最大等效应力呈增大的趋势;随着接管厚度、筒体轴线与斜接管轴线的夹角、筒体厚度的增大,最大等效应力呈减小的趋势;通过应力集中系数的计算,可以控制接管内径和夹角θ=75°～90°减小应力集中系数。所得结论对压力容器设计提供借鉴作用。     

压力容器球壳不连续区域应力分析和强度评定

球壳开孔接管区的应力较高且分布状况较复杂。借助ANSYS Workbench软件,通过建立球壳开孔接管模型,实现压力容器开孔接管区不连续应力的模拟分析,探讨了开孔率、厚度比以及不同受载情况对球壳开孔接管区最大应力的影响,并进行了正交试验和应力评定。结果表明:随着开孔率和内压载荷的增大,最大应力呈增大的趋势;随着厚度比的增大,最大应力呈减小的趋势;厚度比对球壳最大应力的影响程度最大,开孔率对球壳最大应力的影响程度最小;应力评定能满足强度要求,试验结果可为球壳的设计提供借鉴。     

‎Deposition of Ni-tungsten carbide nanocomposite coating by TIG ‎welding: Characterization and control of microstructure and wear/corrosion responses‎

In this study, the effect of the amount of tungsten carbide nanoparticles on the wear and corrosion properties of Ni-tungsten carbide nanocomposite coating which is deposited on steel St37 by Tungsten Inert Gas (TIG) welding was evaluated. For this purpose, surface alloying was firstly conducted on St37 steel by using TIG process with a current of 150 Amps using pure nickel powder and tungsten carbide reinforcement nanoparticles (in 5, 10, 15 and 20 wt%). Then, Transmission Electron Microscopy (TEM), optical microscope, Field Emission Scanning Electron Microscopy (FE-SEM), Energy Dispersive Spectroscopy (EDS), X-ray Diffraction (XRD), microhardness test by Vickers method, abrasion test by sweep method, and electrochemical tests (potentiodynamic polarization and electrochemical impedance spectroscopy) were used in order to characterize the microstructure and tribological properties of the deposited layers. Microstructural observations showed that the deposited Ni-tungsten carbide nanocomposite coating have a dendritic microstructure with a uniform distribution of tungsten carbide nanoparticles, which reduced the dendritic size by increasing the amount of tungsten carbide nanoparticles. The results of this study showed that by increasing the amount of tungsten carbide nanoparticles in the Ni- tungsten carbide nanocomposite coating, the hardness (from the coating surface to the interface of coating/substrate) and wear resistance increased sharply, but the corrosion resistance decreased. Also, the evaluation of the wear mechanism showed that by increasing the amount of tungsten carbide nanoparticles in Ni-tungsten carbide nanocomposite coatings, the wear mechanism in this coating changed from complex abrasive-sheet like to complex adhesive-oxidation.     

Facile synthesis of tungsten carbide-carbon composites for oxygen reduction reaction

Tungsten carbide-carbon composite (XWC-C, where X=10 or 30 represents the tungsten content) supports were prepared by pyrolyzing tungsten-adsorbed poly(4-vinylpyridine)-functionalized carbon. The supports were used to prepare Pt catalysts (Pt/XWC-C) for oxygen reduction reactions (ORR) in alkaline solution. Prepared XWC-C revealed highly dispersed tungsten carbide species composed of WC and W₂C phases. The tungsten carbide species proved to have a positive effect on the dispersion of Pt particles. Compared to the Pt catalyst supported on carbon (Pt/ C), Pt/XWC-C showed higher ORR performance. In addition, the catalytic performance of Pt/XWC-C was enhanced with increasing tungsten carbide content. The highest ORR activity was achieved for the Pt/30WC-C catalyst, which had a 2.9-fold enhanced performance (at 0.8V vs. RHE) compared to that of Pt/C. It is believed that the unique interaction between Pt and the tungsten carbide species was responsible for the enhanced ORR performance of the Pt/XWC-C catalysts.     

Statistical Analysis of Experimental Parameters in Ultrasonic Machining of Tungsten Carbide Using the Taguchi Approach

The objective of this paper is to study the influence of operating parameters of ultrasonic machining of tungsten carbide on the machining characteristics. The effectiveness of the ultrasonic machining process with tungsten carbide is evaluated in terms of the material removal rate and the surface finish quality of the work piece produced. Tungsten carbide as a super hard and high wear-resistant material has been used widely in industries. Powder metallurgy technology is the common method for producing tungsten carbide components. However, this method is obviously too costly and time consuming for small quantity production, such as product prototyping. It is expected to make the prototypes by a material removal process, such as ultrasonic machining. In this paper, an experimental study on the ultrasonic machining of tungsten carbide is presented using a systematic approach. Practical aspects are given on the characteristics of tungsten carbide as functions of the type of abrasive slurry, their size and concentration, nature of the tool material, and the power rating of the machine. The optimum combination of various input factors for the ductile chip formation in the machining of tungsten carbide has been determined by applying the Taguchi approach and the F -test.     

Point load-induced fracture behavior in zirconia plasma spray coating

Heat-resistant coatings prepared by two different spraying methods: atmospheric pressure plasma spraying (APS) and high-pressure plasma spraying (HPPS), were tested using tungsten carbide indenters of different diameters, for the purpose of proposing the best suited method of indentation testing. It was found that with the APS method, the indentation load–depth curve gave the indentation depth and the residual depth smaller than and the yield stress greater than those with the HPPS. On the basis of fracture morphology in the cross-section, it has been conjectured that the APS coating has greater elastic modulus than the HPPS coating, and exhibits high strength exceeding debonding force between bond coat and top coat.     

Preparation and electrocatalytic property of WC/carbon nanotube composite

Tungsten carbide/carbon nanotube composite was prepared by surface decoration and in situ reduction-carbonization. The samples were characterized by XRD, SEM, EDS, TEM, HRTEM and BET, respectively. The XRD results show that the sample is composed of carbon nanotube, tungsten carbide and tungsten oxide. The EDS results show that the distribution of tungsten oxide is consistent with that of tungsten carbide. SEM, TEM and HRTEM results show that the tungsten carbide nanoparticle with irregular granule grows on the outside surface of carbon nanotube homogenously. The electrocatalytic activity of the sample for p-nitrophenol reduction was tested by a powder microelectrode in a basic solution. The results show that the electrocatalytic activity of the sample is higher than that of granular tungsten carbide, hollow globe tungsten carbide with mesoporosity and carbon nanotube purified. The improvement of the electrocatalytic activity of the sample can be attributed to its components and composite structure. These results indicate that tungsten carbide/carbon nanotube composite is one of the effective ways to improve the electrocatalytic activity of tungsten carbide.     

The characterisation and evaluation of highly dispersed tungsten carbide electrocatalysts

The suitability of using highly dispersed tungsten carbide as an inexpensive alternative catalyst to platinum for use in methanol fuel cells has been investigated. The results show that tungsten carbide possesses no activity for the methanol electro-oxidation reaction. Of the tungsten carbide samples examined only those treated with molybdenum produced any measurable oxidation current. Formaldehyde, however, is oxidised on tungsten carbide though the activity is several orders of magnitude lower than that of platinum catalysts. In the potential region where the electro-oxidation of methanol and formaldehyde takes place there is significant corrosion of the tungsten carbide catalyst in aqueous sulphuric acid electrolyte, rendering it unsuitable even as a support for platinum.     

Microstructural Properties of Air Plasma Sprayed Coating Consisting of Tungsten Carbide and Yttria‐Stabilized Zirconia

Thermal Spraying technologies are proven to be capable of producing composite materials and structures. In the present work, an innovative composite coating was produced to achieve high wear and thermal resistant properties in a single‐step process using air plasma spraying (APS) technique. Tungsten carbide has shown high wear resistance and zirconia coatings exhibited excellent tribological and insulation properties. It is speculated that a composite material consisting of zirconia and tungsten carbide exhibits excellent thermomechanical properties. A powder mixture of 50wt% WC‐10wt% Ni (WC‐Ni) and 50wt% ZrO₂‐8wt% Y₂O₃ (YPSZ) was deposited on a low carbon steel substrate using APS technique. Important microstructural properties of WC‐Ni/YPSZ coating such as splat boundaries, pore and grain morphology, microcracks, phase composition, elemental distribution of coatings, and lattice parameters of the crystals were investigated using optical microscopy, scanning electron microscopy (SEM), energy dispersive X‐ray (EDS), and X‐ray diffractometry (XRD). A good adhesion was observed between different phases in tungsten carbide mixed with zirconia coatings. Decarburization process which occurred during APS process resulted in formation of tungsten hemi‐carbide (W₂C) phase in plasma sprayed samples. The calculated crystal size for APS‐deposited coating was smaller than those of feedstock powder.     

碳化钨和天然沸石复合材料在水溶液中的电催化活性(英文)

Tungsten carbide and zeolite nanocomposite was prepared by combining a mechanochemical approach with a reduction and carbonization approach,using natural zeolite and ammonia metatungstate as precursors.The sample was characterized by X-ray diffraction and scanning electron microscope.The results showed that the crystal phase of the sample is composed of zeolite,monotungsten carbide and bitungsten carbide.The mass percentage and the crystallite diameter of tungsten carbide change along with the reacted time.Its electrocatalytic activity was measured with a microelectrode system with three electrodes.The results show that its electrocatalytic property is related to its crystal phase and the mass percentage of tungsten carbide,and its electrocatalytic activity is connected with the property of electrolyte,in which it is measured.Synergistic effect between tungsten carbide and zeolite is found during electrocatalysis.     

Catalytic conversion of cellulose into ethylene glycol over supported carbide catalysts

In the current paper we present a combined catalytic and surface science studies to evaluate the utilization of carbide catalysts for the conversion of cellulose to polyols, especially to ethylene glycol (EG). Based on catalytic studies over a W₂C catalyst, the EG yield has been optimized by varying H₂ pressure, reaction temperature and time. The catalytic performance has been compared for several types of supported catalysts, including tungsten carbides, molybdenum carbides and platinum on different supports. Among all the catalysts, tungsten carbide supported on activated carbon, W₂C/AC, shows the highest EG yield, which is further enhanced to 61% with the promotion of Ni. The corresponding surface science studies indicate that the enhanced EG yield is at least partially due to a weaker bonding between EG and Ni-promoted tungsten carbide surface.     

电沉积镍-钴-碳化钨复合镀层的研究

研究了在镍钴合金镀液中加入碳化钨微粒形成镍－钴－碳化钨得合镀层的共沉积过程。分析了镀液中碳化钨微粒的悬浮量、镀液温度及阴极电流密度对镀层中碳化钨含量的影响,并进一步通过正交试验优选出一种较佳的操作条件。