CrMnN不锈钢的抗空蚀和磨蚀性能

利用旋转圆盘仪对CrMnN不锈钢、20SiMn低合金和OCr13Ni5Mo不锈钢进行了模拟实际工况条件下的空蚀和腐蚀（空蚀和冲刷磨损联合作用）实验。用失重法评价了三种金属材料的抗空蚀和腐蚀性能,并且扫描电镜观察了空蚀形貌。结果表明,CrMnN不锈钢不仅比目前水轮机转轮用材具有更高的抗空蚀性能。而且也具有很好的抗磨蚀性能。深入研究了CrMnN不锈钢的抗损伤机理。     

空间材料的原子氧侵蚀理论和预测模型

低地轨道环境中的原子氧对航天器材料的侵蚀导致材料的性能变坏甚至失效，原子氧的侵蚀机理和防护技术是当前空间环境效应研究的热点．在对原子氧效应机理已有理解的基础上，准确预测空间材料在低地轨道环境中由原子氧引起的侵蚀效应，可对设计者在工程选材和飞行器设计提供帮助。本文综述了近年来发展的原子氧与空间材料相互作用的理论模型和侵蚀速率预测模型，并对各种模型进行了分析，也指出了关于原子氧效应的研究重点．     

Graphene-reinforced epoxy resin with enhanced atomic oxygen erosion resistance

Atomic oxygen (AO) is a dominant component of the low earth orbit and can erode most spacecraft material. We demonstrated the application of graphene to enhance AO erosion resistance of spacecraft polymers. Graphene-reinforced epoxy resin nanocomposites were prepared by solidification of epoxy resin in solution with dispersed graphene flakes and their AO erosion resistance was investigated in a plasma-type ground-based AO effects simulation facility. The nanocomposites were characterized by X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy. Results based on erosion kinetics revealed that a 46 % decrease in mass loss and a 47 % decrease in erosion yield were achieved by addition of only 0.5 wt% of graphene. Further analysis of the surface morphology and composition showed that the graphene nanoflakes could serve as barriers to protect underneath from AO erosion. Thus, this approach provides a novel route for improving durability and reliability of spacecraft material, especially polymers.     

Research on cavitation erosion and wear resistance performance of coatings

Depending on the nature of the working medium and working conditions, corrosive and cavitation damage shall arise to pump’s components. In industrial applications the corrosion-reducing coatings are sprayed on hydraulic components. But it is questionable whether such products actually do help under wear or cavitation loads or not. Abrasive jet wear tests were carried out to determine the wear resistance of coating materials: polymers and ceramics, cast iron, and steel of various types. The samples were loaded for five hours, and finally the wear depth was measured as a determining indicator of the sample’s wear resistance. Results of investigation on anti-erosion performance of epoxy resin, ceramic and Polyurethane (PU) coatings brushed on alloy steel surface were also presented. Cavitation erosion tests were performed on the ultrasonic rig. The mass loss and surface morphology of the specimens were examined by balance analysis and 3-D laser microscopy, respectively. The investigations showed excellent wear-resisting performance of ceramic coatings, which is better than wear-resistance of stainless steel, cast iron and high chrome alloy steel. But the excellent wear-resisting performance could not guarantee a good erosion-resisting performance. The ceramic coatings’ anti-erosion performances were inferior to that of gray cast iron, and hardly comparable to those of stainless steels. The basic factors that influenced coating’s cavitation erosion endurance were adhesion and thickness of coatings. Analysis of coating’s degradation mechanism showed that PU coatings could withstand longer incubation period thus enhancing the materials’ cavitation erosion resistance. Several practical cases were analyzed, showing some guidance for coatings’ application.     

原子氧对航天材料表面的作用与防护 Ⅱ.原子氧敏感材料的防护

综述了原子氧敏感的各种航天材料的防护途径与机理,对空间材料表面改性、空间薄膜以及涂层技术的应用及防护情况进行了讨论。     

光电稳定跟踪平台跟踪控制回路性能测试系统

针对光电稳定跟踪平台跟踪性能测试困难的问题,依据光电产品跟踪系统的特点,设计一套光电平台跟踪控制回路性能测试系统。该系统中将运动物体放置在平行光管或者凹面反射镜的焦面处,通过控制物体的运动规律模拟无穷远处运动目标,实现在实验室内对跟踪角速度、跟踪角加速度等指标的测试。实验表明该系统结构简单,测试准确、方便,测试效率高。     

Finite Element Analysis of Single-Particle Impact on Mild Steel and Spheroidal Graphite Cast Iron

Erosion of materials due to the impact of solid particles is strongly affected by the mechanical properties and microstructures of materials. The experiments in this study showed that maximum erosion occurred at impact angle of 20° for mild steel SS400 and 60° for spheroidal graphite cast iron FDI. This phenomenon has been referred to as the impact angle dependence of erosion in previous studies. In order to clarify the impact angle dependence of erosion on these two materials, 3D finite element (FE) models of single-particle impact on SS400 and FDI were built and analyzed. Considering that erosion occurs due to a combination of cutting and deformation effects, the experimental results were explained from the viewpoint of shear stress and plastic strain on the material surface of FE models. Simulation results showed that for FE models of SS400, plastic strain varied only slightly at different impact angles, whereas the shear stress changed significantly with impact angle, with the maximum value occurring at impact angle of 20°. Thus, shear stress was the main factor affecting the erosion of mild steel, which can explain the experimental observation of maximum erosion occurring at 20° for SS400. On the other hand, for FE models of FDI, shear stress changed little at different impact angles while plastic strain changed significantly with impact angle. The maximum value of plastic strain occurred at impact angle of 50° or 80°, which was also in accordance with the experimental result that maximum erosion occurred at impact angle of 60° for FDI.     

The stability of polymers in low earth orbit

Most organic polymers and some on polymeric materials such as silver or pigments suffer appreciable surface damage in the form of erosion or oxidation when exposed to the low earth orbit (LEO) environment encountered on shuttle flights. Surfaces facing the direction of flight suffer the most damage because of ram effects. Typical thickness losses for plastic films (eg. epoxy, Kapton, Mylar) can be 5 – 10μm. The aggressive chemical nature of the LEO environment (including atomic oxygen and O⁺ ions), aided by the high collision energies of the gases with forward facing surfaces, are thought to be responsible for the erosion and oxidation.     

碳基材料超高速粒子侵蚀的数值模拟

应用动力学理论建立了碳基材料超高速粒子侵蚀的数学模型。在模型中引入了表征材料抵抗侵蚀破坏能力的参数: 冲击破坏侵蚀能和剪切破坏侵蚀能。通过定义多重碰撞修正因子β, 给出了多粒子侵蚀材料体积损失的理论计算公式。计算了石墨和C/ C 靶材在Al₂O₃粒子撞击下, 体积损失比随粒子入射角及入射速度的变化规律。结果表明, 脆性碳基材料在超高速粒子撞击作用下, 冲击破坏与剪切破坏同时发生, 冲击破坏在材料体积损失中起主导作用。计算结果与已有的实验值吻合较好。      

激光陀螺数字式稳频方法的研究

提出了一套激光陀螺数字式稳频方案，在理论分析的基础上，设计并制作出数字式稳频硬件电路，同时编写了相应的稳频控制程序。实验结果表明：激光陀螺数字式稳频方法是可行的，且优于传统的模拟式稳频。     

Simulation of surface roughness on the flow pattern in the casting process

In this investigation a mathematical model has been developed for simulation of the incompressible flow with free surface during mould filling. The simulation 3D melt flow with free surface is based on the SOLA-VOF technique. In the model the effects of variations parameters including heat and mass transfer as well as influences of backpressure, and friction have been considered. The solid and free boundary conditions have been modified and a new algorithm has been developed to calculate the effect of wall–slip ratio, during mold filling. In this algorithm, the effect of wall–slip ratio on the filling pattern has been modeled with an experimental function. In order to verify the computational results, a thin Al–7.5 Si% alloy plate has been poured into a sand mould with a transparent face to take into account the effect of surface roughness on flow pattern, the amount of erosion, and impact of the molten metal on the sand mould, utilizing photography. The comparison between the experimental and the simulation results of sequence filling shows a good consistency that confirms the accuracy of the model for predicting the erosion phenomenon in the moulding materials.     

Influence of composition and processing parameters on mechanical properties and erosion response of Ni–TiB2 coatings

Abstract

Sputtered Ni–TiB₂ coatings have been shown to protect Ti–6Al–4V and Inconel 718 substrates from solid particle erosion. However, before new erosion resistant coatings can be efficiently designed, it is essential that the role of mechanical properties in determining erosion resistance be fully understood. In this investigation, nanoindentation techniques were used to quantify the effects of substrate preparation, coating composition, and sputtering process parameters on the elastic moduli and indentation hardness of thin coatings deposited on Ti–6Al–4V and Inconel 718 substrates. The influence of these parameters on coating adhesion was determined using a conventional scratch test. Elastic moduli, indentation hardnesses, and coating adhesion were correlated with erosion behaviour. The erosion resistance of the coatings that exhibited microscopic ductility is dependent on the nodule diameter and coating properties such as hardness, elastic modulus, and fracture toughness.

MST/1697     

CrAlN抗冲蚀涂层制备及性能研究

为提高钛合金材料抗冲蚀性能,利用真空阴极电弧沉积技术在TC11钛合金上沉积CrAlN涂层,研究靶电流、偏压和气压对涂层结构及性能的影响。采用扫描电镜观察膜层表面和截面形貌,金相显微镜对表面的大颗粒进行定量分析;显微硬度计测量膜层的维氏显微硬度;采用喷砂试验机对涂层的抗冲蚀性能进行测试,通过三维表面轮廓仪测量涂层厚度和侵蚀坑的深度;X射线衍射仪表征涂层中的晶体结构。结果表明:靶电流从70A增大到110A,虽可提高涂层的沉积速率,但会导致涂层表面大颗粒增加,从而降低涂层的抗冲蚀性能;气压从1Pa增大至4Pa,可有效地减少涂层表面颗粒的尺寸及数量,但也会一定程度降低沉积速率及硬度;偏压对CrAlN涂层的结构及性能影响最大,偏压在-50V时涂层呈(200)择优取向,-100V涂层呈(111)择优取向,-200V时,涂层择优取向不明显;且随着偏压的增加,涂层的硬度及抗冲蚀性能增大,在高冲蚀角下,冲蚀的失效机理为脆性失效。结论:工艺参数中靶电流对表面质量的影响最大;涂层的生长取向与偏压密切相关;CrAlN涂层的表面质量及硬度直接影响其抗砂粒冲蚀性能,偏压对涂层抗冲蚀性能影响最大。最终优化的工艺参数为:靶电流90A、偏压-100V、气压4Pa。     

对称型叠层陶瓷喷嘴的结构设计及其冲蚀磨损行为研究

为提高陶瓷喷砂嘴抗冲蚀磨损能力,缓解喷嘴入口、出口的高应力状态,采用热压烧结工艺制备了Al2O3＋（W,Ti）C/Al2O3＋TiC三层对称型叠层陶瓷材料及叠层陶瓷喷嘴.研究结果表明：叠层陶瓷材料表层较之相应单一材料而言,具有更高的硬度和断裂韧性;在相同的冲蚀磨损条件下,叠层陶瓷喷嘴的抗冲蚀磨损性能较非叠层陶瓷喷嘴有显著的提高;试验分析叠层陶瓷喷嘴的最佳层厚比为2.此外,采用有限元法对叠层陶瓷喷嘴在制备过程中的残余应力进行了理论计算,给出了叠层陶瓷喷嘴中残余应力与层厚比的关系.研究表明,残余压应力的存在,细化了晶粒,提高了叠层材料表层的硬度和断裂韧性,是叠层陶瓷喷嘴其抗冲蚀磨损能力提高的原因.理论分析最佳层厚比也为2,理论分析与试验结果相互印证.     

Erosion of conventional and ultrafine-grained materials

The erosion behavior was investigated of wear-resistant coatings of SiSiC and WWC applied to steel and graphite substrates using the controlled nucleation thermochemical deposition (CNTD) process, a refinement of the chemical vapor deposition (CVD) process. This process produces ultrafine equiaxed crystallites with average grain sizes of the order of tens to hundreds of ångströms.The room temperature erosion behavior of these materials was determined and compared with that of other conventional ceramic and metallic composite wear-resistant materials. The effects of various erodents, impingement angles and post-deposition heat treatments were investigated. The CNTD process produces materials with greater erosion resistance than that of conventional CVD materials and can be modified to deposit coatings onto ferrous alloys at low deposition temperatures. The erosion mechanism for CNTD materials is of the brittle type where the erosion rate is determined by the rate of initiation and propagation of cracks. It was found that post-deposition heat treatment of the CNTD WWC deposited at low temperatures improved the material's erosion resistance.     

The effects of laser-induced modification of surface roughness of Al2O3-based ceramics on fluid contact angle

Laser surface treatment of Al₂O₃-based refractory ceramics, by melting and re-solidification, can be successfully applied to producing surfaces that are pore-free, homogeneous and crack-free. Such treated surfaces can lead to an increase in the corrosion and erosion resistances of the materials, due to lower permeability to corrosive species and higher surface hardness, respectively. Furthermore, the corrosion resistance can be influenced by the wetting characteristics of the treated surfaces in service environment. Therefore, it is important to investigate the effect of laser treatment of ceramic materials on the interaction of the surface with the various environmental elements. This work is concerned with an experimental investigation of the effects of laser surface treatment, by melting and re-solidification, on the fluid contact angles of Al₂O₃-based refractory ceramics. These effects are examined by the modification of the surface roughness characteristics induced by laser treatment. Laser-treated surfaces, both containing cracks and crack-free, are compared with untreated surfaces and the results are reported. The untreated surfaces demonstrated considerable non-uniformity in wetting, in contrast to the treated surfaces. The extent of wetting of the laser-treated surfaces containing cracks was proportional to laser power density. This is due to wetting being enhanced, among other factors, by surface roughness, which increased with power density. The crack-free surfaces were the most smooth and, thereby, exhibited the smallest extent of wettability variations. The reduction in wettability after the laser treatment (crack-free) may have an advantage for corrosion resistance.     

表面粗糙度对PS-PVD YSZ陶瓷层性能的影响EI北大核心CSCD

采用PS-PVD工艺在预制有NiCoCrAlYTa黏结层的K417G高温合金上制备YSZ陶瓷层;采用万能拉伸试验机、粒子冲刷仪、静态氧化炉等设备测试PS-PVD YSZ陶瓷涂层的结合强度、抗粒子冲刷和抗高温氧化性能;采用SEM和EDS分析涂层表面、截面形貌和元素分布等。结果表明:表面粗糙度对YSZ陶瓷层拉伸结合强度、抗粒子冲刷和抗高温氧化性能的影响很大。随着粗糙度的增大,结合强度先增大而后减小。Ra=0.40μm表面上沉积的YSZ涂层,其结合强度最高,达到23.5 MPa。拉伸断裂发生在涂层内部,并距离黏结层40~70μm的位置。随着表面粗糙度的增大,冲刷速率先减小而后增大,Ra=0.40μm涂层的抗粒子冲刷性能最好,冲刷速率仅为2.8×10^-3 g/g,表面起伏小和孔隙率低是涂层具有良好抗粒子冲刷性能的重要原因。不同表面粗糙度制备的YSZ涂层均能生成致密连续的热生长氧化物(TGO)层。粗糙度大则生长的TGO起伏大,更容易导致局部增厚和应力集中而失效。     

Fluid jet erosion of tension-softening materials

Fluid jets are increasingly used to process and machine tension-softening materials. Typical applications are drilling, cutting, fragmentation, hydrodemolition and 3D-machining. Tension-softening materials, such as concrete, reinforced ceramics, most rocks and solidified impurities, are quasi-brittle behaving materials characterised by a so-called fracture process zone. Therefore, linear elastic fracture mechanics does not suitably cover these materials. It is also known that conventional strength parameters, such as compressive strength, cannot describe the resistance of this group of materials against fluid jet erosion. In this paper, the behaviour of cement paste, mortar and concrete during the erosion by high-speed waterjets with velocities up to 470 m s^–1 is investigated. The results of SEM-studies are presented that clearly illuminates features of quasi-brittle behaviour, including grain bridging, microcracking and crack branching. It is also found that the erosion process is strongly determined by the size of the aggregate (inclusions) in the material. It is concluded that a non-linear fracture resistance parameter may be suitable to estimate the erosion resistance of the material. It is found that the brittleness B _M – the inverse of the characteristic length of a material – is a suitable resistance parameter. A very good relationship between the brittleness and the volumetric erosion rate estimated from 24 different types of concrete could be obtained.     

Effect of carbides on erosion resistance of 23-8-N steel

Microstructure is one of the most important parameters influencing erosion behaviour of materials. The role of carbides in the matrix is very complicated in controlling the erosion rate of the materials. Conflicting results have been reported in the literature about the effect of carbides on erosion resistance. Carbides are of great importance especially as obstacles against the penetration of erosive particles into the material surface. However, they are susceptible to cracking and causing matrix decohesion which may increase the overall erosion rate. In 23-8-N nitronic steel, carbides present in the form of bands are observed to accelerate the erosion rate. Coarse carbides cause depletion of carbon in the austenite matrix which adversely affects the strain hardening tendency thus causing deterioration in erosion resistance of the bulk material. The dissolution of carbides in the austenitic matrix after solution annealing is observed to improve the erosion resistance of 23-8-N nitronic steel.     

Creep behaviour of injection moulded polyamide 6/organoclay nanocomposites by nanoindentation and cantilever-bending

The creep behaviour of injection moulded PA 6/organoclay nanocomposites was studied by depth-sensing nanoindentation and DMA cantilever-bending. The glass transitions of PA 6 and its nanocomposites were decreased below room temperature upon saturation with water so that the materials could be tested in the rubbery regime. For nanoindentation creep on the skin and core regions of injection moulded samples, whilst organoclay improves the creep resistance of PA 6, the enhancement is due to the decrease of the initial compliance at zero time but the time-dependent creep is actually increased. In contrast, for cantilever-bending creep, organoclay reduces the creep compliance and the time-dependent creep in PA 6. It is suggested that the organoclay imparts a constraint effect on the PA 6 molecular chains, restricting their mobility in the bulk compared to the surface and hence improving their resistance to creep. A modified Halpin-Tsai equation was used to model their creep behaviour under these two loading configurations and compared to experimental data.