纳米羟基磷灰石/钛复合粒子冷喷沉积行为

运用冷喷涂技术在不同喷涂温度和不同硬度基体上沉积单个纳米羟基磷灰石/钛(nHA/Ti)复合粒子,研究喷涂温度与基体硬度对复合粒子冷喷沉积行为的影响规律。采用扫描电子显微镜(SEM)观察沉积后复合粒子的表面形貌及结合形态,结合能谱分析(EDS)沉积后复合粒子中HA的Ca/P比。结果表明,基体为Ti6Al4V和316L不锈钢基体时,粒子碰撞后发生了一定的塑性变形呈现中部隆起的扁平状,粒子周边出现了环形薄带。随着加速气体温度升高,复合粒子变形程度有所增加;基体为HA+Ti涂层基体时,碰撞后粒子呈现近球形嵌入至涂层基体中,随着加速气体温度升高,复合粒子嵌入至涂层基体中深度有所增加,粒子在基体表面粘附率增加。通过对沉积后复合粒子中HA的Ca/P比发现,冷喷沉积后复合粒子中的Ca/P比与原始粉末中基本相同。     

冷喷涂系统中高温气体加热系统的开发

自从上世纪八十年代中期被俄罗斯科学院的A.Papyrin博士发现以来,对冷喷涂工艺的研究一直在开展,冷喷涂技术也因为将成为易于获得具有特定机械、物理性能的金属沉积在各工业领域有着广泛的应用前景.冷喷涂工艺的高沉积率有助于其进一步应用在工业领域.铜、铝、锌、锡、镍等金属可在相对较低温度(低于600℃)的工作气体下产生高于90-95%的沉积.然而,对于MCrAlY、不锈钢和镍基合金涂层,低于600℃的工作气体下产生高沉积是难以实现的.因为这些金属在温度低于600℃时需要更高的临界速度.据报道,在冷喷涂工艺中,临界速度很大程度上取决于粒子温度.具有高温气体加热系统的冷喷涂设备己开发出来,氮气、氦气作为工作气体能达到900℃,以保证制备MCrAlY、钛、不锈钢和镍基合金这样的金属涂层时也能获得高沉积率.     

多颗粒沉积模型预测铜和铝冷喷涂层微观形貌

采用有限元软件ANSYS/LS-DYNA建立了15个颗粒与基板的冷喷涂沉积模型,通过多颗粒沉积模型预测工艺条件、不同颗粒/基板组合的沉积行为和微观形貌;制备了Al和Cu冷喷涂涂层,观察了涂层截面形貌和颗粒变形特征,并与模拟结果进行对比.结果表明,多颗粒沉积模型可预测喷涂条件对颗粒沉积过程及涂层微观特征的影响,以及不同颗粒/基板组合的界面微观形貌.当碰撞速度低时,颗粒变形不充分,颗粒交界处易形成孔洞;随着速度增加,颗粒流变填充孔洞,涂层致密.与颗粒相比,硬基板涂层/基板界面平滑,机械互锁作用小;软基板形成射流状金属挤入颗粒之间,增加结合作用.      

真空冷喷涂致密Al_2O_3陶瓷涂层微观结构的研究

本文选用平均粒径为400nm的Al_2O_3陶瓷粉末,采用真空冷喷涂的方法在玻璃基体上制备了涂层,采用扫描电子显微镜(SEM)、透射电子显微镜(TEM)以及高分辨透射电镜(HR-TEM)等方法对真空冷喷涂氧化铝涂层的微观结构进行了深入分析。结果表明,Al_2O_3颗粒主要是以单个颗粒作为沉积单元,喷涂颗粒高速碰撞基体和已沉积涂层,发生了晶粒细化及塑性变形,在涂层的局部能够观察到由于粒子的强烈撞击而形成的非晶组织。此外,由于粒子高速碰撞过程中发生塑性变形,涂层局部产生了高密度的位错。     

基板预热温度对冷喷涂涂层组织及沉积行为的影响

采用冷气动力喷涂方法在不同温度的基板表面制备了304不锈钢涂层,研究了基板温度对冷喷涂涂层组织及沉积特性的影响。试验结果表明,不同基板温度制备的冷喷涂涂层组织及显微硬度相同,随基板温度的升高,涂层的沉积效率升高;基板表面的氧化膜存在一个临界厚度尺寸,在临界尺寸下,氧化膜易被撞击粒子击破清除,氧化膜的临界厚度为3～4μm。     

真空冷喷涂LiNi_(0.33)Co_(0.33)Mn_(0.33)O_2涂层颗粒沉积行为研究

真空冷喷涂是一种基于室温及真空条件下超细陶瓷粉末粒子的撞击破碎实现涂层沉积的方法。目前,真空冷喷涂技术已经在微电子器件,金属防护以及新能源领域展现了良好的应用前景。本研究将目光转向锂离子电池,基于真空冷喷涂技术,在氧化铝基体上制备了锂离子电池LiNi_(0.33)Co_(0.33)Mn_(0.33)O_2(NMC)三元材料正极涂层,使用扫面电子显微镜(SEM)观察了NMC涂层的表面及截面微观形貌,使用X射线衍射(XRD)对涂层的相结构进行了测试,使用3D激光显微镜表征了涂层的表面粗糙度,系统研究了载气流量、喷涂距离、喷涂次数等沉积条件对NMC涂层微观形貌及粒子沉积行为的影响。结果表明,在真空冷喷涂NMC涂层中可以观察到明显颗粒破碎沉积现象,涂层结构致密。NMC粉末颗粒沉积方式受气流量、喷涂距离、喷涂次数等沉积条件的影响,载气流量的提高会提高粒子撞击速度,从而提高涂层沉积速率,但过高的气流量会导致粒子发生冲蚀,在涂层表面留下凹坑,致使涂层粗糙度增大。喷涂距离过大会导致NMC颗粒撞击速度减小,粒子破碎不充分,涂层呈现出类似团聚粉末堆积的疏松结构。喷涂次数影响涂层厚度,在合适的沉积参数条件下,可以通过调整喷涂次数实现涂层厚度的线性调控。     

冷喷涂技术的应用现状及展望

简要介绍了冷喷涂技术的原理与特点,冷喷涂工艺参数、粒子沉积行为与喷涂后涂层的性能等研究现状,并对冷喷涂技术的应用前景进行了展望。     

冷喷涂金属涂层的耐腐蚀性能的提升方法

沉积温度低的特点使冷喷涂可避免喷涂金属粉末的氧化及对基材的热影响,是制备高致密金属涂层的有效 方法,在耐腐蚀金属涂层制备方面具有广阔的应用前景。然而在粒子高速碰撞沉积过程中,容易因粒子的塑性变 形程度不足而在粒子界面形成孔隙,相互连通的孔隙导致涂层不能隔绝腐蚀介质的渗入,因此不具备长效腐蚀防 护作用。对此,本文首先介绍了冷喷涂金属涂层的显微组织特点;其次,重点从基于热作用、力作用和热力耦合 作用的原位处理或后处理总结了改善冷喷涂金属涂层内部粒子间结合质量,进而提升金属涂层耐腐蚀性能的方法, 包括原位喷丸辅助冷喷涂方法、热处理、激光重熔、搅拌摩擦处理与热轧处理等,最后,针对当前冷喷涂耐腐蚀 涂层的发展现状,总结了亟待解决的问题和发展方向。     

冷喷涂技术及涂层处理工艺的研究进展

相比于热喷涂工艺,近年发展起来的冷喷涂具有明显的优势,冷喷涂工艺可以实现低温状态下的金属涂层沉积,这种工艺过程对粉末粒子结构几乎无热影响．而对粒子的加速效果很好,金属材料沉积过程中的氧化可以忽略。本文介绍了冷喷涂技术的原理和特点,总结了冷喷涂技术在涂层沉积机制、工艺参数和涂层后期热处理三方面的最新研究进展。涂层与基体的界面结合以及涂层之间的粒子结合都是以机械结合为主．由此导致涂层与基体的结合强度不高。如何对冷喷涂涂层进行热处理,使其结合强度有所提高,已成为冷喷涂技术研究的一个新方向。     

冷喷涂Inconel 718高温合金涂层组织及微观硬度

采用冷喷涂技术在马氏体钢表面制备了Inconel 718高温合金涂层,利用SEM、显微硬度计和纳米压痕仪分析了涂层组织和微观硬度。结果表明,涂层厚度可达300μm以上,与基底界面结合良好,底部、中部和顶部涂层微观缺陷数量和尺寸依次增多;冷喷涂沉积过程不会对Inconel 718高温合金粒子的原始组织结构产生显著影响,沉积后粒子的外部轮廓发生了明显的扭曲变形,而心部变形较小;涂层底部、中部和顶部的显微硬度依次降低,与底部涂层相比,中部和顶部涂层显微硬度分别降低10%和21%;涂层平均纳米硬度较原始粒子显著降低,底部和顶部涂层分别降低13.5%和28%;涂层内部微观缺陷分布是影响涂层整体硬度的重要因素。     

Numerical simulation of the effects of the impact velocity on the particle deposition characteristics in cold gas dynamic spraying

In this study,the effects of the impact velocity on the particle deposition characteristics in cold gas dynamic spraying (CGDS) of 304 stainless steel (SS) on an interstitial free (IF) steel substrate are numerical simulated by means of a finite element analysis (FEA).The results have illustrated that when the particle impact velocity exceeds a critical value at which adiabatic shear instability of the particle starts to occur.Meanwhile,the fatten ratio and impact crater depth (or the effective contacting area) increase rapidly.The particle-substrate bonding and deposition mechanism can be attributed to such an adiabatic shear deformation induced by both the compressive force and the slide friction force of particle.The critical velocity can be predicted by numerical simulation,which is useful to optimize the CGDS processing parameters for various materials.     

Numerical simulation of the effects of the impact velocity on the particle deposition characteristics in cold gas dynamic spraying

In this study,the effects of the impact velocity on the particle deposition characteristics in cold gas dynamic spraying(CGDS)of 304 stainless steel(SS)on an interstitial free(IF)steel substrate are numerical simulated by means of a finite element analysis(FEA).The results have illustrated that when the particle impact velocity exceeds a critical value at which adiabatic shear instability of the particle starts to occur.Meanwhile,the fatten ratio and impact crater depth (or the effective contacting area)increase rapidly.The particle-substrate bonding and deposition mechanism Can be attributed to such an adiabatic shear deformation induced by both the compressive force and the slide friction force of particle.The critical velocity can be predicted by numerical simulation,which is useful to optimize the CGDS processing parameters for various materials.     

Experimental Investigations on Slurry Erosion Behaviour of HVOF and HVOLF Sprayed Coatings on Hydraulic Turbine Steel

Slurry erosion behaviour of high velocity oxy fuel (HVOF) and high velocity oxy liquid fuel (HVOLF) sprayed coatings on hydraulic turbine material (i.e. CA6NM steel) was investigated at different levels of various parameters. The 50 % (WC–Co–Cr) and 50 % (Ni–Cr–B–Si) coating powder was deposited on CA6NM steel samples by HVOF and HVOLF thermal spraying techniques. Erosion tests were conducted on self-made erosion test rig with various factors as explained in the "experimentation" section. Coated and uncoated samples of CA6NM steel were investigated by following a design of experiments based on the L₉ Taguchi technique, which was used to obtain the data of erosion test in a controlled way. Four parameters used in L₉ experiment were velocity, impact angle, slurry concentration and average particle size. The study revealed that the velocity, impact angle and slurry concentration were most significant among various parameters, influencing the wear rate of the coatings. The average particle size did not show any significant effect on both the coatings. In comparison, coated samples showed approximately two times better results in erosion resistance than uncoated samples. Scanning electron microscopy of eroded surface showed different mechanisms of erosion on different samples under various conditions.     

1Cr9Mo钢高速气-固两相流冲蚀磨损

采用自制的激波驱动气-固两相流冲蚀磨损试验装置,选取SiO₂、Al₂O₃和SiC颗粒,对煤化工常用材料1Cr9Mo钢进行高速气-固两相流冲蚀磨损试验研究.结合试件表面冲蚀磨损形貌,分析冲击速度、冲击角度、颗粒硬度、颗粒粒径、试件温度等因素对材料的冲蚀磨损率的影响.结果表明:在20℃和400℃下,1Cr9Mo钢的最大冲蚀磨损率均出现在15°-25°的冲蚀角之间,体现出典型塑性材料的冲蚀磨损特征;低角度冲蚀时磨损机理以颗粒的切削作用为主,高角度冲蚀时颗粒垂直撞击材料表面产生凹坑并致使凹坑周围的片状物碎屑从材料表面剥离;试件冲击速度指数在2.3-3.2范围内,磨损率受颗粒硬度影响较大;在相同冲蚀条件下,硬度较高的Al₂O₃和SiC颗粒对试件的磨损率比SiO₂颗粒高一个数量级;磨损率随颗粒粒径的增大呈现先递增后下降的趋势;在400℃时SiO₂颗粒对试件的冲蚀磨损率明显提高,磨损率最大值约为20℃时的3倍.      

Bonding Mechanism from the Impact of Thermally Sprayed Solid Particles

Power particles are mainly in solid state prior to impact on substrates from high velocity oxy-fuel (HVOF) thermal spraying. The bonding between particles and substrates is critical to ensure the quality of coating. Finite element analysis (FEA) models are developed to simulate the impingement process of solid particle impact on substrates. This numerical study examines the bonding mechanism between particles and substrates and establishes the critical particle impact parameters for bonding. Considering the morphology of particles, the shear-instability–based method is applied to all the particles, and the energy-based method is employed only for spherical particles. The particles are given the properties of widely used WC-Co powder for HVOF thermally sprayed coatings. The numerical results confirm that in the HVOF process, the kinetic energy of the particle prior to impact plays the most dominant role in particle stress localization and melting of the interfacial contact region. The critical impact parameters, such as particle velocity and temperature, are shown to be affected by the shape of particles, while higher impact velocity is required for highly nonspherical powder.     

Simulation of Flow Fluid in the BOF Steelmaking Process

The basic oxygen furnace (BOF) smelting process consists of different chemical reactions among oxygen, slag, and molten steel, which engenders a vigorous stirring process to promote slagging, dephosphorization, decarbonization, heating of molten steel, and homogenization of steel composition and temperature. Therefore, the oxygen flow rate, lance height, and slag thickness vary during the smelting process. This simulation demonstrated a three-dimensional mathematical model for a 100 t converter applying four-hole supersonic oxygen lance and simulated the effect of oxygen flow rate, lance height, and slag thickness on the flow of molten bath. It is found that as the oxygen flow rate increases, the impact area and depth increases, which increases the flow speed in the molten bath and decreases the area of dead zone. Low oxygen lance height benefits the increase of impact depth and accelerates the flow speed of liquid steel on the surface of the bath, while high oxygen lance height benefits the increase of impact area, thereafter enhances the uniform distribution of radial velocity in the molten steel and increases the flow velocity of molten steel at the bottom of furnace hearth. As the slag thickness increases, the diameter of impinging cavity on the slag and steel surface decreases. The radial velocity of liquid steel in the molten bath is well distributed when the jet flow impact on the slag layer increases.     

Investigation of inclusion re-entrainment from the steel-slag interface

The mechanism of inclusion elimination from continuous steel casting is investigated at the steelslag interface. Inclusion impact at the interface is considered under the concept of energy balance, with buoyancy forces, fluid dynamic forces, interfacial adhesion, and rebound forces determining whether the particle will pass through the interface or be retained by it. The effects of the inclusion, slag, and steel properties, as well as the effect of inclusion impact velocity, are considered at the interface. The interfacial tension between the slag and the inclusion should be smaller than that between the steel and the inclusion (negative wettability), so that the inclusions can pass into the slag layer and avoid re-entrainment. The inclusion particles that reach an equilibrium state at the steel-slag interface are subject to re-entrainment back into the steel, due to lift forces applied to them by the turbulent boundary layer at the interface. A removal criterion dependent upon the shear stress is introduced, and then the removal rates are calculated from the turbulent burst theory. It is found that the smaller diameter inclusions are trapped at the interface. Of the particles that remain at the interface, it is the larger ones that are more easily removed by the lift forces due to the turbulent shear stress. High slag viscosity is desirable, since it makes inclusion re-entrainment into the casting product more difficult.     

空气外掠钢渣颗粒准则关系式及其影响因素

通过空冷固态高温钢渣颗粒实验,由实验数据拟合平均努塞尔数实验关联式.对空冷高温钢渣颗粒进行三维数值模拟,研究不同绕流雷诺数下的准则关系式,分析空气外掠固态钢渣颗粒影响因素.研究得出空气冷却固态钢渣颗粒的实验关联式与数值计算关联式,实验与数值计算之间误差较小,验证了采用SST k-ω模型计算的可靠性.实验结果表明:钢渣颗粒的平均努塞尔数随着绕流雷诺数、粒径和气体流速的增大而增大.在同等条件下,钢渣粒径对平均努塞尔数的影响作用大于气体流速;模拟空冷高温钢渣颗粒时,直径对钢渣颗粒凝固时间的影响作用最大,导热系数的影响作用次之,来流空气温度影响作用最小.      

充气喷动床内微细粒子的析出率

在一内径92mm,高1000mm的不锈钢充气喷动床反应器内,以三种不同直径的玻璃珠为惰性粒子,采用五种不同的粉末物料为微细粒子,以空气为充气和喷动气体对微细粒子进行淘洗,综合考察了设备结构,物性,以及操作方式等对充气喷动床内微细粒子的析出率的影响.结果表明:五种粉末物料的析出率均随喷动气速的增加先增加而后变化不大,且粉末粒径越小,粒径分布越均匀其析出率越大;对同一惰性粒子床层的高度有一适宜床高;随着惰性粒子粒径增加,粉末物料的析出率先降低而后增加;当充气速度达到最大允许充气速度时粉末物料的析出率最高;随着床层温度的增加,粉末粒子的析出率有所增加.     

Nb、Ti微合金元素对高强结构钢Q690D冲击韧性的影响

利用冲击试验机、光学显微镜、扫描电镜研究了Nb、Ti等微合金元素对高强结构钢Q690D冲击韧性的影响。结果显示,钢种第2相粒子粗化和混晶导致冲击功降低,将钢中Nb、Ti含量分别降低后,第2相粒子粗化和混晶现象显著改善,实验钢在-20 ℃下的冲击功提高至90 J以上。