基于振动时效技术消除和控制涂层内应力的工艺研究

以ZnAl合金和3Cr13合金材料制备电弧喷涂涂层样件,制定振动时效工艺方案,进行电弧喷涂涂层振动时效工艺和振动时效效果的研究。实验结果表明:振动时效能有效降低涂层内应力水平,并均化涂层内应力分布,振动处理后ZnAl合金涂层内应力最多降低49.7%,3Cr13涂层内应力最多降低40.5%。

纳米压痕法测量等离子喷涂铁基涂层表面的残余应力

利用无损的绿色检测技术——纳米压痕法测量等离子喷涂铁基涂层表面的残余应力。通过对比无应力和有应力涂层的载荷-位移曲线,得出涂层表面存在残余拉应力。由于无应力和有应力涂层的压痕周围均有明显的凸起变形,目前广泛使用的Oliver法提取残余应力的特征参量——真实接触面积的公式已不适用。利用之前建立的适用于压痕周围有凸起变形的材料的真实接触面积计算公式得到无应力和有应力涂层的真实接触面积,分析两者之间的差异,最终计算出涂层表面的应力值为188 MPa,与X射线法得到的162 MPa较为符合。

低内应力涂层设计在防雷达波隐身涂料中的应用

针对国内防雷达波隐身涂料存在的不足 ,分析了内应力产生的原因和降低内应力的方法。低内应力涂层的体系设计 ,对提高其涂料性能有明显的作用。

钙长石基涂层增强建筑陶瓷的制备和性能研究

建筑陶瓷强度的提升是实现瓷砖薄型化、轻量化生产的关键因素之一。以方解石、烧滑石、高岭土、石英为主要原料,通过改变涂层原料中锂辉石的添加量,调控涂层的物相组成和热膨胀系数,制备了钙长石为主晶相的预应力涂层增强的建筑陶瓷。同时,研究了涂层厚度、球磨时间、保温时间等工艺参数对建筑瓷砖强化效果的影响。结果表明,当涂层中锂辉石添加量为20 wt.%、涂层厚度为86μm,以及在涂层材料球磨时间3 h、烧成温度1190℃、保温时间30 min的条件下,获得了具有较低热膨胀系数且界面结合良好的预应力涂层,此时涂层与基体的膨胀系数差值为3.17×10^(–6)℃^(–1),陶瓷复合样品的抗折强度达到最大值为99.8 MPa,相较于无涂层的样品(66.3 MPa)强度提高了50.5%。

风机叶片涂层雨蚀研究

研究了风电叶片在雨水冲击下的失效过程,利用有限元方法建立雨水冲击的数值模型,分析了雨滴的冲击角度、直径、涂层性能等对涂层受力的影响,并对双雨滴及四雨滴耦合模型进行了研究。结果表明:风雨耦合流场中叶片最大载荷在叶尖处,涂层的冲击受力与雨滴冲击角度和雨滴直径的大小呈正相关。低模量涂层能大幅降低涂层受冲击时的拉伸应力,小幅增加其压缩应力。同一平面内的双雨滴耦合时,拉伸应力受影响的范围较大,压缩应力受影响的范围较小。不同高度差下的双雨滴耦合中,随着高度差的增大,材料拉伸和压缩应力都呈现先增后减的趋势,其中压缩应力随高度差的变化幅度明显大于拉伸应力。四雨滴耦合时压缩应力对间距的变化更加敏感。涂层失效的过程主要为:涂层表面拉应力疲劳产生微裂纹;液压渗透引起裂纹扩展,涂层质量减少,表面粗糙度增加;表面小范围破坏后形成的凹面结构促进涂层的失效。

管道3LPE防腐涂层管端保护工艺

3LPE防腐涂层是管道外防腐常用的涂层类型,该涂层在管道长期存放过程中,容易出现管端涂层剥离的现象。文章对于该问题产生的机理进行了分析,包括涂层应力的作用机理以及电化学反应的机理,并针对这两种机理提出生产实践中的应对措施,同时对各种措施的优劣进行了分析,工程项目的应用中应结合实际需求选择最适用的管端防护方式。

温度对CVD-TaC涂层组成、形貌与结构的影响

利用TaCl52C3H62H22Ar反应体系,用化学气相沉积法(CVD)成功地在C/C复合材料表面沉积TaC涂层及C2TaC复合涂层。研究了温度对TaC涂层的相组成和表面形貌的影响以及CVD2TaC涂层的沉积机理。结果表明:在1373～1673K温度范围内能够在C/C复合材料表面制备碳化钽涂层,它由TaC和游离碳组成。提高沉积温度和H2/C3H6的流量比,TaC涂层中游离碳的含量减少;随着沉积温度的升高,TaC涂层的颗粒尺寸增大,均匀程度下降;在1573K时颗粒间出现明显的烧结界面,结构致密无裂纹。制备出成分波动的C2TaC复合涂层,该涂层与基体间具有良好的机械相容性。分析了低应力、无裂纹TaC复合涂层的形成机制。

波前传感器电铸镍层应力实时检测精度评估

目的搭建电铸应力实时检测平台,评估其测量精度,并探明电化学沉积过程中镍层平均内应力的变化规律。方法采用横向剪切波前传感器搭建电铸应力实时检测平台,通过测量在铸层应力作用下电铸基底弯曲的曲率半径,利用Stoney公式计算铸层平均应力。采用参考球面反射镜评估横向剪切波前传感器曲率半径的测量精度,并在0.5 A/dm^2电流密度下进行电铸应力实时检测实验,对铸层平均应力测量极限进行评估,同时对检测误差进行分析。结果横向波前传感器曲率半径测量精度为99.22%,在0.5 A/dm^2电流密度下,所搭建的铸层应力实时检测平台可测量的最小厚度为5.1μm,由曲率测量波动带来的应力检测误差为1.3 MPa。实验测得铸层平均应力随铸层厚度的增加而变大,当铸层厚度达到30μm左右,铸层平均应力趋于稳定,应力大小为79.7 MPa。同时发现,当铸层厚度小于30μm时,沿电铸基底长度方向的铸层平均应力明显大于宽度方向铸层平均应力,随铸层厚度的增加,两个方向的应力大小趋于等值。结论采用横向剪切波前传感器搭建的电铸应力检测平台,能有效对铸层应力进行高精度的实时测量,为精密电铸过程中应力变化规律的研究提供了检测技术基础。

边界元法分析功能梯度涂层材料

在常规边界元法中引入几乎奇异积分的解析算法,使边界元法可以分析涂层结构的强度。计算了在赫兹压力作用下,各向同性涂层和功能梯度涂层两种涂层结构中的Tresca应力分布,绘制了应力等值线图。计算发现使用各向同性涂层时,Tresca应力的最大值出现在涂层和基体交界面上,且在交界面上应力存在明显的不连续性。通过边界元法分析,发现采用功能梯度涂层,可以降低最大的Tresca应力值,削减交界面上的应力不连续性。

冷喷涂金属颗粒变形行为数值模拟研究进展

理解冷喷涂中的颗粒变形和沉积行为一直是科学工作的焦点。由于颗粒撞击基底后的瞬时变形行为难以通过实验观测,因此多数研究工作聚焦于数值模拟。总结了一些颗粒撞击基底的建模方法,在前人研究的基础上,针对每个模型的原理及优缺点,分析了每个方法的适用场景,给出了改善模型的方法。综述了颗粒特性、入射角度、气体预热温度等对颗粒变形行为的影响,其中粒径大小、颗粒形状等是影响颗粒变形行为的主导因素,因此重点探讨了颗粒特性的影响。颗粒的撞击变形是影响冷喷涂涂层残余应力分布的重要因素,对涂层残余应力的相关数值模拟研究进行了综述,分析了颗粒变形与颗粒残余应力的关系。最后就目前冷喷涂残余应力建模较单一的形势,探讨了如何建立一种新模型以分析涂层残余应力。

透辉石涂层增强铁尾矿建筑陶瓷的制备及性能研究

以铁尾矿建筑陶瓷砖坯为基体,采用预应力涂层技术提升建筑瓷砖强度。研究了透辉石涂层的配方组成与涂层厚度、保温时间、球磨时间等工艺参数对涂层复合试样抗折强度的影响。研究发现,透辉石涂层最佳配料组成为:白云石32 wt.%、石英56 wt.%、氧化铝12 wt.%。相较于无涂层的基体(103.23 MPa),复合试样抗折强度提升了31.95 MPa,提升幅度为30.95%。随着涂层厚度的增加,复合试样的强度出现先增加后降低的趋势。当涂层厚度为196.45μm时,复合试样的强度最高(143.54 MPa),相比基体的抗折强度提升了40.31 MPa,提升幅度为39.05%。当涂层原料球磨时间为5h时,在1200℃保温0.5h条件下,透辉石涂层的增强效果最佳,制备的具有双面涂层的复合体铁尾矿建筑陶瓷试样抗折强度达到148.51 MPa,较基体提升了45.28 MPa,提升幅度为43.86%。

Cracked elastic substrate strip with functionally graded coating under thermal-mechanical loading

This paper investigates the functionally graded coating bonded to an elastic strip with a crack under thermal- mechanical loading. Considering some new boundary conditions, it is assumed that the temperature drop across the crack surface is the result of the thermal conductivity index which controls heat conduction through the crack region. By the Fourier transforms, the thermal-elastic mixed boundary value problems are reduced to a system of singular integral equations which can be approximately solved by applying the Chebyshev polynomials. The numerical computation methods for the temperature, the displacement field and the thermal stress intensity factors （TSIFs） are presented. The normal temperature distributions （NTD） with different parameters along the crack surface are analyzed by numerical examples. The influence of the crack position and the thermal-elastic non- homogeneous parameters on the TSIFs of modes I and 11 at the crack tip is presented. Results show that the variation of the thickness of the graded coating has a significant effect on the temperature jump across the crack surfaces when keeping the thickness of the substrate constant, and the thickness of functionally graded material （FGM） coating has a significant effect on the crack in the substrate. The results can be expected to be used for the purpose of gaining better understanding of the thermal-mechanical behavior of graded coatings.

涂层基体协同强化对瓷砖强度的影响

采用微观颗粒增强协同预应力涂层复合强化的设计,研究α-Al_(2)O_(3)及莫来石颗粒对建筑瓷砖坯体的相组成、显微结构及抗折强度的影响,在获得最优组成的基础上,进一步研究了原料颗粒度对坯体力学性能的影响。结果表明:当坯体中添加4 wt%的α-Al_(2)O_(3)和6 wt%的莫来石颗粒,球磨时间1.5 h,烧成温度1150℃,保温时间30 min时,可获得抗折强度达到112.3 MPa瓷砖坯体,相较于未强化样品(66.7 MPa)提高了68.4%。在此基础上,将预应力涂层覆盖增强坯体进行复合增强,发现了在CAS涂层中添加3%ZnO时,可以与强化后的坯体在1150℃下进行共烧结,此时复合瓷砖的抗折强度达到了154.5 MPa,与未强化样品相比提高了131.6%。

Effects of thickness and elastic modulus on stress condition of fatigue-resistant coating under rolling contact

The distribution and magnitude of surface substrates were investigated by finite element method and subsurface stresses of the （FEM）. The models of coating single-layer sprayed-coatings on monolithic configurations with different thicknesses and elastic modulus ratios of coating to substrate were introduced, and the effects of thickness and elastic modulus ratio on the stresses were addressed. The calculation results show that the coating/substrate interface shear stress obviously decreases with increasing coating thickness, due to the location of the maximum shear stress moving away from the coating/substrate interface. At the same time, the magnitude of von Mises stress also declines in the case of thicker coatings. However, the high elastic modulus ratio results in extremely high maximum shear stress and the severe discontinuity of the von Mises stress curves, which leads to the intensive stress concentration on the coating/substrate interface. So the coating configurations with the larger coating thickness and lower difference of elastic modulus between coating and substrate exhibit excellent resistant performance of rolling contact fatigue （RCF）.

Finite element analysis of high-pressure hose for radial horizontal wells in coalbed methane extraction

Based on the serial-parallel model of single-layer board and the lamination theory, the forces exerted on different layers of the high-pressure hose and the resulting deformations were analyzed when the hose was radially stretched. An equation was proposed to calculate the anisotropic elastic constant of the composite layer with the wound steel wires. Furthermore, the finite element analysis （FEA） model of the high-pressure hose was established, followed by a simulation of the forces that act on different layers, and their deformations. The simulation results show that the stress imposed on the inner reinforced layer and external reinforced layer of the high-pressure hose are approximately 150 MPa and 115 MPa, respectively, in the presence of inner pressure. The stress of the rubber coating and polyethylene coating is lower. The lowest stress occurs on the inner surface of the high-pressure hose and the rubber coating between the two composite layers. The deformation of the rubber layer in the inner surface of the high-pressure hose decreases gradually along the radial direction from the inner surface to the external surface. The deformation of the reinforced composite layer is less than that of the external surface of the rubber coating. The equivalent stress of the reinforced composite layer is higher than that caused by the inner pressure, due to the presence of both inner pressure and axial tension.

Evaluation of the Interfacial Adhesion between Brittle Coating and Ductile Substrate by Cross-Sectional Indention

The cross-sectional indentation method is extended to evaluate the interfacial adhesion between brittle coating and ductile substrate. The experimental results on electroplated chromium coating/steel substrate show that the interfacial separation occurs due to the edge chipping of brittle coating. The corresponding models are established to elucidate interfacial separation processes. This work further highlights the advantages and potential of this novel indentation method.

Effects of Colloidal Silica Binder on Catalytic Activity and Adhesion of HZSM-5 Coatings for Structured Reactors

HZSM-5 coating using three colloidal silica binders, acidic colloidal silica （ACS）, neutral colloidal silica （NCS） and basic colloidal silica （BCS）, was prepared to study the effect of hinders on their adhesion and catalytic activity. Scanning electron microscopy characterization indicated that the zeolite coating using BCS shows the smoothest surface with higher homogeneity and adherence strength. The specific surface area, relative crystallization and acid site strength of zeolites are also dependent on the binder used. Catalytic cracking of supercritical n- dodecane over the series of zeolite coating with various binders indicated that HZSM-5 coating with BCS exhibits the highest and the most stable catalytic activity compared with other kinds of binders, and also exhibits a stable catalytic activity ascribed to its proper acid property and microstructure.

Characterization of shear stresses in nickel-based superalloy Mar-M247 when orthogonal machining with coated carbide tools

Mar-M247 is a nickel-based alloy which is well known as difficult-to-machine material due to its characteristics of high strength, poor thermal diffusion and work hardening. Calculation of shear stress by an analytical force model to indicate the effect of coating material, cutting speed, feed rate on tool life and surface roughness was conducted experimentally. Cutting tests were performed using round inserts, with cutting speeds ranging from 50 to 300 rn/min, and feed rates from 0.1 to 0.4 mm/tooth, without using cooling liquids. The behavior of the TiN and TiCN layers using various cutting conditions was analyzed with orthogonal machining force model. Cutting results indicate that different coated tools, together with cutting variables, play a significant role in determining the machinability when milling Mar-M247.

Structure design of gradient hard coatings on YG8 and their residual stress analysis by ANSYS

A structure of gradient hard coatings( Ti,TiN,TiCN and TiAlN) is designed,and residual stress is simulated by a finite element method with ANSYS. The influence of the realistic situation including load and temperature on the residual stress of the coatings is investigated. Simulated results show that the realistic situation strongly affects the residual stress. To be specific,i) The main residual stress concentrates on the coatings prepared on YG8 substrate,and the residual stress and its gradient of the coatings are bigger than that of the substrate; ii) TiAlN and TiCN coatings have better resistance compression than that of TiN coatings in the same condition; iii) The improved multilayer structure of the gradient hard coatings produces weaker residual stress but higher anti-pressure of the substrate.

Computer Aided Thermal Stress Analysis of TBC Coated Specimen

Thermal barrier coatings （TBC） have been improved for the engine applications. During working process of the engine, components were subjected to thermal stresses. For simulating thermally stressed engine parts, disc specimen was objected to airflow at the temperatures about 1,000℃. In this study, finite element structural and thermal analyses were carried out on both uncoated （without coating） and ceramic-coated disc specimen using ANSYS code. A 150 micron super alloy bond coating （NiCrAIY） was first applied to the specimen. Then, the disc specimen was covered by 350 micron thickness of Mullit （3Al2O3.2SiO2） as a top coating. These analysis were performed for detecting the possible thermally problem areas. The disc＇s thermal stressed problematic areas were determined by the finite element analysis was helpful for improving the geometry and TBC.