表面完整性对涂层滚动接触疲劳寿命影响的研究进展

疲劳是涂层在滚动接触条件下的主要失效形式。涂层的表面完整性（包括粗糙度、显微结构和结合强度、残余应力、厚度、硬度）直接影响了涂层的接触疲劳失效机理,基本决定了涂层的服役寿命。本文在系统综述国内外关于接触疲劳研究的基础之上,对涂层表面完整性引起的接触疲劳失效机理和参数优化准则进行了总结,并展望了表面完整性参数对接触疲劳影响的研究途径,以期为研究涂层制备工艺与涂层疲劳寿命预测与评估的学者提供参考。     

基体表面异质材料滚动接触疲劳性能与失效机理的研究进展

滚动接触疲劳性能是评价膜层性能的重要指标之一。影响零件滚动接触疲劳性能的因素主要分为膜层自身结构完整性和服役条件两大类。膜层自身结构完整性又受制于涂覆工艺、材料体系、后处理方式等因素。在服役工况确定的情况下,膜层自身结构完整性对零件的接触疲劳性能起决定性的作用。不同的涂覆工艺、材料体系、后处理方式对零件的滚动接触疲劳性能及失效机理的影响不尽相同。本文综述了涂覆工艺、材料体系、后处理方式对基体表面异质材料滚动接触疲劳性能与失效机理的影响,发现对滚动疲劳失效机理也存在作用。最后,总结了目前关于膜层滚动接触疲劳研究中存在的问题,探讨了解决问题的方法,以期为基体表面膜层的接触疲劳寿命预测奠定良好的基础。     

超音速等离子喷涂层的接触疲劳失效研究进展

介绍了超音速等离子喷涂层在服役过程中常见的4种疲劳失效形式(表面磨损、点蚀、分层和剥落)及其发生的机理。综述了涂层结构完整性对疲劳失效的影响,即粗糙度、孔隙率和微裂纹对疲劳失效的作用机制。总结了不同的服役条件(接触应力、润滑状态)对疲劳磨损失效的影响规律,展望了接触疲劳失效机制的研究方向,指出应从涂层内部结构和服役条件来揭示疲劳损伤机理。     

滚动轴承接触疲劳失效的影响因素及其研究现状

滚动轴承接触疲劳失效是滚动轴承的主要失效形式之一。本研究以轴承的制造过程和服役过程为主线，从材料质量、加工工艺、热处理质量、表面状态、润滑状态、设计与装配、服役环境及条件等方面，概括滚动轴承接触疲劳失效影响因素的研究现状，并展望其发展趋势。研究认为，滚动轴承接触疲劳失效是多因素耦合作用的结果，提高滚动接触疲劳寿命应从轴承全寿命周期，包括设计、制造、精度控制以及润滑、装配、服役等各方面进行控制。由于服役特征不同，滚动轴承接触疲劳失效分析必须针对具体失效轴承进行综合分析，才能采取有效的预防措施。     

超音速等离子NiCr/Cr3C2涂层的接触疲劳寿命

采用超音速等离子喷涂技术在45钢基体上制备了NiCr-Cr3C2金属陶瓷涂层,使用球盘式接触疲劳试验机对涂层进行不同载荷条件下的接触疲劳试验。采用范—蒙特福特假设检验验证涂层的疲劳寿命数据,发现其符合Weibull分布,随后建立Weibull失效概率图。通过该图可以直观的得到在同一工作条件下,涂层任意循环次数的失效概率,同时可以在一定范围内,预测某一工作载荷下涂层的接触疲劳寿命。该方法在试验数据较少的情况下,较为精确的表征了涂层的接触疲劳寿命,有效的提高了试验效率,节约了试验成本。     

涂层厚度对火焰热喷涂件拉压疲劳性能的影响

为了研究不同涂层厚度对热喷涂件疲劳性能的影响,应用火焰热喷涂技术在40Cr基体上制备出不同厚度的Ni60A自熔性粉末合金涂层.采用XRD、SEM、EDX等分析手段分析涂层表面的物相与断口微观组织结构.用电液伺服高频疲劳试验机测试喷涂试样及基体试样的疲劳寿命.结果表明:对所设计试样而言,其合理的涂层厚度为0.25 mm;在2 min时间长度的重熔保温后,Ni60A涂层表面主要由Cr7C3、Ni、Cr3Ni5Si2、CrB、Ni3B等相组成;涂层厚度合理时,涂层表面及界面相对于涂层中间部分承受较大的轴向拉压载荷,热喷涂件的拉压疲劳寿命在合理的重熔条件下,高于基体试样的疲劳寿命;当涂层厚度大于0.25 mm时,热喷涂件的拉压疲劳寿命随厚度的增加而呈现总体下降的趋势,热喷涂件的拉压疲劳寿命与涂层中非金属颗粒及孔隙的数量及平均大小密切相关.     

声发射技术在热障涂层失效机理中的研究进展及展望

热障涂层（TBCs）具有优异的高温抗氧化、高温力学和抗热腐蚀性能而备受关注,广泛应用于航空发动机和燃气轮机热端部件中。热障涂层服役环境的恶劣和涂层体系结构的复杂,极易导致涂层发生界面分层或剥落失效,因此通过对热障涂层的裂纹萌生和扩展问题进行实时监测,对于失效机理研究显得尤为重要。简述光激发荧光压电光谱（PLPS）、红外热成像（IRT）、阻抗谱（IS）的原理及其在热障涂层失效行为研究中的应用,重点介绍声发射技术在热障涂层失效机理方面的研究成果。基于声发射的热障涂层失效过程的信号分析和深度处理,结合声发射技术在热障涂层中的参数分析和波形分析,对热障涂层失效过程及失效形态进行模式识别,通过损伤程度的定量评估来进行热障涂层的寿命预测。对声发射技术在热障涂层失效预测及寿命评估指明了方向,并创新性地对未来声发射技术在热障涂层的疲劳损伤方面研究趋势提出展望。     

碳钢/有机涂层在模拟大气环境中的失效研究与寿命预测

针对有机涂层在大气环境中失效过程较长的特点,利用Corrosion Master腐蚀仿真平台对Q235碳钢/有机涂层体系分别在海洋大气、工业大气和海洋工业大气3种腐蚀环境条件下的服役寿命进行预测,并结合腐蚀电化学相关测试与涂层的失效行为研究结果对仿真计算结果进行了分析和验证。结果表明,相同环境条件下仿真模拟计算结果与实验结果具有较好的一致性,仿真技术可以用于金属/有机涂层在大气环境下的失效行为研究,并可实现寿命预测。     

热处理对中频感应重熔NiCrBSi涂层抽油光杆性能的影响

采用火焰热喷涂-中频感应重熔技术在20CrMo抽油光杆基体表面制备NiCrBSi涂层并进行热处理,采用扫描电镜、显微硬度计、X射线应力测试仪、万能试验机和疲劳试验机等仪器,研究了热处理工艺对涂层光杆组织、硬度、表面应力、力学性能和疲劳性能等方面的影响。结果表明,中频感应重熔NiCrBSi涂层的制备和热处理对光杆基材表层组织、硬度和表面应力影响较大,热处理温度对涂层的硬度影响不显著;涂层制备和热处理会显著降低杆体的疲劳性能,重熔处理工艺的抗拉强度最大但塑性指标很差,并在疲劳试验中出现典型脆性断口,高温热处理工艺可以使涂层光杆获得较好的拉伸力学性能;普通20CrMo抽油光杆以磨损、腐蚀和疲劳断裂为主要失效原因,而NiCrBSi涂层/20CrMo光杆疲劳性能的显著降低可能成为其失效的主要原因。     

绿色再制造工程设计基础及其关键技术

绿色再制造工程是一个迅速发展中的新兴学科。再制造工程设计基础和再制造工程技术是该学科的主要组成部分。讨论了再制造工程设计基础中的产品再制造性评价、失效机理。寿命预测,再制造过程模拟与仿真,以及先进表面技术、再制造毛坯快速成形技术、纳米涂层及纳米减摩自复技术、修复热处理、应包快速修复技术、过时产品性能升级技术等再制造工程关键技术的研究内容。     

Plasma Sprayed Coating Using Mullite and Mixed Alumina/Silica Powders

Plasma sprayed ceramic coatings are widely used for thermal barrier coating applications. Commercially available mullite powder particles and a mixture of mechanically alloyed alumina and silica powder particles were used to deposit mullite ceramic coatings by plasma spraying. The coatings were deposited at three different substrate temperatures (room temperature, 300?°C, and 600?°C) on stainless steel substrates. Microstructure and morphology of both powder particles as well as coatings were investigated by using scanning electron microscopy. Phase formation and degree of crystallization of coatings were analyzed by x-ray diffraction. Differential thermal analysis (DTA) was used to study phase transformations in the coatings. Results indicated that the porosity level in the coatings deposited using mullite initial powder particles were lower than those deposited using the mixed initial powder particles. The degree of crystallization of the coatings deposited using the mixed powder particles was higher than that deposited using mullite powder particles at substrate temperatures of 25 and 300?°C. DTA curves of the coatings deposited using the mixed powders showed some transformation of the retained amorphous phase into mullite and alumina. The degree of crystallization of the as sprayed coatings using the mixed powder particles was significantly increased after post deposition heat treatments. The results indicated that the mechanically alloyed mixed powder can be used as initial powder particles for deposition of mullite coatings instead of using mullite powders.     

超音速电弧喷涂铝涂层的耐蚀特性

采用光学显微镜、电子扫描显微镜研究了超音速电弧喷涂铝涂层的显微组织结构的及喷涂粒了状态;采用拉伸试验和硬度计测试了涂层结合强度、三度,采用中性盐雾试验对铝涂 耐腐蚀性进行实验,结果表明超音束电弧喷涂铝涂层孔隙率低、组织致密,结合强度和硬芳较高、耐腐蚀性能优越,铝、Ａｃ铝俣金涂层的耐腐蚀性能几乎相同。     

Recent Developments in Metal Spraying by the Powder Process

General principles of metal spraying by the powder process are described, and an account is given of an improved powder-spraying pistol. In this apparatus, powder is conveyed into an oxy-gas flame by any desired conveying gas under pressure: this allows the application of denser, less oxidized and better adherent coatings of zinc, aluminium, etc., than does the older spraying pistol wherein the powder is sucked into the pistol in an air stream, and also the spraying operation is faster and more efficient.

A simple quantitative adhesion test for sprayed metal coatings is described.

Some recent specialized techniques and applications are outlined, including the production of sprayed coatings of very low and of very high resistivity, the spraying of steels, the production of “aluminized” coatings by powder spraying followed by heat treatment, the production of hard, non-porous surfaces by “flaming” special sprayed coatings, and the improvement of the adhesion of zinc and aluminium coatings to be had either by an undercoat of sprayed steel or by preheating the base metal.     

Enhancement of the corrosion properties of cold sprayed Ti–6Al–4V coatings on mild steel via silica sealer

The pore formation associated with the cold spray process requires the development of an economical sealer to enhance the corrosion resistance of Ti–6Al–4V coatings on a mild steel substrate. Herein, a sound method is developed to seal pores in the cold sprayed Ti–6Al–4V coatings with silica sealer. Potentiodynamic polarization tests in 3.5 wt% sodium chloride electrolyte were employed to investigate the corrosion resistance of cold sprayed Ti–6Al–4V coatings fabricated at two standoff distances (30 and 70 mm) before and after the sealing process. The polarization resistance of cold sprayed Ti–6Al–4V coatings significantly increased by >80% after the sealing process. The electrochemical responses of cold sprayed Ti–6Al–4V were dependant on sealing the pores with agglomerated silica nanoparticles as observed by scanning electron microscopy and energy-dispersive X-ray analysis. The increase in polarization resistance makes the sealer an effective treatment for cold sprayed Ti–6Al–4V coatings used in marine environments and other engineering applications. This sophisticated sealing process can reduce the deposition cost by reducing the thickness of Ti–6Al–4V coatings and increasing their lifetime on metal components.     

Microindentation and Inverse Analysis to Characterize Elastic-Plastic Properties for Thermal Sprayed Ti2AlC and NiCoCrAlY

Elastic-plastic material properties for HVOF sprayed Ti₂AlC (sprayed with Maxthal 211 powder) and plasma sprayed NiCoCrAlY coatings were investigated using modeling and experimental Berkovich microindentation. Optical microstructure evaluations were also performed. The theories of Hertz, Oliver and Pharr were combined with finite element analysis for extracting the material properties. Empirically based material models for both thermal sprayed Ti₂AlC and NiCoCrAlY coatings are proposed.     

Powder/processing/structure relationships in WC-Co thermal spray coatings: A review of the published literature

Thermally sprayed coatings based on tungsten carbide are widely used but not yet fully understood, particularly with regard to the chemical, microstructural, and phase changes that occur during spraying and their influence on properties such as wear resistance. The available literature on thermally sprayed WC-Co coatings is considerable, but it is generally difficult to synthesize all of the findings to obtain a comprehensive understanding of the subject. This is due to the many different starting powders, spray system types, spray parameters, and other variables that influence the coating structures and cause difficulties when comparing results from different workers. The purpose of this review is to identify broad trends in the powder/processing/structure relationships of WC-Co coatings, classified according to powder type and spray method. Detailed comparisons of coating microstructures, powder phase compositions and coating phase compositions as reported by different researchers are given in tabular form and discussed. The emphasis is on the phase changes that occur during spraying. This review concerns only WC-12% Co and WC-17% Co coatings, and contrasts the coatings obtained from the cast and crushed, sintered and crushed, and agglomerated and densified powder types. Properties such as hardness, wear, or corrosion resistance are not reviewed here.     

Advanced microstructural study of suspension plasma sprayed titanium oxide coatings

Suspension plasma sprayed titanium oxide coatings were analyzed using transmission electron microscope (TEM) and using Raman spectroscopy. The suspensions used to spray were formulated using fine rutile pigment, water, alcohol or their mixtures, and a small quantity of dispersant. TEM study realized using a “face-to-face” preparation technique enabled to visualize a lamellar shape of grains and their columnar growth. The Raman spectroscopy was made for the samples prepared using different operational spray parameters. The investigations showed the presence of rutile and anatase phase in coatings sprayed using rutile fine powder.     

The deformation and cooling of ceramic particles sprayed with a thermal radio-frequency plasma under atmospheric conditions

Common thermal-spray techniques use the strong acceleration of powder particles to produce dense ceramic coatings with high bond strength. The residence time of the powder particles within the plasma jet is correspondingly low, and only relatively small particles can be molten. In this work, on the contrary, an inductively coupled radio-frequency (RF) inductively coupled plasma (ICP) torch was used to spray large oxide-ceramic powder particles under atmospheric conditions. The slow plasma flow of a RF plasma leads to large residence times of the powder particles, so that the powder size of the feedstock can be 100 μm and more. It was observed that these particles will not be strongly accelerated in the plasma and that their velocity at the moment of impact is in the range of 10 to 20 m/s. Ceramic coatings were ICP sprayed with a low porosity and a high bond strength, similar to direct current (DC) or high-velocity-oxygen-fuel (HVOF) sprayed coatings. The morphology of ICP-sprayed particles on smooth steel surfaces, as a function of the surface temperature, is described and compared with DC plasma-sprayed splats. Furthermore, the degree of deformation was measured and determined by different models, and the pronounced contact zones formed between the pancake and the substrate were investigated. The ICP-sprayed ceramic coatings show some special properties, such as the absence of metastable crystalline phases, which are common in other spray technologies.     

A new application field of plasma spraying technique to environmental depollution

To expand the application of plasma spraying technique, TiO2 coatings were prepared using agglomerated anatase TiO2 powder to solve the environmental problems. The composition and photocatalytic activity of plasma sprayed TiO2 coatings were investigated systematically. The content of anatase TiO2 in the sprayed coatings was approximate to 7%- 15%, which was influenced by the melting state of TiO2 powder in plasma spraying process. The surface of sprayed coating was very rough and the arithmetical mean deviation of the surface profiles (Ra) was in the range of 5.7 - 8.8 μm. Under lower arc current, the surface of the coating became rougher. The anatase to rutile phase transformation temperature of agglomerated anatase TiO2 powder was approximate to 1 173 K. The TiO2 coating sprayed under the arc current of 400 A had good photocatalytic activity for the relative high content of anatase phase in it. It is concluded that the application of plasma spraying technique to environmental field has been developed.     

The effects of microstructural features on the performance gap in corrosion resistance between bulk and HVOF sprayed Inconel 625

It is commonly observed that there is a performance gap between the corrosion resistance of thermally sprayed coatings and the equivalent bulk material. This is attributed to the significantly modified microstructure of the sprayed coatings. However, currently there is no detailed understanding of which aspects of microstructural modification are primarily responsible for this performance gap. In this work several deliberately microstructurally modified versions of the Ni-based superalloy Inconel 625 were produced. These were subjected to potentiodynamic electrochemical testing in 0.5 M H₂SO₄ to investigate the links between specific microstructural features and electrochemical behaviour. Samples were prepared by high-velocity oxy-fuel (HVOF) thermal spraying, laser surface remelting using a high power diode laser and conventional powder sintering. Microstructural features were examined by optical and scanning electron microscopy and X-ray diffraction. Potentiodynamic testing was carried out on the following forms of Inconel 625: wrought sheet; HVOF sprayed coatings; sintered powder compacts; laser melted wrought sheet and HVOF sprayed coatings. Using the corrosion behaviour, i.e. passive current density, of the wrought sheet as a baseline, the performance of different forms of Inconel 625 was compared. It is found that a fine dendritic structure (with associated microsegregation) produced by laser remelting wrought sheet has no significant effect on corrosion performance. Up to 12% porosity in sintered powder samples increases the passive current density by a factor of only around 2. As observed previously, the passive current density of HVOF sprayed coatings is 20-40 times greater. However, HVOF coatings subjected to laser surface remelting are found to have a passive current density close to that of wrought material. It is concluded that, whilst porosity in coatings produces some decrease in corrosion resistance, the main contributing factor is the galvanic corrosion of localised Cr-depleted regions which are associated with oxide inclusions within HVOF sprayed samples.