热喷涂TiB2-Ni复合涂层组织结构和力学性能

采用团聚烧结方法制备TiB₂-Ni复合粉末喂料,并采用大气等离子喷涂和高速火焰喷涂两种喷涂方法制备了TiB₂-Ni涂层,比较分析了两种涂层的显微组织、物相组成、孔隙率、硬度和断裂韧性.结果表明,与等离子喷涂相比,高速火焰喷涂制备的TiB₂-Ni涂层具有更高的致密度,TiB₂含量,硬度和断裂韧性.两种涂层中TiB₂都没有发生明显的脱硼,氧化,但等离子喷涂过程中TiB₂向金属相中发生了溶解生成了大量脆性Ni₂₀Ti₃B₆相,并降低了涂层中TiB₂的含量,这是涂层硬度和断裂韧性相对较低的主要原因.     

Effect of processing parameters on the microstructures and corrosion behaviour of high‐velocity oxy‐fuel (HVOF) sprayed Fe‐based amorphous metallic coatings

A FeCrMoMnWBCSi amorphous metallic coating was prepared by using high‐velocity oxy‐fuel spray. The influence of processing parameters on microstructure, porosity level, amorphous phase fraction and corrosion behaviour of the coatings was characterised by scanning electron microscopy, X‐ray diffraction, differential scanning calorimeter and electrochemical methods. The results indicated that the microstructures of the coatings were sensitive to the spray parameters considerably. Porosity and unmelted particle proportion decreased with the oxygen/fuel (O/F) ratio and increased with the powder feed rate. The trend of oxides content was opposite to the porosity and unmelted particle proportion. The coatings obtained with higher O/F ratio and lower powder feed rate exhibited higher hardness. The low coating hardness was mainly due to the high porosity especially when the porosity was higher than 1.21%. The spraying parameters strongly affected the amorphous phase fraction. There was a critical passive current density for balancing the porosity and the amorphous phase fraction. Corrosion resistance is dominant by the amorphous phase fraction when the porosity is less than 1.21%, while by porosity when it is higher than that. Open‐circuit potential, potentiodynamic polarisation and electrochemical impedance spectroscopy results showed that the coatings obtained with the O/F ratio of 4.2 and the powder feed rate of 40 g/min exhibiting the best corrosion resistance in 1 wt% sodium chloride solution.     

Effect of Feedstock Size and its Distribution on the Properties of Detonation Sprayed Coatings

The detonation spraying is one of the most promising thermal spray variants for depositing wear and corrosion resistant coatings. The ceramic (Al₂O₃), metallic (Ni-20 wt%Cr) , and cermets (WC-12 wt%Co) powders that are commercially available were separated into coarser and finer size ranges with relatively narrow size distribution by employing centrifugal air classifier. The coatings were deposited using detonation spray technique. The effect of particle size and its distribution on the coating properties were examined. The surface roughness and porosity increased with increasing powder particle size for all the coatings consistently. The feedstock size was also found to influence the phase composition of Al₂O₃ and WC-Co coatings; however does not influence the phase composition of Ni-Cr coatings. The associated phase change and %porosity of the coatings imparted considerable variation in the coating hardness, fracture toughness, and wear properties. The fine and narrow size range WC-Co coating exhibited superior wear resistance. The coarse and narrow size distribution Al₂O₃ coating exhibited better performance under abrasion and sliding wear modes however under erosion wear mode the as-received Al₂O₃ coating exhibited better performance. In the case of metallic (Ni-Cr) coatings, the coatings deposited using coarser powder exhibited marginally lower-wear rate under abrasion and sliding wear modes. However, under erosion wear mode, the coating deposited using finer particle size exhibited considerably lower-wear rate.     

Improvement of wear resistance of plasma-sprayed molybdenum blend coatings

The wear resistance of plasma sprayed molybdenum blend coatings applicable to synchronizer rings or piston rings was investigated in this study. Four spray powders, one of which was pure molybdenum and the others blended powders of bronze and aluminum-silicon alloy powders mixed with molybdenum powders, were sprayed on a low-carbon steel substrate by atmospheric plasma spraying. Microstructural analysis of the coatings showed that the phases formed during spraying were relatively homogeneously distributed in the molybdenum matrix. The wear test results revealed that the wear rate of all the coatings increased with increasing wear load and that the blended coatings exhibited better wear resistance than the pure molybdenum coating, although the hardness was lower. In the pure molybdenum coatings, splats were readily fractured, or cracks were initiated between splats under high wear loads, thereby leading to the decrease in wear resistance. On the other hand, the molybdenum coating blended with bronze and aluminum-silicon alloy powders exhibited excellent wear resistance because hard phases such as CuAl₂ and Cu₉Al₄ formed inside the coating.     

Microstructure and properties of pLASMA-sPRAYED Mo-Mo2C composites

Thermally sprayed molybdenum coatings are used in a variety of industrial applications, such as auto-motive piston rings, aeroturbine engines, and paper and plastics processing machinery. Molybdenum ex-hibits excellent scuffing resistance under sliding contact conditions. However, plasma-sprayed molybde-num coatings are relatively soft and require dispersion strengthening (e.g., Mo₂C) or addition of a second phase (e.g., NiCrBSi) to improve hardness, wear resistance, and thus coating performance. In this study, Mo-Mo₂C composite powders were plasma sprayed onto mild steel substrates. Considerable decarburi-zation was observed during air plasma spraying—a beneficial condition because carbon acts as a sacrifi-cial getter for the oxygen, thereby reducing the oxide content in the coating. Finer powders showed a greater degree of decarburization due to the increased surface area; however, the starting carbide con-tent in the powder exerted very little influence on the extent of decarburization. The friction properties of Mo-Mo₂C coatings were significantly improved compared to those of pure molybdenum under con-tinuous sliding contact conditions. It also was found that the abrasion resistance of the coatings improved with increasing carbide addition.     

Microstructure and properties of tungsten carbide coatings sprayed with various high-velocity oxygen fuel spray systems

This article reports on a series of experiments with various high-velocity oxygen fuel spray systems (Jet Kote, Top Gun, Diamond Jet (DJ) Standard, DJ 2600 and 2700, JP-5000, Top Gun-K) using different WC-Co and WC-Co-Cr powders. The microstructure and phase composition of powders and coatings were analyzed by optical and scanning electron microscopy and x-ray diffraction. Carbon and oxygen content of the coatings were determined to study the decarburization and oxidation of the material during the spray process. Coatings were also characterized by their hardness, bond strength, abrasive wear, and corrosion resistance. The results demonstrate that the powders exhibit various degrees of phase transformation during the spray process depending on type of powder, spray system, and spray parameters. Within a relatively wide range, the extent of phase transformation has only little effect on coating properties. Therefore, coatings of high hardness and wear resistance can be produced with all HVOF spray systems when the proper spray powder and process parameters are chosen. This paper originally appeared in Thermal Spray: Meeting the Challenges of the 21st Century; Proceedings of the 15th International Thermal Spray Conference, C. Coddet, Ed., ASM International, Materials Park, OH, 1998. This proceedings paper has been extensively reviewed according to the editorial policy of the Journal of Thermal Spray Technology.     

Effect of Ceramic Particles on Properties of Cold-Sprayed Ni-20Cr+Al2O3 Coatings

Cold spraying is a thermal spray process enabling the production of metallic and metal-ceramic coatings with low porosity and low oxygen content, capable of, e.g., resisting corrosion. The aim of this study was to characterize the microstructural and mechanical properties of cold-sprayed Ni-20Cr+Al₂O₃ coatings and to clarify the effect of the hard particles on different coating properties. Accordingly, the research focused on the microstructure, denseness (impermeability), adhesion strength, and hardness of the coatings. Scanning electron microscopy (SEM) analysis and corrosion tests were run to gain information on the through-porosity. Ceramic addition in cold-sprayed Ni-20Cr+Al₂O₃ coatings improved their quality by lowering their porosity. Moreover, hardness was slightly higher than those of cold-sprayed Ni-20Cr coating, indicating a hardening effect by the ceramic particles. The addition of Al₂O₃ also made it possible to use high gas temperatures without nozzle clogging, which affects coating properties, such as coating thickness, denseness, and hardness.     

Microstructure and corrosion resistance of molybdenum and aluminum coatings thermally sprayed on 7075-T6 aluminum alloy

Pitting corrosion upon 7075-T6 high strength aluminum alloy, often associated with cathodic intermetallic particles decreases its fatigue life by a factor of about 6 to 8. In order to improve the corrosion resistance of this alloy, arc spray coatings of molybdenum and aluminum are applied. The open circuit potential and potentiodynamic polarization measurements made in 3.5% NaCl naturally aerated solution reveal that the molybdenum coating, which has an excellent hardness, shifts the 7075-T6 corrosion potential (E _corr) to noble values and increases slightly the corrosion current density (i _corr). On the contrary, when the aluminum coating alloy is applied, both E _corr and i _corr are shifted to better values. The increase of i _corr of the alloy when molybdenum coating is applied can be attributed to the high porosity present into the coating. On the other hand, microstructure observations of the aluminum coating reveal a small porosity, which helps the formation of passive oxide film that protects the coating against a further corrosion.     

Consolidation of Al2O3/Al Nanocomposite Powder by Cold Spray

While the improvement in mechanical properties of nanocomposites makes them attractive materials for structural applications, their processing still presents significant challenges. In this article, cold spray was used to consolidate milled Al and Al₂O₃/Al nanocomposite powders as well as the initial unmilled and unreinforced Al powder. The microstructure and nanohardness of the feedstock powders as well as those of the resulting coatings were compared. The results show that the large increase in hardness of the Al powder after mechanical milling is preserved after cold spraying. Good quality coating with low porosity is obtained from milled Al. However, the addition of Al₂O₃ to the Al powder during milling decreases the powder and coating nanohardness. This lower hardness is attributed to non-optimized milling parameters leading to cracked particles with insufficient Al₂O₃ embedding in Al. The coating produced from the milled Al₂O₃/Al mixture also showed lower particle cohesion and higher amount of porosity.     

不同(Mo+B)/(Ni+Cr)质量比的原位合成MoB/NiCr涂层的组织结构与性能

采用超音速火焰喷涂技术沉积含3种不同(Mo+B)/(Ni+Cr)质量比（1:1,2:1和3:1）的Mo-B-Ni-Cr球磨复合粉末以原位反应制备获得MoB/NiCr涂层。采用扫描电子显微镜（SEM）和X射线衍射仪（XRD）分析了MoB/NiCr涂层的组织结构和物相。同时讨论了不同(Mo+B)/(Ni+Cr)质量比对涂层的组织结构、硬度、结合强度和耐腐蚀性能的影响。研究结果表明,(Mo+B)/(Ni+Cr)质量比为1：1的MoB/NiCr涂层孔隙率最低及涂层厚度最大。在3种涂层中均原位反应生成了Mo₂NiB₂三元硼化物,且随着(Mo+B)/(Ni+Cr)质量比的增加,涂层中三元硼化物含量随之增加,涂层的硬度值增加,结合强度反而随之降低;由于涂层中三元硼化物的原位生成,MoB/NiCr涂层的硬度值均高于316L不锈钢基体。通过能谱和XRD分析发现,经过360 h熔融锌腐蚀试验后,涂层表层中没有发现锌元素及其金属间化合物,然而随着(Mo+B)/(Ni+Cr)质量比的增加,涂层的孔隙率增加及厚度降低。最后,综合分析可得,相比其他涂层,(Mo+B)/(Ni+Cr)质量比为1:1的MoB/NiCr涂层具有更好的耐熔融锌腐蚀能力。     

Influence of parameters of the HVOF thermal spray process on the properties of multicomponent white cast iron coatings

High velocity oxi-fuel (HVOF) thermal spray process has been used in order to deposit a new alloy known as multicomponent white cast iron. The coatings were characterized in terms of macrostructure, phase composition, porosity and hardness. Coating characteristics and properties were found to be dependent on the particles size range, spray distance, gases flow rate and oxygen to propane ratio. For set of parameters utilized in this job a narrow particle size range between 20 and 45 μm with a spray distance of 200 mm and oxygen to propane ratio of 4.6 are the preferred coating parameters. Coating porosity of 0.9% and hardness of 766 HV were obtained under these conditions.     

电热爆炸定向喷涂法制备钼涂层

运用电热爆炸定向喷涂新方法在45#钢基体上制备了钼涂层。借助扫描电镜以及能谱仪对涂层的组织结构、形貌以及涂层成分进行了分析。借助显微硬度测试仪对涂层硬度进行了测试。利用图像分析软件对涂层的晶粒尺寸进行了测量。实验表明：涂层组织晶粒细小，涂层硬度提高，HV值最大到达14110MPa，为原始硬度的3倍，且涂层致密，孔隙率低。能谱分析表明，喷涂过程没有发生氧化现象。     

Effect of Spraying Powders Size on the Microstructure,Bonding Strength,and Microhardness of MoSi2 Coating Prepared by Air Plasma Spraying

Molybdenum disilicide (MoSi₂) coatings were deposited on carbon steel by air plasma spraying technology with different feedstock powder sizes (i.e., powder A: ?15 + 2.5 μm, powder B: ?30 + 15 μm, powder C: ?54 + 30 μm, powder D: ?74 + 54 μm and powder E: ?106 + 74 μm). Phase composition and microstructure of coatings were characterized by x-ray diffraction (XRD) and scanning electron microscope. The bonding strength and microhardness of coatings were also evaluated. The XRD results show that there exists mutual transformation between T-MoSi₂ and H-MoSi₂ phase and part of Mo-rich phases are formed because of oxidization during the spraying process. With the increase of spraying powders size, the content of Mo-rich phases (Mo or Mo₅Si₃) and molybdenum oxide (MoO₃) in coatings decreases, and that of disilicide-rich phase (MoSi₂) in coatings increases. The oxidation degree of MoSi₂ particle gradually decreases during the spraying process with the increase of spraying powders size. The MoSi₂ is the main phase of the as-sprayed coatings when the spraying powders size is beyond 30 μm. With the increase of spraying powders size, the porosity of the as-sprayed coating increases, and the bonding strength of the coating gradually decreases. The hardness of coatings first increases and then decreases with the increase of spraying powders size.     

Sliding and abrasive wear resistance of thermal-sprayed WC-CO coatings

We studied the resistance of the coatings to abrasive and unlubricated sliding wear of 40 WC/Co coatings applied by high velocity oxygen fuel (HVOF), high-energy plasma spray (HEPS), and high velocity plasma spray (HVPS), using commercial and nanostructured experimental powders. The hardness of the coatings varies from 3 to 13 GPA, which is much lower than that of sintered samples (10 to 23 GPA) because of the porosity of the coatings. Phase analysis by x-ray diffraction revealed various amounts of decarburization in the coatings, some of which contain WC, W₂C, W, and η phase. The abrasive and sliding wear resistance is limited by the hardness of the samples. For a given hardness, the wear resistance is lowered by decarburization, which produces a hard but brittle phase. Nanocarb powders have the shape of thin-walled hollow spheres that heat up rapidly in the gun and are more prone to decarburization than commercial materials. The work shows that, in order to obtain the performance of nanostructured coatings, the powder and spray techniques must be modified.     

Optimized HVOF titania coatings

A series of spray parameters was tested for a titania (TiO₂) feedstock, and the in-flight particle temperature was measured for each setting combination. The parameter set that resulted in the highest particle temperature was selected for producing coatings for further study and analysis. With this parameter set, the majority of the sprayed particles had temperatures (at least superficially) above that of the melting point of titania. The hardness (H), elastic modulus (E), and elasticity index (H/E ratio) on the cross section and top surface of these HVOF-sprayed titania coatings were evaluated using the Knoop technique and Vickers hardness measurements. The distribution of elastic modulus and hardness values was analyzed via Weibull statistics. The coating microstructure and phase composition were evaluated using scanning electron microscopy (SEM) and x-ray diffraction (XRD) analysis, respectively. The porosity level was determined via image analysis. It was observed that the coatings were uniform and very dense, consisting of rutile as the major phase. The optimized spray conditions allowed the production of thick coatings (∼740 μm), which were shown to be in a state of residual compressive stress using Almen strip measurements.     

Characterization of thermal sprayed nanostructured WC-Co coatings derived from nanocrystalline WC-18wt.%Co powders

Nanostructured WC-Co coatings were synthesized using high velocity oxygen fuel (HVOF) thermal spray. The nanocrystalline feedstock powder with a nominal composition of WC-18 wt.%Co was prepared using the novel integrated mechanical and thermal activation (IMTA) process. The effects of HVOF thermal spray conditions and powder characteristics on the microstructure and mechanical properties of the as-sprayed WC-Co coatings were studied. It was found that the ratio of oxygen-to-hydrogen flow rate (ROHFR) and the starting powder microstructures had strong effects on decarburization of the nano-coatings. Decarburization was significantly suppressed at low ROHFR and with the presence of free carbon in the powder. The level of porosity in the coatings was correlated with the powder microstructure and spray process conditions. The coating sprayed at ROHFR=0.5 exhibited the highest microhardness value (HV_300g=1077), which is comparable to that of conventional coarse-grained coatings.     

Characterization of plasma sprayed Fe-17Cr-38Mo-4C amorphous coatings crystallizing at extremely high temperature

A Fe-17Cr-38Mo-4C alloy powder was plasma sprayed by three processes: an 80 kW low-pressure plasma spray (LPPS), a 250 kW high-energy plasma spray (HPS), and a 40 kW conventional plasma spray (APS). The as-sprayed coating obtained by the LPPS process is composed of only amorphous phase. As-sprayed coatings obtained by the HPS and APS processes are a mixture of amorphous and crystalline phases. The three as-sprayed coatings exhibit a high hardness of 1000 to 1100 DPN. The amorphous phase in these coatings crystallizes at a high temperature of about 920 K. A very fine structure composed of hard ϰ-phase and carbides is formed after crystallization. The hardness of the coating obtained by LPPS reaches a maximum of 1450 DPN just after crystallization on tempering and retains a high hardness more than 1300 DPN after tempering at high temperatures of 1173 or 1273 K. The corrosion potential of the amorphous coating is the highest among the three coatings and higher than that of a SUS316L stainless steel coating. The anodic polarization measurements infer that the corrosion resistance of the amorphous coating is superior or comparable to SUS316L stainless steel coating in H₂SO₄ solution.     

铝合金基体电热爆炸喷涂钼涂层的制备工艺与性能

采用电热爆炸喷涂技术在铝合金基体上制备钼涂层,用SEM、划痕仪、显微硬度计、表面粗糙度仪、微磨损试验机等表征了涂层性能。借助正交试验方法分析了钼涂层制备中各工艺参数对涂层质量的影响,确定了最佳工艺参数。结果表明:用电热爆炸喷涂方法制备的钼涂层均匀致密,孔隙率低;涂层与基体形成冶金结合,结合强度高;涂层硬度为基体的4.9倍,体积磨损量仅为基体的11.2%,耐磨性大幅增加。电爆炸喷涂的工艺参数中,对涂层质量和结合力影响最大的是喷涂距离,其次是喷涂次数,影响最小的是喷涂电压。     

氧乙炔火焰喷焊制备自熔性合金涂层及其性能研究

目的研究镍基自熔性合金喷焊涂层成形机理,比较不同合金材料制备涂层的综合性能,以获得综合性能最佳的喷焊材料。方法以四种不同成分的镍基自熔性合金粉末作为喷焊材料,通过氧乙炔火焰在45钢基材表面进行喷焊。使用金相显微镜、X射线衍射、扫描电子显微镜等对喷焊层进行显微结构分析,并利用维氏硬度计、磨损试验机等对喷焊涂层性能进行对比分析。结果氧乙炔火焰制备的涂层与基体呈现良好的冶金结合,涂层和基体在喷焊过程中发生元素扩散,生成了金属间化合物,基体的整体性能有显著改善。随着材料中Cr、B、Si等合金元素含量的增加,喷焊时涂层中生成的BCr、Ni17Si3等共晶硬质相含量上升,促使涂层的显微硬度、耐磨性能等得到显著提升。其中,Ni60A涂层提升最为显著,其涂层硬度相当于基体硬度的2.5倍,耐磨性为基体的18.1倍。Ni25A涂层提升最小,其显微硬度是基体的1.3倍,耐磨性是基体的6.6倍。结论喷焊状态下的Ni60A涂层与基体冶金结合良好,涂层表面质量好,涂层性能最佳。     

Structural, Mechanical and Erosion Properties of Yttrium Oxide Coatings by Axial Suspension Plasma Spraying for Electronics Applications

Yttrium oxide (Y₂O₃) coatings have been prepared by axial suspension plasma spraying with fine powders. It is clarified that the coatings have high hardness, low porosity, high erosion resistance against CF₄ -containing plasma and retention of smooth eroded surface. This suggests that the axial suspension plasma spraying of Y₂O₃ is applicable to fabricating equipment for electronic devices, such as dry etching. Surface morphologies of the slurry coatings with splats are similar to conventional plasma-sprayed Y₂O₃ coatings, identified from microstructural analysis. Dense coating structures with no lamellar boundaries have been seen, which is apparently different from the conventional coatings. It has also been found that crystal structure of the suspension coatings mainly composed of metastable monoclinic phase, whereas the powders and the conventional plasma spray coatings have stable cubic phase. Mechanism of coating formation by plasma spraying with fine powder slurries is discussed based on the results.