Novel structured yttria-stabilized zirconia coatings fabricated by hybrid thermal plasma spraying

Yttria-stabilized ZrO₂ powders with initial sizes of 5–22 μm were chsosen as feedstock for hybrid thermal plasma deposition. At 100 kW RF input power, the microstructures of the deposited coatings varied from mostly sprayed splats to physical-vapor-deposited nanostructures when the powder feeding rate was reduced from 4 to 1 g/min. At a powder feeding rate of 2 g/min, a peculiar layered coating consisting of both structures was deposited at a rate over 50 μm/min, which is promising for the fabrication of next-generation novel thermal barrier coatings.     

Microstructure of YSZ Coatings Deposited by PS-PVD Using 45 kW Shrouded Plasma Torch

In this study, a conventional 80 kW class plasma spraying system was used to produce yttria-stabilized-zirconia (YSZ) coatings by PS-PVD at a pressure of 100 Pa. A shroud was attached in the front of the plasma nozzle to restrain expansion of plasma jet. The torch was operated at an arc power of 45 kW and YSZ coatings were deposited at a powder feed rate of 0.2 g/min. Optical emission spectroscopy was used to diagnose the particle state in plasma jet. The surface morphology and cross-sectional morphology of coatings was characterized by field emission scanning electron microscope. It is found that the amount of YSZ evaporation is significantly enhanced through using a shroud. The coatings with a hybrid microstructure of splats and nanoclusters were deposited perpendicular to the coatings. The nanostructured clusters deposited out of the vapor are presented at splat interfaces. It is evident that using powders specially designed for PS-PVD and controlling heating of plasma jet to spray particles, PS-PVD deposition for a hybrid microstructure consisting of vapor phase deposit can be realized through conventional plasma spray system. Columnar grain structured YSZ can also be deposited by pure vapor phase at the side surface of the substrate.     

Vacuum plasma spray deposition of YSZ-NiO-Ni coatings at different Ar and H2 gas flow rates

The work presents results of the experimental investigation of vacuum sprayed yttria stabilized zirconia, nickel oxide, nickel (YSZ-NiO-Ni) ceramic composite coatings deposited on Al₂O₃ ceramic and stainless steel substrates produced at different Ar and H₂ gas flow rates. The Ar and H₂ gas flow was varied according to the factorial plan design. It is shown that for the used vacuum plasma spray YSZ and NiO powder mixture the produced coatings were composed of three phases mainly: cubic YSZ (c-YSZ), cubic NiO (c-NiO), and cubic Ni (c-Ni). The quantitative X-ray diffraction (XRD) analysis was used to evaluate each phase amount in the coatings. It was found that the vacuum spray technique enables formation of composite layers with a variable composition and that phase content in the coatings can be controlled choosing the Ar and H₂ gas flow rates. The electrical conductivity measurements revealed that a variation of the phase content in the YSZ-NiO-Ni composites is responsible for the existence of different electrical conduction mechanism and rapid change in the conductivity of coatings with the used powder content. The surface morphology and the cross-section analysis by scanning electron microscope (SEM) have shown porous structures of the deposited coatings.     

大气等离子喷涂工艺参数对Al2O3涂层性能的影响

为了提高燃烧器工艺烧嘴的使用寿命,在UMCo-50基材表面大气等离子喷涂Al2O3层。采用正交试验法对喷涂工艺参数进行了优化,运用微观形貌分析、X射线衍射分析并结合强度及显微硬度等测试方法,系统研究了喷涂主气流量、功率和送粉量对AI2O3涂层综合性能的影响规律。结果表明:喷涂主气流量、功率和送粉量对Al2O3涂层性能具有交互性影响,在40L/min Ar,48 kW和30g/min条件下可以获得性能较好的Al2O3涂层,极大地提高了UMCo-50基材的抗高温氧化和耐磨性能,使之具有广阔的应用前景。     

激光熔化沉积工艺参数对CoCrFeNiMn系高熵合金成形的影响

目的 用激光熔化沉积法制备Co Cr Fe Ni Mn系高熵合金,以得出最优成型方案。方法 通过正交试验方法,以沉积层的显微硬度为评价指标,分析激光功率、激光扫描速度和送粉速度对沉积层成型质量的影响程度,并得出激光增材制造的最佳工艺组合。结果 当激光功率超过2 000 W时,沉积层表面开始出现烧蚀现象,沉积层表面出现波纹,熔池宽度不均匀;当激光扫描速度为5、7 mm/s时,沉积层相对较均匀,表面平坦;当送粉速度为0.7 r/min时,送入金属粉末的量的增加使沉积层体积增大,宽度变均匀。结论 最佳工艺参数为：激光功率P=2 000 W、扫描速度V_g=7mm/s、送粉速度V_f=0.7r/min。多道沉积时,搭接率为50%其成型性最优,制备得到的材料抗拉强度为453.7 MPa,伸长率为27.5%。     

Effects of argon and oxygen flow rate on water vapor barrier properties of silicon oxide coatings deposited on polyethylene terephthalate by plasma enhanced chemical vapor deposition

Plasma polymer coatings were deposited from hexamethyldisiloxane on polyethylene terephthalate (PET) substrates while varying the operating conditions, such as the Ar and O₂ flow rates, at a fixed radio frequency power of 300 W. The water vapor transmission rate (WVTR) of the untreated PET was 54.56 g/m²/day and was decreased after depositing the silicon oxide (SiO_x) coatings. The minimum WVTR, 0.47 g/m²/day, was observed at Ar and O₂ flow rates of 4 and 20 sccm, respectively, with a coating thickness of 415.44 nm. The intensity of the peaks for the Si-O-Si bending at 800-820 cm^− 1 and Si-O-Si stretching at 1000-1150 cm^− 1 varied depending on the Ar and O₂ flow rates. The contact angle of the SiO_x coated PET increased as the Ar flow rate was increased from 2 to 8 sccm at a fixed O₂ flow rate of 20 sccm. It decreased gradually as the oxygen flow rate increased from 12 to 28 sccm at a fixed Ar carrier gas flow rate. The examination by atomic force microscopy revealed a correlation of the SiO_x morphology and the water vapor barrier performance with the Ar and O₂ flow rates. The roughness of the deposited coatings increased when either the O₂ or Ar flow rate was increased.     

Novel photocatalytic TiO2 coatings produced by HVOF thermal spraying process

Titanium dioxide coatings were deposited by high velocity oxy-fuel spraying (HVOF) using agglomerated nano-powders. Different spraying parameters were used to determine their influences on the crystallite structure and photocatalytic performance of the coatings. The as-sprayed TiO₂ coatings were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Photocatalytic efficiency of the elaborated samples was evaluated from the conversion rate of ethanol. A high anatase content of 80% by volume was achieved for the coating deposited by a 120 ml/min fuel flow rate. The results show that the as-sprayed TiO₂ HVOF coatings were highly photocatalytically reactive for the degradation of ethanol.     

A study on sliding and erosive wear behaviour of atmospheric plasma sprayed conventional and nanostructured alumina coatings

Alumina coatings on stainless steel substrate (SS304) were deposited by using atmospheric plasma spray technique with a feed stock of manually granulated and sieved nano Al₂O₃ powder. The hardness, sliding, and erosive wear of the nanostructured alumina coatings (NC) were investigated and compared with that of conventional alumina coatings (CC). Pin-on disc type sliding wear test on the alumina coatings (NC and CC) was performed with load varying from 30 N to 80 N at a sliding speed of 0.5 m/s. Pot type slurry erosion test of the coatings was conducted for different concentrations of Al₂O₃ and a mixture of Al₂O₃ and SiO₂ slurry. The microstructural features of both NC and CC of alumina were characterized by using FE-SEM/EDS and SEM analysis to substantiate the failure of coatings due to wear. Wear and erosion resistance of nano alumina coating is better than the conventional alumina coating as observed in the present work. The bimodal structure of NC contributes for the enhanced wear resistance. The high fracture toughness of NC is due to suppression of cracks by partially melted particles in the coatings.     

SiOx plasma thin film deposition using a low-temperature cascade arc torch

Plasma thin films were deposited from gas mixtures of hexamethyldisiloxane (HMDSO) and oxygen (O₂) using a low-temperature cascade arc torch (LTCAT). Various properties of the deposited HMDSO plasma coatings, including refractive index (RI), surface contact angle, and hardness were evaluated. The characterization results using X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, ellipsometry, and water contact angle measurements indicated that, with increased O₂ addition, the deposited HMDSO plasma thin films were of inorganic SiO_x nature. It was also found that, in the LTCAT plasma system, O₂ addition significantly improves the hardness of the resulting HMDSO plasma coatings. The film hardness of the deposited HMDSO plasma coatings measured by a standard pencil test (ASTM D3363-05) reached 6H with increased O₂ addition in the HMDSO/O₂ gas mixture. Such hard plasma coatings could be potentially used for many important industrial applications, such as anti-scratch coatings on plastic glasses and various plastic lens materials.     

Characterization of bi-phased Zr2ON2–ZrO2 coatings deposited by RF magnetron sputtering

The aim of this work is to develop zirconium oxynitride coatings by RF magnetron sputtering on silicon substrates. The film properties were analyzed as a function of oxygen flux percentage in two different inert gas atmospheres namely argon and helium. At low oxygen flux percentage, Zr₂ON₂ and ZrO₂ phases are observed from the structural characterization by X-ray diffraction. The atomic ratio of nonmetallic to metallic atoms (N + O)/Zr content varies from 1.22 to 2.03 for zirconium oxynitride films deposited in argon atmosphere and from 1.43 to 2.33 for films deposited in helium atmosphere. The thickness of the film was measured by surface profiler and the growth rate decreases from 11.33 to 5.1 nm/min for films deposited in argon atmosphere and from 7.01 to 3.75 nm/min for films deposited in helium atmosphere with increase in oxygen flux percentage. The films deposited are hydrophobic and the contact angle was measured by contact angle measuring system. Higher surface roughness and maximum contact angle values of 100° and 103° are observed for films deposited in argon and helium atmosphere respectively at low oxygen flux percentage (2.5%). The surface energy of films was calculated by two methods: Owens-Wendt's geometric mean and Wu's harmonic mean approach. The elevated surface energy values were observed with increase in oxygen flux percentage. The stress measurements of the deposited films were done by sin²ψ X-ray diffraction method which depends on the variation of Zr₂ON₂ and m-ZrO₂ phases.     

Co-deposition of aluminide and silicide coatings on γ-TiAl by pack cementation process

Thermochemical analyses were carried out for a series of pack powder mixtures for deposition of aluminide and for co-deposition of aluminide and silicide coatings on -TiAl by the pack cementation process. Based on the results obtained, experimental studies were undertaken to identify optimum pack powder mixtures for depositing adherent and coherent aluminide and silicide coatings. Pack powder mixtures activated by 2 wt% AlCl₃ was used to aluminise -TiAl at 1000°C. With proper control of pack compositions and coating conditions, an aluminide coating of TiAl₃ with a coherent structure free from microcracking was deposited on the substrate surface via inward diffusion of aluminium. The results of thermochemical calculations indicated that co-deposition of Al and Si is possible with CrCl₃ · 6H₂O and AlCl₃ activated pack powders containing elemental Al and Si as depositing sources. Experimental results obtained at 1100°C revealed that CrCl₃ · 6H₂O is not suitable for use as an activator for co-depositing aluminide and silicide coatings on -TiAl. It caused a significant degree of degradation instead of coating deposition to the substrate. However, adherent coatings with excellent structural integrity consisting of an outer TiSi₄ layer and an inner TiAl₃ layer were successfully co-deposited at 1100°C and 1000°C using pack powder mixtures activated by AlCl₃. IT is suggested that such coatings were formed via a sequential deposition mechanism through inward diffusion of aluminium and silicon. Discussion is presented on the issues that need to be considered to ensure the deposition of aluminide and silicide coatings with coherent structure free from microcracking on -TiAl by the pack cementation process.     

A comparative study on thermally sprayed alumina based ceramic coatings

Aluminium oxide is relatively cheap material, abundant almosteverywhere and therefore it is widely used for thermal sprayapplications. Various alumina based powder containing 13 wt. Titania, two different 40 wt.% Zirconia and three differentcompositions of alumina-zirconia-chromia were deposited byatmospheric plasma spraying (APS) and high power plasma spraying(HPPS). The coatings obtained were evaluated by optical microscopy,microhardness measurements, X-ray diffraction and porositymeasurements. Moreover, abrasion and friction wear resistance wereevaluated by using Pin-on-Disc machine. Microhardness values of APScoatings are relatively high as compared to HPPS coatings except inalumina-zirconia-chromia coatings. HPPS have higher hardness values.APS coatings are much coarser and show higher porosity values thanHPPS coatings. The best wear/friction behaviour exhibited coatingAl₂O₃-40 wt.% ZrO₂ that deposited from agglomerated andsintered powder type.     

A comparative study of Inconel 625 laser cladding by wire and powder feedstock

It has been established that laser cladding technique is useful for enhancing surface performances, hence extending the life of many components in severe corrosive-wear environments. However, a comparative study of the surface performances of laser coatings made via powder and wire feeding systems has not been performed. Inconel 625 powder and wire were deposited on the AISI 304 substrate using similar processing parameters. The microstructure, together with the depth of substrate penetration and the degree of dilution of the deposited tracks, was examined using an optical microscope and a scanning electron microscope (equipped with an energy-dispersive spectrometer). The micro-hardness was measured using a Vickers hardness tester. At optimized parameters, laser tracks of Inconel 625 wire and powder had a strong metallurgical bond at the track–substrate interface and no crack and pore were deposited. Due to the higher laser beam infiltration and a larger depth of substrate penetration, higher substrate dilution was observed in the powder-fed tracks. The tracks comprise continuous ?-matrix and secondary compounds (rich in Nb and Mb). However, finer dendritic microstructure and higher number density of inter-dendritic precipitates were observed in a typical powder laser track compared with the corresponding wire laser track. The typical powder laser track demonstrated higher hardness (245 HV_0.3) compared with the corresponding wire laser track (224 HV_0.3).     

基于PSO–BP–GA混合算法的激光熔覆工艺多目标优化

目的 为了提高镍基高温合金熔覆涂层的综合质量,提出了一种基于PSO–BP–GA混合算法的激光熔覆工艺优化方法。方法 选取工艺参数（激光功率、扫描速度、送粉速率）为优化变量、熔覆层质量（稀释率、显微硬度、热影响区深度）为优化目标,根据正交试验结果建立PSO–BP神经网络预测模型,采用线性加权法和层次分析法建立熔覆层质量的综合评价体系,结合GA算法探寻综合质量最优的工艺参数组合。结果 PSO–BP神经网络模型预测值与试验值之间的相对误差不超过6%,最优工艺参数组合如下：激光功率为2 158 W、扫描速度为10.4 mm/s、送粉速率为2.9 r/min,其熔覆层稀释率降低了70.4%、显微硬度增大了25.4%、热影响区深度减少了41.8%。结论 该算法为制备出高性能镍基高温合金熔覆涂层提供了一定的参考与借鉴。     

Comparison of the coatings deposited using Ti and B4C powder by reactive plasma spraying in air and low pressure

The coatings were deposited by reactive plasma spraying (RPS) in air and low-pressure plasma spraying (LPPS) based on the reaction between Ti and B₄C powder, respectively. The thermal spray powder of Ti and B₄C added with powder Cr (metallic binder) in air is compared with that without powder Cr addition in the low pressure. (Prior to deposition, the powder was screened and separated for RPS whereas spray drying, sintering and sieving were done for LPPS.) The phase composition and the microstructure of coatings were studied by X-ray diffractometer (XRD) and scanning electron microscopy (SEM). The anti-corrosion property of coatings was also investigated. It is found that the coating prepared by RPS, which is more densification, is composed of TiN, TiB₂, and a small phase fraction of titanium oxides. The composition of the coating deposited by reactive LPPS is TiB₂, Ti(C, N), Ti₄N_3−x and impurity phase of Ti₅Si₃. There is no appearance of titanium oxides in low pressure. The coatings have the typical lamellar structure and adhere to the bond coating well. The mean Vickers microhardness value of the coating deposited by RPS is higher than that of the coating deposited by LPPS. Furthermore, the corrosion resistance of the coating deposited by RPS is superior to that of the coating prepared by LPPS in near neutral 3.5 wt% NaCl electrolyte.     

The preparation of hard and super‐hydrophilic MgB2 coating by spray pyrolysis deposition

In this study, we report spray pyrolysis deposition using an alternative precursor solution for the fabrication of MgB₂ films. Polycrystalline MgB₂ films were prepared by spray pyrolysis, a precursor solution of magnesium diboride nanoparticles, sodium hypophosphite, sodium succinate, sodium acetate and dimethyl sulfoxide on AZ91 magnesium alloys. The spray was carried out using argon as carrier gas at a temperature of 150 °C and a spray rate of 5 ml/min for 60 min. After spraying, the deposited samples were annealed at 300 °C for 15, 30 and 45 min in order to investigate morphological changes and crystallization behaviour. The microstructure, hardness and wettability properties of approximately 30 μm coatings were investigated by X‐ray diffraction, scanning electron microscopy, microhardness tester and contact angle meter. Produced coatings showed dense and homogenous structural formation with strong grain connections. As‐deposited MgB₂ films showed the most pronounced preferred orientation with the (101) reflection and the highest hardness value compared to other annealed coatings at different times. Besides, all the synthesized coatings had a super‐hydrophilic surface.     

Microstructural and tribological characterization of air plasma sprayed nanostructured alumina–titania coatings deposited with nitrogen and argon as primary plasma gases

Air plasma sprayed nanostructured Al₂O₃–13wt%TiO₂ coatings were deposited as a function of critical plasma spray parameter (CPSP), defined as the ratio of arc power to primary gas flow rate, using nitrogen and argon as the primary plasma gases. Microstructural features including percentage of α-Al₂O₃ phase, percentage of partially melted/unmelted regions, microhardness, and wear characteristics were evaluated for the deposited coatings. Effect of CPSP on microstructural and wear characteristics of coatings deposited with nitrogen was found to be relatively small. In contrast, significant effect of CPSP on coating characteristics was found for coatings deposited with argon. In wear tests, while strong effect of normal load on weight loss was observed for coatings deposited with nitrogen, weight loss for coatings deposited with argon was nearly independent of applied normal load, at least for coatings deposited at the highest CPSP.     

Microstructure of direct current and pulse magnetron sputtered Cr-B coatings

Chromium diboride thin films possess desirable combinations of properties (such as high hardness, wear resistance, chemical inertness, high thermal and electrical conductivity), which are attractive for a wide range of potential industrial applications. However, these properties depend strongly on the deposition process and parameters. Investigation of the resultant coating structures could explain certain differences between them, giving important information about the characteristics of the deposition process (which in this particular case is a recently developed method involving magnetron sputtering of loosely packed blended powder targets) and pointing out directions for improvement.In this paper, Cr-B coatings deposited by direct current (DC) and DC-pulse magnetron sputtering of loosely packed blended powder targets are characterised by transmission electron microscopy (TEM) techniques (electron diffraction and bright-field/dark-field imaging). The structures of the coatings deposited with different parameters are investigated and compared, and the effect of oxygen contamination on the structure is discussed.Coatings with an extremely fine, nanocolumnar structure were observed. DC sputter deposited (and generally non-stoichiometric) Cr-B coatings exhibit a short range ordered ‘zone T’ microstructure, while DC-pulse deposited stoichiometric CrB₂ coatings are dense and defect-free, crystalline and show strong preferred orientation.A small amount of contamination by oxygen of the interfacial sub-layers (due to the target material being a powder) of the DC-pulse magnetron sputter deposited stoichiometric CrB₂ (and near-stoichiometric CrB) coatings was found to affect the structure by suppressing nanocolumnar growth and promoting equiaxed, nanometer-sized grains, close to the coating/substrate interface. The majority of the coating however remained nanocolumnar.     

Deoxidisation and phase analysis of plasma sprayed TiO2 by X-ray Rietveld method

It is fundamentally important to determine the deoxidisation and phase compositions of plasma sprayed TiO₂ coatings containing anatase. In the present study, plasma sprayed porous TiO₂ coatings containing anatase were prepared using anatase powder and both Ar-He-H₂ and Ar-He-N₂ plasma gases. The deoxidisation of TiO₂ and phase compositions of the starting powder and the prepared coatings were examined using X-ray Rietveld method by refining their crystalline parameters and scale factors. The refined oxygen occupancies showed that there were about 0.08 and 0.1 formula units of oxygen deficiencies for the rutile and anatase phases of the coatings, respectively. Such degrees of deoxidisation and the other crystalline parameters appeared independent of the plasma spraying process parameters. With considerations of the presence of organic adhesive in the starting powder and the formation of titanium ethoxide in the coatings, the degrees of deoxidisation estimated by the X-ray Rietveld method were slightly higher than those quantified by the thermogravimetry curves. The phases of the coatings determined from the refined scale factors were mainly composed of rutile with 10.0% to 22.5% anatase by weight, and the latter content increased with decreasing the intensity of the plasma jet.     

SiO2 thin film deposition on the inner surface of a poly(tetra-fluoroethylene) narrow tube by atmospheric-pressure glow microplasma

SiO₂ thin films were deposited on the inner surfaces of a commercial poly(tetrafluoroethylene) narrow tube with an inner diameter of 0.5 mm using tetraethoxysilane/O₂ feedstock gases and He carrier gas by atmospheric-pressure microplasma-enhanced chemical vapor deposition. A glow microplasma was generated inside the tube by radio frequency (RF) capacitively coupled discharge. X-ray photoelectron spectroscopy spectra showed that the tube inner surface was covered by a SiO₂ thin film. Transparent SiO₂ thin films were obtained with a deposition rate of 230 nm/min at an RF power of 6 W and substrate temperature of 100 °C. The wettability of the SiO₂-coated tube was about 3 times as large as that of an untreated sample tube.