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1.
《Advanced Powder Technology》2022,33(7):103640
The velocity and thermal behavior (temperature, enthalpy, solid fraction) of atomized droplets in a metal spray play the most important role in the spray forming process. These properties mainly determine the materials yield and the final product quality (e.g., porosity, microstructure) of the as-sprayed materials. Changing the gas temperature in the atomization process directly influences these droplet properties in the spray. To understand the droplet behavior in the spray at various atomization gas temperatures (i.e., room temperature RT 293 K, 573 K, 873 K), numerical simulations using computational fluid dynamics (CFD) techniques have been performed and validated by experiments. A series of atomization runs (powder production and spray-forming with AISI 52100 steel) has been conducted at different atomization gas temperatures and pressures with a close-coupled atomizer (CCA). The in-situ temperature detection of the deposit surface (pyrometer) and in the substrate (thermocouples) has been performed to observe the effect of particle properties on the deposit. The result shows that hot gas atomization provides smaller droplets with faster velocity in the spray, affecting the droplet impact and deformation time in the deposition zone. A higher solid fraction of the smaller droplets by hot gas atomization also reduces the deposit surface temperature. Increasing the substrate diameter further decreases the deposit surface temperature without compromising the deposit quality (i.e., porosity) and also refines the grain size. Pre-heating of the substrate up to 573 K results in lower porosity in the vicinity of the substrate. 相似文献
2.
The microstructure and the aqueous corrosion resistance of coatings produced by High Velocity Oxy-Fuel (HVOF) spraying techniques has been investigated. Two types of spraying processes have been employed i.e., Topgun HVOF using propylene gas and Met-Jet II HVOF with kerosene liquid fuel together with two forms of Ni-20%Cr powders i.e., water and inert gas atomised. The oxide, porosity and the amount of melted material in the coatings were characterised using scanning electron microscopy (SEM) and X-ray diffraction (XRD), whilst the corrosion resistance of the coatings and the ability to protect the underlying mild steel substrate was evaluated by use of a salt spray chamber and potentiodynamic tests.MetJet II produced coatings from gas-atomised powder with a lower oxide content, a reduction in porosity and less melted material, as the residence time of particles in the combusted gas stream was shortened. Water atomised powder formed a higher volume fractions of unmelted material and porosity when compared with gas-atomised powder coatings. This was encouraged by the presence of a thin oxide layer, which formed during the production of the water-atomised powder. The orientation of oxides and pores in the coatings had a major effect on their aqueous corrosion behaviour. Better protection for the underlying steel substrate (>3000 h exposure in a salt spray test) was obtained with the coating produced from the gas-atomised powder with the MetJet II system, which had the lowest porosity/oxide content running perpendicular to the substrate surface. The major factor in preventing attack on the mild steel substrate is the amount of interconnecting porosity which allows the corrodant to percolate through the coating. 相似文献
3.
A. P. de Bribean Guerra N. Ellendt V. Uhlenwinkel P. S. C. Pereira da Silva C. Bolfarini 《Materialwissenschaft und Werkstofftechnik》2014,45(7):568-573
The aim of this study is to evaluate the microstructure of a recycled AA7050 alloy processed by spray forming followed by hot extrusion and swaging. Machining chips from an aircraft manufacturer were used as raw material. The microstructure was investigated by optical microscopy (MO) and scanning electronic microscopy (SEM). The spray formed deposit was homogenized at 743 K, 8 h, extruded at 693 K with a deformation rate of 0.1 s–1 and an extrusion rate of 156:1, producing a bar with 8.0 mm in diameter. Due to a specific combination of high extrusion temperature and deformation rate, partial recrystallization occurred and different grain sizes were obtained through the extruded cross section. After extrusion, the 8.0 mm bar was processed by rotary swaging in several steps up to a 2.0 mm final diameter. The resulting microstructure revealed a cold worked structure, with no recrystallization. Tensile tests were performed in both cases and the slant type of fracture reveals that Portevin Le‐Chatelier effect took place in this alloy. Moreover, the efficacy of extrusion and rotary swaging parameters to reduce the porosity, intrinsic to the spray form process, was analyzed, as well the distribution of intermetallic particles. 相似文献
4.
An alloy containing Pb-12% Sn-12% Sb with small addition of copper and arsenic was spray deposited employing two different
atomization gas pressure and nozzle to substrate distances. The temperature of the spray-deposit was measured during deposition
at a distance of 2 and 10 mm above the substrate-deposit interface. Thermal profile data indicated small variation in temperature
with time during deposition stage whereas during post deposition stage an exponential decrease in temperature was recorded.
Second phase particle size along the thickness of the deposit varied from 4 to 8 μm compared to 70 to 80 μm size of these
particles in the as cast alloy. Maximum porosity occurred in the section of the deposit near the contact surface of the substrate
and also in its peripheral regions. X-ray diffraction analysis exhibited the formation of additional Cu2Sb phase in the spray-deposit and CuSn and Cu3.3Sb phases in atomized powders compared to that of the as cast alloy. The microstructural evolution during spray deposition
of this alloy is discussed. 相似文献
5.
Arne Röttger Sebastian L. Weber Werner Theisen Balasundaram Rajasekaran Robert Vaßen 《Advanced Engineering Materials》2009,11(12):1015-1022
Within this work, HVOF sprayed coatings based on X220CrVMo13‐4 cold work steel were applied to a S235JR construction steel substrate. The investigations focus on the influence of particle size and spray parameters on the coating microstructure, analyzed by means of optical microscope (OM) and scanning electron microscopy (SEM). Additional XRD measurements and micro hardness plots across the interface between substrate material and coating were carried out. Furthermore, the influence of particle size on the detected phases and coating porosity was studied. The results were compared with an X220CrMoV13‐4 reference sample produced by HIP. 相似文献
6.
A three‐dimensional shape model, tracing the coordinates of the moving surface of a growing flat deposit spray‐formed using a scanning gas atomizer, has been developed in this study. Mass flux distributions in the spray cones generated by the scanning atomizer under a typical spray forming condition have been revealed for the shape modeling. Geometrical evolution of flat deposits in spray forming has been investigated based on analysis of the scanning mechanism of the atomizer. The influence of processing conditions on the shape and dimensions of flat deposits have been simulated and discussed. Finally, the shape modeling has been validated by experimental investigations. 相似文献
7.
In order to meet the requirements of micro cold forming tools, a new co‐spray forming process has been applied to produce graded materials from two different tool steels in this study. The two steel melts were atomized and co‐sprayed simultaneously onto a flat substrate, resulting in a flat graded deposit when the two sprays were overlapped. To eliminate porosity and break up carbide network, the graded deposits were further hot rolled. The resultant graded tool steels were investigated with respect to porosity, element distribution, microstructure, hardness, strength, and toughness. The degree of overlapping of the two sprays determined the concentration gradient of the chemical elements in the deposits. The overlapping of the spray cones also contributed to low porosity in the gradient zone of the deposits. The porosity in the graded deposits could be essentially eliminated by means of hot rolling. The carbides and grain structures of the hot rolled tool steels were fine and homogeneous. By means of combining different tool steels in a single deposit, different microstructures and properties were combined. 相似文献
8.
Aluminium‐magnesium‐scandium alloys offer good weldability, high corrosion resistance, high thermal stability and the potential for high strength by precipitation hardening. A problem of aluminium‐scandium alloys is the low solubility of about 0.3 mass‐% scandium when using conventional casting methods. The solution of scandium can be raised by higher cooling rates during solidification. This was realised by spray forming of Al‐4.5Mg‐0.7Sc alloys as flat deposits. Further cooling rates after solidification should also be high to prevent coarse precipitation of secondary Al3Sc. Therefore a cooling device was designed for the spray formed flat deposits. The flat deposits were rolled at elevated temperatures to close the porosity from spray forming. Microstructures, aging behaviour and tensile properties of the rolled sheets were investigated. Strength enhancements of about 100 MPa compared to conventional Al‐Mg‐Sc alloys were achieved. 相似文献
9.
Specimens of 0.8 mm thick regular and interstitial free (IF) drawing steel sheet have been nitrided in fluidised bed for 2 hours at 620 °C and 560 °C with and without a post‐oxidation, and slow and accelerated cooling. As a result, surface hardness, yield and tensile strength of the sheets increased considerably without a critical loss of ductility. Resistance welds between the sheets did not lose their original strength after nitriding‐oxinitriding. Nitrided‐oxinitrided at 620 °C and then powder painted sheets, as compared with powder painted raw sheets, were more corrosion resistant in neutral salt spray and climatic tests. Some mechanical and anticorrosion properties of the IF steel sheet that had undergone the nitriding‐oxinitriding processes were definitely better than those of equally processed regular steel sheet. 相似文献
10.
Chao Zhang Bingbing Zheng Jie Wang Yifan Luo 《Materials and Manufacturing Processes》2018,33(10):1107-1114
Solution precursor plasma spray process was used to deposit single particles and coatings of tungsten oxide (WO3), and the microstructures of single particles and coatings were characterized by field emission scanning electron microscopy. The effects of substrate temperature and spraying distance on the microstructure of single particles and coatings were studied. In the case of WO3 particles, the particle spheroidization degree became better as the increase in substrate temperature. When the substrate temperature increased up to 200°C, bubble-like morphologies appeared. For the deposited WO3 coatings, a highly porous structure was obtained when a 100?mm spraying distance was used. Besides, the grain size of coatings decreased through increasing the spraying distance from 60 to 100?mm. 相似文献
11.
《Computational Materials Science》2006,35(1):13-26
The diameter, velocity and temperature of stainless steel and tungsten carbide cobalt particles applied onto stainless steel substrates using a high velocity oxy-fuel (HVOF) torch were measured. The microstructure of the coatings produced was examined using a scanning electron microscope and coating thickness, porosity and roughness measured. Using the experimental spray parameters as inputs to a 3-D stochastic model we simulated coating formation. Measured values of coating thickness and porosity agreed well with predicted values while calculated surface roughness was somewhat higher than that observed in experiments. An object oriented finite element code (OOF) developed at the National Institute of Standards and Technology was used to calculate residual stresses in the coating. The model uses an adaptive meshing technique to discretize the coating microstructure into a mesh suitable for finite element analysis. To define the coating geometry we used either micrographs of coating cross-sections or computer generated images of coatings. Similar values of residual stress are obtained in either case. High stresses are present at the interface between the coating and substrate. The magnitude of stresses increases significantly with coating thickness. Stresses are relieved by voids such as pores or cracks in the coating. Residual stresses increase with coating temperature and can be decreased by preheating the substrate. 相似文献
12.
《International Journal of Inorganic Materials》2000,2(2-3):277-280
The deposition of CeO2 films on fused-silica substrates by spray pyrolysis of a water–ethanol solution of a cerium nitrate precursor has been studied. Polycrystalline films have been obtained at a substrate temperature of 300–450°C after annealing of the deposit in air at temperatures in the range 350–500°C. It has been established that the best uniform ceria films with nanometric scale grains are prepared at a substrate temperature of 400°C with 0.5 h annealing of the deposit at 500°C. At lower spraying temperatures large CeO2 crystallites have been observed on the film surface along with the fine grains. When the substrate temperature exceeds 400°C, numerous cracks caused by thermal stresses appear in the films. 相似文献
13.
The economy of the spray forming process is restricted by the generation of overspray, which in many cases cannot be re‐introduced into the process by re‐melting or co‐injection. Especially for small deposits, such as small diameter tubes (diameter <100 mm), the amount of overspray can become large in conventional spray‐forming processes. In this work, an alternative process with a pressure‐gas‐atomizer operating at low melt flows is presented. Tubes with diameters of 50 mm and 90 mm were spray‐formed and analyzed regarding yield and porosity. It was found that yields up to 96% can be achieved with porosities below 1% if proper process parameters are identified and used. An evaluation of the yield and the corresponding achievable porosity is conducted to identify resource‐efficient sets of parameters. 相似文献
14.
E. Schüller L. Krone M. Bram H. P. Buchkremer D. Stver 《Materialwissenschaft und Werkstofftechnik》2004,35(5):326-331
As a promising method to produce thin porous NiTi sheets, Wet Powder Spraying (WPS) is applied for NiTi powders. Layers with a thickness of 150 μm are obtained from pre‐alloyed NiTi powders with a particle size of < 12 μm. Optimized process control for spraying and sintering was used. Microstructure and phase formation is characterized. The sheets with a porosity of 15 % show a high pseudoelastic flexibility at room temperature. Phase transformation temperatures are determined by Differential scanning calorimetry (DSC). The one way effect could be demonstrated. 相似文献
15.
以金刚石和无机溶胶为原料,采用喷雾干燥法制备金刚石-陶瓷结合剂复合粉体,将粉体压制、烧结,获得金刚石-陶瓷结合剂烧结体。采用扫描电镜和激光粒度分析仪对复合粉体的形貌和粒径分布进行表征,借助综合热分析仪选取复合体的烧结温度,利用抗折试验机、扫描电镜和X射线衍射分别对喷雾干燥法和熔融法所制烧结试样的抗弯强度、断面形貌及物相进行分析。结果表明:经喷雾干燥的复合粉体为球形,易于成型,且复合粉体尺寸分布范围较宽,利于提高坯体致密度;选取金刚石-陶瓷结合剂复合体的烧结温度为820℃,在此温度下结合剂可实现对金刚石的黏结和包裹;烧结后,随陶瓷结合剂含量增加,两种工艺所制试样的抗弯强度均有提高,气孔率都相应降低;当结合剂含量为32%(质量分数)时,喷雾干燥法所制烧结试样的微观结构均匀,易析晶,抗弯强度和气孔率分别为99.46MPa和38.55%;熔融法所制试样的抗弯强度和气孔率分别为72.42MPa和39.89%。 相似文献
16.
In the present research, mechanically alloyed Ni-Al powder was utilized to develop plasma sprayed coatings, and the effect of the spray distance and heat treatment on the phases, microstructure, and hardness of the coat- ings were examined. Coatings were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and through microhardness measurements. Although mechanically al- loyed Ni-Al powder showed no intermetallic phases, the coatings did. Different spray distances from 5 to 19 cm were employed for plasma spray and the specimens were heat treated at different temperatures, then the amount of oxides, porosity and hardness of the coatings were changed according to the spray condition. The thermal energy of the plasma spray caused the formation of NiAl phases while particles flew to the substrate or after that. Extreme increase in heat treatment temperature and spray distance resulted in oxidation and reduction in the quality of the coating. Furthermore, the best spray distance and heat treatment temperature to gain the NiAl intermetallic coating were established. 相似文献
17.
18.
M. A. Taha A. F. Yousef K. A. Gany H. A. Sabour 《Materialwissenschaft und Werkstofftechnik》2012,43(11):913-923
Selective laser melting is a laser‐based additive manufacturing process applying layer manufacturing technology and is used to produce dense parts from metallic powders. The application of selective laser melting on carbon steels is still limited due to difficulties arising from carbon content. This experimental investigation aims at gaining an understanding of the application of the process on ultra high carbon steel, which is a special alloy with remarkable structural properties suitable for different industrial applications. The feedstock ultra high carbon steel (2.1% C) powder, 20 μm to 106 μm was prepared by water atomizing technique. This powder was used for the selective laser melting to build specimens 10×10×40 mm in dimensions. To decrease the thermal stresses during layer by layer building, laser scanning was done through 5×5 mm random island patterns while layer thickness was 30 μm. Laser beam diameter, maximum power output, layer thickness and scan speed range were 0.2 mm, 100 W, 30 μm and 50–200 mm/s respectively. The process was done inside high purity nitrogen environment, with less than 0.5% oxygen content. The results illustrate the influence of scan speed from 50 to 200 mm/s on product geometry and dimensions, surface roughness, internal porosity and cracks, microstructure and surface hardness. The effect of post heat treatment by heating and holding for one hour (annealing) at different temperatures of 700°C, 750°C, 950°C is studied. The results indicate that selective laser melting is able to produce near to 95% density of ultra high carbon steel parts with acceptable geometry and surface quality. Porosity cracks, and microstructure formed during the process could be controlled through proper selection of process parameters and post heat treatment. Industrial ultra high carbon steel products can be rapidly fabricated by selective laser melting. 相似文献
19.
High strength metal coatings are promising for reducing the cavitation damage of ship rudders. Cold spraying offers the opportunity to produce coatings that have similar properties as respective bulk material. In this study, conditions for cold spraying CuAl10Fe5Ni5 bronze are evaluated for the use at ship rudder applications. The spray parameter sets were varied with respect to nozzle type, process gas pressure and temperature. Single particle impact morphologies were investigated by scanning electron microscopy and categorized into different classes to obtain information on the deformation behavior. Within the selected parameter regime, coatings were processed with deposition efficiencies of up to 70%. The coating microstructures were analyzed by optical microscopy to gain information on spraying conditions for minimum porosity. For the higher parameter sets, porosities of less than 2% were obtained. Coating performance was investigated by cavitation test procedures. These first results show that cold sprayed bronze coatings still faces challenges with respect to powder properties. With further optimization, respective coatings could have a high potential for ensuring a good performance in rudder protection. 相似文献
20.
采用恒电位极化和电化学阻抗谱(EIS)技术研究了青岛天然海水中不同极化电位下高锰铝青铜的保护电流密度和表面状态随时间的变化过程,利用扫描电镜(SEM)和能谱X射线(EDX)分析了阴极极化产物的微观形貌和元素组成。结果表明,极化168 h后,-0.8 V和-0.5 V两种极化电位下,高锰铝青铜表面都能够形成明显的钙质沉积层,主要成分都是CaCO_3;-0.8 V的极化电位下,高锰铝青铜虽然表面形成了铁锰氧化物,但其稳定保护电流密度更低,钙质沉积层膜电阻和电荷转移电阻值更高,钙质沉积层结构也更加致密。因此,-0.8 V的极化电位比-0.5 V的极化电位对高锰铝青铜具有更高的阴极保护效率。 相似文献