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101.
102.
This paper presents an investigation of the influence of plasma spray process conditions on the in-flight particle behavior
and their cumulative deposition to form a coating on the substrate. Three-dimensional computational fluid dynamics (CFD) analyses
were performed to model the in-flight particle behavior in the plasma-spray process and their deposition on the substrate.
The plasma spray was modeled as a jet issuing from the torch nozzle through the electrical heating of the arc gas. In the
model, particles were injected into the plasma jet where they acquired heat and momentum from the plasma, some got melted
and droplets were formed. By means of a droplet splatting model, the particle in-flight data generated by the CFD analyses
were further processed to build up an imaginary three-dimensional deposition profile on a flat stationary substrate. It is
found that the powder carrier gas flow rate influences the particle distribution on the substrate by imparting an injection
momentum to the particles that were directed radially into the plasma jet in a direction perpendicular to the plasma jet.
The larger sized particles will acquire higher injection momentum compared with the smaller sized particles. This causes particle
distribution at the substrate surface that is elliptical in shape with the major axis of ellipse parallel to the particle
injection port axis as illustrated in Fig. 1. Larger particles tend to congregate at the lower part of the ellipse, due to
their greater momentum. The distribution of particle size, temperature, velocity, and count distribution at the substrate
was analyzed. Further, based on the size and the computed particle temperature, velocity histories, and the impact sites on
the substrate, the data were processed to build up a deposition profile with the Pasandideh-Fard model. The shapes of deposition
profiles were found to be strongly driven by the segregation effect. 相似文献
103.
104.
The melting, evaporation and oxidation behaviors as well as the solidification phenomena of tungsten and molybdenum in induction plasma were studied. Scanning electron microscopy was used to examine the morphology and the cross section of plasma-processed powders. X-ray diffraction was used to analyze the oxides formed on the particle surface of these two metals. The influence of spray chamber pressure on the spheroidization and oxidation phenomena was discussed. The results show that fewer Mo particles than W particles are spheroidized at the same powder feed rate under the same plasma spray condition although molybdenum has a lower melting point. A small fraction of tungsten is evaporized and condensed either on the surface of tungsten particles nearby or on the wall of spray chamber. Tungsten oxides were found in tungsten powder processed under soft vacuum condition. Extremely large grains form inside some spheroidized particles of tungsten powder. 相似文献
105.
1 INTRODUCTIONTraditionallysinteredNdFeBmagnetcanmeettherequirementofdimensional precisionthroughpost machining ,whichusuallyresultsin 4 5 %ofma terialloss.Post machiningnotonlywastestherareearthresources ,butalsoincreasesthe productioncost .Moreover ,itisdifficulttopreparehomogeneousworkpieceswithlargedimensionandcomplicatedshapeduetosomeuncontrollablefactorsinthecon ventionalsintering process .Ontheotherhand ,al thoughthebondedNdFeBmagnethasbetterforma bilityanddimensionalprecision ,… 相似文献
106.
107.
108.
109.
利用等离子喷涂设备将Ti与羟基磷灰石(HA)的混合粉末喷射入水,采用扫描电子显微镜和X射线衍射仪研究了Ti HA入水颗粒的形态和相组成,结果表明,经等离子熔融喷射入水后,钛粒子的尺寸小于HA粒子,主要原因之一是HA内形成了空心结构,空心结构的形成是由于HA在熔融时生成气相P2O5和H2O,它们在颗粒内聚集形成气泡,入水Ti HA粒子主要是由晶相和非晶相HA,分角相磷酸三钙(TCP)和磷酸四钙(TTCP)以及Ti的化合物所组成,由于与Ti的混合,HA的分解加剧,而Ti与HA粒子的融合及元素的扩散在飞行过程中已经发生。 相似文献
110.
A. Kobayashi 《Journal of Materials Engineering and Performance》1996,5(3):373-380
The surface nitridation of titanium was carried out at a low pressure in nitrogen atmosphere using a gas tunnel type plasma
jet. The titanium nitride (TiN) film, 10 μm thick and 2000 HV, could be formed in 10 s. The structure of the TiN film was
investigated by XRD. The Vickers hardness on the surface of the film was measured. The effects of deposition conditions on
the properties of TiN films (TiN thickness,Vickers hardness, etc.) were investigated, and the advantage of this deposition
method was identified from those results. 相似文献