共查询到20条相似文献,搜索用时 15 毫秒
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Power particles are mainly in solid state prior to impact on substrates from high velocity oxy-fuel (HVOF) thermal spraying.
The bonding between particles and substrates is critical to ensure the quality of coating. Finite element analysis (FEA) models
are developed to simulate the impingement process of solid particle impact on substrates. This numerical study examines the
bonding mechanism between particles and substrates and establishes the critical particle impact parameters for bonding. Considering
the morphology of particles, the shear-instability–based method is applied to all the particles, and the energy-based method
is employed only for spherical particles. The particles are given the properties of widely used WC-Co powder for HVOF thermally
sprayed coatings. The numerical results confirm that in the HVOF process, the kinetic energy of the particle prior to impact
plays the most dominant role in particle stress localization and melting of the interfacial contact region. The critical impact
parameters, such as particle velocity and temperature, are shown to be affected by the shape of particles, while higher impact
velocity is required for highly nonspherical powder. 相似文献
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前驱物颗粒的形貌对钴粉形貌的影响 总被引:13,自引:0,他引:13
研究了球形草酸钴、球形Co(OH)2的制备方法及其颗粒形貌和晶体结构,并以此为前驱物还原制备金属钴粉,对钴粉颗粒形貌与其前驱物颗粒形貌之间的关系进行了分析讨论。 相似文献
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Karimpour M. Eatezadi S. R. Hasani S. Ghaei A. 《Metallurgical and Materials Transactions B》2019,50(4):1597-1607
Metallurgical and Materials Transactions B - In this study, the mechanism of nonisothermal oxidation of magnesium powder was determined using a tension analysis, which was performed by mathematical... 相似文献
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按照内燃机的新规定和规范,需要降低其油耗和排放。超音速火焰喷涂可以用来喷涂耐磨涂层,这一工艺具有很大潜力。热喷涂涂层能提高内燃机的效率,减少发动机气缸壁的损耗,提高持久性和耐磨性,从而达到促进发动机减耗的目的。热喷涂工艺同样可以达到耐腐蚀的要求,如使用合金和陶瓷粉末,就可以在现代的内燃机里使用生物燃料。此外,热喷涂涂层的特殊表面结构,包括其多孔性,可以让气缸保持在润滑摩擦的状态,甚至是在相对移动量较小处也可以减小摩擦,如顶部和底部的正中心处。另外,表面开放孔隙可以减少油耗,从而减少内燃机的污染物排放。运用HVOF和HVSFS工艺可以喷涂各种材料,包括最最新的纳米级粉末。经过喷涂的气缸和引擎由于其摩擦系数,磨损和油耗等重要因素,被认为是现代化的部件。 相似文献
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喷涂粒子在等离子体射流中的加热历程及熔化状态研究 总被引:2,自引:0,他引:2
本文通过对水中收集的等离子喷涂熔融粒子进行粒度分析及形貌观察,研究了喷涂粒子在普通大气等离子喷涂(APS)及超音速大气等离子喷涂(SAPS)射流中的加热历程及熔化状态。实验观察到氧化钇部分稳定的纳米颗粒团聚造粒的氧化锆(Y-PSZ)球形粉末颗粒在APS及SAPS射流中传热传质过程中的熔融与"细化"现象有明显不同:在SAPS射流中,尺寸较大(粒径在几十微米)的颗粒大部分形成了十分细小的(小于5μm)颗粒;相对而言,APS中的熔融粒子仍以十几微米以上较大粒径的半熔融粒子为主。进一步研究表明,大尺寸粒子在等离子射流中先从表层熔化,逐渐向颗粒内部扩展,形成柱晶熔区,属典型的梯度熔化模式,最终芯部存留大量细小未熔一次粒子,即所谓半熔融状态;相应的SAPS中大量粒径小于5μm的小颗粒在超音速等离子体射流中整体迅速熔化(即所谓等温熔化模式)。对熔融或半熔融粒子撞击基体后的扁平化过程进行分析表明:在APS射流中扁平粒子的直径一般在100μm以上,且周围飞溅较多,导致典型的层状多孔的粗大组织结构,层间出现较多平行横向裂纹;而SAPS大量细小熔滴撞击基体后,冷却更快,多呈无明显飞溅的直径约10~30μm圆盘状,形成大量细密柱晶交错堆垛而成的、无明显分层的特殊结构。对收集粒子进行X-射线衍射相分析表明,APS及SAPS两种工艺下的熔融粒子均未发生明显相变,相组成主要为室温下非转变四方氧化锆(t’-ZrO2),说明喷涂粒子在高温等离子射流的加热历程中,其晶体结构和化学成分未发生明显变化。 相似文献
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A new numerical simulation model is developed by using an interface-enriched eXtended Finite Element-Level Set (XFE-LS) method to study the solute-induced melting of additive powder particles (APPs) during transient liquid phase (TLP) bonding. The robust model captures rapidly occurring concurrent interfacial events at multiple propagating liquid-solid interfaces to simulate the melting behavior. In contrast to the critical assumption in analytical models, numerical calculations show that solute-transport into the APPs during the equilibration of the liquid composition is a significant factor that affects the APPs melting behavior. Also, the study shows that the solute-transport dependence of extent of APPs melting is influenced by the kinetics of solid-state solute diffusion within the particles. The understanding generated by the numerical analysis has resulted in the use of interlayer powder mixture that contains base-alloy APPs to produce single crystal TLP joint that has matching crystallographic orientations with single crystal substrate material, at a substantially reduced processing time, which has been previously considered unfeasible. 相似文献
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将微量硅酸钠以不同浓度的水溶液形式掺杂到蓝色氧化钨中并在相同的条件下还原成钨粉。结果表明,还原钨粉的粒度随硅酸钠掺杂量的增加而增加,少量掺杂还使还原钨粉的松装密度增加。对还原钨粉表面的扫描电镜及x射线光电子能谱分析结果显示,掺杂到蓝色氧化钨中的硅酸钠最终以Na_2SiO_3和SiO_2二种分子形式存在并以微粒状分布在还原钨粉的表面。掺杂微量硅酸钠还使还原钨粉中的二次颗粒增加。 相似文献
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采用电脱氧法,以Nb2O5烧结片为阴极,石墨棒为阳极,在CaCl2-NaCl混合熔盐中制备金属铌.分别研究了压制压力、烧结温度对阴极片微观结构和电脱氧反应及其产物的影响.实验结果表明,烧结温度和压制压力对Nb2O5烧结片的晶粒尺寸、孔隙度和孔隙尺寸具有明显的影响,从而影响到电脱氧的反应速率和效果.晶粒细、孔隙度高和连通性好的烧结氧化铌阴极能够提高电脱氧的反应速率和效果.研究表明,12MPa压制成型后经1 200℃烧结的阴极片,电脱氧效果最佳. 相似文献
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等离子喷枪采用内送粉方式后,喷涂功率对YSZ热障涂层微观结构和性能有着独特的作用,高功率下制备的涂层结合强度反而较低。本文研究了内送粉等离子喷枪在高功率(42.5 kW)和低功率(33.6 kW)时距喷嘴出口90 mm处的粒子熔化状态(粒子温度、粒子飞行速度、粒度分布及扁平粒子形貌)。研究结果表明,采用高喷涂功率时,由于等离子射流较高的热焓值使粒子迅速熔化并细化成粒径较小的熔滴,熔滴在撞击基体前发生再凝固降低了扁平粒子间的粘结。涂层出现横向裂纹,结合强度平均值仅为22.58 MPa。采用小喷涂功率时,既能保证粒子熔化良好又不会导致粒子发生明显细化。涂层结合强度平均值为37.25 MPa,随试片弯曲180(°)后仅出现一处剥落,1100℃炉中保温10 min取出后迅速置于水中淬冷130次后,试片中部涂层完好,显示出良好的抗热震性能。 相似文献
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Influence of Porosity on Piping Models of Levee Failure 总被引:1,自引:0,他引:1
A piping model based on Darcy's law is developed. An analysis of data pertaining to different soil particle sizes and varying porosity shows that the choice of the permeability function is critical for the piping model. The permeability relations, which depend only on the grain size, are of limited value. 相似文献
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Studies of the effect of the extrusion and sintering regimes on the pore structure of steel 45N4D2M, made from partially alloyed iron powder, showed that the porosity of the powder products can be reduced to below 10% by pre-sintering the extruded products at 700–850°C to remove work-hardening that occurs during the first extrusion and then extruding the product again at 400–600 MPa to additionally compact it to a relative density of 0.90–0.93. Within the investigated density range (0.81–0.93), a decrease in porosity is accompanied by a monotonic increase in all of the mechanical properties of sintered steel 45N4D2M: a 1% reduction in porosity makes it possible to increase σu and σ0.2 by 30 MPa, increase σb by 65 MPa, increase δ by 0.1 %, increase KC by 2.3 J/cm, and increase hardness by 10 HB. It was established that, other conditions (chemical composition, the structure of the metallic matrix) being equal, the properties of the sintered steel are determined mainly by the final porosity and are independent of the parameters of the compaction operation in which they are obtained. 相似文献
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钒钛磁铁矿金属化球团固结机理研究 总被引:2,自引:0,他引:2
以转底炉工艺为基础,在实验室模拟条件下,研究了钒钛磁铁矿金属化球团的固结机理。讨论了配碳量(C/O)、还原温度、还原时间对球团金属化率和抗压强度的影响,确定了金属化球团的固结机理。研究发现:钒钛磁铁矿金属化球团的抗压强度主要与金属铁相的数量和形态以及金属化球团内孔隙的大小有关;金属化球团孔隙的大小主要取决于配碳量高低和脉石所形成的渣相对金属化球团内部孔隙的填充状态;金属铁相的数量和形态则取决于金属化球团的还原程度。随着还原温度升高和还原时间延长,金属化球团内部金属铁相密集度增加,渣相流动性改善,从而导致金属化球团孔隙减少且变小,球团强度增加。 相似文献
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为了研究YSZ粉末特性对热障涂层性能的影响,选择三种通过造粒烧结工艺制备的商用YSZ粉末,测试对比了粉末颗粒的各项性能,发现三种粉末仅致密度存在显著差异。在两种不同功率条件下采用等离子喷涂工艺利用三种YSZ粉末制备了热障涂层,观察了涂层的金相组织和断口形貌,测试了涂层孔隙率和结合强度,并采用电弧风洞考核了涂层的服役性能。研究结果表明,粉末致密度对涂层性能有显著影响,致密度高的YSZ粉末喷涂过程中熔融状态更好,涂层的孔隙率更低,结合强度更高;针对致密度低的粉末,增大喷涂功率可改善粉末的熔融状态,从而改善涂层的性能。经工艺调控制备的孔隙率和结合强度相近的涂层具有相当的隔热防护效果。 相似文献
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Metallurgical and Materials Transactions A - The densification and bonding of aluminum powder subjected to ultrasonic vibration under uniaxial pressure were characterized and their mechanisms were... 相似文献