7055铝合金粉末的氩气低压雾化技术

将传统环缝喷嘴结构改造为Laval型出气口,以实现低压高效雾化制粉,利用该喷嘴进行7055铝合金氩气低压雾化制粉实验,对Laval型喷嘴的雾化能力、熔滴凝固特性与粉末微观组织进行研究。结果表明：与传统紧耦合喷嘴相比,Laval 型喷嘴具有更好的低压雾化能力,在较低雾化压力下即可获得超音速雾化气流,雾化压力为0.4,0.6和0.8 MPa时雾化粉末的质量中径d50分别为63.5,57.1和43.4μm,大部分合金粉末呈球形或类球形;雾化熔滴凝固过程中产生大量尺寸在0.5~2.5μm范围内的细小枝晶组织,枝晶间距λ与粉末粒径d近似满足如下关系：λ=0.1923 d 0.547;雾化粉末具有快速凝固特性,冷却速率达到104~105 K/s,随熔滴粒径增大而减小。     

高温合金雾化熔滴的热传输与凝固行为

采用雾化过程热传输数学模型计算了高温合金雾化熔滴飞行速度、对流换热系数、温度分布、固相分数和冷却速度随熔滴尺寸和飞行距离的变化,给出了其变化趋势及引起变化的原因,并讨论了雾化压力和合金过热度对上述参数的影响     

组合雾化过程中熔滴的飞行动力学与热历史的数值模拟

采用数值模拟方法研究组合雾化过程中熔滴的飞行动力学以及冷却凝固过程与熔滴随飞行距离的变化关系,模拟过热度和旋转盘转速对熔滴飞行和冷却凝固的影响规律。结果表明:在组合雾化过程中,熔滴尺寸显著影响熔滴的动力学和热历史过程,熔滴越小,速度变化越快,飞行距离越短。过热度对于熔滴的冷却凝固影响不明显,但大的过热度会延缓熔滴的凝固过程。因此,大的过热度不利于雾化室的设计。旋转盘的旋转速度对于熔滴热历史的影响稍大于过热度的影响,高转速可以缩短熔滴冷却凝固过程的飞行距离。通过测量二次枝晶间距,推算出实验制得粉末的冷却速率范围为10~3~10~6 K/s,与数值计算的结果基本一致。     

不同雾化压力下GH3536合金粉末制备和气雾化过程模拟

使用真空感应熔炼气体雾化方法，在不同雾化压力(7、8、9 MPa)下制备了球形GH3536合金粉末。通过使用多相流模型和离散相模型对喷嘴下方区域进行了数值模拟，再现了不同雾化气压下的一次雾化和二次雾化过程。实验和模拟的结果表明：回流区的气体速度和滞止压力随雾化气压的提高而增加，雾化气压的增加使粉末粒度不断减小，模拟结果与实验结果吻合，验证了雾化模型的可靠性。提高雾化气压可提高细粉收得率，但颗粒尺寸的减小和颗粒形貌的改变会对粉末的流动性能造成直接影响，在雾化压力8 MPa下制备的粉末具有最佳的流动性和松装密度，分别为14.34 (s·50g^-1)和4.728 g·cm^-3。     

FeNiCrSiMoMnC合金气雾化熔滴的运动与传热行为模拟分析

气雾化过程中合金液流被高压气流破碎后,要飞行一段距离才开始冷却凝固,这称为熔滴的飞行过程。本文以重载耐磨耐腐蚀激光熔覆涂层用FeNiCrSiMoMnC合金为对象,通过建立熔滴飞行过程的模型,并对该过程进行数值模拟,计算讨论了雾化气体初始速率、熔滴直径对熔滴的速度、传热系数等参数的影响。结果表明,熔滴速度呈现先增大至最大值后逐渐减小的趋势,且随熔滴直径的增大,熔滴速度最大值点逐渐降低;传热系数与速度曲线相反,呈先下降后上升的趋势,极小值为2kg/d,熔滴直径越大,与气体速度差越小,传热系数越小;随气体初始速率的增大,熔滴最大速度点上移,同时传热系数也逐渐增大。     

雾化气体和熔滴速度的研究

从理论与实验两方面研究了雾化气体流速场和雾化熵滴与气体流场的交互作用,建阙雾化气体和熔滴流速的数学模型,探讨了雾化熵滴对雾化气体流速的影响。     

AH36薄板激光-电弧复合焊熔滴过渡与熔池分析

采用激光-电弧复合焊,激光前置焊接海工钢AH36薄板。利用高速摄像分析熔滴过渡特征与影响因素。运用计算流体力学体积分数法建立固液气三相流体动力学模型。采用高斯面热源、高斯旋转体热源和双椭球热源表征复合焊热源。数值模型考虑了表面张力、电磁力、浮力、反冲压力、蒸发冷凝、蒸发换热等多种物理场的耦合作用。对熔滴过渡冲击及其对熔池形貌、流动与温度的影响进行研究。结果表明,熔滴冲击熔池可促进熔池流动与传热。熔滴过渡受电磁力与蒸气反冲压力抑制,致使大熔滴出现。适当增加激光功率可降低熔滴表面张力,增加熔滴过渡频率,减小熔滴尺寸。激光功率过大或光丝间距过小时,出现熔滴破裂与飞溅。     

气体压力对雾化颗粒大小的影响

文章研究了气体压力大小在雾化粉末工艺过程中的影响。结果表明,在限制式的喷嘴结构中,当熔体温度、气流喷射角度确定的条件下,气体压力较小,雾化颗粒不能形成,熔体会在导管中凝固或形成倒锥形的粘结块;随着气体压力的增加,粉末球化程度增大,平均颗粒减小。     

超声雾化制取纳米结构粉末

瑞士开发出一种新振子进行双重超声雾化 ,可工业化生产纳米结构金属粉末。新雾化装置将两种超声雾化方法 (超声气体雾化与张力波雾化 )有机结合起来 ,克服了它们各自的局限性。新装置分两步击碎熔态金属 ,从而解决了熔体流直径不能过大的问题。熔态金属流首先导向由超声频率激发的管状共振器的内壁 ,熔态金属润湿这种振动基体 ,通过张力波雾化被击碎。同时 ,在进入同一管中的惰性气体中产生非稳态冲击波 ,这种压力脉冲进一步击碎张力波雾化的熔滴。它的一大进步是 ,开发出了“锤”型超声振子 ,比传统的两金属块三明治振子提高了频率、振幅与…     

超音速气雾化喷嘴中抽吸压力变化规律的研究

对超音速气雾化喷嘴中抽吸压力ΔP的变化进行了试验研究,重点考察了雾化气体压力P0、气流夹角α、导液管锥顶角β及突出长度h对抽吸压力的影响。试验结果表明,在(0.5～4.0MPa)雾化压力范围内,抽吸压力皆呈负压状态。但抽吸压力变化分三阶段:随着雾化压力的增加,雾化压力在0.5～1.5MPa范围内,抽吸压力减小;雾化压力在1.5～3.5MPa之间时,抽吸压力逐渐增大,并达到一个最大值;当雾化压力超过3.5MPa后,抽吸压力又逐渐降低。锥顶角越大,抽吸压力越大;而雾化压力升高到或大于3.23MPa时,随着突出长度的增加,抽吸压力逐渐减小。     

Characterization of spray atomization of 3003 aluminum alloy during linear spray atomization and deposition

Linear spray atomization and deposition is an attractive technique to produce near-net-shape deposits, such as aluminum sheet and strip. In the present study, phase Doppler interferometry (PDI) was used in a backscatter mode to characterize, in situ, the droplet size and velocity distributions during linear spray atomization and deposition of a 3003 aluminum alloy. The PDI measurements were obtained along axes corresponding to the direction parallel to the nozzle slit and to the direction perpendicular to the slit. The PDI results delineate the temporal and spatial distribution of the droplet size and velocity during the metal spray. Both point and “line” measurements were obtained and are reported. The line measurements resulted from the integration of measurement made along a line scan obtained in real time (i.e., not ensemble averaged). Postrun analysis of the droplet size distribution using laser diffraction and sieving techniques is also reported. The PDI point measurements revealed that droplet size and velocity distribution were relatively invariant with time. The line measurements of droplet velocity showed that the droplet axial velocity exhibits a bimodal behavior, which becomes more apparent with increasing atomizing gas pressure, a result of droplet recirculation inside the spray chamber. In addition, the peak in the droplet axial velocity distribution increased as atomizing gas pressure increased. The line characterization also showed that the droplet size distribution became more homogeneous with increasing gas pressure, and that the distribution characteristic diameters of droplets decreased consistently with increasing gas pressure. Postrun characterization of the droplet size distribution of the entire metal spray using diffraction and sieving methods indicated that the mass (volume) median diameter D ₅₀ and the Sauter mean diameter (SMD) D ₃₂ decreased with increasing gas pressure in a manner consistent with PDI results.     

气体雾化法制备锡粉的技术研究

在自行设计的限制式雾化喷嘴为核心的雾化装置上 ,用气体雾化法制备锡粉。研究了雾化压力对液锡雾化效果的影响 ,对锡粉粒径的大小和分布进行了分析。实验发现 ,颗粒粒度的分布服从对数 正态分布规律 ;当其它条件一定时 ,雾化压力越小 ,体积平均直径dvm,Sauter平均直径dvs和中位径dm 的值就越大即颗粒越粗 ;不同压力下几何标准偏差σg 值均约为 3 1 ,σg 值越大即颗粒尺寸分布范围较宽。通过显微镜观察 ,发现制备的锡粉大部分为泪滴形或球形。     

两相雾化除尘参数对热轧机组除尘效率的影响

为了提高热轧机组除尘效率,降低热轧现场粉尘污染,研究了两相雾化除尘技术的气压、液压对雾场参数的影响。首先,在理论分析的基础上进行雾场的数值模拟;其次,搭建试验平台进行喷雾试验,验证了所建模型的准确性。分析了不同气、液两相的压力组合对雾场参数的影响,着重分析了对雾滴粒径的影响。结果表明,随着气相压力和液相压力的增大,喷雾场中雾滴粒径减小。雾滴粒径主要受气相压力的影响,且随气相压力的增大变化率降低。在气压为0.6 MPa,液压为0.55 MPa时的雾场参数对氧化铁皮粉尘的去除效果较好。现场应用表明,在此参数组合下,机架出口牌坊上方距机架3 m处,粉尘平均浓度由369.1 mg/m3以上降至23.9 mg/m3以下,粉尘去除率达到了93.5%,表明降尘效果良好。     

Reactive atomization of silicon to formin situ oxide sintering aids

The present investigation demonstrated the feasibility of using reactive atomization to produce Si powder within situ oxide sintering aids. With further process optimization, this powder may be an alternative starting material to the conventional, mechanically blended, Si-plus-oxide powder used to produce commercial sintered reaction bonded silicon nitride (SRBSN). In the reactive atomization approach, yttrium and aluminum additives were introduced into silicon metal during induction melting. Reactive atomization was accomplished using a N₂-5 pct O₂ mixture as the atomization gas. During atomization, oxygen in the atomization gas reacted with Y and Al in the Si melt to produce Y₂O₃ and Al₂O₃, which act asin situ sintering aids. The reactive atomized powder demonstrated a Gaussian distribution with a mean diameter of 36 μm. The powder fines (<38 μm) were used to produce cold isostatically pressed compacts that were subsequently reaction bonded and sintered. The results demonstrate that β-Si₃N₄ formed during reaction bonding and sintering. The density of the SRBSN was 77 pct of theoretical. Transmission electron microscopy (TEM) studies indicated the presence of a glassy phase on the grain boundaries, which is typical in SRBSN and indicative of the presence of thein situ sintering aids. A kinetic model was used to study the influence of processing parameters, such as droplet temperature and oxygen partial pressure, on the kinetics of oxide formation during reactive atomization. The results suggest that the volume fraction of oxides increases with increasing droplet temperature and oxygen partial pressure in the atomization gas mixture. This article is based on a presentation made in the “In Situ Reactions for Synthesis of Composites, Ceramics, and Intermetallics” symposium, held February 12–16, 1995, at the TMS Annual Meeting in Las Vegas, Nevada, under the auspices of SMD and ASM-MSD (the ASM/TMS Composites and TMS Powder Materials Committees).     

A numerical study of oxidation behavior during reactive atomization and deposition

The oxidation behavior of droplets during reactive atomization and deposition (RAD) is analyzed on the basis of a numerical framework proposed here. Commercial 5083 Al is chosen as a model material; moreover, in the numerical model, nonspherical droplets are approximated as cylinders with a length/diameter ratio of 3. An equation that represents the growth rate of the oxide phases, together with models that describe the dynamic and thermal behavior of droplets, is implemented in an effort to elucidate the oxidation behavior of individual droplets. The numerical results reveal that the oxidation rate of a droplet is extremely high and that the oxide phase grows very rapidly initially, eventually attaining a steady state of limited oxide growth. The overall volume fraction of oxide phases in the RAD material increases with increasing atomization pressure, superheat temperature, and O₂ concentration, whereas it decreases with increasing melt flow rate. The oxygen concentrations in the RAD powders and deposited materials predicted on the basis of numerical analysis are in good agreement with the results from chemical analysis when O₂ concentration is lower than 16 vol pct.     

紧耦合气雾化技术制备选区激光熔化用18Ni300合金粉末的研究

基于紧耦合气雾化技术制备符合选区激光熔化用18Ni300合金粉末, 重点研究了雾化压力对粉末粒度(中值粒径, D₅₀)、粒度分布、球形度、氧含量、流动性和松装密度等特性的影响。结果表明: 雾化压力对上述粉末特性影响显著, 当雾化压力在3.5 MPa到4.5 MPa范围时, 随着压力的提高, 粉末粒度降低、表面形貌改善、流动性变好、松装密度增加。当雾化压力为4.5 MPa时, 所制备的粉末综合特性最优, 粉末粒度(D₅₀)为34 μm, 球形度为0.77, 氧含量为0.02%(质量分数), 流动性为17.4[s·(50g)-1], 松装密度为4.32g·cm-3, 15~53 μm粒径范围粉末收得率为38.1%, 满足选区激光熔化技术对金属粉末性能的要求。     

Kinetics of ceramic particulate penetration into spray atomized metallic droplet at variable penetration depth

The present study provides insight into the physical interactions that take place when an injected ceramic particulate collides with an atomized metallic droplet during spray atomization and deposition processing of particulate reinforced metal matrix composites. A model is developed to predict the extent of penetration for a given particulate velocity, and the critical velocity for complete penetration. In the model, the initial kinetic energy of the injected particulates or the atomized droplets is considered as the driving force for penetration; the change in surface energies and the work done by viscous drag in the droplet melt are considered as the forces resisting penetration. As examples, Al/graphite and Al/SiC systems are analyzed to demonstrate the applicability of the model. The influence of the particulate size and the fraction of solid phase in the atomized droplet on the critical velocity and the penetration depth is also examined.     

伴有Marangoni效应的渣/金熔滴融合行为的数值模拟

摘要：以静止渣/金熔滴为对象,运用VOF方法考察熔滴相际间碰撞融合界面行为。当相同直径同种熔滴碰撞融合时,融合速度周期性振荡,不断衰减,并且随着熔滴直径的减小,振荡周期变短,振荡峰值降低。在相同直径不同种熔滴碰撞融合情形下,可观测到明显的Marangoni效应,表面张力梯度差的存在促使熔滴向表面张力小侧移动,且表面张力较大的熔滴位于表面张力较小的熔滴上,可为钢铁冶炼过程中的热质传递强化提供理论依据。