高频感应熔化金属丝气雾化制备球形钛粉

提出了新型低成本球形钛粉气雾化制备技术——高频感应熔化金属丝气体雾化技术(Wire induction heating-gas atomization,WIGA),研究了雾化气体压力、熔体温度、送料速度对粉末性能的影响。结果表明:所制钛粉末的形貌为球形,球形度较高,粉末表面存在少量"卫星球"颗粒,占比约为1%;提高雾化压力、熔体温度和降低送丝速度均使粉末平均粒径D50减小。实验所得最佳雾化参数为:雾化气体压力4.0 MPa,熔体温度2 000℃,送料速度0.8m/min,在此条件下得到的钛粉末平均粒径为41.8μm。     

等离子旋转电极雾化法制备高品质Ti-6.5Al-1.4Si-2Zr-0.5Mo-2Sn合金粉末

旨在制备高品质Ti-6.5Al-1.4Si-2Zr-0.5Mo-2Sn粉末,为后续粉末高温钛合金构件的制备奠定基础。首先采用真空自耗电弧熔炼(VAR)技术制备Ti-6.5Al-1.4Si-2Zr-0.5Mo-2Sn合金铸锭,对铸锭进行化学成分检测,并分析其合金元素损耗、成分均匀性以及显微组织和物相组成。利用制得棒料,采用等离子旋转电极雾化法(PREP),选取不同转速制备得到钛合金粉末,将粉末筛分成不同粒度范围。研究了棒料转速与粉末理化性能间的关系。采用X射线衍射分析仪(XRD)、扫描电镜(SEM)、金相显微镜(OM)分别分析了粉末的物相组成、形貌和微观组织。研究表明:通过独特的压制电极设计,可制得成分均匀、元素损耗小的钛合金铸锭,且各合金元素含量满足国标的要求。铸锭微观组织为层片状结构,基体中存在少量大小不均的Ti5Si3硅化物相。PREP法制得的钛合金粉末呈正态分布,且球形度好,无空心球和卫星球。随着转速增加,小颗粒粉末占比增加,大颗粒粉末占比大幅度降低。粉末颗粒以胞状组织为主,存在少量的枝晶。合金粉末主要由α′马氏体相组成。相比合金铸锭,粉末中各合金元素略有损耗,O元素质量分数小于0.1%,有利于制得高性能的粉末钛合金。     

Particle defects and related properties of metallic powders produced by plasma rotating electrode process

Flowability, particle size distribution and particle inner pore features for powders of Ti-6Al-4V, 316-steel, and Co-29Cr-6Mo alloys produced by plasma rotating electrode process (PREP) at various rotation speeds are analyzed by using scanning electron microscopy (SEM) and synchrotron X-ray computed tomography (CT). The results show that powder flowability is related to particle size distribution, surface morphology and dynamic friction coefficient of the alloy itself. This results in the higher powder flowability at low rotation speed than that at high rotation speed. Average particle size is roughly proportional to the square root of the reciprocal of rotation speed. In addition, particle size has an important effect on the particle porosity and the number faction of hollow powder in coarse powder is obviously larger than that in fine powder. Meanwhile, the alloy composition also plays a key role on porosity due to the various surface tension of alloys.     

Influence of Processing Parameters on Granularity Distribution of Superalloy Powders during PREP

In order to investigate the influence of processing parameters on the granularity distribution of superalloy powders during the atomization of plasma rotating electrode processing (PREP), in this paper FGH95 superalloy powders is prepared under different processing conditions by PREP and the influence of PREP processing parameters on the granularity distribution of FGH95 superalloy powders is discussed based on fractal geometry theory. The results show that with the increase of rotating velocity of the self-consuming electrode, the fractal dimension of the granularity distribution increases linearly, which results in the increase of the proportion of smaller powders. The change of interval between plasma gun and the self-consuming electrode has a little effect on the granularity distribution, also the fractal dimension of the granularity distribution changed a little correspondingly.     

Microstructure and properties of hot isostatically pressed powder and extruded Ti25V15Cr2Al0·2C

Abstract

The influence of process route on the microstructure and tensile behaviour of specimens prepared from hot isostatically pressed powders and extruded ingot of the burn resistant alloy, Ti–25V–15Cr–2Al–0·2C (wt-%), has been investigated. Samples based on gas atomised (GA) and plasma rotating electrode process (PREP) powders have been studied. Microstructural examination shows that many PREP powder particles are single crystals, whereas GA particles are polycrystalline. The mechanical properties of hot isostatically pressed specimens have been assessed using tensile testing monitored by acoustic emission, while microstructures have been characterised by synchrotron X-ray microtomography and optical and analytical scanning electron microscopy. Tomographic examination revealed a small fraction (<0·002 vol.-%) of pores in samples made from hot isostatically pressed GA powders, but no porosity was detected in samples made from hot isostatically pressed PREP powder. In view of their similar tensile behaviour, it is concluded therefore that the porosity does not contribute to the scatter and poor ductility in these hot isostatically pressed samples. These pores increased in size and volume fraction after heat treatment above the hot isostatic press temperature. The large scatter in tensile properties of both hot isostatically pressed GA and PREP samples was correlated with the presence of large (100–400 μm) circular crack initiation sites on the fracture surfaces, but the origin of these initiation sites has not been identified.     

ELECTROLYTICAL PLATING PROCESS ON POWDER PARTICLES

The basic ideas of the earlier developed model of electrolytical plating of metallic powder particles have been applied for calculation of the amount of Ni coating layer on Fe powder particles. The shapes of the calculated curves are in good agreement with the experimental results. The reasons for low current efficiency on the powder particles are explained. Besides the important parameters such as the size of the powder particles and density of the electrolyte - powder suspension, mainly the influence of rotation speed of the suspension in cathodic compartment upon the amount of metal deposited on powder has been analysed. The influence of this parameter upon the electrode process becomes remarkable with increasing rotation speed which has been explained by combination of two effects: the contact resistance between the powder particles and the solid electrode, and the charging - discharging process of the double layers on the powder particles.     

功率对EIGA制备3D打印用TC4合金粉末特性的影响

与传统的雾化制粉技术不同,电极感应熔炼气体雾化(EIGA)技术是采用预合金棒料为电极,无坩埚感应加热,熔化后直接滴落雾化区被惰性气体雾化的技术.该技术由于在熔炼过程中液态金属与坩埚不接触,有效地减少了钛合金粉末中的夹杂物,改善了合金粉末的质量.本文利用自主设计制造的EIGA制粉设备,采用激光粒度分析仪、扫描电镜(SEM)、X射线衍射仪(XRD)等分析手段,研究了不同功率参数对雾化制备TC4合金粉末的粒度分布、组织形貌、空心球等的影响.研究表明:EIGA法制备的TC4合金粉末整体球形度均较好,空心球缺陷较少,空心球率低于3%.熔炼功率较低时,粗颗粒粉末较多,且存在一定比例不规则的棒形和哑铃状粉末颗粒;当功率提高到62 k W时,细粉比例明显提高,不规则形状的粉末颗粒基本消失.随着功率的升高,粉末中的氧含量呈增加趋势,但仍基本保持在0.08%~0.10%较低范围内.功率为56 k W时,粉末松装密度最好,为2.686 g/cm3,松装密度比为60.63%,符合激光3D打印用TC4钛合金粉末松装密度比要求.     

高温钛合金Ti-60粉末的制备和表征

采用感应熔炼气体雾化法制备了掺杂稀土Nd的高温钛合金Ti--60粉末。 结果表明, 在制备过程中合金元素几乎没有烧损, 增氧量小于100×10^-6; 粉末的平均粒度(d₅₀)约为100 μm, 满足正态分布, 雾化气体的压力增大则粉末的粒度减小; 粉末的形貌大多呈球形, 只有少量的形状不规则; 部分粉末是空心的, 其比例随着粉末粒度的增加而增大; 粉末表面有明显的凝固特征, 具有清晰的二次枝晶; 随着Nd含量的增加, 粉末表面富Nd稀土相的析出增加; 粉末由针状 α' 马氏体组织构成, 当真空退火温度超过700℃时马氏体开始微量分解, 当温度升高到850℃时马氏体大量分解。     

Centrifugal atomization of stainless-steel rotating rods melted by a high-power LASER beam

316L grade stainless steel powders were produced by centrifugal atomization during the melting of a rotating rod heated by a high-power LASER beam. The feasibility has been demonstrated by atomizing a range of stainless steel rods. The atomization process has been observed via high-speed imaging and fragmentation regimes have been identified according to a literature review on the rotating electrode process (REP). Results were compared with literature data and an existing prediction model for such a process. High-speed observation can monitor the present process and it is shown that a solidified layer of metal is formed at the edge of the rod during the process inducing metal flake ejection due to the centrifugal stresses. Effects of incident LASER beam power density, ejection speed and oxygen content of the surrounding atmosphere on the particle size distribution and the sample surface have been studied and compared with literature data on classical REP atomizers. The study focuses on the production of irregular particles during the atomization process and highlights the influence of the oxygen content in the surrounding atmosphere on the fragmentation regime and the resulting particle size distribution.     

Effects of process parameters on surface morphology of metal powders produced by free fall gas atomization

There are a number of process parameters which affect the characteristics of metal powders produced by free fall gas atomization. In the following work effects of various process parameters like apex angle of atomizer, focal length of atomizer, number of nozzles, diameter of nozzles, diameter of liquid metal delivery tube, superheat of liquid metal and type of metal etc. were studied on their surface morphology. It was observed that shape of powder particles depends on apex angle, superheat of liquid metal, type of metal and particle size range within a powder collective. Other parameters like focal length of atomizer, number of nozzles, diameter of nozzles and diameter of liquid metal delivery tube were found to have no effect on the shape of powder particles. However, Surface porosity and solidification shrinkage were observed on almost all types of metal powders.     

雾化介质对SnAgCu系无铅焊锡雾化粉末特性的影响

实验利用自行设计的超音速雾化制粉装置,研究了不同雾化介质对SnAgCu系无铅焊锡粉末有效雾化率、粒度分布及球形度的影响.结果表明:在一定雾化条件下,氦气雾化粉末具有最高的有效雾化率、良好的粒度分布,且球形度最好;氮气雾化的粉末具有较好的综合性能;与氦气、氮气相比,氩气雾化粉末综合性能较差;空气雾化粉末雾化率较高,但粉末较粗、表面粗糙.     

液体金属和合金的固-气两相流雾化的研究

采用铁粉作为固体雾化介质,研究固-气两相法的雾化工艺。通过对Al-30％Si的研究,结果表明:固-气两相流雾化制粉与普通气体雾化相比,能有效减小雾化粉末的粒度,提高细粉收得率,普通气体雾化制粉得到的粉末平均颗粒尺寸为150μm,固-气两相流雾化粉末的平均颗粒尺寸为50μm;使冷却速度显著提高,达到10~4～10~5K/s,相比普通气体雾化提高了10～100倍,使Al-30％粉末的微观组织明显细化,固-气两相流能量利用率增加。     

Development of an Imaging System and Its Application in the Study of Cutting Fluid Atomization in a Turning Process

Airborne inhalable particulates in the workplace can represent a significant health hazard, and one of the primary sources of particles is mist produced through the application of cutting fluids in machining operations. One of the principal mechanisms associated with cutting fluid mist formation is atomization. Atomization is studied by applying cutting fluid to a rotating workpiece such as found in a turning process. In order to properly study the atomization mechanism, an imaging system was developed. This system extends the size measurement range typically achievable with aerosol sampling devices to include larger particles. Experimental observations reveal that workpiece rotation speed and cutting fluid flow rate have significant effects on the size of the droplets produced by the atomization mechanism. With respect to atomization, the technical literature describes models for fluid interaction with the rotating workpiece and droplet formation via drop, ligament, and film formation modes. Experimental measurements are compared with model predictions. For a range of rotation speeds and fluid application flow rates, the experimental data are seen to compare favorably with the model predictions.     

热等静压温度和粉末粒度对Ti2AlNb合金组织与性能的影响

采用无坩埚感应熔炼超声气体雾化法制备了成分为Ti-22Al-24Nb-0.5Mo(原子分数, %)的预合金粉末,通过预合金粉末热等静压工艺制备了Ti₂AlNb粉末冶金合金。研究结果表明,热等静压温度显著影响Ti₂AlNb粉末冶金合金的显微组织,需严格控制。为了对比研究,选取了平均粒度分别为70 μm和200 μm的两种Ti₂AlNb预合金粉末,制备坯料并测试性能,探讨了粉末粒度的选取原则,分析了粉末粒度对Ti₂AlNb粉末冶金合金显微组织和力学性能的影响。研究结果表明,粉末粒度对合金室温拉伸强度无显著影响,但会对高温拉伸强度和高温持久寿命产生显著影响,由粗粉(平均粒度200 μm)制成的合金高温持久寿命较细粉(平均粒度70 μm)的降低大约40%。     

Experimental investigation on the effect of melt delivery tube position on liquid metal atomization

Metal powders are often made by gas atomization of liquid metal. During the process, liquid metal which flows from a melt delivery tube (MDT) is atomized by high speed gas discharging from a gas nozzle. In this work, the effect of the melt delivery tube position on atomization outcomes such as the yield, mass median diameter, and spread of the particle size distribution, is studied experimentally. A melt atomization setup (pilot-scale) is used to produce tin powder by gas-atomization. Three MDT positions, namely, intruded, extruded and flush with respect to the gas nozzle, are chosen for this study. Three pressure regimes (atmospheric, aspiration and pressurization) are established by varying the relative distance between the MDT and the gas nozzle exit for the three positions. Experimental investigations revealed that the intruded position produces powder with lower mean particle sizes and lower spread than the extruded configuration. The intruded position also gives a significantly higher yield compared to the extruded and flush positions at low gas flow rates, and hence appears to be the most suited for metal atomization using a free-fall configuration.     

Impact of process flow conditions on particle morphology in metal powder production via gas atomization

Additive manufacturing processes as for instance selective laser melting or electron beam melting are becoming more common and just turning into standard manufacturing processes for metal components. Nevertheless, these processes are still new compared to classic powder metallurgy manufacturing routes such as pressing and sintering. Hence not all necessary requirements for the powders in use are fully known yet. This makes an increase in control of the powder properties a crucial task to achieve. To reach this goal one must understand the different influences on the powder production process from the beginning of the whole production route. In this work, the influence of the spray chamber flow on the particle morphology is examined. The nozzle system used to produce the metal powders is a close-coupled atomization system with a convergent-divergent gas nozzle configuration. The particle morphology as well as the particle size distribution have been analyzed to examine the influence of the atomization gas flow compared to an additional use of a coaxial gas flow. To review the changes of the flow patterns, computational fluid dynamic simulations have been performed. The particle trajectories were calculated to assess the change in particle behavior as well. Atomization experiments have been conducted with an AISI 52100 (1.3505) steel in a small batch atomization plant to evaluate the influence of the change in flow on the particle size distribution and circularity. The experimental results show that a use of additional coaxial gas leads to an increase in particle circularity up to 10% for relevant particle sizes. An approach for the quantification of satellite occurrence is given by examination of the shift of the particle size distribution to smaller diameters.     

Aluminium powder particles produced by SAMD technique: typical characteristics and correlations between processing conditions and powder size

Abstract

The present paper consists of two parts. In the first part the principles of a new method of metal powder production, termed 'solid assisted melt disintegration (SAMD)' are discussed and the typical characteristics of the produced powder are outlined. In the second part the effects of some processing parameters on the size distribution and mean diameter of the powder are reported. The SAMD method involves mixing solid particles (i.e. alumina) with the liquid aluminium alloy aided by mechanical agitation. The shear force induced by the impeller is transferred to the metal via the non-wetting solid medium and results in melt disintegration. The resulting mixture of aluminium droplets and alumina particles are subsequently cooled in air and screened through 300 μm sieve to separate alumina from solidified aluminium powder particles. The SAMD technique has demonstrated the capability to produce a wide particle size distribution. The small sized particles (i.e. <53 μm) exhibited irregular shapes, but larger ones were mostly spherical. These powder particles were dense (pore free) without attached satellite particles and exhibited a relatively coarse microstructure. The processing parameters investigated include the size of Al₂O₃ particles, Al₂O₃/Al weight ratio, stirring speed and stirring time. It was concluded that there exists an optimum value for each of the aforementioned parameters corresponding to a minimum in the mean particle size.     

温度及搅拌速度对纳米氢氧化镍性能的影响

采用化学沉淀法制备出片状和棒状混合的纳米β-Ni（OH）_2,将纳米粉体以 8%比例掺入到球镍中制成复合电极,研究了反应温度和搅拌速度对纳米粉体结构、形貌及其复合电极电化学性能的影响,结果表明,反应温度升高,纳米颗粒粒径增大;搅拌速度提高,粒径减小;复合电极的放电比容量随反应温度和搅拌速度提高先增大后减小,当反应温度为 50℃、搅拌速度为 600 r/min时,相应的复合电极放电比容量最大,达到了 263.3 mAh/g,比纯球镍电极放电比容量（239.4 mAh/g）提高了约 10%。研究还显示,复合电极的放电比容量与其粉体的压实密度有直接对应关系,其放电比容量和放电平台均高于纯球镍电极。     

Effect of rotation speed and milling time to attain Nb-10Hf-1Ti alloy powders on morphology and microstructure of Nb-10Hf-1Ti powder

The mechanical alloying process was employed to produce C103 alloy with Nb-10% Hf-1% Ti (wt.%) composition using Nb, Hf and Ti powders. The mechanical alloying process was performed in an argon atmosphere in the chamber and bullets of tungsten carbide with a ball-to-powder weight ratio (BPR) of 20:1 at rotation speed of 200, 300 and 400 rpm for 2, 5 and 8 h. At rotation speeds of 200 and 300 rpm particle size decreased and became more spherical during MA. While increasing milling time at 400 rpm caused agglomeration of particles. XRD results showed that increasing milling time at a constant rotation speed has no considerable effect on reduction of crystallite size, but the lattice strain is strongly affected by it and increased obviously with further rotation speed. The results showed that the optimum milling time and rotation speed to attain Nb-10Hf-1Ti alloy powders with the least amount of contamination and appropriate morphology are 5 h and 300 rpm, respectively.     

Computer simulation of morphology and packing behaviour of irregular particles, for predicting apparent powder densities

This paper describes a methodology for prediction of powder packing densities which employs a new approach, designated as random sphere construction (RSC), for modelling the shape of irregular particles such as those produced by water atomization of iron. The approach involves modelling an irregular particle as a sphere which incorporates smaller corner spheres located randomly at its surface. The RSC modelling technique has been combined with a previously developed particle packing algorithm (the random build algorithm), to provide a computer simulation of irregular particle packings. Analysis of the simulation output data has allowed relationships to be established between the particle modelling parameters employed by the RSC algorithm, and the density of the simulated packings. One such parameter is η, which is the number of corner spheres per particle. A relationship was established between η (which was found to have a profound influence on packing density), and the fractional density of the packing, fd. Vision system techniques were used to measure the irregularity of the simulated particles, and this was also related to η. These two relationships were then combined to provide a plot of fractional density for a simulated packing against irregularity of the simulated particles. A comparison was made of these simulated packing densities and observed particle packing densities for irregular particles, and a correlation coefficient of 0.96 was obtained. This relatively good correlation indicates that the models developed are able to realistically simulate packing densities for irregular particles. There are a considerable number of potential applications for such a model in powder metallurgy (PM), process control. In combination with on-line particle image analysis, the model could be used to automatically predict powder densities from particle morphology.