Spheroidization of Nd-Fe-B Powders by RF Induction Plasma Processing

以不规则形的钕铁硼粉为原料,使用射频等离子体球化处理工艺,制备球形钕铁硼粉.研究了原料的加料速率和粉末粒度对粉末球化率的影响.通过扫描电子显微镜观察对比了等离子球化处理前后粉末及截面形貌,采用X射线衍射方法测试分析了球化过程中氧化物的生成.检测了球化前后粉末的松装密度及其粒度分布.结果表明:不规则形状的钕铁硼粉经等离子球化处理后其球化率可达到100％,松装密度由2.778 g/cm3提高到3.785 g/cm3,粉末流动性由43.3 s/50 g提高到27.5 s/50 g.该粉末适用于凝胶注膜成型及注射成型.     

球形钨粉的制备及应用

球形钨粉以其良好的流动性、高的松装密度和振实密度广泛应用于喷涂、增材制造等材料制备领域。本文以不规则形状钨粉颗粒为原料,采用射频等离子球化技术制备球形钨粉,并对球形钨粉进行铺粉及成形实验效果评价。在射频等离子球化过程中,研究球化工艺参数（送粉速率、送粉位置）和原料粉末形态对球化结果的影响。在铺粉实验方面,研究粉末特征和铺粉层厚对铺粉效果的影响。采用扫描电子显微镜、激光粒度分析仪和BT-100粉体综合特性测试仪对球化处理前后粉末的形貌、粒度、流动性、松装密度和振实密度进行测试和分析。结果表明：经过球化处理后,钨粉颗粒呈规则球形,表面光滑,球化率可达100%,流动性、松装密度和振实密度得到明显提高。球化率高的粉末流动性好,铺粉效果好;随着层厚的增加,铺粉效果逐渐得到改善;采用合适粒径的球形钨粉打印的钨薄壁件表面相对光洁,尺寸精度高。     

感应等离子体制备高纯致密球形钼粉研究

利用感应等离子体技术制备出高纯致密球形钼粉,实现了钼粉的球化、致密化、细化和纯化,同时研究了感应等离子体功率和原料粉粒度对球化率的影响。采用扫描电子显微镜、X射线衍射仪和激光粒度分析仪对球化处理前后粉末的形貌、物相和粒度分布进行测试和分析。结果表明,形状不规则的原料钼粉,经等离子体球化处理后得到球形度好、表面光滑、分散性良好、球化率几乎可达100%的球形钼粉。球化处理后,钼粉粒度变细,且粒度分布更集中。相同工艺条件下,随着等离子体功率的增加,钼粉的球化率先增大后降低,当等离子体功率为25 kW时钼粉球化效果最好,粒度较小的钼粉球化率较高。随着钼粉球化率的提高,粉末的流动性得到显著改善,松装密度也得到提高。钼粉末的流动性由40 s/50 g提高为11 s/50 g,松装密度由2.3 g/cm~3提高到6.1 g/cm~3。     

直流电弧热等离子体球化处理TA1粉末工艺研究

采用直流电弧热等离子体对不规则TA1粉末进行球化处理。利用金相显微镜、扫描电子显微镜、粒度粒形分析仪、霍尔流速计、斯科特容量计及氧氮分析仪等分析测试手段,研究球化工艺对粉末组织形貌、粒度分布、球形度、流动性、松装密度及氧含量的影响。结果表明,球化处理可将不规则形状TA1粉末球化为表面附着亚微米颗粒的实心球形;球形粉末内部组织由等轴状α相转变为长条状α相。球化处理使TA1粉末平均粒径和氧含量降低,球形度升高。原料粉末粒度越小、等离子体发生器功率越高,球化后粉末平均粒径越小,球形度越高;但会导致球化后粉末中亚微米颗粒含量增加、粉末流动性变差、松装密度降低;去除亚微米颗粒可以提高粉末流动性,并进一步降低氧含量。     

等离子球化制备球形CaF2/BaF2共晶粉末*

探究了使用大气等离子喷涂设备制备适合热喷涂使用的球形CaF2/BaF2共晶粉末的可能性。68%BaF2、32%CaF2粉末(质量分数)经过1 100℃真空烧结后,形成致密的块状氟化物共晶。机械破碎后的氟化物共晶经过等离子焰流重熔后得到了球形的氟化物共晶。使用F14-1流动性和松装密度测定仪测量球化前后粉末的流动性和松装密度。采用扫描电子显微镜,XRD表征球化前后粉末的形貌和物相组成。结果表明:球化后的粉末呈现较好的球形,球化后粉末的流动性和松装密度较球化前也有较大的改善:球化后共晶粉末的流动时间为55.20s/50g,松装密度为1.89g/cm3;另外,球化后共晶粉末还表现出良好的高温润滑性能:含有10%CaF2/BaF2共晶(质量分数)的镍基涂层在600℃和800℃的平均摩擦因数都小于0.3。     

感应等离子体工艺对制备致密球形钼粉的影响

研究了原料钼粉携带气体流量和钼粉加料速率对感应等离子球化钼粉形貌和粒度的影响。球化前后钼粉的微观形貌用扫描电镜(SEM)观测,粉体物相用X射线衍射仪(XRD)分析,等离子体处理前后钼粉的松装密度和振实密度分别用斯科特容量计和振实密度仪检测。结果表明,等离子体处理后产品仍为纯金属钼粉,形状由不规则变为球形,颗粒平均粒径由原料的40～70 μm减小至35~60 μm,振实密度由2.5 g/cm³提高到5.8 g/cm³。制备球形钼粉最佳工艺参数为：加料速率45 g/min,携带气体流量0.6 m³/h。感应等离子体是制备高纯致密球形钼粉的有效技术。     

等离子体球化处理和放电等离子烧结制备钡钨阴极多孔钨基体

采用等离子体球化处理和放电等离子烧结(SPS)相结合的方法制备了钡钨阴极多孔钨基体。研究了等离子体球化处理工艺参数对钨粉的球化率和性能的影响规律,以及SPS制备的多孔钨基体的微观组织和相应钡钨阴极的发射性能。结果表明:当喂粉速率和载气流量分别为2.4 g/min和4.0 L/min时,可得到球化率大于98%,且表面光滑、球形度高的球形钨粉;经球化处理后,钨粉的松装密度和流动性显著提高。与原料钨粉相比,采用球形钨粉制备得到的多孔钨基体的孔隙结构和分布均得到显著改善,且开孔率由18.3%提高至19.7%;相应的钡钨阴极在1050℃下的饱和脉冲发射电流密度由8.7 A/cm~2提高至11.2 A/cm~2。     

射频等离子体制备球形钛粉

以不规则形状的大颗粒TiH2粉末为原料,采用射频等离子球化处理技术制备出微细球形Ti粉。采用扫描电子显微镜、X射线衍射和激光粒度分析测试方法对粉末形貌、物相和粒度进行测试。结果表明:大颗粒的TiH2粉末的脱氢分解、爆碎和球化处理在等离子体中一步完成,得到微细球形粉末。其相组成主要为Ti和残余TiH相;球形粉末在1.3×10-4Pa真空条件下,经750℃、2h脱氢处理后得到单相球形Ti粉。颗粒平均粒径由原来的100~150μm减小至20~50μm,球化率可达到100%。随着加料速率的增加,粉末的球化率降低。采用射频等离子体处理TiH2粉是制备微细球形钛粉的一种新方法。     

选区激光熔化成形用钽粉射频等离子体球化研究

以不规则状钠还原钽粉为原料,采用射频等离子体球化技术制备高纯致密球形钽粉,实现了还原钽粉的球化、致密化和纯化。研究了送粉速率、载气流量、反应室压力等工艺参数对钽粉球化率及粉体特性的影响,并探索了球化钽粉的选区激光熔化成形适用性。结果表明：不规则状钠还原钽粉,经射频等离子体球化处理后可得到表面光滑、内部致密、高纯低氧、球化率可达100%的球形钽粉。球化处理后,钽粉粒度分布变窄。钽粉的球化率随送粉速率的增大而降低,随载气流量的增加先升高后减小。弱负压更有利于获得较高球化率的钽粉。随着球化率的提高,钽粉的流动性能显著改善,松装密度与振实密度明显提高。当送粉速率为30g/min,载气流量为5.0slpm,反应室压力为12.0Psi时,球形钽粉霍尔流速提高到5.98s/50g,松装密度由3.503g/cm_³提高到9.463g/cm_³,振实密度由5.344g/cm_³提高到10.433g/cm_³,且氧含量由0.076%降低至0.0481%。另外,射频等离子体球化钽粉具有良好的选区激光熔化成形适用性,其试样致密度ρ≥99.5%,抗拉强度σ_b=693MPa,屈服强度σ_0.2=616MPa,延伸率δ=28.5%。     

选区激光熔化成形用钽粉的射频等离子体球化

以不规则状钠还原钽粉为原料,采用射频等离子体球化技术制备高纯致密球形钽粉,实现了还原钽粉的球化、致密化和纯化。研究了送粉速率、载气流量、反应室压力等工艺参数对钽粉球化率及粉体特性的影响,并探索了球化钽粉的选区激光熔化成形适用性。结果表明:不规则状钠还原钽粉,经射频等离子体球化处理后可得到表面光滑、内部致密、高纯低氧、球化率可达100%的球形钽粉。球化处理后,钽粉粒度分布变窄。钽粉的球化率随送粉速率的增大而降低,随载气流量的增加先升高后降低。弱负压更有利于获得较高球化率的钽粉。随着球化率的提高,钽粉的流动性能显著改善,松装密度与振实密度明显提高。当送粉速率为30 g/min,载气流量为5.0 L/min,反应室压力为82.7 kPa时,球形钽粉霍尔流速提高到5.98 s/50g,与不规则形钠还原钽粉相比,松装密度由3.503 g/cm~3提高到9.463 g/cm~3,振实密度由5.344g/cm~3提高到10.433g/cm~3,且氧含量由0.076%降低至0.0481%。另外,射频等离子体球化钽粉具有良好的选区激光熔化成形适用性,其试样致密度ρ≥99.5%,抗拉强度σ_b=693 MPa,屈服强度σ_(0.2)=616 MPa,延伸率δ=28.5%。     

W-Ni-Fe三元合金等离子球化过程的SPH仿真研究

针对表面张力影响下的W-Ni-Fe三元合金,通过光滑粒子流体动力学(SPH)建立了仿真多元金属液滴碰撞融合过程的数值模型,获得了流体在等离子球化过程中的流场和温度分布。结果表明,W的占比越高、粒径越小、环境温度越高、Marangoni力越大,则球化度越好。根据SPH模拟结果选择了平均粒径1.5μm的W粉、平均粒径4.1μm的Ni粉和平均粒径2.4μm的Fe粉为原料,按照质量比W∶Ni∶Fe=90∶7∶3进行喷雾造粒,在等离子焰流温度为8000℃条件下球化,球化后的三元合金粉末球形度好,内部致密。球化后颗粒流动性为11.62 s/50 g,松装密度10.66 g/cm3,有利于使用铺粉方法进行3D打印。证实了SPH仿真结果可靠,该模拟结果可用于指导难熔金属W的等离子球化制备工艺。     

Study on behaviors of tungsten powders in radio frequency thermal plasma

This paper describes an investigational study of the spheroidization of refractory metal tungsten powders by radio frequency thermal plasma, with emphasis on the melting, solidification and growth behavior of the tungsten powder particles during the spheroidization process. The flight time and melting time of tungsten powder particles in the plasma were estimated, and the growth behavior of the tungsten powder particles was analyzed in detail by investigating the change in the average particle size before and after plasma spheroidization. The morphology and spheroidization rate were analyzed using field emission scanning electron microscopy. The flight time and melting time for tungsten powder particles with radius of 7.8 μm were calculated to be 9.3 ms and 2.9 ms, respectively. The change in powder particle size during the process showed that the growth of tungsten powder particles was mainly caused by the coalescence of droplets in the thermal plasma system. The experimental results demonstrated that the spheroidization rate can reach up to 95% under the operating conditions used in this work.     

射频等离子体球化钨粉的选区激光熔化成形研究

以不规则的钨粉为原材料,采用射频等离子体球化技术制备了球形钨粉,重点研究了选区激光熔化制造纯钨零件,系统研究了工艺参数(激光功率、扫描速度)对制备的纯钨样品致密化、显微组织、显微硬度和压缩性能的影响,从而反馈指导钨粉球化工艺参数的优化。结果表明：球化后钨粉形状规则且球化率高于98%,钨粉的振实密度和松装密度增大,流动性增强。同时球化后的钨粉具有良好的选区激光熔化适用性,打印样品件的致密度在84%-95.6%之间。研究发现,随 激光功率的增大,打印件的致密度、显微硬度和抗压强度呈先上升后下降的趋势,裂纹和孔洞减少。随着扫描速度的增大,打印件的致密度和硬度降低,裂纹增多。因此探究合适的打印参数对钨粉的选区激光熔化成形有着重要意义。     

Effect of the feeding rate on microstructure and properties of plasma spheroidized GH4169 powder

The growing interest in additive manufacturing of GH4169 alloy was accompanied by the demand on spherical GH4169 powders with high performance.The powder particles were treated by radio frequency plasma with the different feeding rates.The microstructure and morphology,the particle size distribution of as-treated powders were studied by scanning electron microscopy and laser particle size analysis.It was demonstrated that GH4169 powders with extremely fine followability were obtained by radio frequency plasma spheroidization technology.With the same plasma parameters,the spheroidization efficiency of the particles varied with the feeding rates.When the rate of the powder feeding rates was too small,the excessive absorption of the heating by the powders caused vaporization,then the collection decreased.When the feeding rates was too large,the powder particles were insufficiently absorbed,resulting in defects in the powders.The microstructure of the as-treated spherical particles was mainly cell crystals,columnar crystals,and even microcrystals.Under the suitable plasma parameters,the resulting powders haved a slightly increased average particle size,excellent spheroidization,surface smoothness,followability,and bulk ratio.     

Induction plasma spheroidization of tungsten and molybdenum powders

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.     

感应等离子体球化热喷涂粉体材料研究进展

介绍了传统非等离子体法制备球形粉体方法--雾化法和喷雾造粒法,分析了其在热喷涂球形粉体制备过程中存在的优势和局限性。综述了等离子球化技术在热喷涂粉体材料领域中的应用现状,并深入讨论了感应等离子体球化过程中不同的工艺条件对粉体球化率和形貌的影响:原料粉体状态决定了球化后粉体的平均粒径,降低粉体原始粒径可以提高熔融程度,粒径分布较窄的原始粉体有利于得到高球形度粉体;适当增大输入功率和工作气体流量,可降低细小颗粒的粘附现象;工作气体的种类会影响等离子焰炬的热焓值;送粉速率需要结合粉体性质择优选取。这些关键影响因素对热喷涂粉体性能的调控机制,以及深入认识等离子体作用条件下的热喷涂粉体球化机理,提供了有力的理论支撑。总结和展望了感应等离子球化技术在热喷涂陶瓷粉体材料制备中存在的问题和发展方向,感应等离子体球化技术作为制备高纯度、无污染热喷涂球形粉体材料的一种新技术,具有广阔的应用前景。     

Statistical design of experiments for the spheroidization of powdered alumina by induction plasma processing

The principal factors controlling the spheroidization process of Al₂O₃ powder in the induction plasma are the position of the powder injector, the powder feed rate, and their interactions. A higher level of powder feed rate (4.2 kg/h) has been achieved at the r.f. plate power of 40 kW with the application of response surface methodology (RSM). Under these loading conditions, the spheroidization of the Al₂O₃ powder of −44+15 μm size attained 94.9%, while for Al₂O₃ of −89 + 44 μm size, 83.3% spheroidization was achieved.     

Properties evolution of additive manufacture used tungsten powders prepared by radio frequency induction plasma

In this study, radio frequency induction plasma was adopted to improve tungsten powder properties to meet the requirements of additive manufacturing process. After plasma spheroidization process operated, tungsten particles changed from irregular shape to uniform spherical shape. The average size and oxygen content of raw tungsten powders were both decreased, meanwhile, the laser absorption coefficient was increased by plasma spheroidization process. Furthermore, a series of tests were carried out for raw and spherical tungsten powders to investigate the influence of plasma spheroidization process on powder flowability evolution. The results displayed that, plasma spheroidized powders had a better comprehensive flowability, such as basic flow property, aerated flow property, compressibility, permeability and shear property, comparing to raw tungsten powders. In conclusion, plasma spheroidized tungsten powders met demands of additive manufacturing process very well.