Characterization of 17-4PH stainless steel powders produced by supersonic gas atomization

17-4PH stainless steel powders were prepared using a supersonic nozzle in a close-coupled gas atomization system. The characteristics of powder particles were carried out by means of a laser particle size analyzer, scanning electron microscopy （SEM）, and the X-ray diffraction （XRD） technique. The results show that the mass median particle diameter is about 19.15 prn. Three main types of surface microstructures are observed in the powders： well-developed dendrite, cellular, and cellular dendrite structure. The XRD measurements show that, as the particle size decreases, the amount of fcc phase gradually decreases and that of bcc phase increases. The cooling rate is inversely related to the particle size, i.e., it decreases with an increase in particle size.

Design and evaluation of a Laval-type supersonic atomizer for low-pressure gas atomization of molten metals

A Laval-type supersonic gas atomizer was designed for low-pressure gas atomization of molten metals. The principal design ob-jectives were to produce small-particle uniform powders at lower operating pressures by improving the gas inlet and outlet structures and op-timizing structural parameters. A computational fluid flow model was developed to study the flow field characteristics of the designed atom-izer. Simulation results show that the maximum gas velocity in the atomization zone can reach 440 m＆#183;s-1;this value is independent of the atomization gas pressure P0 when P0〉0.7 MPa. When P0=1.1 MPa, the aspiration pressure at the tip of the delivery tube reaches a mini-mum, indicating that the atomizer can attain the best atomization efficiency at a relatively low atomization pressure. In addition, atomization experiments with pure tin at P0=1.0 MPa and with 7055Al alloy at P0=0.8 and 0.4 MPa were conducted to evaluate the atomization capa-bility of the designed atomizer. Nearly spherical powders were obtained with the mass median diameters of 28.6, 43.4, and 63.5μm, respec-tively. Compared with commonly used atomizers, the designed Laval-type atomizer has a better low-pressure gas atomization capability.

Process modeling gas atomization of close-coupled ring-hole nozzle for 316L stainless steel powder production

The paper aims at modeling and simulating the atomization process of the close-coupled ring-hole nozzle in vacuum induction gas atomization(VIGA)for metallic powder production.First of all,the primary atomization of the ring-hole nozzle is simulated by the volume of fluid(VOF)coupled large eddy simulation(LES)model.To simulate the secondary atomization process,we use the method of selecting the droplet sub-model and the VOF model.The results show that the ring-hole nozzle forms a gas recirculation zone at the bottom of the delivery tube,which is the main reason for the formation of an annular liquid film during the primary atomization.In addition,the primary atomization process of the ring-hole nozzle consists of three stages:the formation of the serrated liquid film tip,the appearance and shedding of the ligaments,and the fragmentation of ligaments.At the same time,the primary atomization mainly forms spherical droplets and long droplets,but only the long droplets can be reserved and proceed to the secondary atomization.Moreover,increasing the number of ring holes from 18 to 30,the mass median diameter(MMD,d_(50))of the primary atomized droplets decreases first and then increases,which is mainly due to the change of the thickness of the melt film.Moreover,the secondary atomization of the ring-hole nozzles is mainly in bag breakup mode and multimode breakup model,and bag breakup will result in the formation of hollow powder,which can be avoided by increasing the gas velocity.

Processing soft ferromagnetic metallic glasses:on novel cooling strategies in gas atomization,hydrogen enhancement,and consolidation

Processing soft ferromagnetic glass-forming alloys through gas atomization and consolidation is the most effective technique to produce bulk samples.The commercial viability of these materials depends on commercial purity feedstock.However,crystallization in commercial purity feedstock is several orders of magnitude faster than in high purity materials.The production of amorphous powders with commercial purity requires high cooling rates,which can only be achieved by extending the common process window in conventional gas atomization.The development of novel cooling strategies during molten metal gas atomization on two model alloys({(Fe0.6Co0.4)0.75B0.2Si0.05}96Nb4 and Fe76B10Si9P5)is reported.Hydrogen inducement during liquid quenching significantly improved the glass-forming ability and soft magnetic properties of{(Fe0.6Co0.4)0.75B0.2Si0.05}96Nb4 powders.Spark plasma sintering experiments verified that amorphous rings could be produced regardless of the cooling strategies used.While the saturation magnetization was almost unaffected by consolidation,the coercivity increased slightly and permeability decreased significantly.The magnetic properties of the final bulk samples were independent of feedstock quality.The developed cooling strategies provide a great opportunity for the commercialization of soft ferromagnetic glass-forming alloys with commercial purity.

气雾化微细金属粉末的生产工艺研究

介绍了气雾化微细金属粉末的生产工艺。金属熔炼、雾化制粉，粉末分级及收集都是在保护气氛中进行，气体喷嘴和漏液嘴紧密耦合并用高压气体雾化。生产的金属粉末颗粒为球形，流动性好，氧含量低，细粉收得率高，可为粉末冶金及相关行业提供优质的金属粉末原料。

真空熔炼高压气体雾化制粉技术及设备

介绍了气体雾化粉的品种、用途及工业化生产。还介绍了真空熔炼-高压气体雾化制粉所需的设备。