丝电爆法制备球形W-25%Re合金粉末的组织和性能研究

Microstructures and Properties of Spherical W-25%Re Alloy Powders Produced by Wire Electrical Explosion Method

丝电爆法常用于金属纳米粉的制备,以直径为0.3 mm的W-25%Re(质量分数)合金丝为原料,采用丝电爆法制备微米级球形W-25%Re合金粉末,对获得的粉末进行组织和性能表征。结果表明:丝电爆法制备的粒径5~35,35~60,60~165和>165μm球形W-25%Re合金粉末球形度高,球化率几乎可达100%。粒径为5~35,35~60和60~165μm球形W-25%Re合金粉末的流动性良好,松装密度和振实密度较高。粒径<5μm球形W-25%Re合金粉末的物相为四方晶系W0.4Re0.6相、立方晶系W_(0.8)Re_(0.2)和W_(3)Re相,粒径为5~35,35~60,60~165和>165μm球形W-25%Re合金粉末物相均为立方晶系W_(13)Re_(7)相。W-25%Re合金粉末粒径从8.945μm增大到217.98μm,粉末颗粒表面组织从无明显晶态、胞状晶逐渐转变为树枝晶,粉末粒径d与二次枝晶间距λ的关系为:λ=0.727+5.59×10^(-3)d。球形W-25%Re合金粉末颗粒内部较为密实,无明显孔洞缺陷。丝电爆法制备的微米级球形W-25%Re合金粉末综合性能良好,其中粒径5~35μm球形W-25%Re合金粉末球形度好、粒度分布集中、氧含量低、流动性好、松装密度和振实密度高,可以很好地满足选区激光熔化(SLM)技术对粉末性能的要求。

Wire electric explosion method involves introducing a large pulse current into metal wire to create an electric explosion process,resulting in the production of metal powders.This method is commonly used to produce nano-scale spherical powders and offers advantages such as small size,low energy consumption,and high performance of the resulting spherical metal powders.This study utilized W-25%Re(mass fraction,the same below)alloy wire with a diameter of 0.3 mm as the raw material and employed the wire electric explosion method to produce micron-sized spherical W-25%Re alloy powders.The findings offered valuable insights for the efficient production of high-quality micron-sized spherical refractory alloy powder for selective laser melting(SLM)applications.The spherical W-25%Re alloy powder prepared in the experiment was categorized into five kinds particle size ranges:<5,5~35,35~60,60~165 and>165μm.These particle sizes were chosen for analysis to investigate the microstructures and properties of spherical W-25%Re alloy powders.The powders morphology,laser particle size,flowability,apparent density,tap density,oxygen content and phase were measured using scanning electron microscope,laser particle size analyzer,flowability and apparent density tester,multi-functional powder physical property tester,oxygen and nitrogen analyzer,and X-ray diffraction(XRD).The particle size 5~35,35~60,60~165 and>165μm exhibited excellent sphericity,a high spheroidization rate.The particle size<5μm featured small particle size and large specific surface area,leading to strong van der Waals forces among particles and potential agglomeration.Additionally,the particle size 5~35,35~60,60~165 and>165μm demonstrated nearly 100%spheroidization rate.Except for the powder with particle size<5μm,which had a wide distribution range due to severe agglomeration,the particle size distribution of the other four powders were narrow and relatively concentrated.The powders with a particle size of<5μm were smaller and more active.The oxygen content of the powder raw materials was significantly increased,while powders with a particle size of>165μm might introduce impurities due to waste residues,leading to a relatively high oxygen content.Furthermore,powders in other particle size ranges of oxygen content similar to that of W-25%Re alloy wire,aligning with the principle that finer powders had higher activity and oxygen content.Re content in the powder varied depending on the particle size.For particles with particle size<5μm,Re content was 28.03%,slightly higher than that of the raw material wire.In contrast,Re content in powders of other particle size segments closely matched that of the raw material.This discrepancy might be due to impurity oxygen combining with rhenium at high temperatures during wire explosion,forming volatile oxides that adhere to powder particles upon cooling.The larger specific surface area of particles with particle size<5μm led to more oxide deposition,resulting in a slightly higher Re content compare to the raw wire material.Except for powders with particle size<5μm,which tended to agglomerate and had poor fluidity,and powders with particle size>165μm,which were often discarded as waste,the flowability of powders with particle size of 5~35,35~60 and 60~165μm were 6.95,5.09 and 5.34 s·(50 g)^(-1),respectively,indicating good flowability,and their apparent densities were 12.00,11.42 and 11.57 g·cm^(-3),respectively,while tap densities were 13.2,12.3 and 12.6 g·cm^(-3).The minimal variation in bulk and tapped densities within this particle size range suggested that the prepared powder exhibited good sphericity and density.For particles with particle size<5μm,the phases were the tetragonal crystal system W(0.4)Re(0.6)phase,cubic crystal system W_(0.8)Re_(0.2)and W_(3)Re phase.For particles with particle size of 5~35,35~60,60~165 and>165μm exhibited cubic crystal system W(13)Re7 phase.When particle size increased from 8.945 to 217.98μm,the solidification structure on the surface of the powder particles gradually changed from a lack of obvious crystalline state and cellular crystals to dendrites.The relationship between the particle size(d)and the secondary dendrite arm spacing(λ)was expressed as:λ=0.727+5.59×10^(-3)d.As the particle size increased,the secondary dendrite arm spacing also increased,demonstrating a linear correlation between the two.The interior of spherical W-25%Re alloy powders exhibited high density and had no obvious defects.As the particle size increased,the internal grain structure changed from cellular crystals to dendrites.The micron-sized spherical W-25%Re alloy powders,producing through wire electric explosion,demonstrated excellent overall properties.The particles with particle size of 5~35μm possessed high sphericity,uniform particle size distribution,low oxygen content,good fluidity,high bulk density and tap density.These characteristics made it well-suited for meeting the powder performance requirements of SLM technology.