选区激光熔化成形用钽粉射频等离子体球化研究

Study on RF plasma spheroidization of tantalum powder for selective laser melting

摘要:

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%。

Abstract:

Tantalum powder was prepared by RF plasma process from irregular sodium reduced tantalum powder, and spherical, pore-free powder with lower oxygen content was obtained. The effects of feeding rate, carrier gas flowing rate and pressure of reactor chamber on spheroidization efficiency and powder properties were studied. The selective laser melting process of spherical tantalum powder was also explored. The results showed that tantalum powder after plasma processing possess smooth surface , high internal density, high purity and low oxygen content, and the spheroidization ratio was almost 100%.The particle size distribution became narrow after spheroidizing. Spheroidization efficiency decreased with the increasing of feeding rate, while increased firstly and then decreased with the increasing of carrier gas flowing rate. Meanwhile, lower negative pressure in reactor chamber was more favorable to obtain powder with high spheroidization efficiency. With the increasing of spheroidization efficiency, the powder flow ability, apparent density and tap density were significantly improved. The processing parameters, the feeding rate, carrier gas flowing rate and reactor pressure were optimized at 30g/min, 5.0 slpm, and 12.0 psi, respectively. Compared to the raw materials, the spherical tantalum powder hall velocity reached 5.98s/50g, the apparent density increased from 3.503g/cm3 to 9.436g/cm3 and the tap density also improved from 5.344g/cm3 to 10.433g/cm3. It was interesting to find that the oxygen content is decreased from 0.076% to 0.0481% after the plasma process. Finally, spherical tantalum powder was proved to be compatible with selective laser melting process. The SLM parts with high dense (≥99.5%) were obtained and the tensile, the yield strength and the elongation were 693MPa, 616MPa, and 28.5%, respectively.