Preparation of spherical MoNbTaW refractory high entropy alloy powder by RF plasma
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摘要: 以喷雾造粒制备的MoNbTaW粉末为原料，通过射频等离子体制备球形MoNbTaW难熔高熵合金粉末，研究了球化功率、载气流量、鞘气成分对粉末球化率的影响。利用扫描电子显微镜、X射线衍射仪、激光粒度分析仪、霍尔流速计和纳米压痕测试系统分别对球化处理前后的粉末形貌、物相、粒度、流动性和显微硬度进行了测试和分析。结果表明： 球磨后粉末未发生合金化，球化后粉末完全转变为体心立方相；等离子体功率由32 kW增大到40 kW，球化率提高，接近100%；载气流量由1 L/min增加到4 L/min，球化粉末表面纳米颗粒减少，更加光滑，球化率接近100%，而继续增加到7 L/min，粉末出现未熔颗粒；在鞘气中添加氢气有助于提高球化率。球化处理后，粉末粒度分布变窄，振实密度由 2.00 g/cm3提高到8.33 g/cm3，松装密度从1.43 g/cm3提升到7.24 g/cm3，霍尔流速（50 g计）由50.8 s提升至8.5 s，显微硬度达到8.57 GPa 。
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关键词:
- MoNbTaW难熔高熵合金 /
- 球磨 /
- 喷雾造粒 /
- 射频等离子体 /
- 球化率
Abstract: MoNbTaW powder prepared by spray granulation was used as raw material to prepare spherical refractory high entropy MoNbTaW alloy powder by RF plasma spheroidization. The effects of spheroidizing power, carrier gas flow and sheath gas composition on the spheroidization rate of powder were studied. The morphology, phase, particle size, fluidity and microhardness of the powder before and after spheroidization were measured and analyzed by scanning electron microscope, X-ray diffractometer, laser particle size analyzer, Hall velocity meter and nanoindentation test system. The results show that the powder is not alloyed after ball milling, and the powder is completely transformed into body-centered cubic phase after spheroidization. When the plasma power was increased from 32 kW to 40 kW, the nodulization rate increased and the nodulization rate was close to 100%. When the carrier gas flow rate was increased from 1 L/min to 4 L/min, the surface nanoparticles of the nodulization powder decreased and became smoother, and the nodulization rate was close to 100%. After the carrier gas flow rate was further increase to 7 L/min, the powder appeared unmelted particles. Adding hydrogen in the sheath gas was helpful to improve the spheroidization rate. After spheroidization, the particle size distribution narrowed. As a result, the vibration density was increased from 2.00 g/cm3 to 8.33 g/cm3, the loose density increased from 1.43 g/cm3 to 7.24 g/cm3, and the Hall flow rate increased from 50.8 s/50 g to 8.5 s/50 g. The resulted microhardness reached up to 8.57 GPa. -
图 3 球磨干磨不同时间下粉末SEM形貌
Figure 3. SEM morphology of powder under different ball dry grinding time
（a）2 h；（b）4 h；（c）8 h；（d）12 h
图 4 喷雾干燥粉末SEM形貌（a）低倍，（b）高倍和EDS面分布
Figure 4. SEM images of spray-dried powder (a) low magnification; (b) high magnification
图 5 不同等离子体功率制备的粉末 SEM形貌（低倍图和高倍图）
Figure 5. SEM photos of powders prepared by different plasma powers
(a)(b) 32 kW； (c)(d)40 kW
图 6 不同载气流量制备的粉末SEM形貌
Figure 6. SEM photos of powders prepared with different carrier gas flow rates
（a）1 L/min；（b）4 L/min；（c）7 L/min
图 7 不同鞘气成分制备的粉末 SEM形貌
Figure 7. SEM photos of powders prepared with different sheath gas components
（a）Ar；（b）Ar/He；（c）Ar/H2
图 9 不同尺寸球化粉末的横截面SEM形貌和电子背散射衍射谱
（a）（b）直径80 μm粉末；（c）（d）直径130 μm粉末
Figure 9. SEM and EBSD of cross-section of spheroidized powder with different sizes
图 10 未完全合金化球化粉末SEM形貌及EDS分析结果
Figure 10. SEM image and EDS analysis results of incomplete alloyed spheroidized powder
图 11 造粒粉末经射频等离子球化合金化的示意
Figure 11. Schematic diagram of granulated powder alloyed by RF plasma spheroidization
图 12 造粒粉末（a）和球化粉末（b）横截面SEM形貌以及球化粉末横截面EDS面分布
Figure 12. SEM and EDS of cross section of granulated powder (a)and spheroidized powder (b)
图 13 合金粉末加载-卸载纳米压痕曲线和压痕照片
Figure 13. Nano-indentation curve and indentation photo of loading and unloading of alloy powder
表 1 射频等离子体球化MoNbTaW难熔高熵合金工艺参数
Table 1. Process parameters of radio-frequency plasma spheroidization for MoNbTaW refractory high entropy alloy
序号 功率/kW 送粉速率/
（g·min−1）载气流量/
（L·min−1）鞘气成分 鞘气流量/
（L·min−1）1 32 10 4 Ar 75 2 32 10 4 Ar/H2 75/5 3 32 10 4 Ar/He 75/5 4 40 10 4 Ar/H2 75/5 5 40 10 1 Ar/H2 75/5 6 40 10 7 Ar/H2 75/5 
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表 2 球磨干磨不同时间喷雾造粒粉末的D10、D50、D90数值和C、O含量
Table 2. D10, D50 and D90 values and carbon and oxygen content of spray granulation powder with dry ball milling for 2, 4, 8, 12 h
球磨时间/h D10/μm D50/μm D90/μm w(C)/% w(O)/% 2 1.98 5.44 14.3 0.22 0.28 4 1.69 4.58 12.7 0.35 0.31 8 1.15 2.75 8.70 0.44 0.42 12 1.12 2.88 14.6 0.57 0.52 造粒 15.8 34.7 66.1
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表 3 造粒粉末、球化粉末C、O含量
Table 3. Carbon and oxygen contents of granulated powder and spheroidized powder
% 粉末种类 C含量 O含量 W 0.0036 0.016 Mo 0.0031 0.081 TaH 0.004 0.038 NbH 0.016 0.0084 球磨干磨8 h后 0.44 0.42 造粒后 2.96 ＞1.50 球化后 0.058 0.55
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