Tungsten powders and Ce doped powders were prepared by hydrogen reduction combined with the liquid-solid doping method. The phase composition, particle size and powder morphology of Ce doped tungsten powders were anal...Tungsten powders and Ce doped powders were prepared by hydrogen reduction combined with the liquid-solid doping method. The phase composition, particle size and powder morphology of Ce doped tungsten powders were analyzed by X-ray diffrac-tion, scanning electron microscopy and transmission electron microscopy, respectively. The results indicated that 10000 ppm Ce doped tungsten oxide powders were consisted of WO3 phase and Ce4W9O33 phase. The hydrogen reduction of Ce doped tungsten powders was basically accomplished at 800 oC for 3 h. The size of Ce doped W powders was remarkably decreased compared to the undoped W powders. The phase of Ce4W9O33 was reduced to Ce2 （WO4）3 phase and Ce2W2O9 phase during the process of hydrogen reduction. Moreover, Ce2 （WO4）3 phase and Ce2W2O9 phase were observed form their morphologies, where the doping content of Ce was more than 100 ppm. The ternary phase embedding into W particles was assigned to Ce2 （WO4）3, while the ternary phase distrib-uting among W particles corresponded to Ce2W2O9. The phase of Ce2 （WO4）3 might be the nucleus of W particles and increase the number of the nucleus. And the particles of Ce2W2O9 covered WO2 particles and might inhibit the growth of W particles. These two reasons resulted in the decrease of the size of Ce doped W particles. Uniform fine W powders were fabricated with the doping content of Ce more than 100 ppm.展开更多
Spherical powders with good flowability and high stacking density are mandatory for powder bed additive manufacturing. Nevertheless, the preparation of spherical refractory tungsten and tungsten alloy powders is a for...Spherical powders with good flowability and high stacking density are mandatory for powder bed additive manufacturing. Nevertheless, the preparation of spherical refractory tungsten and tungsten alloy powders is a formidable task. In this paper, spherical refractory metal powders processed by high-energy stir ball milling and RF inductively coupled plasma were investigated. By utilizing the technical route, pure spherical tungsten powders were prepared successfully, the flowability increased from 10.7 s/50 g to 5.5 s/50 g and apparent density increased from 6.916 g cm-3 to 11.041 g cm-3. Alloying element tantalum can reduce the tendency to micro- crack during tungsten laser melting and rapid solidification process. Spherical W-6Ta （%wt） powders were prepared in this way, homogeneous dispersion of tantalum in a tungsten matrix occurred but a small amount of flake-like shape particles appeared after high-energy stir ball milling. The flake-like shape particles can hardly be spheroidized in subsequent RF inductively coupled plasma process, might result from the unique suspended state of flaky particles under complex electric and magnetic fields as well as plasma-particle heat exchange was different under various turbulence models. As a result, the flake-like shape particles cannot pass through the high-temperature area of thermal plasma torch and cannot be spheroidized properly.展开更多
基金Project supported by the National Science and Technology Support Plan(2011BAC10B04)the National High Technology Research and Development Plan(863 Program,2012AA061902)+1 种基金the National Natural Science Foundation of China(50904035)the National Academy of Sciences Alliance Special Jiangxi Goods([2013]No.7)
文摘Tungsten powders and Ce doped powders were prepared by hydrogen reduction combined with the liquid-solid doping method. The phase composition, particle size and powder morphology of Ce doped tungsten powders were analyzed by X-ray diffrac-tion, scanning electron microscopy and transmission electron microscopy, respectively. The results indicated that 10000 ppm Ce doped tungsten oxide powders were consisted of WO3 phase and Ce4W9O33 phase. The hydrogen reduction of Ce doped tungsten powders was basically accomplished at 800 oC for 3 h. The size of Ce doped W powders was remarkably decreased compared to the undoped W powders. The phase of Ce4W9O33 was reduced to Ce2 （WO4）3 phase and Ce2W2O9 phase during the process of hydrogen reduction. Moreover, Ce2 （WO4）3 phase and Ce2W2O9 phase were observed form their morphologies, where the doping content of Ce was more than 100 ppm. The ternary phase embedding into W particles was assigned to Ce2 （WO4）3, while the ternary phase distrib-uting among W particles corresponded to Ce2W2O9. The phase of Ce2 （WO4）3 might be the nucleus of W particles and increase the number of the nucleus. And the particles of Ce2W2O9 covered WO2 particles and might inhibit the growth of W particles. These two reasons resulted in the decrease of the size of Ce doped W particles. Uniform fine W powders were fabricated with the doping content of Ce more than 100 ppm.
文摘Spherical powders with good flowability and high stacking density are mandatory for powder bed additive manufacturing. Nevertheless, the preparation of spherical refractory tungsten and tungsten alloy powders is a formidable task. In this paper, spherical refractory metal powders processed by high-energy stir ball milling and RF inductively coupled plasma were investigated. By utilizing the technical route, pure spherical tungsten powders were prepared successfully, the flowability increased from 10.7 s/50 g to 5.5 s/50 g and apparent density increased from 6.916 g cm-3 to 11.041 g cm-3. Alloying element tantalum can reduce the tendency to micro- crack during tungsten laser melting and rapid solidification process. Spherical W-6Ta （%wt） powders were prepared in this way, homogeneous dispersion of tantalum in a tungsten matrix occurred but a small amount of flake-like shape particles appeared after high-energy stir ball milling. The flake-like shape particles can hardly be spheroidized in subsequent RF inductively coupled plasma process, might result from the unique suspended state of flaky particles under complex electric and magnetic fields as well as plasma-particle heat exchange was different under various turbulence models. As a result, the flake-like shape particles cannot pass through the high-temperature area of thermal plasma torch and cannot be spheroidized properly.
