Ultrafast synthesis of nanocrystalline molybdenum powder by thermal plasma and its sintering behavior

Hu, Peng; Chen, Tingyi; Li, Xiaojing; Gao, Jia; Chen, Shuqun; Zhou, Wei; Wang, Jinshu

doi:10.1016/j.ijrmhm.2019.104969

Cited by 15 publications

(8 citation statements)

References 42 publications

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“…Compared with the traditional sintering of pure molybdenum microsized powders ( is about 254 kJ/mol), the activation energy of nanosized molybdenum powder is effectively decreased during the microwave sintering process, which is responsible for the formation of fine-grained and fully densified compact at rather low temperature of 1450 °C. microhardness firstly increased with the increasing temperature, and reached the maximum value of 359.51 HV at 1250 °C, which was about 10.7 % increase over the maximum hardness value of 321 HV obtained by thermal sintering of the same Mo powder without microwave field, [6] and also much higher than the values reported in other works. [4,14,15,26,27] Then the hardness of the compacts started to decrease when the sintering temperature further increased.…”

Section: Densification Kinetics Of Mo During Microwave Sintering Processcontrasting

confidence: 49%

“…Nanocrystalline molybdenum powder was synthesized by thermal plasma synthesis route as illustrated in our previous work, [6] and as obtained powder was then pressed at 400 MPa for 5 min to form the green compact with diameter and thickness of 10 mm and 1 mm, respectively. The relative density was determined to be about 47.6 % of theoretical density.…”

Section: Experimental 21 Fabrication Of Mo Compactsmentioning

confidence: 99%

“…[5] In our previous work, quasi-spherical Mo nanopowders with average size of 30 nm was synthesized by thermal plasma synthesis route, and the sintering results illustrate that Mo compact with a relative density of 99.13 % and grain size of 7 μm is achieved at the low temperature of 1500 °C. [6] Although nanocrystal sintering could effectively promote the densification and suppress grain coarsening, as-fabricated compact still possesses over-large grain size which needs to be further solved.…”

Section: Introductionmentioning

confidence: 99%

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Densification Behavior and Microstructure Evolution of Mo Manocrystals by Microwave Sintering

Wang¹,

Li²,

Hu³

et al. 2021

ES Mater. Manuf.

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Fabrication of full-densified Mo metal with fine grain size and uniform microstructure is highly desired to improve its mechanical property. In this work, microwave-field-assisted thermal sintering was utilized to promote the fast densification of Mo nanocrystals, and the compact with high relative density of 99.8 % and fine grain size of 2.09 μm was obtained at 1450 °C for 0.5 h with heating rate of 20 °C/min, which is much superior to the compact with density of 99.13 % and grain size of 7 μm fabricated by traditional thermal sintering at 1500 °C for 1 h. Further theoretical and experimental investigation reveals that effective volume heating transfer with low activation energy provides strong driven-force for densification of nanosized Mo powder at low temperature.

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Section: Densification Kinetics Of Mo During Microwave Sintering Processcontrasting

confidence: 49%

Section: Experimental 21 Fabrication Of Mo Compactsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Densification Behavior and Microstructure Evolution of Mo Manocrystals by Microwave Sintering

Wang¹,

Li²,

Hu³

et al. 2021

ES Mater. Manuf.

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“…In Figure we summarized the Vickers hardness ( H avg ) of dense refractory metals produced by PM as a function of G avg . [ 44–78 ] While the beneficial grain boundary strengthening clearly holds, most of the data points in the literature fall in the coarse‐grained (CG) regime with G avg > 1 µm and only a few ones (high‐entropy or oxide‐dispersed strengthened refractory metal alloys) reach to 500 nm < G avg < 1 µm in the fine‐grained (FG) regime. Recently, we have introduced pressureless two‐step sintering (TSS) to refractory metals and alloys and made technological breakthroughs in producing dense UFG W, Mo, and W‐Re alloys to record‐fine grain sizes around 300 nm.…”

Section: Introductionmentioning

confidence: 99%

Powder Metallurgy Route to Ultrafine‐Grained Refractory Metals

Zhang

et al. 2023

Advanced Materials

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Ultrafine‐grained (UFG) refractory metals are promising materials for applications in aerospace, microelectronics, nuclear energy, and many others under extreme environments. Powder metallurgy (PM) allows to produce such materials with well‐controlled chemistry and microstructure at multiple length scales and near‐net shape manufacturing. However, sintering refractory metals to full density while maintaining a fine microstructure is still challenging due to the high sintering temperature and the difficulty to separate the kinetics of densification versus grain growth. Here an overview of the sintering issues, microstructural design rules, and PM practices towards UFG and nanocrystalline refractory metals are sought to be provided. The previous efforts shall be reviewed to address the processing challenges, including the use of fine/nanopowders, second‐phase grain growth inhibitors, and field‐assisted sintering techniques. Recently, pressureless two‐step sintering has been successfully demonstrated in producing dense UFG refractory metals down to ≈300 nm average grain size with a uniform microstructure and this technological breakthrough shall be reviewed. PM progresses in specific materials systems shall be next reviewed, including elementary metals (W and Mo), refractory alloys (W‐Re), refractory high‐entropy alloys, and their composites. Last, future developments and the endeavor towards UFG and nanocrystalline refractory metals with exceptionally uniform microstructure and improved properties are outlined.

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“…The spheroidization and refinement of many refractory metals and ceramic powders have been achieved using RF plasma, such as tantalum, tungsten, and AlO 3 powders [ 26 , 27 , 28 , 29 , 30 , 31 ]. However, there are few reports on the preparation of spherical molybdenum powder by RF plasma, especially ultra-fine molybdenum powder [ 32 ]. In this paper, irregular ammonium paramolybdate (APM) powders under the carrying of powder delivery gas entered the hydrogen plasma flame (up to 8000 °C), underwent rapid cracking, reduction, and then were quenched to synthesize ultra-fine spherical metal molybdenum particles.…”

Section: Introductionmentioning

confidence: 99%

Controllable Preparation of Spherical Molybdenum Nano-Powders by One-Step Reduction of APM in Radio Frequency Hydrogen Plasma

Wang

Chen

et al. 2022

Materials

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Spherical molybdenum nano-powders were in-situ ultrafast synthesized from ammonium paramolybdate (APM) raw materials in a one-step reduction method by radio frequency (RF) hydrogen plasma. Due to the extreme conditions of the RF plasma torch such as its high temperature and large temperature gradient, the injected raw APM powder was quickly gasified and then reduced into nano-sized metal molybdenum (Mo) powder. The influences of APM powder delivery rate and H2 concentration on the properties of the obtained powders were investigated. Field-emission scanning electron microscope (FESEM), transmission electron microscope (TEM), X-ray diffraction (XRD), nanolaser particle analyzer, and specific surface area method were used to characterize the morphology, phase, and particle size distribution of the powders. The results showed that the nano-sized Mo powder obtained by hydrogen plasma treatment had a quasi-spherical morphology and an average particle size of about 30 nm. The particle size could be successfully adjusted by varying H2 concentrations. In addition, spherical nano-sized MoO3 powder could be obtained when no H2 was added into the RF plasma.

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Ultrafast synthesis of nanocrystalline molybdenum powder by thermal plasma and its sintering behavior

Cited by 15 publications

References 42 publications

Densification Behavior and Microstructure Evolution of Mo Manocrystals by Microwave Sintering

Densification Behavior and Microstructure Evolution of Mo Manocrystals by Microwave Sintering

Powder Metallurgy Route to Ultrafine‐Grained Refractory Metals

Controllable Preparation of Spherical Molybdenum Nano-Powders by One-Step Reduction of APM in Radio Frequency Hydrogen Plasma

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