Grain agglomeration in solid-liquid mixtures under microgravity conditions

German, Randall M.

doi:10.1007/bf02653886

Cited by 8 publications

(3 citation statements)

References 12 publications

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“…[ 34 ] When a W powder compact is sintered in the presence of the activator phases, densification can be initiated at low temperatures of ≈1200–1500 °C. Considering the structure and chemistry of activator phases, at present, the mechanisms evolve into liquid‐phase sintering, [ 118,119 ] solid‐state activated sintering, [ 36,114,120 ] and nanophase separation sintering. [ 121–124 ] The former two approaches have been extensively studied in the past few decades yet only provide limited effects in grain refinement.…”

Section: Recent Progress In Sintered Refractory Metals Alloys and Com...mentioning

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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Section: Recent Progress In Sintered Refractory Metals Alloys and Com...mentioning

confidence: 99%

Powder Metallurgy Route to Ultrafine‐Grained Refractory Metals

Zhang

et al. 2023

Advanced Materials

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“…The driving mechanism and the effects on the microstructure of the grain migration are the object of many studies. 21,43,44,45,46,47,48,49 In the present work, the assumption proposed by German and Liu 48 is followed. In their study, the grain dispersion and contact engagement during liquid-phase sintering are considered to be the consequences of the action of the shear stresses induced by the specimen's reshaping.…”

Section: Solid Grain Settlementmentioning

confidence: 99%

“…For materials, for which large differences between low-and high-viscosity -phase densities can be present in the specimen, the gravitational settlement, and a final microstructural gradient can occur, as suggested in different works. 21,46,48 Considering the different viscosity between the two phases (low-and high-viscosity) and the limited and the distance that the high-viscosity phase can travel, the settling derived from the influence of the gravitational forces during the sintering can be described through the Stokes' approach. If the assumptions of the negligible edge effect and grain aggregation can be considered 47 then it is possible to use the Stokes' law for describing the settling velocity of a single grain at low Reynolds number and in an unbounded low-viscosity phase:…”

Section: Solid Grain Settlementmentioning

confidence: 99%

Influence of gravity on sintering of 3D‐printed powder components

et al. 2021

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Present technologies of additive manufacturing (such as binder‐jetting, stereolithography, robocasting, etc.) of complex‐shape powder‐components necessitate fine‐tuning of sintering as applied to highly porous 3D‐printing products. The densification of low‐density, complex shapes requires control of the gravity‐related phenomena to ensure a nearly full and distortion‐free densification. The present study addresses these issues through the involvement of comprehensive finite element simulations, the determination of the additively manufactured powder specimens’ sintering behavior, and the experimental validation of the developed models describing sintering of 3D‐printed objects. The paper describes the application of a numerical approach based on continuum mechanics‐based modeling of the gravity‐induced distortions during sintering of 3D‐printed powder components. The validation of the model is conducted through the comparison with the experimental results obtained for the sintering of the beam‐shape components printed using ceramic stereolithography technology. A practical semi‐analytical criterion, which can be used for sintered 3D‐printed parts’ design recommendations applicable to various material systems, is derived. Based on the obtained design criterion, a design map is developed indicating the allowable 3D‐printed elements’ configurations enabling the avoidance of the excessive gravity‐induced shape distortions.

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Review: liquid phase sintering

2009

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Liquid phase sintering (LPS) is a process for forming high performance, multiple-phase components from powders. It involves sintering under conditions where solid grains coexist with a wetting liquid. Many variants of LPS are applied to a wide range of engineering materials. Example applications for this technology are found in automobile engine connecting rods and high-speed metal cutting inserts. Scientific advances in understanding LPS began in the 1950s. The resulting quantitative process models are now embedded in computer simulations to enable predictions of the sintered component dimensions, microstructure, and properties. However, there are remaining areas in need of research attention. This LPS review, based on over 2,500 publications, outlines what happens when mixed powders are heated to the LPS temperature, with a focus on the densification and microstructure evolution events.

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Grain agglomeration in solid-liquid mixtures under microgravity conditions

Cited by 8 publications

References 12 publications

Powder Metallurgy Route to Ultrafine‐Grained Refractory Metals

Powder Metallurgy Route to Ultrafine‐Grained Refractory Metals

Influence of gravity on sintering of 3D‐printed powder components

Review: liquid phase sintering

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