Theoretical and experimental investigations of local overheating at particle contacts in spark plasma sintering

Collard, Christophe; Trzaska, Zofia; Durand, Lise; Chaix, Jean‐Marc; Monchoux, Jean‐Philippe

doi:10.1016/j.powtec.2017.08.033

Cited by 44 publications

(27 citation statements)

References 31 publications

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“…For example, in identical conditions (applied voltage, time, etc. ), the final temperature is 550 K for r / R = 0.02 and 1250 K of r / R = 0.06 ( r and R being the neck and particle radii, respectively), as discussed in our previous work …”

Section: Fem Simulations Of Local Joule Overheatingmentioning

confidence: 71%

“…Figure A shows an example of current density map in the particles at t = 36 s for contact size r / R = 0.06 ( r and R being the neck and particle radii, respectively). Other examples of calculations, and a discussion of the repartition of the current within the particles, can be found in . We present here the main results.…”

Section: Fem Simulations Of Local Joule Overheatingmentioning

confidence: 87%

“…Mesh refinement was tested in order to check the dependency of the results with the meshing and the size of elements. Other simulation details, concerning notably the delicate meshing procedure at the necks, are discussed elsewhere …”

Section: Fem Simulations Of Local Joule Overheatingmentioning

confidence: 99%

“…To account for this unexpected result, the effect of thermal conductivity alone has been assessed, in a reference case without the Joule heating (heat conduction problem). The details are given in . The calculations simulate the case when 1000°C temperature step is imposed at the contacts of single particles 100 μm in diameter at t ≈ 0 (Figure A).…”

Section: Fem Simulations Of Local Joule Overheatingmentioning

confidence: 99%

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Spark plasma sintering microscopic mechanisms of metallic systems: Experiments and simulations

et al. 2018

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The microscopic densification mechanisms of metallic systems (TiAl, Ag-Zn) by spark plasma sintering (SPS) have been studied by simulations and experiments. Finite element simulations showed that, despite very high current densities at the necks between metallic powder particles (≈5 × 10 4 A/cm 2 ), only very limited Joule overheating can be expected at these locations (<1°C), because of very fast heat diffusion. The microscopic plasticity mechanisms under these high electric currents have been studied by transmission electron microscopy. For this purpose, thin foils have been extracted by focused ion beam at the necks between TiAl powder particles. This is the first time, to the best of our knowledge, that microscopic plasticity mechanisms at the necks between powder particles are investigated by TEM during densification of a metallic powder. Dislocation glide and climb mechanisms were identified, followed by recovery and recrystallization.The elementary mechanism kinetically controlling these phenomena is proposed to be bulk diffusion of Al, which activation energy (360 kJ/mol) is close to the activation energy measured for densification (308 ± 20 kJ/mol). Comparisons of densification kinetics by SPS (≈60-110 A/cm 2 ) and by hot pressing (0 A/cm 2 ) showed no influence of current on these mechanisms. Finally, reaction experiments in the Ag-Zn system did not show any influence of very high currents (>1000 A/cm 2 ) on diffusion kinetics. Consequently, densification by SPS occurs by classical mechanisms not affected by the current. K E Y W O R D Sdiffusion/diffusivity, electron microscopy, intermetallic systems, plasticity, spark plasma sintering

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Section: Fem Simulations Of Local Joule Overheatingmentioning

confidence: 71%

Section: Fem Simulations Of Local Joule Overheatingmentioning

confidence: 87%

Section: Fem Simulations Of Local Joule Overheatingmentioning

confidence: 99%

Section: Fem Simulations Of Local Joule Overheatingmentioning

confidence: 99%

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Spark plasma sintering microscopic mechanisms of metallic systems: Experiments and simulations

et al. 2018

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“…However, Ye et al [79] argue that, in calculations conducted by Song et al, the temperatures are overestimated, as not heat dissipation from the contact area into the particle volume though thermal conduction is taken into account. Theoretical and experimental analysis of the SPS process of TiAl powders detected no overheating of the inter-particle contacts [80]. In the experimental part of this work, metallographic investigations were used in search of local structural changes in the alloy in the vicinity of the inter-particle contacts.…”

Section: Fabrication Of Porous Materials By Partial Densification mentioning

confidence: 99%

Fabrication of Porous Materials by Spark Plasma Sintering: A Review

2019

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Spark plasma sintering (SPS), a sintering method that uses the action of pulsed direct current and pressure, has received a lot of attention due to its capability of exerting control over the microstructure of the sintered material and flexibility in terms of the heating rate and heating mode. Historically, SPS was developed in search of ways to preserve a fine-grained structure of the sintered material while eliminating porosity and reaching a high relative density. These goals have, therefore, been pursued in the majority of studies on the behavior of materials during SPS. Recently, the potential of SPS for the fabrication of porous materials has been recognized. This article is the first review to focus on the achievements in this area. The major approaches to the formation of porous materials by SPS are described: partial densification of powders (under low pressures, in pressureless sintering processes or at low temperatures), sintering of hollow particles/spheres, sintering of porous particles, and sintering with removable space holders or pore formers. In the case of conductive materials processed by SPS using the first approach, the formation of inter-particle contacts may be associated with local melting and non-conventional mechanisms of mass transfer. Studies of the morphology and microstructure of the inter-particle contacts as well as modeling of the processes occurring at the inter-particle contacts help gain insights into the physics of the initial stage of SPS. For pre-consolidated specimens, an SPS device can be used as a furnace to heat the materials at a high rate, which can also be beneficial for controlling the formation of porous structures. In sintering with space holders, SPS processing allows controlling the structure of the pore walls. In this article, using the literature data and our own research results, we have discussed the formation and structure of porous metals, intermetallics, ceramics, and carbon materials obtained by SPS.

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Elucidating the Multi‐Scale Temperature Evolution and Densification Mechanisms of Amorphous Powders During Spark Plasma Sintering: Experiments and Modeling

et al. 2022

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With unique atomic stacking structures and outstanding performances, amorphous alloys have been formulated during the past several decades via various solidification techniques. [1,2] The cooling rates required to produce amorphous alloys are generally as high as 10 4 -10 5 °C s À1 . [3,4] This imposes restrictions on manufacturing amorphous alloys into giant-sized and geometrically complex parts. Nevertheless, amorphous alloys exhibit viscous-like behavior in the supercooled liquid region (SLR). Micron-sized amorphous powders can be fabricated from most alloy systems, even those having low glass-forming ability. [4] These provide a practical approach to densifying amorphous powders via powder metallurgy (P/M) processes. [5,6] Among the various P/M techniques available, spark plasma sintering (SPS) is promising for consolidating amorphous powders due to its fast heating rate and short cycle time. [5] In the past decade, consolidation of amorphous powders using the SPS process has been reported for Zr-based, [7,8] Ti-based, [9][10][11] Fe-based, [12] and Cu-based [13] alloys.The amorphous powders are heated to the SLR and densified by viscous flow. [10] However, the crystallization tendency is more intense with the increased temperature. [14] Therefore, the research focuses on fast densification while maintaining the amorphous structure. Amorphous powders' densification and crystallization dynamics race each other. Temperature is the key factor affecting this competitive process. Local overheating can lead to partial crystallization, resulting in severe embrittlement. For example, Nowak et al. reported that excessive overheating is generated in the vicinity of particle necks during the initial stages and is responsible for partial devitrification. [15] Similar phenomena have been widely observed in Fe-based [16] and Al-based amorphous alloys. [17] Despite the significant advantages of SPS, its further popularization is hindered by severe temperature and stress gradients, [18] especially for complex-shaped and large-sized parts. Therefore, it is of great concern to figure out the temperature field evolution in the amorphous alloys prepared by SPS. However, to the authors' knowledge, the current understanding of the temperature distribution in amorphous alloys prepared by SPS is limited.The temperature gradients in the sintering molds and samples can be divided into inhomogeneity at the macro and particle scales. In terms of the macroscopic temperature field, Song et al. developed a coupled thermal-electric-mechanical model to simulate the SPS process of Fe powders, [19] which concerns

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Theoretical and experimental investigations of local overheating at particle contacts in spark plasma sintering

Cited by 44 publications

References 31 publications

Spark plasma sintering microscopic mechanisms of metallic systems: Experiments and simulations

Spark plasma sintering microscopic mechanisms of metallic systems: Experiments and simulations

Fabrication of Porous Materials by Spark Plasma Sintering: A Review

Elucidating the Multi‐Scale Temperature Evolution and Densification Mechanisms of Amorphous Powders During Spark Plasma Sintering: Experiments and Modeling

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