Elektrische Leitfähigkeit von kugelförmigem Kupferpulver unter Druck

Herger, P.

doi:10.1007/bf01846003

Cited by 6 publications

(4 citation statements)

References 1 publication

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“…The higher resistivity compared to the powders without surface oxide layer can be attributed to the area of metallic contact being smaller than the contact area due to the remaining oxide fragments. The pressure necessary to destroy the oxide layer increases with its thickness [49].…”

Section: Results Anddiscussionmentioning

confidence: 99%

Fundamental principles of spark plasma sintering of metals: part I – Joule heating controlled by the evolution of powder resistivity and local current densities

Trapp

Kieback

2019

Powder Metallurgy

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In this study, the evolution of the electrical resistivity of metal powders during densification and the resulting current flow through punch, powder compact, and die is investigated. The evaluation of the accompanying Joule heating identifies the graphite punches as main heating element providing more than 90% of the heat. The high electrical resistance of the punches and the low resistance of the graphite die as parallel electrical load to the specimen determine the current flow in the tool. For powder particles with intact oxide layers, virtually no current flows through the compact. On the other hand, for a powder resistivity below 10 −3 Ωcm about 50% of the current flows through the compact. This fraction is constant despite further decreasing resistivity of the compact during densification. A constant current through the specimen has important implications for the microscopic temperature distribution and the understanding of the so-called 'spark plasma effects'.

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Section: Results Anddiscussionmentioning

confidence: 99%

Fundamental principles of spark plasma sintering of metals: part I – Joule heating controlled by the evolution of powder resistivity and local current densities

Trapp

Kieback

2019

Powder Metallurgy

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“…This is typically the case for thicker and non-conducting to weakly conducting oxide layers. If the oxide layer stays intact, it presents an additional film resistance for the electrical current but the latter flows homogeneously through the whole contact [12,15,16]. In any case, the electrical current leads to an inhomogeneous temperature distribution in the powder particle, whereby the highest temperature, , can be found at z = 0.…”

Section: Microscopic Temperature Distribution: a Simplified Analytica...mentioning

confidence: 99%

Fundamental principles of spark plasma sintering of metals: part II – about the existence or non-existence of the ‘spark plasma effect’

et al. 2020

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The mechanisms of densification in spark plasma sintering (SPS) were investigated both analytically and numerically for a model system of two spherical metallic powder particles. From the microscopic temperature distribution, the possibility of a micro-local overheating of the particleparticle contacts was analysed for different particle sizes, contact geometries, materials, and electrical loads. It is shown that, for particles below the size of one millimetre, local overheating is below one Kelvin. Subsequently, the material transport by thermomigration, electromigration, and diffusion driven by surface curvature and external pressure was derived from microscopic field distributions obtained from analytical calculations and finite-element simulations. The results show that, while the mechanical pressure accelerates material transport by orders of magnitude, the electrical current and the temperature gradients do not. It is also shown that pulsing the current has no significant influence on the densification rate.

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“…The difficulties in understanding the process lie in the interplay of these factors and the non‐uniformity. The material properties change during the process as they depend on temperature, but especially on the contact radius between the particles and the nature of their surface (oxide layers) . The pressure in the particle contacts is locally magnified compared to the globally applied mechanical pressure by geometrical reasons.…”

Section: Introductionmentioning

confidence: 99%

“…The material properties change during the process as they depend on temperature, but especially on the contact radius between the particles and the nature of their surface (oxide layers). 5,6 The pressure in the particle contacts is locally magnified compared to the globally applied mechanical pressure by geometrical reasons. Additionally, the temperature should not be completely homogeneous on a microscopic scale as more Joule heat is generated in the contact zone between the particles than in their center due to the larger local resistance.…”

Section: Introductionmentioning

confidence: 99%

Temperature Distribution in Metallic Powder Particles During Initial Stage of Field‐Activated Sintering

Trapp

Kieback

2015

J. Am. Ceram. Soc.

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The temperature distribution in copper and martensitic steel spheres has been investigated for the initial stage of field-activated sintering (FAST)/spark plasma sintering (SPS) using capacitor discharges (CD) with applied voltages from one to 15 V as model experiments. At first, the evolution of the contact resistance between the spheres has been studied. The results show the reduction in the contact resistance after discharge with increasing electrical load, yet no significant dependence on the length or number of the discharge pulses. Thereby the initial resistance is only decreased distinctly if at least a certain minimal voltage was applied. Subsequently, the melting of thin coatings of different metals on copper spheres has been studied and the occurrence of molten phase and its melting point were assigned to the corresponding discharge current. Extrapolation from the currents necessary to melt the coating layers in the CD experiments to lower values typical for FAST was used to estimate the contact overtemperature in the latter case. Resulting values for copper range from 0.05 K for normal heating with 100 K/min to 5 K for maximum current output.

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Elektrische Leitfähigkeit von kugelförmigem Kupferpulver unter Druck

Cited by 6 publications

References 1 publication

Fundamental principles of spark plasma sintering of metals: part I – Joule heating controlled by the evolution of powder resistivity and local current densities

Fundamental principles of spark plasma sintering of metals: part I – Joule heating controlled by the evolution of powder resistivity and local current densities

Fundamental principles of spark plasma sintering of metals: part II – about the existence or non-existence of the ‘spark plasma effect’

Temperature Distribution in Metallic Powder Particles During Initial Stage of Field‐Activated Sintering

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