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

Abstract

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'.

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

“…Other research explicitly states minimal supertemperatures for real SPS conditions or an extrapolation to those [13,19,[28][29][30][31]. Scarce experimental data for large current densities support this findings [10,19,32]. The results obtained from analytical calculations confirmed by FE simulations support the finding of minimal supertemperatures.…”

“…For a tool with punches and die made from the same type of graphite, a fraction of 40 to 60% of the total electric current flows through the electrical conductive powder compact if its resistivity is sufficiently low [10]. If all the particle-particle contacts are assumed equal, this fraction of the current does not change despite further densification of the powder compact.…”

A critical review on spark plasma sintering of copper and its alloys

“…This process is repeated intermittently until the compact achieves full densification. As a result, it causes homogeneous grain size distribution, as well as restricts grain Semenov et al [104,[134][135][136] modeled the SPS process by thermo-electro-mechanical approach. Two limiting conditions have been investigated (i) low mechanical pressure and (ii) high mechanical pressure.…”

Microstructure and Mechanical Properties of Spark Plasma Sintered Mg-Zn-Ca-Pr Alloy

“…Spark plasma sintering is an advanced powder metallurgy technique that can be used in the production of implants from Mg alloys. SPS allows fast densification at lower temperature in contrast to conventional sintering techniques, resulting in the retention of nanocrystalline structures and non-equilibrium alloys produced by HEMA, and associated properties [34,35]. SPS is advantageous for sintering metallic powders due to its ability to produce a sample with an ultra-fine microstructure without defects and pores [36,37].…”