Sintering Mechanisms of Metals Under Electric Currents

Abstract

This chapter concerns the microscopic mechanisms involved in densification of metallic powders submitted to high electric current pulses like in the SPS technique. Because metallic systems exhibit high electric conductivity, focus is made on evaluating the sensitivity of the densification mechanisms on the current. Thus, a first part is devoted to the influence of electric currents on elementary metallurgical phenomena (diffusion, plasticity…) which are involved in densification. Then, after recalling the micromechanical models of densification, the SPS kinetics is described, and analyzed in the framework of these models, with emphasis on the role of the current. Finally, theoretical and experimental investigations on electrically-induced mechanisms at the scale of the powder particle contacts, are presented: dielectric breakdown of oxide layers, arcs and plasma, Joule overheating, electroplasticity and electromigration. Then, conclusions are drawn on the most probable mechanisms, and on the role of the current.

Microstructure Evolution in a Fast and Ultrafast Sintered Non-Equiatomic Al/Cu HEA

“…For SPS-1100 samples (Figure 4b), this phenomenon approximately occurs at an earlier temperature of 900 • C. Above 1000 • C, the volume shrinkage from the porosity reduction finishes. From 1050 • C, the punch shows a negative displacement indicating the thermal expansion of the bulk sample already fully densified at that temperature, this last phenomenon has been already seen on some SPS studies [41]. Once the holding time has finished, the equipment releases the applied pressure and starts cooling the HEA.…”

Microstructure characterization of high temperature mechanisms in a Nb–Ti–Si alloy

“…The [40-100] µm fraction was sieved out of the produced powder. Then, cylindrical samples 36 mm in diameter and 8 mm thick were processed by spark plasma sintering (SPS) from the sieved powder following usual procedures [19], using a Sumitomo 2080 equipment. The main parameters were the following.…”

Heat Treatment Influencing Porosity and Tensile Properties of Field Assisted Sintered AlSi7Mg0.6

“…FAST sintering is a powder consolidation technique that uses a direct electric current and comparatively high sintering pressures to obtain powder consolidation and sintering within very short process times [ 11 ] (see Figure 1 ). Monchoux [ 12 ] speaks of the unprecedented speed of this process and that particularly fine microstructures are achieved by this technology, especially with regard to metals. A fine structure usually means an increase in strength.…”