Field effects during consolidation of metallic powders

High electric current has been shown to enhance sintering kinetics during consolidation of many ceramic and metallic based powder materials using the process known as Electric Field Assisted Sintering (EFAS) or Spark Plasma Sintering (SPS). More recently, processes employing higher voltages and electric field strengths than these “current assisted” techniques have been shown to dramatically increase the sintering kinetics in ceramic materials in what has become known as “flash sintering”. While much work has been conducted in the area of ceramics little attention has been paid to higher field processing of metallic powders, and in general, the fundamental mechanisms governing enhanced kinetics during field assisted sintering of metallic powders are poorly understood. Furthermore, EFAS processes are typically complex and employ many variables which may include pressure, temperature, current, and electric field, the effects of which can be difficult to decouple. In this work aluminum 5083 (AA5083) alloy powders are processed using pressure-less sintering while applying DC electric fields ranging from 0-300 V/cm to examine the effect on the sintering kinetics of AA5083 powder. In-situ sintering kinetics were quantified using digital image correlation (DIC) and it was found that the application of a DC field results in a discontinuous change in volume at a critical temperature similar to the flash effect observed in ceramics. Microstructural characterization was used to confirm the flash corresponds to formation of necks due to sintering in the material. The temperature at which this phenomena occurs was found to decrease with increasing field strength. Joule heating during the flash was quantified using full field IR camera measurements and found to not generate enough heat to account for the enhanced sintering kinetics observed. Micromechanical modeling is used to quantify localized Joule heating at particle-particle contacts to further explore the possibility of enhanced kinetics due to localized thermal runaway, and to predict evolution of electrical conductivity with density of the compact