Formation of Aluminum Particles with Shell Morphology during Pressureless Spark Plasma Sintering of Fe-Al Mixtures: Current-Related or Kirkendall Effect?

Dina Dudina,Amiya Mukherjee,Boris Bokhonov

doi:10.3390/ma9050375

Abstract

A need to deeper understand the influence of electric current on the structure and properties of metallic materials consolidated by Spark Plasma Sintering (SPS) stimulates research on inter-particle interactions, bonding and necking processes in low-pressure or pressureless conditions as favoring technique-specific local effects when electric current passes through the underdeveloped inter-particle contacts. Until now, inter-particle interactions during pressureless SPS have been studied mainly for particles of the same material. In this work, we focused on the interactions between particles of dissimilar materials in mixtures of micrometer-sized Fe and Al powders forming porous compacts during pressureless SPS at 500–650 °C. Due to the chemical interaction between Al and Fe, necks of conventional shape did not form between the dissimilar particles. At the early interaction stages, the Al particles acquired shell morphology. It was shown that this morphology change was not related to the influence of electric current but was due to the Kirkendall effect in the Fe–Al system and particle rearrangement in a porous compact. No experimental evidence of melting or melt ejection during pressureless SPS of the Fe–Al mixtures or Fe and Al powders sintered separately was observed. Porous FeAl-based compacts could be obtained from Fe-40at.%Al mixtures by pressureless SPS at 650 °C.

Highlights

In electric current-assisted sintering of conductive materials, the current passes directly through the compact making inter-particle contacts parts of the electric circuit
We present the evolution of particle morphology in Fe–Al mixtures under conditions of pressureless
The ternary carbide AlFe3 C was the first phase to form at the inter-particle contacts in the porous

Summary

Introduction

In electric current-assisted sintering of conductive materials, the current passes directly through the compact making inter-particle contacts parts of the electric circuit. Processes occurring at inter-particle contacts play a key role in the formation of bulk materials from separate powder particles and, require special attention. If pulsed current is applied, the contacts that complete the electric circuit change with every pulse leading to uniform sintering [1]. The contact formation mechanisms between particles of the same material during electric current-assisted sintering have been addressed in detail in a number of studies [2,3,4,5,6,7,8,9,10,11]. Burenkov et al [2,3] found evidence of electric erosion between metal

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