Transient liquid phase sintering of high density Fe 3 Al using Fe and Fe 2 Al 5 –FeAl 2 powders Part 2 – Densification mechanism analysis

Abstract

The use of Fe₂Al₅–FeAl₂ prealloyed powders and heating rates >150 K min⁻¹ overcomes the formation of density restricting Kirkendall porosity in the Fe–Al system. X-ray diffraction, electron probe micro analysis and differential thermal analysis suggest that the absence of a persistent liquid, experienced when liquid phase sintering with elemental powders, is overcome. Homogenisation is greater during heating at a rate of 20 K min⁻¹ than for 150, 250 or 400 K min⁻¹ and homogenous Fe₃Al forms across the compact at temperatures below the melting point of the liquid forming constituent, indicating that a liquid will not form under such processing conditions. The maximum density achieved under the processing conditions in the present study is 92% of theoretical density. The presence of large pores shortly after liquid formation suggests that the remaining porosity is largely due to powder agglomeration during mixing.