Transient liquid phase sintering of high density Fe_3Al using Fe and Fe_2Al_5-FeAl_2 powders Part 2 -- Densification mechanism analysis

摘要

The use of Fe_2AI_5-FeAI_2 prealloyed powders and heating rates >150 K min~(-1) overcomes the formation of density restricting Kirkendall porosity in the Fe-AI 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 Fe_3AI 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 percent 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.