Abstract
Influence of Al powder addition on the sintering process of Fe powder compact was made by means of dilatometric and microscopic examinations, X-ray diffraction, E.P.M.A. and D.T.A. The results were summarized as follows.
(1) An intermediate phase (Fe2Al5) was produced by the interaction of molten Al and solid Fe at the melting point of Al at 660°C, where an expansion and an exothermic phenomenon were observed in the Fe-Al mixed powder compacts.
(2) This expansion was due to the penetration of molten Al into the interfaces between Fe particles, leaving pores at the place where the solid Al had been located.
In this stage, the cracks were generated at these interfaces in the case of ore reduced Fe-Al mixed powder compacts. It was very difficult to eliminate the large pores and the cracks in more advanced stages of the sintering process. The exothermic phenomenon was thought to be caused by the formation of Fe2Al5.
(3) It was proved that for the carbonyl Fe-Al mixed powder compacts of composition over y-loop, the sintering was remarkably accelerated by the process stabilizing the a-Fe phase with the diffusion of Al into the Fe matrix from Fe2Al5 at high temperature.
On the other hand, the sintering of ore reduced Fe-Al mixed powder compacts was disturbed by the difficulties to uniformly diffuse Al into larger Fe particles and to repair the cracks.
