Abstract
By using flame spraying gun, Al alloy powders containing 8 wt%Fe were solidified rapidly by collision onto the stainless steel vessel out of which was cooled by ice water.
Characterization of these powders were carried out by referring to X-ray diffraction analysis, secondary electron microscopic observation and electron probe X-ray micro analysis. Results obtAlned were as follows:
(1) At higher cooling rate, i.e., -105K/s, fine spherical primary AlmFe (m=4.4) metastable phase was observed to form in large part of powders, and rest parts were composed of typical cellular dendrite. At medium or lower cooling rate, asicular or angular shaped primary Al3Fe stable phase plus Al3Fe-Al eutectics were observed to form in a small part of as-flamed powders.
(2) Cooling rates of powders were estimated from the lamellar type eutectics of AlmFe-Al and the arm spacing of secondary dendrite of a-Al; the effective cooling rate was approximately 1×105K/s.
(3) According to the point analysis of EPMA in the field of a-Al, Fe concentration was about 1.5 wt% (0.7 at%). On the contrary, the lattice constant of a-Al in Al-8 wt%Fe alloy powder was exactly the same as that of pure Al within experimental error. In addition, fine spherical precipitates in a-Al were observed in SEM images. Then we concluded that the solubility of Fe in a-Al was very small or nearly equal to the equilibrium state at the cooling rate -105 K/s.
(4) The mAln phases formed in rapidly solidified Al-8 wt%Fe alloy powders by flame spraying method were composed of a-Al, stable Al3Fe and metastable AlmFe phases. And metastable Al6Fe phase was observed to form slightly in powders at a relatively lower cooling rates.
