| Rapidly solidified powders were fabricated by using gas atomizer in Al_(100-(x+y))Mm_xNi_y(x+y≤16 at%) alloys. The Microstructures of rapidly solidified powders are dependent upon alloy composition and powder size. It was found that Ni addition is very effective for amorphous formability in gas atomized Al-Misch metal-Ni alloy powders. In the powder diameter less than 20 ㎛, as the amount of Ni are increased, microstructures are changed from equilibrium phase consisting of fcc-Al and various metallic compounds(Al₄Ce, Al_(11)La₃,……) to amorphous or mixed phase consisting of super saturated fcc-Al, compound and amorphous. Thermal stability of non-equilibrium amorphous phase in Al_(84),_Mm_8Ni_8 powder was significantly higher than that of Al_(88)Mm₄Ni_8 powder. For example, crystallization temperature of gas-atomized powder is about 578 K for Al_(84)Mm_8Ni_8 and 444 K for Al_(88)Mm_8Ni_8 alloy. Al_(84)Mm_8Ni_8 powder has a obvious glass transition temperature(T_g). As powder size is increased, amorphous formability of powders is decreased slightly in the same composition. This phenomena is presumed to result from difference in the degree of supercooling on the various size of powder. |
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