The Critical Thickness for the Formation of Fe-, Ni- and Co-Based Amorphous Alloys with Metalloids

概要

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Effect of metalloid composition on the amorphous phase formation of iron-, nickel- and cobalt-based alloys has been studies as a function of the thickness of ribbon using a special melt-quenching apparatus, which enables the roller revolving at high speeds, such as 5000 rpm, to stop in a short time of 1-2s and produces a long ribbon with a contimuous variation in thickness in the range of about 20-400 μm in one ejective operation. The maximum critical thickness is about 250 μm for Fe_<75>Si_<10>B_<15>, 160 μm for Co_<72.5>Si_<12.5>B_<15> and 225 μm for Ni_<75>Si_8B_<17>, which are located near the center of their amorphous-forming region, decreases with increasing or decreasing silicon and/or boron content and is about 20-30 μm near the boundary between amorphous and crystalline phases. In addition, the maximum critical thickness of Fe_<80>-(P, B, Si, C)_<20> alloys increases in the order of Fe-P-Si, Fe-B-C, Fe-B-P, Fe-B-Si and Fe-P-C system and reaches about 200 μm for Fe_<80>P_<14>C_6. From the data on the critical thickness, the amorphous-forming ability depends largely on the type of base metal as well as the metalloid compositions even in the composition ranges of the formation of an amorphous single phase.
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