X-ray-absorption fine structure study on devitrification of ultrafine amorphous Ni-B alloys

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Abstract
X-ray-absorption fine structure (XAFS), x-ray diffraction, and differential thermal analysis have been combined to investigate the structure of ultrafine amorphous Ni70B30 alloy during the crystallization process. The XAFS results demonstrate that a fcc-like nanocrystalline Ni phase with a medium-range order is formed at 573 K where the first exothermic process is observed. We confirmed that the metastable intermediate states consist of the two phases, i.e., nanocrystalline Ni and crystalline Ni3B alloy. The results support the Riveiro et al.’s scenario [J. Magn. Magn. Mater. 188, 153 (1998)] for the devitrification of NiB alloy, in that crystalline phases of Ni3B and Ni-rich NiB alloy are formed as the intermediate states. Based on the complementary information obtained by the three techniques, we present a simple mechanism of crystallization process for the ultrafine amorphous Ni70B30 alloy.