XAFS Study on Solid State Amorphization Process of MgNi Alloys

摘要

The local structure changes in MgNi_2 powder mixture during mechanical alloying process were examined by extended x-ray absorption fine structure (XAFS) technique. The Bragg peaks in XRD profile corresponding to Mg-crystal disappeared at 5 hours from the commencement of milling. This indicates that a part of Ni atoms diffuse into hcp-Mg crystal, and disintegrate the hcp-Mg crystalline structure, The radial structure function (RSF) change around the Ni atom shows that the fcc-Ni crystalline structure remains until 10 hours of milling. At 20 hours of milling, 2nd, 3rd and 4th nearest neighbor peaks in the RSF disappeared. This indicates that the fcc-Ni crystalline structure disintegrated and changed to amorphous structure. For the MgNi_2 amorphous alloy, the results of numerical fitting of Ni K-edge EXAFS indicated that the coordination number of Mg and Ni atom around a Ni atom are 4.5 and 4.8, and Ni-Ni and Ni-Mg atomic distances are 0.241 nm and 0.269 nm, respectively.