STRUCTURAL-CHANGES IN B2 COZR COMPOUND DURING AMORPHIZATION PROCESS BY MECHANICAL MILLING

A structural study of the B2 CoZr compound during amorphization reaction by high energy ball milling was done using extended X-ray absorption fine-structure (EXAFS) measurement to discuss the micromechanism of amorphization. The B2 CoZr compound powder was prepared by arc melting and annealing. The mechanical milling was done using a vibrating mill. A change in the radial distribution function, provided by the Fourier transform of EXAFS signal, around the Co atom shows that the Zr atom at the first-nearest neighbor around a Co atom is replaced by Co atom at the second-nearest neighbor; simultaneously the crystalline structure disintegrates and the amorphization reaction occurs. When the accumulated strain energy, e.g. the nanocrystal grain boundary energy, is comparable with the difference to drive the crystalline-to-amorphous phase transformation in CoZr, the amorphization reaction starts.