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

A structural study of the B2 CoZr compound during amorphization reacti on by high energy ball milling was done using extended X-ray absorptio n 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 Fourie r 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 struct ure disintegrates and the amorphization reaction occurs. When the accu mulated strain energy, e.g. the nanocrystal grain boundary energy, is comparable with the difference to drive the crystalline-to-amorphous p hase transformation in CoZr, the amorphization reaction starts.