FORMATION OF NANOCRYSTALLINE FCC PHASE BY MECHANICALLY DRIVEN CRYSTALLIZATION

Ball milling has been performed on the Al-Ti and Al-Ti-C powder mixtur es in a planetary ball mill. The structural changes of the as-milled p owder samples have been characterized by X-ray diffraction (XRD), tran smission electron microscopy (TEM) and differential thermal analysis ( DTA). The results obtained show that an amorphous phase is formed at a n early milling stage, and transits later to a nanocrystalline f.c.c. metastable phases. In addition, crystallization of the amorphous phase upon heating results in the equilibrium phases instead of the f.c.c. phase. This indicates that the crystallization induced by ball milling is different from that by annealing. The contamination of nitrogen an d oxygen has a significant influence on the crystallization during bal l milling.