Abstract:The microstructure evolution of nanocrystalline anatase during high energy planetary milling was studied by X-ray diffraction and transmission electron microscopy. The results show that mechanical activation induces the transformations from anatase to srilankite and rutile at room temperature and under ambient pressure, which should primarily be attributed to the rise of local temperature and pressure at the collision sites of the powders and the balls. In addition, the additional energy caused by defects, lattice distortion and the refinement of the crystallite is responsible for the transformations. As milling time increases, anatase phase content reduces and the amounts of both srilankite and rutile phase increase. And the transformation from srilankite to rutile phase takes place by further milling. In anatase phase, the crystallite size decreases and lattice strain rises with milling time. There is no indication of the formation of amorphous phase during milling.

Key words:  nanocrystalline anatase; transformation; ball milling