Structure of a phase induced with Xe-ion irradiation-implantation in gamma-TiAl

A phase transformation in gamma-TiAl intermetallic alloy was found to be in duced with 50 keV Xe-ion irradiation-implantation at doses larger than 2.2x 10(18) ions m(2) at room temperature. The structure and the chemical compos ition of the induced phase were investigated with high-resolution transmiss ion electron microscopy and energy-dispersive X-ray spectroscopy. The zones of the induced phase have sizes up to about several tens of nanometres. Th e phase has a hexagonal structure with a = 0.286 nm and c = 0.462 nm. The c rystallographic orientation relationship between the phase (P) and the gamm a-TiAl matrix is (001)(P)//(1 (1) over bar 1)(gamma) and [100] (P)//[011](g amma). The [Al]/[ Ti] atomic composition ratio in the phase is analysed to be 56/44, slightly different from that of the matrix, 51/49. These results suggest that the induced phase is an Al solid solution of alpha-Ti alloy ph ase, which has different structural parameters and chemical composition fro m those of the reported phase. It is suggested that the size of the ions is important in the phase transformation.