Thermal stability of irradiation-induced metastable lattice structures in NiTi intermetallic compound

To investigate the thermal stability of the ion-irradiation induced metastable lattice structures in bulk samples of NiTi intermetallic compound, they were irradiated with 16 MeV Au ions at room temperature, and were subsequently annealed up to 823 K. The lattice structures of the irradiated samples and the annealed samples were examined by using the x-ray diffraction. The measurements have also been performed for NiTi irradiated at 523 K. The amorphous state induced by 16 MeV Au ion irradiation at room temperature recovers to the intrinsic B19' structure by the thermal annealing above 673 K. The lattice structure, however, hardly changed even after the irradiation at 523 K. The experimental result implies that the thermal motion of atoms in NiTi during the irradiation is much more effective for the recovery of the irradiation effect. The effect of thermal annealing on the surface hardness is also discussed. (author)