MOLECULAR DYNAMICS STUDY ON TEMPERATURE EFFECT AND RADIATION-DEDUCED DEFECT FORMATION IN hcp-Ti

The radiation-induced defects formed in nuclear structure materials in the initial stage of displacement cascade and the subsequent changes in their microstructures and mechanical properties are the primary causes of their failure. Unfortunately the formation and aggregation of point defects are hard to be found only by probed experiments. In this work, the displacement cascade occurring in hcp-Ti system has been investigated by using molecular dynamics. After building the atomic model, by setting different PKA (primary knock-on atom) directions and PKA energies respectively, the evolution of simulated radiation-induced point defects in displacement cascade was studied and its two major characteristics, displacement and thermal spikes, have been given. The transient temperature distribution, local melting region variation in the damage zone caused by radiation as well as the peak and surviving numbers of Frenkel pairs were quantitatively estimated. For hcp-Ti, in the PKA energy region of 0.5-9.0 keV, the effect of PKA velocity direction on survival defect number is very small. Both the defect number at stable state and its maximum value have approximately linear relationship with the PKA energy. In the radiation evolution stage, the defects about 95 percent have recovered, the defect and temperature distribution caused by displacement cascade are asymmetric. The simulation method used in this paper would provide an effective way for the study on the evolution and micromechanism of radiation-induced point defects in displacement cascade.