Cascade collapse in copper and nickel

In-situ TEM (transmission electron microscope) studies of the development of the damage structure produced by heavy ion irradiations have been performed in copper and nickel to investigate the possibility that melting occurs in local regions within displacement cascades. These experiments reveal that, as the ion dose increases, additional loops form from isolated displacement cascades, and, more surprisingly, that some of the preexisting loops are annihilated, change position, size, and/or Burger's vector. It was also found that the probability for loop formation and the defect image size are greater in copper than in nickel even at temperatures well below Stage III. It will be demonstrated that these observations provide supporting evidence, albeit indirect, that local melting occurs within the cascade core. These results will be compared to the molecular dynamic computer simulations of the damage created by low-energy self-ions in copper and nickel.