Transmission Electron Microscopy Study In-Situ of Radiation-Induced Defects in Copper at Elevated Temperatures

Abstract

Portions of ABSTRACTNeutrons and high-energy ions incident upon a solid can initiate a displacement collision cascade of lattice atoms resulting in localized regions within the solid containing a high concentration of interstitial and vacancy point defects. These point defects can collapse into various types of dislocation loops and stacking fault tetrahedra (SFT) large enough that their lattice strain fields are visible under diffraction-contrast imaging using a Transmission Electron Microscope (TEM). The basic mechanisms driving the collapse of point defects produced in collision cascades is investigated in situ with TEM for fcc-Cu irradiated with heavy (100 keV Kr) ions at elevated temperature. The isothermal stability of these clusters is also examined in situ.Areal defect yields were observed to decrease abruptly for temperatures greater than 300°C. This decrease in defect yield is attributed to a proportional decrease in the probability of collapse of point defects into clusters. The evolution of*the defect density under isothermal conditions appears to be influenced by three different rate processes active in the decline of the total defect density. These rate constants can be attributed to differences in the stability of various types of defect clusters and to different loss mechanisms. Based upon observed stabilities, estimations for the average binding enthalpies of vacancies to SFT are calculated for copper. INTRODUCTIONMicrostructures can greatly influence the physical properties of materials. Of particular interest is the effect of irradiation on the microstructures of materials subjected to environments containing high fluxes of energetic particles, such as nuclear reactors or space environments. It is important to understand the basic mechanisms of defect formation and the kinetics governing their behavior and interaction. Kinetics are strongly driven by temperature. In studying the formation of radiation-induced defects at elevated temperature and their isothermal stability, valuable insights into these mechanisms can be deduced. Many of the previous investigations at elevated