In-situ HVEM studies of radiation-induced segregation in Ni-Al alloys during simultaneous irradiation with electrons and ions

The effects of 75-keV Ne{sup +} and 300-keV Ni{sup +} bombardment on electron radiation-induced segregation (RIS) in a Ni-9at.% Al alloy were investigated in-situ using the HVEM (high voltage electron microscope) / Tandem accelerator facility at Argonne National Laboratory. The radial component of defect fluxes generated by a highly-focused 900-keV electron beam was used to induce segregation of Al atoms towards the center of the electron irradiated area via the inverse Kirkendall effect. The radial segregation rate was monitored by measuring the increase in the diameter of the Al enriched zone within which {gamma}{sup `}-Ni{sub 3}Al precipitates form during irradiation. Both dual electron-ion and pre-implanted ion- electron irradiations were performed in an attempt to separate the contributions of energetic displacement cascades and implanted ions acting as defect trapping sites to RIS suppression. It was found that 75-keV Ne{sup 3} implantation has a retarding effect on RIS

Effects of ion implantation and temperature on radiation-induced segregation in Ni-9Al alloys

Effects of Ne and Sc implantation on radiation-induced segregation (RIS) in Ni-9at.%Al were studied in-situ using the high-voltage electron microscope/Tandem accelerator at ANL. A highly-focused 900- keV electron beam generated radial defect fluxes which, in turn, induced transport of Al atoms toward the center of the electron- irradiated area via the inverse Kirkendall effect. Radial segregation rate of Al atoms was monitored by measuring the diameter of the {gamma}{prime}-Ni{sub 3}Al zone which formed in the Al-enriched area during irradiation. Ne and Sc implantation effects on RIS were investigated at 550 C; Ne effects were also examined at 625 C to determine effect of temperature on ability of Ne to act as defect trapping sites, causing RIS suppression. It was found that the RIS suppression effect of Ne increased with irradiation temperature and that Sc had a small RIS suppression effect which increased with Sc implantation dose. Ne bubbles which formed during implantation are believed to be responsible for its strong suppression effect. 6 figs, 12 ref

Effects of Ion Implantation and Temperature on Radiation-Induced Segregation In Ni-9Al Alloys

Effects of Ne and Sc implantation on radiation-induced segregation (RIS) in Ni-9at.%Al were studied in-situ using the high-voltage electron microscope/Tandem accelerator at ANL. A highly-focused 900- keV electron beam generated radial defect fluxes which, in turn, induced transport of Al atoms toward the center of the electron- irradiated area via the inverse Kirkendall effect. Radial segregation rate of Al atoms was monitored by measuring the diameter of the {gamma}{prime}-Ni{sub 3}Al zone which formed in the Al-enriched area during irradiation. Ne and Sc implantation effects on RIS were investigated at 550 C; Ne effects were also examined at 625 C to determine effect of temperature on ability of Ne to act as defect trapping sites, causing RIS suppression. It was found that the RIS suppression effect of Ne increased with irradiation temperature and that Sc had a small RIS suppression effect which increased with Sc implantation dose. Ne bubbles which formed during implantation are believed to be responsible for its strong suppression effect. 6 figs, 12 ref

Disorder-induced amorphization

Many crystalline materials undergo a crystalline-to-amorphous (c-a) phase transition when subjected to energetic particle irradiation at low temperatures. By focusing on the mean-square static atomic displacement as a generic measure of chemical and topological disorder, we are led quite naturally to a generalized version of the Lindemann melting criterion as a conceptual framework for a unified thermodynamic approach to solid-state amorphizing transformations. In its simplest form, the generalized Lindemann criterion assumes that the sum of the static and dynamic mean-square atomic displacements is constant along the polymorphous melting curve so that c-a transformations can be understood simply as melting of a critically-disordered crystal at temperatures below the glass transition temperature where the supercooled liquid can persist indefinitely in a configurationally-frozen state. Evidence in support of the generalized Lindemann melting criterion for amorphization is provided by a large variety of experimental observations and by molecular dynamics simulations of heat-induced melting and of defect-induced amorphization of intermetallic compounds