Abstract
Multiple-layer dislocation loops of varied character were observed and analyzed in pure nickel and Ni-base alloy solid solutions (Ni-Al, Ni-Ti and Ni-Cr) under proton and nitrogen ion irradiation at elevated temperatures (350 to 550 degree C) and generally low doses (up to approximately 6 dpa). The double and triple layer faulted loops observed were most frequently interstitial edge loops lying on left brace 111 right brace with Burgers vectors of the type 1/3 111 direction. Unfaulted triple-layer loops were also observed and analyzed to be perfect prismatic loops, each loop having a different 1/2 110 direction type Burgers vector inclined to the left brace 111 right brace loop planes. A small fraction of the loops consisted of 1/3 111 direction interstitial edge loops with vacancy-type secondary loops. The results are discussed in light of recent theoretical considerations on loop nucleation and growth. It is concluded that impurity enhanced nucleation is the dominant mechanism of multiple loop nucleation.