High-voltage electron irradiation studies of several overaged γ/γ' alloys

Abstract

Abstract The formation of irradiation-induced dislocation loops was studied in four Ni-base γ/γ' alloys, severely overaged so that the influence of individual γ/γ' interfaces could be investigated. The alloys, Ni-14.07% Al, Ni-12.68% Si, Ni-18% Cr-7% Al and Nimonic PE-16 were irradiated, using 1 MeV electrons, for various times at an irradiation temperature of 425° C to produce dislocation loops. Void formation was also induced in overaged PE-16 at an irradiation temperature of 490° C. In the binary alloys the distribution of dislocation loops was fairly uniform throughout the γ and γ' phases, the semicoherent interfaces having no apparent influence on loop formation. The Ni-Si alloy was more radiation damage resistant than the Ni-Al alloy. In the ternary alloy the nucleation and growth of dislocation loops were evidently somewhat easier in the matrix than in the γ' phase, but the coherent γ/γ' interfaces did not influence the spatial distribution of loops. The situation in PE-16 was vastly different; both dislocation loops and voids nucleated and grew preferentially in or near the coherent γ/γ' interfaces. A model is proposed which qualitatively accounts for these observations by invoking the large difference in the chemical constituents of the γ and γ' phases in PE-16 and the manner in which this factor affects the production of Frenkel pairs and the nucleation of dislocation loops and voids. Some consequences of this model are briefly discussed.