The interaction of dislocation loop and γ' precipitate in nickel based alloys

Abstract

The nucleation and growth of interstitial loops during irradiation has a : ontrolling effect on the subsequent swelling behaviour of metals. In nickel based alloys containing ordered γ' precipitate (Ni₃Al, Ti), interactions occur between the nucleated loops and γ' particles. This effect has been studied in two nickel based alloys using a High Voltage Electron Microscope. For the case of Nimonic 80A alloy containing 18% volume fraction : gamma;' precipitate, dislocation loop-particle interactions obeyed the developed isotropic elasticity theory.²'³'¹² Consequently, rather low dislocation densities were developed and the swelling resistance was high during electron irradiation. In Nimonic 115A alloy, loop nucleation and growth was dependent on the availability of interfacial dislocation surrounding the γ' particles. With regard to the swelling behaviour of γ' hardened alloys, it : s concluded that several mechanisms contribute to make these materials resistant. Coherency strains at the γ' particles reduce the density of : limbing dislocations. The γ' precipitate affects the climb efficiency of the : ucleated dislocations by: pinning the dislocation line, thus introducing a line tension force : hich opposes dislocation climb and reduces swelling; reducing the available volume of material in which dislocation loops : an nucleate and grow.