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A copper-palladium alloy of 52:48 atomic percent composition was irradiated with 14-MeV copper ions, 14.8-MeV neutrons, and 1.8-MeV electrons to determine the order-disorder transformation of this material under different irradiation conditions. Ordered copper-palladium (CuPd) specimens were irradiated with 14-MeV copper ions to doses as high as 5 dpa and at temperatures up to 823 K. Initially disordered samples were irradiated at 473 and 523 K to similar doses. At temperatures below 473 K, initially ordered CuPd was completely disordered at low doses. The effect of the damage rate was found to be secondary within the conditions investigated. The disordering process was accompanied by a change in the crystal structure from body-centered cubic (bcc) to face-centered cubic (fee). Irradiation above 523 K to 3 dpa did not result in any disorder. Rapid reordering due to vacancy motion is believed to be responsible for the conservation of the ordered structure. An initially disordered sample irradiated at 523 K remained disordered, indicating that the radiation-induced transformation depends on the initial state of the material. An order-dependent vacancy migration energy was proposed. Similar samples were also irradiated with neutrons and with 1.8-MeV electrons at cryogenic temperatures. For neutron irradiation, a replacement to the displacement ratio of 24 was obtained, whereas electron irradiation led to a lower ratio of 3, indicating the importance of damage energy spectrum. Isochronal annealing results from the neutron-irradiated samples show that atomic size plays an important role for interstitial reordering. Annealing of the electron-irradiated specimen resulted in a higher state of order than that of the starting material.
ion irradiation, neutron irradiation, electron irradiation, order-disorder transformation, copper palladium alloy, phase transformation
Associate professor, Materials Engineering, Auburn University, Alabama,
Lawrence Livermore National Laboratory, Livermore, CA
University of Wisconsin, Madison, WI