Grain boundary diffusion and segregation of Ni in Cu

Grain boundary (GB) diffusion of Ni-63 in polycrystalline Cu was investigated by the radiotracer technique in an extended temperature interval from 476 to 1156 K. The independent measurements in Harrison's C and B kinetic regimes resulted in direct data of the GB diffusivity D-gb and of the so-called triple product P = s center dot delta center dot Dgb (s and delta are the segregation factor and the diffusional GB width, respectively). Arrhenius-type temperature dependencies for both the Dgb and P values were measured, resulting in the pre-exponential factors D-gb(0) = 6.93 x 10(-7) m(2) s(-1) and P-0 = 1. 89 x 10(-16) m(3) s(-1) and the activation enthalpies of 90.4 and 73.8 kJ mol(-1), respectively. Although Ni is completely soluble in Cu, it reveals a distinct but still moderate ability to segregate copper GBs with a segregation enthalpy of about 17 kJ mol(-1). (C) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.