Ag grain boundary diffusion and segregation in Cu: Measurements in the types B and C diffusion regimes

Grain boundary (GB) diffusion of Ag-110m in polycrystalline Cu was measured under the conditions of the Harrinson's type B (962-675 K) and type C (565 -452 K) diffusion regimes. In the B-type diffusion regime, the triple produ ct P = s deltaD(gb) (s is the segregation factor and delta the GB width) wa s found to follow the Arrhenius law P =(1.4(-0.4)(+0.6)).10(-15).exp{-[(69. 1+/-2.5)kJ.mol(-1)]/RT} m(3) s(-1). The measurements under the C regime con ditions directly established the temperature dependence of the GB diffusion coefficient D-gb, D-gb = (1.7(-0.5)(+0.7)).10(-4).exp{-[(108.6+/-1.9)kJ.mo l(-1)]/RT} m(2) s(-1). Combining both results and assuming as usual delta c ongruent to5.10(-10) m the segregation factor s was determined to follow an Arrhenius dependence s = s(0) exp (-H-s/RT) with the pre-exponential facto r s(0) = (1.6(-1.0)(+1.4)).10(-2) and the segregation enthalpy H-s= -39.5+/ -4.0 kJ.mol(-1). Experimental conditions were analyzed to figure the factor s resulting in the curvature of the radiotracer profiles. Probable non-line ar segregation was shown to give only marginal (if any) effect. The initial parts of the profiles are well described by accounting for the GB motion d uring diffusion anneal. The analysis shows that a hypothetial dislocation-e nhanced volume diffusion at low temperatures cannot disturb the C-regime co nditions in the present experiments. The very small tracer concentrations a pplied in the types B and C diffusion measurements indeed allow us to estab lish equilibrium GB segregation at negligible concentrations of solute atom s. The results are compared with the available literature data obtained by direct measurements with non-negligible solute concentrations. (C) 2001 Act a Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.