No abstract

Self-diffusion in chromium single crystals has been measured over the temperature range 1073 to 1446 K. These data, when combined with earlier measurements from this laboratory over the. range 1370 -2090 K, yield a plot of lnD vs 1/T, which is straight over ten orders of magnitude in the diffusion coefficient D. The high values of the preexponential factor (1280+ 230 cm's ') and activation enthalpy (4.58+ 0.03 eV) are not readily interpreted in terms of a specific diffusion mechanism. They appear to be too high to be interpreted in terms of a monovacancy mechanism. The possible contribution of divacancies and self-interstitials are discussed.

The diffusion of. "Nb in niobium has been measured between 1353 and 2693 K. The data showed nonlinear Arrhenins behavior and fit the expression D = [8 X 10 'exp ( -3.62 eV/kT)+ 3.7exp ( -4.54 .eV/kT)] cm'sec '. The data are interpreted in terms of a single-vacancy-divacancy mechanism. The effect of oxygen on niobium self-diffusion was measured over the temperature range 1750 -2690 K. There was no measurable difference in the diffusion coefficient obtained from samples with 500-wt-ppm 0, and samples with less than 10-wt-ppm 0,.

No abstract

No abstract