MEASUREMENT OF IMPURITY DIFFUSION OF Al IN Ni AND (beta)-Ti BY LASER INDUCED BREAKDOWN SPECTROMETRY (LIBS)

摘要

Laser Induced Breakdown Spectrometry (LIBS) has been used to determine the impurity diffusion coefficients of Al in Ni and (beta)-Ti over the temperature range of 1273 to 1623 K and 1223 to 1573 K, respectively. The volume diffusion coefficients for Al in Ni and impurity diffusion found in this study are in good agreement with previously published result obtained by SIMS measurements and ranged from 3.78 X 10~(15) to 1.92 X 10~(12) m~2s~(-1) . It was also found that the diffusivities of Al between 1573 and 1623 K (i.e., just below the melting temperature, T_m=1728 K) are higher than those expected, assuming a linear temperature dependence on an Arrhenius plot. These positive deviations from an Arrhenius line indicate the possibility of a divacancy diffusion mechanism. To clarify this phenomenon, more careful experiments will be needed. The grain boundary diffusion coefficient s(delta)D_(gb) was also calculated by using the volume diffusivity and processing the tails of the measured profiles. The temperature dependence of the grain boundary diffusion coefficients can be expressed by linear Arrhenius equations. The values of activation energy for volume and grain boundary diffusion were 290 and 187 kJmol~(-1), respectively. Moreover, the volume diffusion coefficients for Al in (beta)-Ti impurity diffusion found in this study are significantly larger than those found in previous investigations, and show a non-linear behavior with a distinct upward curvature with increasing temperature. It is evident that such unusual experimental values resulted from the impurities, especially Fe, Si, O in the Ti specimen during annealing, as shown in the results of chemical analyses. Such impurities are supposed to accelerate the Al impurity diffusion in the matrix. The grain boundary diffusivity s(delta)D_(gb) was also calculated by using the volume diffusivities and processing the tails of the measured profiles. The temperature dependence of the grain boundary diffusion coefficients can be expressed by linear Arrhenius equations. The values of pre-exponential factor and the activation energy for grain boundary diffusion were 4.13 X l0~(-6) m~3s~(-1) and 258 kJmol~(-1), respectively. The value of the activation energy is about 77 kJmol~(-1) smaller than that previously found for volume diffusion.