The diffusivity of B in single crystals (75.9at%Ni) was measured at between 773 and 1345K by means of secondary ion mass spectrometry, using stable 10B and 11B isotopes. It was found that the data (table 80) obeyed an Arrhenius relationship of the form,

D (m2/s) = 1.53 x 10-4exp[-227.6(kJ/mol)/RT]

When compared with Ni self-diffusion in this material, which occurred via thermal vacancies, the B diffusion was found to be 1000 to 10000 times faster. This was compatible with an interstitial diffusion mechanism. It was noted that the diffusion path of the B atoms was affected by their preferred occupation of octahedral sites in the L12 lattice. It was concluded that this behavior could explain the relatively high activation enthalpy for interstitial atom migration in the ordered compound.

Fast Diffusion of Boron in the Intermetallic Compound Ni3Al. Frank, S., Sodervall, U., Herzig, C.: Intermetallics, 1997, 5[3], 221-7

Table 81

Arrhenius Parameters for Diffusion in Ni3Al