The diffusivity was measured, at temperatures ranging from 1004 to 1422K, by using 2 techniques to determine the concentration profiles. The diffusion of 63Ni radiotracer in polycrystalline 75.2at%Ni samples was monitored at temperatures ranging from 1223 to 1422K by using serial sectioning and liquid scintillation counting techniques. At 1004 to 1259K, the profiles were measured by means of secondary ion mass spectrometry, using a highly-enriched 64Ni tracer and crystals of 75.9at%Ni material. It was found that the diffusion coefficient obeyed a linear Arrhenius relationship:

D(m2/s) = 0.000359 exp[-303(kJ/mol)/RT]

This suggested the operation of a vacancy mechanism. It was concluded that Ni self-diffusion in this material occurred only via thermal vacancies. This conclusion was in accord with studies that had shown that, regardless of the composition, no constitutional vacancies were to be found in this compound.

S.Frank, U.Södervall, C.Herzig: Physica Status Solidi B, 1995, 191[1], 45-55

Table 164

Arrhenius Parameters for 59Fe Grain Boundary Diffusion in Ni3Al