The diffusion coefficients were measured at 489 to 774K. The 16O was injected by ion implantation. The diffusion penetration profiles were then measured by exploiting the 16O(d,p)17*O nuclear reaction. The temperature dependences of the O diffusivity were described by:

V-1Si:     D(m2/s) = 1.1 x 10-5 exp[-131.5(kJ/mol)/RT]

V-5Fe:     D(m2/s) = 3.0 x 10-6 exp[-128.9(kJ/mol)/RT]

V-5Mo:     D(m2/s) = 2.9 x 10-7 exp[-115.2(kJ/mol)/RT]

V-5Nb:     D(m2/s) = 2.9 x 10-6 exp[-128.3(kJ/mol)/RT]

V-5Cr:     D(m2/s) = 1.0 x 10-7 exp[-110.6(kJ/mol)/RT]

V-3Ti-2Si:     D(m2/s) = 9.0 x 10-5 exp[-163.6(kJ/mol)/RT]

V-5Ti:     D(m2/s) = 3.1 x 10-4 exp[-171.8(kJ/mol)/RT]

It was found that the addition of Si hardly affected O diffusion, whereas the addition of Fe or Nb decreased the diffusivity by 20 to 70%, and the addition of Cr or Mo decreased the activation energy by 10 to 15% (table 320). The most marked alloying effect was observed in the case of the V-3Ti-2Si and V-5Ti alloys. The diffusivity in V-5Ti was about 2 orders of magnitude lower than that in V. It was concluded that this was evidence for a trapping effect due to Ti, and the binding energy was estimated to be about 52kJ/mol.

H.Nakajima, S.Nagata, H.Matsui, S.Yamaguchi: Philosophical Magazine A, 1993, 67[3], 557-71

Table 321

Heats of C Transport in V-Ti Alloys