Grain boundary diffusion of Ni in NiTi shape-memory alloy

Ni grain boundary diffusion was measured in slightly Ti rich polycrystalline NiTi shape-memory alloy in the temperature range of 428-678K. Grain boundary tail in the penetration plots could only be detected below 700 K. The temperature dependence of the grain boundary triple product P (P=delta D(b)k, delta: grain boundary width, D-b: grain boundary diffusion coefficient, k: segregation factor) can be represented by the following Arrhenius parameters: preexponential factor: P-0=2.6x 10-(18) m(3)s(-1), activation energy: Q(b)=90 kJmol(-1). The order of magnitude of the triple product NiTi at a reduced temperature scale is similar to that of the grain boundary diffusivity measured in other B2 systems, but the detection of it is difficult, because there is not enough contrast between the volume and the grain boundary diffusion.