Ultra-fast diffusion rates were largely reported in ultrafine-grained (UFG) materials procuded by severe plastic deformation (SPD) and were explained by the formation of specific non-relaxed high-angle "deformation-modified" grain boundaries exhibiting an increased free energy density, higher diffusion rates and a significant residual microstrain [1]. The increase of the grain boundary (GB) diffusion coefficients accounts for one to several orders of magnitude with respect to relaxed interfaces with similar misorientation characteristics [1]. In this work, using both radiotracer and SIMS techniques [2] Cr diffusion in UFG Ni was investigated at low temperatures ranging from 403 to 603 K and a whole spectrum of possible grain boundary states was addressed. The combination of the two methods provided unprecedented insights into structure properties relationships in severely deformed Ni. Abnormally high diffusion rates of Cr are measured and the presence of the deformation-modified state of a fraction of the high-angle GBs is verified. For the first time, a co-existence of relaxed and deformation-modified high-angle GBs in UFG Ni is unambiguously established, addressing the different interfaces by different techniques on the same samples. The temperature/time evolution of the deformation-modified state of high-angle GBs is followed by dedicated measurements of the atomic transport and the microstructure characteristics. The combination of the two complementary techniques allows a unique cross-scale multi-level characterization of the grain boundary diffusion properties spread over a large number of orders of magnitude in the same material. References [1] X. Sauvage, G. Wilde, S.V. Divinski, Z. Horita, R.Z. Valiev, Materials Science and Engineering: A. 540 (2012) pp. 1-12. [2] D. Gärtner, L. Belkacemi, V.A. Esin, F. Jomard, A.A. Fedotov, J. Schell, J.V. Osinskaya, A.V. Pokoev, C. Duhamel, A. Paul, S.V. Divinski, Diffusion Foundations. 29 (2021) pp. 31-73.