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Valiev. Microstructures 2023;3:2023004 https://dx.doi.org/10.20517/microstructures.2022.25 Page 3 of 9

Figure 1. Two types of Hall-Petch slopes within different characteristic length scales: d - grain size, below which the contribution of
cr1
nanostructural features (nanoparticles, substructure and others) becomes significant in the strengthening of SPD-processed materials;
d - grain size, below which the contribution of grain boundary segregation and non-equilibrium grain boundaries becomes significant
cr2
[5]
in UFG materials. Reproduced with permission, Copyright 2013, John Wiley and Sons .

Figure 2. Hall-Petch relationships for Al 1100 and Al-3%Mg supported by the yield stress of nanostructured alloys Al-3%Mg, 1570 and
[11]
7475. Reproduced with permission, Copyright 2010, Elsevier .

This study pays special attention to experiments achieving a high-strength state in commercially pure (CP)
Ti Grade 4 subjected to processing by ECAP and HPT. The material (composition, wt.% Fe - 0.5, O - 0.4,
C - 0.08, N - 0.05, H - 0.015 and Ti - base) is favored by medical professionals for its biocompatibility and is
2
a popular material for medical applications. CP Ti is widely used for implants because its strength is crucial