The statistical theory of flow stress, including yield strength, for polycrystalline materials under quasi-static plastic deformation suggested in [arxiv:1803.08247[cond-mat.mtr-sci], arxiv:1805.08623[cond-mat.mtr-sci]] is developed in the framework of a two-phase model. Analytic and graphic forms of the generalized Hall-Petch relations are obtained for samples with BCC (alpha-phase Fe), FCC (Cu, Al, Ni) and HCP (alpha-Ti, Zr) crystalline lattices at T=300K with different values of grain-boundary (second) phase. The maximum of yield strength and respective extremal grain size of the samples are shifted by changing of the second phase. Temperature dependence in the range 100-350K for yield strength (using the example of Al) revealed its increase for closely packed nano-crystalline samples with the growth of temperature. An enlargement of the second phase in a sample neutralizes this property.
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