Deciphering the quantitative relationships between age-induced hierarchical microstructure characteristics and tensile properties of Ti20C alloy

Hierarchical microstructure (HM) shows excellent comprehensive properties, but the relationship between mechanical properties and HM characteristics is not clear. In this work, seven HMs of Ti20C were tailored by aging treatments, containing equiaxed α (α_ep), lamellar α of micron and submicron scale (α_lp-i, α_lp-ii) and transformed β_t (with nano-scale precipitated phases ω/α_s in β). Different combinations of strength and plasticity were achieved. It was found that, the different phase interfaces hindered dislocation transferring, and ω/α_s phase restricted dislocation movements in β_t, which resulted in strength improvement. Moreover, HM was quantitatively characterized, then the relationship between HM characteristics and yield strength (R_p0.2), elongation after fracture (A) was precisely deciphered by referring to Hall-Petch formula and mixing law. It was found that the influence of β_t, α_lp-ii, α_ep and α_lp-i on R_p0.2 decreased orderly. The decrease in the thickness of α_lp-ii and increase in the volume fraction (VF) of β_t, α_lp-ii, were the most effective methods to improve R_p0.2. For A, the VF of β_t was negatively correlated with it, but the equivalent circle diameter (ECD) of α_ep and the thickness of α_lp-i, α_lp-ii were positively correlated with it. Specifically, α_ep and α_lp-ii had a higher contribution to plasticity than α_lp-i, and the increase in the ECD (or thickness) and VF of α_ep and α_lp-ii was most beneficial to improve plasticity.