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 alpha (alpha ep), lamellar alpha of micron and submicron scale (alpha lp-i, alpha lp-ii) and transformed beta t (with nano-scale precipitated phases omega/alpha s in beta). Different combinations of strength and plasticity were achieved. It was found that, the different phase interfaces hindered dislocation transferring, and omega/alpha s phase restricted dislocation movements in beta t, which resulted in strength improvement. Moreover, HM was quantitatively char-acterized, then the relationship between HM characteristics and yield strength (Rp0.2), elongation after fracture (A) was precisely deciphered by referring to Hall-Petch formula and mixing law. It was found that the influence of beta t, alpha lp-ii, alpha ep and alpha lp-i on Rp0.2 decreased orderly. The decrease in the thickness of alpha lp-ii and increase in the volume fraction (VF) of beta t, alpha lp-ii, were the most effective methods to improve Rp0.2. For A, the VF of beta t was negatively correlated with it, but the equivalent circle diameter (ECD) of alpha ep and the thickness of alpha lp-i, alpha lp-ii were positively correlated with it. Specifically, alpha ep and alpha lp-ii had a higher contribution to plasticity than alpha lp-i, and the increase in the ECD (or thickness) and VF of alpha ep and alpha lp-ii was most beneficial to improve plasticity.