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

Abstract

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 (αep), lamellar α of micron and submicron scale (αlp-i, αlp-ii) and transformed βt (with nano-scale precipitated phases ω/αs in β). Different combinations of strength and plasticity were achieved. It was found that, the different phase interfaces hindered dislocation transferring, and ω/αs phase restricted dislocation movements in βt, which resulted in strength improvement. Moreover, HM was quantitatively characterized, 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 βt, αlp-ii, αep and αlp-i on Rp0.2 decreased orderly. The decrease in the thickness of αlp-ii and increase in the volume fraction (VF) of βt, αlp-ii, were the most effective methods to improve Rp0.2. For A, the VF of βt was negatively correlated with it, but the equivalent circle diameter (ECD) of αep and the thickness of αlp-i, αlp-ii were positively correlated with it. Specifically, αep and αlp-ii had a higher contribution to plasticity than αlp-i, and the increase in the ECD (or thickness) and VF of αep and αlp-ii was most beneficial to improve plasticity.