Enhancing strength-ductility synergy of TiBw/Ti55 composites by introducing a bimodal grain structure

The enhancement of strength-ductility synergy of discontinuous titanium matrix composites (TMCs) during thermomechanical processing is of great importance for the application of manufacture components in the aerospace industry. This work aimed to enhance the strength-ductility synergy of TiB whisker reinforced Ti55 (TiBw/Ti55) composites by introducing the heterogeneous microstructure into TMCs via the hot-forging technique. The Ti55 alloy and TiBw/Ti55 composites were first isothermally compressed in order to construct the processing maps for optimizing the hot-forging parameters. A bimodal grain structure (BGS) consisting of submicron and micron α grains was introduced in the hot-forged Ti55 alloy and TiBw/Ti55 composites due to the occurrence of dynamic recrystallization, and the network architecture of TiBw in TMCs was preserved by applying a height reduction of 30 %. The yield strength and ultimate tensile strength of TMCs increased by >150 MPa by applying the hot-forging, wherein there was no loss of elongation. The Ti55 alloy showed an increase in strength but a decrease in elongation from 13.8 % to 9.6 % by applying the hot-forging. The submicron α grains and dislocations introduced by hot-forging effectively strengthened Ti55 alloy and TMCs, and the hot-forging induced TiBw rotation also strengthened TMCs to a minor extent. The enhanced strength-ductility synergy in TMCs was due to the effective load transfer from the matrix to the TiBw alleviated the strain-hardening effect in the Ti55 matrix of TMCs and thus there was the space for the micron α grains to carry further deformation.