Strength and plasticity coordination improvement mechanism in network structure TiBw/TA15 composite via multi-DOF forming

Abstract

TiBw/TA15 composite with network TiB whisker (TiBw) reinforcement architecture, exhibits high strength but limited plasticity, presenting a significant challenge in enhancing the plasticity of TiBw/TA15 composites. In the current work, strength and plasticity coordination improvement of TiBw/TA15 composite is achieved through the application of multi-degrees of freedom forming (multi-DOF forming) technology. The α phase spheroidization behaviour and strength-plasticity coordination improvement mechanisms are investigated. The results elucidate that increasing deformation amount through multi-DOF forming leads to more pronounced α phase spheroidization and refinement. This effect is attributed to the generation of substantial strain along the deformation path, particularly in the regions where hard TiBw particles rotate (i.e., the tips of TiBw). Additionally, the impediment of dislocation movement by TiBw causes dislocations to accumulate along these rotation regions via single slip and cross slip mechanisms, thereby accelerating the α phase spheroidization process. Furthermore, with increasing deformation amount, the strength and plasticity are coordinately improved. The tensile strength and elongation increase linearly from 972 MPa to 1239 MPa (increased by 27.5 %) and from 5.6 % to 7.9 % (increased by 41.1 %) as the deformation condition advanced from the sintered state to the 40 % deformation condition, respectively. Improved plasticity can be attributed to the refinement of grains and TiBw, promoting more uniform plastic deformation and reducing stress concentrations during tensile testing. The strengthening mechanisms encompass load transfer strengthening facilitated by TiBw, grain refinement strengthening and dislocation pinning effect caused by TiBw.