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 has high strength but poor plasticity. It is challenging to improve the plasticity of TiBw/TA15 composites. In the current work, strength and plasticity coordination improvement of TiBw/TA15 composite is achieved by multi-degrees of freedom forming (multi-DOF forming) technology. The α phase spheroidization behaviour and strength-plasticity coordination improvement mechanism are studied. It is revealed that with increasing deformation amount of multi-DOF forming, α phase spheroidization and refinement become more obvious, and the mechanism is that the rotation of hard TiBw particles causes large strain in the deformation path, i.e., the rotation regions of TiBw tips. Meanwhile, when dislocation movement is blocked by TiBw, the dislocation gradually piles up along the rotation regions of TiBw tips by single slip and cross slip, which accelerates α phase spheroidization behaviour. Moreover, 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 grain and TiBw refinement, which leads to more uniform plastic deformation and fewer stress concentrations in the tensile process. The strengthening mechanism can be attributed to the load transfer strengthening of TiBw, grain refinement strengthening and dislocation strengthening.

Keywords: TiBw/TA15 composite, Network TiB whisker, Multi-DOF forming, Strength and plasticity coordination improvement