Tensile Mechanical Behaviors Of In Situ Ti-Based Metallic Glass Matrix Composites

Due to the unique internal structure of metallic glass (MGs), MGs exhibit superior mechanical properties, the tensile strength of MGs approaches to the perfect crystal. The discovery of metallic glasses triggered a flood of research on MGs, and MGs have great potential to be utilized as structural materials. MGs have excellent hardness, strength, stiffness, and elastic limit. However, the room-temperature brittleness and strain-softening are not only the most serious problems which limit their engineering applications, but also limits the research of the deformation mechanism. The introduction of the second crystal phase to the amorphous matrix to form composite can significantly improve tensile ductility, based on the well ductility, the deformation mechanism and dendrite size dependence of tensile plasticity are discussed.A new Ti-based metallic glass matrix composites (MGMCs) are fabricated, which contain～41vol%of large dendrites with a size of～0.8-1.2μm, The newly developed Ti-based MGMCs exhibit excellent tensile strength of～1,650MPa and a tensile strain of-2.5%at room temperature. During the tensile deformation, the work hardening is scarcely found in this alloy. Thus, the deformation of the in-situ metallic glass matrix composite is simply described with two stages:(1) elastic and (2) softening deformation stages. Two simple models are adapted to simulate each stage. In the supercooled liquid region (at613K), superplastic homogeneous deformation, which is the feature of monolithic BMGs, is not observed. The mechanical properties at613K are sensitive to the strain rates, the yield strength drops from1390MPa to960MPa, when the strain rate decreases from1×10-2/s to1×10-3/s, while the displacement is almost increased by twofold.In-situ dendrite/metallic glass matrix composite (MGMC) with a composition of Ti46Zr2oVi2Cu5Bei7exhibits ultimate tensile strength of1510MPa and fracture strain of about7.6%. A tensile deformation model is established, based on the five-stage classification:(1) elastic-elastic,(2) elastic-plastic,(3) plastic-plastic (yield platform),(4) plastic-plastic (work hardening), and (5) plastic-plastic (softening) stages, analogous to the tensile behaviors of common carbon steels. The constitutive relations strongly elucidate the tensile deformation mechanism. In parallel, the simulation results by finite-element method (FEM) are in good agreement with the experimental findings and theoretical calculations. The present study gives a mathematical model to clarify the work hardening of dendrites and softening of the amorphous matrix. Furthermore, the model can be employed to simulate the tensile behavior of in-situ dendrite/MGMCs.Three Ti-based metallic glass matrix composites (MGMCs) with different sizes of dendrites exhibit excellent mechanical properties. Different sizes of dendrites lead to different tensile properties, the size of dendrites plays an important role in gaining the tensile ductility of the in-situ MGMCs. The dependences of the ductility and the size of the dendrites in the in-situ MGMCs can be illustrated by an inverted U-shaped curves. The tensile deformation behavior of the present composites is classified into three stages, each stage and effects of the changed sizes of dendrites are investigated by focusing on the evolution of dislocations in dendrites and shear bands in amorphous matrix.