Mechanical Property And Microscopic Deformation Mechanism Of In-situ Ti-based Metallic Glass Matrix Composites Deformed At High Temperature

Bulk metallic glasses?BMGs?have received widespread attention from researchers in various countries due to their unique mechanical properties,such as high elastic limit,high yield strength,and excellent corrosion resistance,etc.Nevertheless,when deformed at room temperature,BMGs occur brittle fracture due to the rapid expansion of highly localized shear bands,which limits the practical application of BMGs in structural engineering.In order to improve the macroscopic room temperature plasticity of the BMG,the metallic glass matrix composite?MGMC?is prepared by introducing an in-situ or ex-situ second phase into the metallic glass matrix,and the second phase can effectively hinder the rapid expansion of the single shear band and induce multiple shearing,improveing the macro-plasticity.Ti-based MGMCs have broad application prospects in the aerospace industry due to their combination of high strength,high hardness of BMGs and high specific strength,excellent fracture toughness of Ti alloys.In this paper,the relationship between the microstructure,the applied deformation conditions of Ti-based MGMCs and the high temperature mechanical properties was explored,the high temperature superplastic deformation of the material was achieved.The superplastic deformation mechanism was revealed by high resolution transmission electron microscopy?HRTEM?,the constitutive model was built and the thermoplastic forming?TPF?map was got,then,the mechanical properties of the Ti-based MGMCs after high temperature deformation were studied,which provided experimental and theoretical basis for the actual processing and engineering application of in-situ MGMCs.?1?Uniaxial tensile and compression mechanical properties of Ti₄₇Zr₁₉Be₁₅V₁₂Cu₇?atom%?MGMCs were investigated at high temperature?580K⁷00 K?.It was found that the yield strength decreased with increasing temperature under both conditions,the strength ratio of compression to tension increased with rising temperature.In the supercooled liquid region?SLR?,the superplastic deformation was accompanied by the work hardening under the compressive load,and the plasticity reduced under tensile loading conditions and exhibited strain softening characteristics.Under tensile loading,the increased in local fluctuations and the inhomogeneity between the dendrites and the amorphous matrix leaded to the formation of voids near the interface and the unstable deformation eventually broke.Under compressive loading,the local fluctuation of the strain disappeared and the whole body exhibited stable uniform deformation,which leading to large plastic deformation and even superplastic deformation.?2?Due to superplastic deformation can be achieved under compressive condition in the SLR.Uniaxial compression mechanical behavior of Ti₄₀Zr₂₄V₁₂Cu₅Be₁₉,Ti₅₈Zr₁₆V₁₀Cu₄Be₁₂ and Ti₆₂Zr₁₂V₁₃Cu₄Be₉ were research at various strain rate(1×10^-4/s¹×10^-2/s)and different temperatures?620 K⁶60K?.It was found that with the increase of dendritic size and volume fraction,the raise of strain rate and the decrease of temperature,the yield strength of MGMCs increased.Stress-strain curves not only exhibited Newtonian and non-Newtonian homogeneity deformation characteristic,but also shew distinct work hardening behavior.The strain rate sensitivity of Ti-based MGMCs was dominated by glass matrix,while the work hardening characteristic was related to the high density dislocation in dendritic phases,similar to Ti alloy.The test results were drawn to TPF map according to the deformation mechanism,guiding the thermoplastic forming and processing of Ti-based MGMCs.The constitutive relationship established by the strain-compensated Arrhenius model fitted well with the compression mechanical behavior of Ti-based MGMCs in SLR,providing a good perspective for the thermoforming?such as forging?.?3?The compression behavior of Ti₄₆Zr₂₀V₁₂Cu₅Be₁₇ MGMCs with different compression degrees in SLR was studied.It was found that the dendrites only changed position before the end of stress overshoot,and they underwent severe plastic deformation and existed obvious orientation during the work hardening process.The hardness of the dendritic phase increased continuously,and the hardness of the metallic glass matrix decreased slightly due to the increase of free volume in the overshooting stage.As the strain increasing,the relaxation and crystallization increased the hardness.Furthermore,the mechanical behavior at room temperature was tested.At the peak of the stress overshoot,the yield strength can reach 1800 MPa,and there is of⁴%plastic deformation.At the end of the high temperature stress overshoot,the room temperature still had²%plastic deformation.After plastic fracture,the surface presents a large number of shear steps and molten vein-like shear bands,while the surface is smoother and smoother after brittle fracture.