Study On Mechanical Properties Regulation And Deformation Behavior Of Ti-based Metallic Glass Composites

The unique structure of metallic glasses gives them some excellent properties.Nowadays,in-situ metallic glass composites which introducing?-stabilizer element to precipitate the body-centered cubic dendrites in the metallic matrix during rapid solidification have been rendered as an effective way to alleviate the catastrophic brittle failure caused by the unobstructed propagation of individual shear band in monolithic bulk metallic glass.In order to study the discretization of mechanical properties of metallic glass composite and realize the active and accurate control of its mechanical properties,some measures such as thermal cycling treatment,high pulse magnetic field and interstitial element addition were adopted to change the internal structure of amorphous matrix and dendrites.Based on this,this paper carried out studies on the compression,tensile and low-temperature mechanical properties of interstitial elements on Ti-based metallic glass composites,as well as the analysis on the micro-deformation mechanism,and obtained some research results as follows:(1)The effect of thermal cycling was shown to be negligible for Ti-based metallic glass composites,and the strengthening effect of pulsed magnetic field treatment on dendrites is also relatively weak due to the effect of amorphous matrix.(2)An effective method to control the mechanical properties of Ti-based metallic glass composites:The deviation of the content of interstitial elements will cause great dispersion to the mechanical properties of metallic glass composites,and different interstitial elements have different effects on the properties.Since even the introduction of nitrogen as high as 14000 PPM in the composite will not cause the instability of amorphous matrix.The material obtained the ultra high yield strength of 2350 MPa and still had a certain compression plasticity at room temperature.Therefore,the addition of nitrogen can be used as an effective means to actively regulate the mechanical properties of Ti-based metallic glass composites.(3)The cause of the embrittlement of Ti-based amorphous composites caused by excess oxygen element and the failure mechanism in the process of deformation:Excessive oxygen in the amorphous matrix will harm its glass forming ability and thermal stability.The result of instability of the amorphous matrix is the formation of local nanocrystals in the amorphous matrix and the formation of multi-oriented nanoscale polycrystalline particles near the dendrite in the amorphous matrix.The chains of polycrystalline particles that surround the dendrites destroy the good two-phase interface in metallic glass composites.The interface between the harder precipitated polycrystals and the matrix will exhibit a higher stress concentration and preferential formation of shear bands during deformation.The distance between each polycrystal is very small,which is conducive to mutual absorption of adjacent shear bands and the formation of microcracks.These nanoscale polycrystalline phases cannot prevent the microcracks from spreading.Thus,microcracks will form at the position of the polycrystalline phase and pass through the crystals one by one.(4)A new microscopic coordinated deformation model of Ti-based bulk metallic composites during tensile deformation:Different from the two previously found deformation modes of‘tensile'and‘shear',this mode is characterized by the irregular but completely fitted deformation steps between the two dendritic fragments which are separated by the tortuous matrix.This model describes the coordinated deformation behavior of dendrites and matrix in the microscopic plastic flow process and can be used to interpret the good balance of strength and ductility of metallic glass composites.(5)The reason of low temperature plasticity of Ti₄₈Zr₂₀Nb₁₂Cu₅Be₁₅ metallic glass composites and the optimum service temperature of metallic glass composites:The amplification effect of low temperature environment on the sensitivity of interstitial elements of composites is the reason for the dispersion of mechanical properties of metallic glass composites at low temperature.In addition,the change of shear modulus of dendrite and amorphous matrix with temperature can also explain the good low temperature plasticity of Ti₄₈Zr₂₀Nb₁₂Cu₅Be₁₅ metallic glass composite.With the decrease of ambient temperature,the yield strength of amorphous matrix and dendrite increases synchronously.Due to the difference of strength growth rate between amorphous matrix and dendrite in the process of temperature reduction,there will be an extreme point of strength difference between them.Based on this,it is proposed that there is an optimal service temperature of amorphous composites with both strength and plasticity increasing,and the optimal service temperature of Ti₄₈Zr₂₀Nb₁₂Cu₅Be₁₅amorphous composites is preliminarily predicted.