Dynamic Mechanical Relaxation Behaviors Of Metallic Glasses And Composites

Due to the unique disordered structure,metallic glass has excellent mechanical,physical and chemical properties,such as high strength,high fracture toughness,excellent friction resistance and corrosion resistance.Since the plastic deformation of metallic glass is highly localized in shear bands,it usually lacks plasticity at room temperature due to the rapid expansion of a single shear band.Crystalline phases have been introduced into the glass matrix to hinder the expansion of the shear band and induce multiple shear bands to achieve the purpose of improving plasticity.In addition,since the metallic glass system is in an metastable energy state,it has a complicated structural relaxation behavior.In this paper,the dynamic mechanical relaxation behavior is taken as the main line of research.On the one hand,the dynamic mechanical relaxation behaviors of the ex-situ and in-situ metallic glass composites were studied,and the influence of the crystal on its mechanical relaxation behavior was analyzed;On the other hand,the dynamic mechanical behavior of the Cu₆₄Zr₃₆ metallic glass was studied by molecular dynamic simulation,and the relationship between the microscopic atomic structure and the macroscopic dynamic mechanical behavior was established.The main findings and conclusions are as follows:（1）The evolution characteristics of the dynamic mechanics of Zr-based metallic glass and Ta-doped metallic glass composites with temperature and frequency were studied.The results show that the content of Ta particles added has a significant effect on the mechanical relaxation behavior of Zr-based metallic glass.The main loss modulus curves of the four components were fitted with the help of the Kohlrausch-Williams-Watts（KWW）equation.The fitting parameter₍(2（2） decreased from 0.58 to 0.45 with the increase of Ta content,indicating that the component with high Ta content has greater dynamic non-uniformity.At the same time,as the Ta content increases,the relaxation peak of the loss modulus main curve shifts to the low frequency direction,which means that the presence of the crystalline phase hinders the movement of the amorphous matrix atoms in the system,making it take longer to complete the relaxation process.（2）The dynamic mechanical relaxation behavior of in-situβ-Ti dendrite reinforced Ti₄₈Zr₂₀V₁₂Cu₅Be₁₅ metallic glass matrix composite was studied.It is found that there is an abnormal“shoulder”in the loss modulus curve below the glass transition temperature.Combining the abnormal exothermic peak on the DSC curve and high-resolution transmission electron microscopy image analysis,it is found that the abnormal loss modulus change is caused by the precipitation of new nanocrystals in theβ-Ti dendrite phase during the temperature rise process."Quasi-point defect"model is used to establish the relationship between the correlation factorχand the concentration of atomic defects in the glass matrix.Based on the analysis of atomic mobility,it is found that there is an obvious transition in the dynamic mechanical behavior with the glass transition temperature as the boundary.Under the theoretical framework of"quasi-point defects",the atomic configuration is considered to be hierarchically related,that is,the atomic structure below the glass transition temperature is frozen and its atomic mobility remains unchanged.In addition,as the annealing time increases,the loss modulus gradually decreases and the storage modulus increases,which can be attributed to the decrease in defect concentration and atomic mobility caused by annealing.The expansion exponential relaxation equation is used to describe the evolution of the loss factor tanδwith annealing time.The expansion exponent factorβ_aging reflects the broad distribution behavior of relaxation time,which corresponds to the dynamic non-uniformity characteristics in amorphous materials.（3）The dynamic mechanical relaxation behavior of in-situ metastableβ-Ti dendrite Ti_45.7Zr₃₃Cu_5.8Co₃Be_12.5 metallic glass matrix composites was studied.The study found that the storage modulus showed a large increase in the modulus below the glass transition temperature.This abnormal behavior corresponds to the exothermic peak of the glass transition temperature observed on the DSC curve.After XRD test and high-resolution electron microscopy image combined with selective electron diffraction pattern analysis,it was determined that it originated from the partial metastableβ-Ti toω-Ti phase transition during heating.In addition,the study found that annealing treatment and thermal history effects have a significant effect on the structural relaxation.After the temperature aging treatment,due to the decrease of the defect concentration and the completion of the phase transition fromβ-Ti toω-Ti,the overall amplitude of the storage modulus increases and the behavior of the abnormal modulus disappears.This research provides an idea for regulating the dynamic mechanical behavior of metallic glass and its composite materials in the future.（4）Using molecular dynamics simulation technology,the Cu₆₄Zr₃₆ metallic glass was applied with periodic stress of different loading modes to obtain dynamic complex modulus.The conversion relationship between the different complex modulus was established.The applicability of the principle of dynamic correspondence in metallic glass materials was verified,and the relationship between the elastic constants in statics was extended to the viscoelastic domain,which laid the foundation for the prediction of the dynamic complex modulus of metallic glass under complex loading modes.Under dynamic mechanical loading,the structure of the icosahedral atomic cluster is relatively stable,and remains almost in its original position,thus contributing to the storage modulus（elastic part）,while most other atomic clusters undergo irreversible atomic displacement.It corresponds to the loss modulus（the energy lost due to inelastic deformation）in metallic glass,indicating that the mechanical relaxation behavior originates from the structural heterogeneity of metallic glass.