Experimental And Molecular Dynamics Study On Damping Properties Of TiNi-Cu Layered Composites

Damping materials have important applications in many fields such as industry,defense and aerospace.Since the damping performance and elastic performance of traditional single-component metal damping materials are difficult to achieve,and there is often an inverse relationship between the two properties,this work is dedicated to the development of metal-layered composite materials with high damping properties,aiming to coombine the advantages of high elastic modulus and high damping performance of component metal materials.Further more,molecular dynamics method is implemented to explore the microscopic mechanism of metal damping and the effect of compounding on damping performance.In terms of experiments,Ti Ni-Cu-Ti Ni three-layered metal composite material was prepared by spark plasma sintering method.The designed thickness of Cu layer is 0.1,0.2,0.3mm and the thickness of Ti Ni layer is 7mm and 10 mm.The content of Ni atom in Ti Ni is about 50.4 at.%.First,the heat treatment process is determined by the characterization of the raw materials;then the interface structure and fracture surface morphology of the composite material are characterized by optical microscope and scanning electron microscope.The mechanical properties of the composite material are studied using unidirectional tensile experiment and three-point bending.Finally,the damping characteristics of the composite material were studied through dynamic thermomechanical analysis,and the structure of the composite material was optimized.On this basis,the interface structure was designed to obtain higher damping performance.Experiments show that this method can produce dense composite materials.After solution-aging treatment,a diffusion solid solution layer is formed at the interface of the Cu layer and the Ti Ni layer,the tensile strength is greater than 900 MPa,and the elongation is about 9%.The composite material is the most excellent structure is 10 Ti Ni-02 Cu,its low-frequency damping coefficient is as high as 0.055,and the loss modulus is as high as 2800 MPa,which is significantly improved compared with Ti Ni raw materials.Since the mechanical and damping properties of the composite material are higher than the predicted value by the Reuss elastic mechanics model,it is inferred that the composite provides part of the damping,mainly due to caused by the Cu layer and the phase transformation damping led by the diffusion solid solution layer on both sides of the Cu layer and the thermal mismatch effect.The contribution of the thermoelastic damping is small.To further explore the microscopic mechanism of composite damping,nonequilibrium molecular dynamics was applied.The feasibility of the method to simulate the damping effect was first verified,and two criteria for the microstructure of Ti Ni phase transition system were proposed Then for the models of the perfect Ti Ni single crystal under different temperatures,Ti Ni single crystal models with different orientation in martensitic state and Ti Ni model with precipitated phase,the tension and compression cycle simulations with different amplitudes were carried out,and the damping performance was discussed by analyzing the shape and area of the stressstrain hysteresis loop.Finally,for the compounding effect,a Ti Ni model undergoing pre-strain and a series of Ti Ni models containing a certain concentration of vacancies were established to study the contribution of pre-strain and vacancy content to the damping performance.Simulations show that Ti Ni exhibits higher phase transition damping near the martensitic transformation point,the mechanism of which is related to structural fluctuations and the formation of martensite nucleoblasts;the damping performance of martensitic Ti Ni alloy is affected by orientation and amplitude Under certain conditions,the movement of the martensite twin boundaries will lead to strong damping;Ti3Ni4 precipitation phase is incompatible with the deformation of the matrix,which will lead to viscoelastic damping.For composite materials,the model undergoing pre-compression exhibits stronger phase change damping.1% phase change will increase the hysteresis loop area by 45%;on the one hand,the vacancy will suppress the formation of martensite,on the other hand,it will induce hysteresis elastic damping.Through experiments and simulation studies,it can be concluded that Ti Ni-Cu composites made by compounding can effectively increase the loss modulus of metal materials;compounding can improve the damping performance of composites by thermal mismatch strain and introduction of vacancies;molecules The dynamic simulation method is expected to become an advantageous tool for the study of damping mechanism.