多孔金属薄膜阻尼减振微观机理研究

研究了多孔金属薄膜的阻尼性能和微观机理. 采用分子动力学方法及扫描电镜(SEM) 原位观察实验手段对多孔金属薄膜阻尼进行研究, 得出金属薄膜应变滞后于应力周期性变化以及弹性势能周期性衰减的规律, 并通过应变滞后应力的时间差求得损耗因子; 从微观结构上可看出, 在薄膜孔缺陷附近\langle110angle晶向上经历了位错产生、 并且位错呈阶梯状向前发射的变化; 在SEM原位拉伸、卸载实验中观察到有微裂纹的萌生、斜向阶梯扩展、收缩及消失的周期过程. 结果表明: 在周期载荷作用下, 多孔金属薄膜的孔缺陷附近产生的位错可以挣脱开弱钉扎点并限制在强钉扎点上, 由于位错的变化及附近晶界间的相对滑动产生内摩擦, 消耗了系统的部分弹性势能, 引起金属薄膜的阻尼减振效应, 从而揭示了多孔金属涂层阻尼产生的微观机理.

Micro-mechanism of damping vibration attenuation on porous metal coating

Based on molecular dynamics method and in-situ scanning electron microscopy (SEM) observations, the damping efficiency of the porous metal coating is discussed in this paper. Molecular dynamics simulation is performed to study the plastic deformations of Cu films with vibration. In the simulation, embedded atom method (EAM) is selected and in the method an interatomic potential function is used. And porous copper coating is carried out for calculating by using velocity-verlet algorithm. The plastic deformation is due to the dislocation nucleation near free surfaces, and the dislocation is shaped into forward emission in the <110> crystal orientation near the defects. At the same time, the change curves of stress and strain are drawn by origin software. Damping factor (η) is calculated by using the time of strain lagging stress. The regulation of elastic potential energy attenuation is obtained by energy calculation. On the other hand, in-situ tensile/compression experiment is conducted by the FEI Quanta 200 SEM with a maximum load capacity of 2 kN at room temperature. A copper layer is deposited on the surface of the polyimide film by the electron beam evaporation deposition method. The thickness of the copper layer is 10 μm and the thickness of polyimide is 175 μm. Using the scanning electron microscope, microstructures of the coating are observed. It could be seen that the coating and the polyimide film are both better in compactness. Using in-situ testing machine at SEM, the samples with and without copper coatings are respectively tested under tensile and unloading. The rate of displacement loading is 2 mm/min, the results of load (F) and displacement (l') are printed every 0.1 s. The loading direction is horizontal. During in-situ tensile/compression test, the straining is stopped several times in order to make the observations and take micrographs. The digital SEM images are directly transferred to a computer via a direct memory access type A/D converter, which can rapidly capture clear images of the 1024×943 pixel frames. The simulations and experimental results indicate that the dislocation near defects get rid of weak pinning points and limit to the strong pinning point, the internal friction is generated due to the change of dislocation and the relative sliding near grain boundary, and the stored elastic potential energy is consumed, which causes the damping effect of the film.