Study On The Micromechanical Behavior Of Polycrystalline Beryllium Surface

Because of its excellent physical and mechanical properties such as high hardness,high meltingpoint,high specific heat and dimensional stability,beryllium metal is widely used in aerospace,automobile manufacturing,nuclear weapons manufacturing and other fields.At present,the research on the properties of beryllium metal mainly focuses on the macro scale,and the exploration of its mechanical behavior at the micro-nano scale is still in its infancy.Beryllium is a polycrystalline material,and the random distribution of grain orientation has a great influence onthe mechanical properties of beryllium.Therefore,it is important to obtain information about the excitation response of beryllium mechanics.In this paper,thecontinuous stiffness measurement module of the nanoindentation micromechanical test and assembly system is used to perform nanoindentation test on polycrystalline beryllium under normal temperature conditions,and five nanoindentation tests of 10 mN,15 mN,20 mN,25 mN and 30 mN are applied to it,and the response of nano-indentation behavior to the mechanicalbehavior of polycrystalline beryllium is deeply explored,and the indentation morphology afterindentation test and EBSD technology are combined with scanning electron microscopy to obtain the different crystal plane orientations of polycrystalline beryllium grains.The influence of different crystals of beryllium on its microscopic hardness,elastic modulus,residual area,elastic work,plastic work,stiffness and other mechanical parameters is analyzed.Finally,the nano-indentation loading and unloading process is analyzed numerically,and the effects of residual stress and grain size on hardness,load-depth curve,residual depth and other parameters are explored.The stress mechanism of beryllium metal is deeply revealed,and the mechanical properties of beryllium metalare provided as a reference for the application of beryllium metal.This article concluded the following:(1)The microscopic hardness H and elastic modulus E decreased with the increase of the maximum pressure depth hmax and gradually stabilized,reflecting the indentation size effect.Themaximum load is not sensitive to changes in microhardness and modulus of elasticity.(2)Elastic work We,plastic work Wp,and total work Wt all increased with the increase of the maximum load,and the proportion of plastic work η has no necessary correlation with the change of the maximum load Pmax.Under the same maximum load,both the plastic work Wp and the total work Wt increased with the increase of residual depth hf(Olliver-Pharr method acquired),while the elastic work We tend to decrease with the increase of residual depth.(3)The residual depth hf,the residual depth hfsem(SEM acquired),the maximum pressure depth hmax and the maximum force Pmax are positively correlated once as a function,and the residual depth hf,the residual depth hfsem and the contact depth hc increased with the increase of the maximum pressure depth hmax.(4)The grain orientation has a significant effect on the load-compression depth curve(P-h curve).Under the same load conditions,the anisotropy of polycrystalline beryllium significantly decreased the microscopic hardness H,elastic modulus E and stiffness S of the material,and significantly increased the residual area Af and plastic work Wp and proportion of plastic work η increased with the increase of grain angle θ under the same maximum load Pmax.(5)The p-h curve simulation results of ABAQUS finite element software simulating the nanoindentation indentation and unloading process are in good agreement with the experimental curve,which verifies the accuracy of the model.The residual tensile stress has a tendency to increase the size of the indentation and the hardness to decrease,while the residual compressive stress has a tendency to decrease the size of the indentation and increase the hardness.The increase of grain size increases the indentation depth and reduces the hardness.