Mechanical Analysis Of Low Melting Point Alloy Based On AFM Nano Indentation Experiment

With the emergence of nano science and technology,the characteristics of materials at the nano-scale are favored by many domestic and foreign researchers.Study on mechanical properties of nanoscale materials are increasingly being the focus of attention.Low melting point alloy refers to fusible alloy melting point of232?.This article used low melting point alloy Bi_31.6Sn_19.6In_48.8 as the object of study,with melting point at ⁶0?.It could be widely used in thermal conductivity for the modern high-speed computers or microelectronics.Nowadays,for Bi_31.6Sn_19.6In_48.8studies mostly have focused on the melting point,expansion rate,density and other parameters.But it is relatively little research on the mechanical properties of Bi_31.6Sn_19.6In_48.8 hardness,Young's modulus and viscoelastic parameters.Therefore this article tries to use AFM indentation study on mechanical properties of Bi_31.6Sn_19.6In_48.8.The Oliver-Pharr method is used to calculate nano hardness and Young's modulus of the low melting point alloy from load-indentation depth curves.The experimental results show that under certain loading rate,the indentation depth increased non-linearly with the increase of indent force.And it has certainly elastic recovery and permanent deformation.The absolute indentation depth increases gradually with the increasing of indent forces,however,resident depth behaves differently.It could be attributed to the heterogeneous structure in low melting point alloy.There is no significant difference between these hardness data at same loading levels.Hardness of Bi_31.6Sn_19.6In_48.8 does not show an obvious decrease with the increase of indent forces.This means that no size effect is presented in hardness.By contrast,Young's modulus decreases gradually with the increasing of indent forces.This size effect is commonly thought to arise from the confining effect of the fine grain sizes in Bi_31.6Sn_19.6In_48.8.In the original experiment,each loading rate individually by 0.848?m/s,1.01?m/s,2.01?m/s,5.37?m/s loads to the maximum load,and then unload the loading process at the same rate to 0.With increasing loading rate,Bi_31.6Sn_19.6In_48.8 measured nano hardness and Young's modulus increases.It shows Bi_31.6Sn_19.6In_48.8 nano hardness and Young's modulus measurements correlated with a loading rate.On the basis of the original AFM indentation experiment,through the lowmelting point alloy and the low melting point alloy doped with 0.1% graphene respectively contained 20 s.Under the influence of a constant indentation depth,it analysis of stress with time gradually decay,and then get its viscoelastic parameters.The experimental results show that under the influence of a constant indentation depth,both samples exhibit stress relaxation then quickly within about 20 s tend invariant properties.And indentation force relaxation of the low melting point alloy doped with0.1% graphene is greater than the low melting point alloys.The low melting point alloy doped with 0.1% graphene becomes very soft.It instantaneous modulus decrease of about 60%.That is load-deformation curve of the instantaneous compression is more flatter.