| Since the discovery of graphene,it has attracted great interest from scientists because of their special optical,electrical,thermal,and mechanical properties.In particular,when graphene is used as a coating material,it can significantly improve the thermal,optoelectronic,anti-corrosion and anti-wear properties of the substrate material.The interfacial behaviors of graphene coatings on substrate aluminum materials are investigated using the molecular dynamics（MD）method.The main research contents are organized as follows:（1）The influences of tensile strain rate and temperature on the interfacial properties of multilayered graphene are investigated using the classical MD simulation method.The results show that the interfacial strength increases with the increase of the tensile strain rate.However,when the loading rate is increased to 1e10 s-1,the interfacial strength tends to be stable.In addition,the study also shows that the interfacial strength increases with the increase of temperature,but when the temperature reaches 350K,the interfacial strength decreases,which is due to the temperature effect of the thermal expansion coefficient of multi-layer graphene.Moreover,the parameters of the cohesive zone model of interlayer interfaces in the multilayer graphene are obtained based on our MD results.（2）A cohesive zone model（CZM）based on a traction-separation（T-S）relation is developed to simulate the interfacial behavior between graphene-coating and aluminum（Al）substrate.The CZM parameters,which are very difficult to be obtained directly from experiments,are determined using the MD simulation.Specifically,the MD simulations under the normal and shear loadings are conducted on graphene-coating/Al interface to derive its T-S relation and then the relevant interfacial behavior for the composite is identified.The MD results show that the behavior of the interface between graphene-coating and Al substrate under normal and shear loading is temperature dependent.The maximum normal tensile stress at the interface decreases gradually,when the temperature increases from 150 K to 600 K.But the maximum shear stress increases firstly as temperature increases from 150 K to 450 K and then decreases as temperature increases from 450 K to 600 K.In the end,the CZM parameters are determined and then imported into the finite element（FE）model.The blister test results obtained by the FE method are in good agreement with those obtained by the MD simulations.These results suggest the proposed approach is efficient in determining the CZM parameters of the interfacial behavior between the substrate and the ultrathin coating.（3）In addition,the interfacial properties between the graphene coating and the defective aluminum（GA-defect）are investigated using the MD simulation method.The results show that the influence of defects on the interfacial properties of the system decreases with the increase of the defect Q value（Q is the distance from the center of the rectangular defect to the surface of the Al matrix）.The results also show that the change in the P value of the defect（P value is the length of the bottom of each isosceles triangle in the serrated defect）causes changes in the Al-C bond and van der Waals forces,which affects the strength of the tensile strength and the cohesive energy.（4）The influences of graphene layers and temperature on the interfacial properties of multilayered graphene-coating/Al substrate system are investigated using the tensile simulation and bulging tests.Tensile load simulations show that when the number of graphene layers is less than three layers,the maximum tensile strength and cohesive energy increase,and when the number of graphene layers is greater than three layers,the maximum tensile strength and cohesive energy decreases,which is due to the range of Van der Waal’s force;In addition,the bulging test simulation show that the reaction force increases with the increase of the number of graphene layers.However,when the graphene layer is more than seven layers,the reaction force tends to be stable.Finally,tensile load simulations also show that the maximum tensile strength gradually decreases with the increase of temperature.And the blister test simulations also show that the reaction force decreases with the increase of graphene layers under the temperature of 600K,when the temperature is higher than or equal to 600K,we find that the variation of reaction force is abnormal.This phenomenon may be related to the softening of aluminum substrate.We find through the simulation that the results obtained by the two methods are different.The main reason is that the interface strength between the graphene layers is less than the interface strength of the graphene/Al,which causes the multi-layer graphene to be set as the loading region for the tensile simulation,and the bulging test pushes off multilayer graphene,so the graphene does not require additional processing and is more reasonable in the interface performance test. |
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