Research On Single And Cyclic Dynamic Nanoindentation In Micro/Nano Scales

In the service process,materials often involve high strain rate.For example,micro/nano scale hard films,which protect machining tools,tend to experience high velocity impact under live condition.It is difficult to evaluate properties in the Quasi-static(10^-510^-3 s^-1)method and the traditional kinetic experiment.The nano-impact technology is based on the impact of the pendulum which has high spatial and temporal resolution,the accuracy of the load and displacement,showing obvious advantages in describing the dynamic failure behavior of material at micro/nano scale.However,the main impact experimental parameters of nano-impact,the undenstanding of the contact with the basic physical processes,and the quantitative analysis methods are relatively weak,and the method is infancy to be used to obtain the dynamic mechanical properties of film such as dynamic hardness,dynamic toughness,and fatigue resistance.Therefore,the study about the basic physical processes of nano-impact and quantitative analysis of dynamic mechanical properties is carried out.First of all,for the plastic single crystal Al?110?material,the effect of impact distance and load is analyzed with depth,and nano-impact physical model,an instantaneous load and energy analysis method are established.The differences of dynamic hardness obtained by the two methods?contact stress method and energy method?were further studied.It was found that due to the negligible extra energy during the indentation and rebound phases,the dynamic hardness obtained the energy method has higher error at a shallow depth.Compared with quasi-static results,it was found that the dynamic hardness exhibits a more severe indentation size effect,and when the residual depth h_r is less than 3000 nm,the dynamic hardness is higher than the quasi-static hardness value because the high strain gradient inside the indentation leads to a increasing density of geometrically necessary dislocations,which can enhance hardening.Secondly,the dynamic toughness of CrN hard film based on the above impact model and energy analysis method was studied.The results show that the displacement-time curve appears abrupt change during the impact contact process.Through the analysis of the focused ion beam method,it is found that micro-cracks occur inside the film.Finally,based on the energy method,the fracture work of the material is 35.92 nJ.The fracture toughness of the CrN film calculated in the indentation fracture method is 8.66 MPa·m^1/2,with the reported results in the same order of magnitude.The difference may be caused by different film thickness and matrix.Finally,the failure behavior of single-layered TiN film and nano-multilayered AlTiN film on cemented carbide was studied by multi nano-impact method.The results show that the method can evaluate the fatigue failure performance of the film well and high sensitivity of the impact load.Compared to the multi-impact results reported of TiN and TiAlSiN film on high-speed steel,It is found that impact resistance of the film is significantly affected by intrinsic mechanical properties and structure of the films at low impact load?5 mN?;while at the high load?25 mN?,the initial impact resistance of the film also shows the same phenomenon;In addition,statistical analysis shows that the dimensionless parameter of?h₁-h_s?/?h_f-h₁?can be used to evaluate the fatigue failure behavior of the film.