Research On The Effects Of Sample Tilt On Nanoindentation Test Of Berkovich Indenter

The nanoindentation testing technology has made great achievements in the application and development of the last thirty years,and has gradually developed into one of the mainstream technologies for the testing of micromechanical properties of materials.However,with the development of electronic and computer related precision manufacturing technology,the size of micro products,test pieces and the thickness of surface modification layer are becoming smaller and smaller,which makes the impact of nanoindentation testing error more and more prominent.Among the factors that affect the test error,the sample tilt has attracted much attention because of its universality,the randomness of its distribution and the complexity of the mechanism of nanoindentation testing.In this paper,the influence of the sample tilt on the results of nanoindentation test in the process of sample preparation and sample clamping is studied by means of theoretical analysis and experimental research.Firstly,in view of the complexity of the Berkovich indenter on the tilted surface,a theoretical analysis model for the projection contact area of the Berkovich indenter on the sample tilt is established.The results show that the tilt angle of the specimen will affect the size of the actual projected area of contact in the indentation test,and this effect increases with the increase of the angle.At the same time,the rotation angle also affects the projected area of contact of the indentation.When the rotation angle is 60 degrees,the error of the projection contact area is the largest.Therefore,in order to ensure the error of the projected area of contact within the range of permissible error,the absolute value of tilt angle should be small enough and the angle of the rotation angle should be controlled.The influence of the sample tilt on the results of nanoindentation test is studied by experiments.In order to solve the problem that the sample is difficult to prepare with the specific tilt angle and the inclined direction in the experiment,a method of using thin film to deal with the sample is put forward.According to this method,the influence of the 6 important factors:the load-displacement curve,the indentation depth,the contact stiffness,the projection contact area,the hardness and the modulus is emphatically analyzed.Taking load loading and displacement loading as two starting points,the two methods are compared and analyzed.It is found that there is a wide correlation between the results of nanoindentation test,and all of them will have different degrees of influence under sample tilt.At the same time,the sample tilt will lead to the measurement error of the analysis model,and the error in the two loading modes is different,the measurement error of the elastic modulus is greater in the displacement loading mode,and the error of the hardness measurement under the load loading mode is greater.According to the analysis model of the projected area of contact for the Berkovich indenter and the conical indenter,the error of projected area of contact for the pyramid indenter of different cone angle and the conical indenter are compared.The results show that Berkovich indenter is more affected than the other indenter under the same tilt condition.Finally,according to the error of projected area of contact for the different indenter,the maximum feasibility tilt angle of the specimen under the nanoindentation test for the different indenter is derived.The determination method of the feasibility angle of the specimen in the Berkovich nanoindentation test is put forward,which indirectly guides the preparation of the nanoindentation test specimen and the calibration of the equipment.