Manufacturing And Measuring Techniques Of High-accuracy Diamond Vickers Indenter

With the development of nano science and technology,the demand for mechanical properties evaluation of material surface layer,film,coating and micro component became huger,which makes nanoindentation technology flourish.It is the performance of nanoindenter and the accuracy of diamond indenter that mainly affects the results of nanoindentation.Vickers indentation test has become the main method of nano indentation experiment because of its advantage that the load size does not affect the measurement results.However,it is extremely difficult to make the four cones of the Vickers indenter intersect at only one point,which usually meet at one line on the top of the indenter.Therefore,most of nanoindentation experiments usually use Berkovich indenter which has the same area function as Vickers indenter.According to the development of the domestic and foreign technology in this field,the end line length of foreign high-accuracy diamond Vickers indenter is less than 200 nm,and the best is 50 nm,while the one made at home is greater than 500 nm,which doesn’t meet minimum international standards:250nm.Therefore,the following technical difficulties should be broken through in this paper: manufacturing diamond Vickers indenter,on which length of end line is about 50 nm,and determining geometry of Vickers indenter accurately.Firstly,based on the true shape of the diamond Vickers indenter,we establish a geometrical model of the indenter tip,clarify how the end line on the indenter top being formed,propose a method to control the end line,derive a new area function,and analyze the influence of geometric error on the area function.Diamond crystal is a strongly anisotropic material and the four conical faces lapping direction of the indenter must be consistent required by the method of control the end line,because of which <100> direction is selected as the axis of the pyramid.Then,based on the dynamic micro tensile strength of diamond crystal indifferent directions and on any plane,two kinds of design schemes are optimized according to the principle of wear resistance,which is that the projection of the pyramid edge at the(100)plane parallels to <100> direction and 45° with the <100> direction.Secondly,the geometric error of the indenter is analyzed by combining the lapping equipment and the geometrical model of the indenter.The distribution rule of the end line length is calculated by the probability theory.It is found that the reasonable selection of the lapping sequence of four cone surfaces can effectively reduce the impact of processing errors on the end line.At the same time,the lapping experiment also fined that the vibration of the grinding wheel not only increases the radius of the indenter,but also affects the actual height of the tapered surface material,thus affecting the accuracy of the indenter.Based on the finite element modal analysis and laser detection of axial vibration,the causes of vibration are analyzed and an effective method for controlling the axial vibration of the lapping wheel is established,which significantly improves the accuracy of the indenter.Secondly,the mechanical lapping method is used to manufacture the diamond indenter in this paper,and single factor experiment is carried out on the five important process parameters of the diamond grinding wheel’s grain size,rotational speed,grinding pressure,reciprocating stroke and frequency.The influence of each process parameter on the precision of the indenter is analyzed,and process parameters is optimized to make the length of the end line less than 60 nm and the radius of the indenter less than 70 nm.According to the two kinds of design schemes,the high-accuracy diamond Vickers indenter with the end line 57 nm,the radius of end line 70 nm and the radius of pyramid edge 52 nm was ground with the process parameters optimized.In addition,the geometrical morphology of the diamond Vickers indenter is tested and evaluated by optical microscope,atomic force microscope(AFM)and confocal laser scanning microscopy(CLSM).End line,radius and area function of the indenter can be determined by fitting the AFM acquired smaller-scale topographies,while the angles between the opposite faces,the included angles between any two edges of diamond pyramid and the angle between the pyramid axis and holder axis can be determined by fitting the CLSM acquired larger-scale topographies.Finally,in order to test the comprehensive performance of the indenter,nano indentation is carried using the diamond Vickers indenters manufacturing in this topic and foreign.The results show that the diamond Vickers indenter manufacturing in this topic up to the international standard ISO 14577 and have the same performance with the imported indenters.