Several Theoretical Problems Of Indentation And Scratch Testing And Experimental Research Based On Self-made Instruments

Failure of materials and related products is resulted from micro deformation, damageand defect. In recent years, research on mechanical properties of materials in micro/nanoscales is given increasing attention. With high load and displacement resolutions,micro/nano indentation and scratch testing has been a commonly used method to evaluatemechanical properties of materials in micro/nano scales, expressing important scientificsignificance and broad application prospects in fields of materials science, semiconductors,thin films, biomechanics, biomedical engineering and so on. Up to now, America, Swiss,UK, etc. have mastered this technology and there are commercial indentation and scratchinstruments in these countries. However, research on indentation and scratch testingtechnology in China begins relatively late, and there is no commercial home-grownindentation and scratch instrument.On the one hand, there are many problems by importing indentation and scratchinstruments from abroad such as high cost, time-consuming, high-end technology embargo,and so on. On the other hand, because we don’t master the key technologies of indentationand scratch testing and completely rely on foreign testing instruments, functions of thecommercial instruments can not be extended according to requirements, which makesrelated research work in China be always in the state of follow-up study and restrictsresearch progress seriously. So, it has important significance to study the key technologiesof indentation and scratch testing and develop indentation and scratch instruments withour own intellectual property rights. Meanwhile, some theoretical problems such ascalibration and error correction of indentation and scratch instruments are still needed tobe further investigated.Aimed at the current deficiencies in indentation and scratch testing technologies andinstruments at home and abroad, basic theories and technologies of indentation and scratchtesting such as testing theory, structure design, fabrication, assembling, measuring andcontrol, debugging, calibration and so on, are studied in this paper. Ex situ and in situ indentation and scratch instruments with our own intellectual property rights aredeveloped, by which typical applications are carried out. The main contents are listed asfollows:(1) The classical data analysis method—Oliver&Pharr method is discussed firstly, andthen emphasis is put on three factors, determination of the residual indentation depth, thesample preparation method and the tilt between the indenter and the sample surface, whichaffect indentation testing results but are not studied in detail up to now. For the case thatunloading curves are incomplete or there are obvious elbow phenomena, a method byfitting partial unloading curves to determine residual indentation depth hfis proposed.Influences of two different sample preparation methods, mechanical polishing and plungecutting, on the serrated flow and creep behaviors of a bulk metallic glass duringindentation testing are studied by comparison tests. Two methods, the residual indentationmorphology measuring method and the three-point measuring method, are presented toquantificationally evaluate the tilt between the indenter and sample surface. Byexperiments, feasibility of these two methods are verified respectively.(2) Design, analysis and experimental investigation of an ex situ indentation andscratch testing system are carried out. Related theoretical and technological issues, such asstructure design and analysis, layout optimization, dynamic modelling, control system setup, calibration, performance testing, and so on, are addressed. After that, an ex situindentation and scratch testing system is developed successfully. A new method isproposed to measure compliance of indentation instruments, by which instrumentcompliance of the indentation testing module is obtained, and it is0.425nm/mN.Indentation testing results of the standard sample—fused quartz verify the feasibility ofthe proposed method. Performances of the indentation testing module are tested byexperiments, and results indicate that for the general experimental environment withvibration isolation platform but without constant temperature treatment, the loadresolution of the indentation testing module is higher than10μN and the noise floor is lessthan30μN. The displacement resolution is1nm and the noise floor is about2nm.Nanoindentation testing results of the standard sample—fused quartz indicate that theindentation testing module has good repeatability and testing accuracy. A two-axis loadsensor is designed by integrating an I-shaped structure and eight strain gauges, which canbe used to measure the lateral load and the normal load simultaneously. A decoupling algorithm is presented to obtain the lateral load and the normal load. Calibrationexperiments and decoupling analysis are carried out to obtain the correspondingdecoupling parameters.(3) Applications of the self-made ex situ indentation and scratch testing system insingle crystal silicon and the bulk metallic glass are carried out. Via the indentation testingmodule, statistical laws of indentation-induced pop-out in unloading curves of singlecrystal silicon are studied. Indentation response of single crystal silicon under tensionstress is revealed by a self-made tension stress loading unit. Indentation comparison testsare carried out by the Berkovich indenter and the cube-corner indenter respectively tostudy indenter dependent indentation behaviors of the bulk metallic glass, such asadhesion, serrated flows, shear bands, and so on. Mechanical behaviors of the bulkmetallic glass are analyzed via the scratch testing module. Possible reasons leading tofluctuations of the lateral load and the friction coefficient during the scratch testing arediscussed. The phenomenon that unsymmetric scratch induces unsymmetric deformationof the bulk metallic glass around borders of the residual scratch is observed.(4) By combination of the stepper motor and the piezoelectric stack, an in situindentation instrument is developed. Output performances, closed-loop control, calibrationof the instrument are studied by experiments. In situ indentation experiments of the InP(Indium phosphide, InP) wafer and the bulk metallic glass indicate that the developed insitu indentation instrument has good compatibility with the scanning electron microscope,and it can be used to carry out in situ indentation tests of materials inside the vacuumchamber of the scanning electron microscope.(5) A novel piezo-driving principle is proposed by means of the parasitic motion of theelastic body. Based on this principle, a scratch module with the large motion range isdeveloped using two piezoelectric stacks. Driving processes and output performences ofthe scratch module are investigated via theoretical analysis and experiments. Based on theprevious in situ indentation instrument, an in situ indentation and scratch instrument isdeveloped by integrating the designed scratch module, which is compatible with thescanning electron microscope. Friction between the indenter and the sample surface aswell as material removal mechanism especially when lots of chips are accumulated on therake face of the indenter is studied.