Study On The Methods Of Nanoindentation Testing

Nanoindentation testing is a newly-developed experimental method for mechanicalproperties on the basis of those traditional experimental methods including Brinell's andVickers' methods for hardness. Through continually controlled and recorded the data ofload and displacement during the periods of loading and unloading, Meso-mechanicalmethod can provide many mechanical property indexes including instrumentalizedindentation hardness, Young's modulus, indentation creep, indentation relaxation andfracture toughness etc. The nanoindentation produced by American MTS Corp. is one ofthe most advanced instruments in the world for nano-mechanical property measurement.Nanoindetation is a method for micro- and meso- mechanical property measurement. Thepurpose of our research is to make some contribution to the development ofnanoindentation through the study on the influencing factors, relations amongnanoindentaion hardness, Martens hardness and Vickers hardness, the uncertaintyanalysis for the experimental results of nanoindentation, and applications of thin-filmtesting samples in nanoindentation. And some of the work which has been done in thispaper was still not carried out by others according to domestic present reporting.Based on the study on the influencing factors in nanoindentation experiments, the resultsshowed that: a) In terms of nano-scale indentation, 1% relative displacement of contactzero will lead to an about 4% relative error to nanoindentation hardness, and an about 2%relative error to modulus, b) The intender area function should be checked periodically, orthe measuring result will be inaccurate. The relative errors to hardness resulted from thearea function are twice as those resulted from modulus, c) During the computation process,the fitting parameter of unloading rigidity curve can be selected in the range from 20% to80%. d) Indentation hardness and indentation modulus were obtained from the function ofdepth though Continuous Stiffness Measurement (CSM). It's a good method for testing themechanics of thin films. But the testing result is not as same as that from unloading method,especially in indentation hardness, e)The adjacent separation for indentation should beover 25 times of the largest depth for indentation in terms of Berckvich's and Vickers'indenter.By studying on relations among nanoindentation hardness, Vickers hardness and Martenshardness, it was found that the relations varies with different indenters and samples ofdifferent hardness levels. When using Vickers indenters, the values of Vickers hardnessare about 0.0877 times of those of nanoindentation hardness and Martens hardness areabout 0.8333 times of nanoindentation hardness; while to Berchvich indenters, values ofVickers hardness are about 0.0901 times of nanoindentaion hardness and Martenshardness are about 0.9009 times of nanoindentation hardness. High-purity fused silica and high hardness steel GCr15 were choosed in this study. Statisticresearch on the indentation with the depth of 2000nm were carried out to study its surfaceand depth uniformity, it was found that the degree of roughness of high-purity fused silicacan reach 0.006μm for its smooth surface. Thus, the surface uniformity and depthuniformity of high-purity fused silica were good due to its amorphous and isotropy. Toevaluate by coefficient of variability, the surface uniformity of Young's modulus was 0.56%,the depth uniformity was 0.83%, and the surface uniformity of nanoindentation was 0.73%,the depth uniformity was 0.99%. According to F formula, the distribution of Young'smodulus and hardness of the samples can be considered to be uniform. In terms of highhardness steel GCr15, despite its only 3μm hidden needle-type martensite, its surfaceroughness can reach about 0.008μm, mainly for its multi-phased alloy structure. Thus, thenanoindentation will be affected largely, and the influence to indentation depth is relativelysmall. According to F formula, the surface Young's modulus of steel is asymmetrical.As many factors should be considered in the uncertainty of the result of nanoindentation,through comparison experiment and it found that the repeatability of the tested fusedsilica's indentation modulus is 2.96% and the reproducibility is 9.33%. The repeatability ofthe tested fused silica's indentation hardness was 4.48% and the reproducibility was11.35%. The repeatability of the tested GCr15 steel's indentation modulus was 9.31%, thereproducibility was 22.36%. The repeatability of the tested GCr15 steel's indentationhardness was 15.67% and the reproducibility was 26.60%. It is obvious that the uncertaintyof GCr15 steel is a bit higher than that of fused silica. Meanwhile, uncertainty ofnanoindentation experiment were attained though repeatbility and reproducility. It's asimple method on evaluating the uncertainty of nanoindentation experiment. Though theinfluence which come from the change of original point and vary of area function toindentation modulus is 2 times of indentation hardness, the values of total uncertainty onindentation hardness is almost no different on indentation modulus. It found that: becausea) ISO 14577-1:2002 does not have strict rules for experimental condition (such as theequipment adjust and the control of experimental process, b) different labs may havedifferent understanding and execution on the ISO standard, c) equipment of differentfactories differs a lot from each other and thus has different accuracy, the test result willhave some difference. The influence from the times of test can be ignored when the testingtimes are over five.Lastly, the influence of the current several methods to test results of thin film samples wasstudied. The results showed that for 200nm super-thin films, the method of DCM CSMhardness & Modulus for Thin Films in DCM tum out a relatively reliable result. In theprocess of testing thin-films, it was found that the influence of indentation hardness andindentation modulus was different from the thickness of thin-films. The ratio of indentationdepth to thin-films' thickness is the most important factor in testing of the indentationhardness and the indentation modulus. Through the experimental analysis of the 10.4μmsurface white-bright layers of nitridized samples, it can be found that nanoindentation is arelatively good method to test the white-bright layers. Meanwhile, the results also show that the modulus of white-bright layers of nitridized samples was about 306GPa, the hardnessdegree was about 14.3GPa, which provides an effective analysis method for themechanical properties testing of nitridized layers.