rus
Issue #1/2014
A.Useinov, K.Kravchuk, I.Maslenikov
Obtaining of Tomograms of the Mechanical Properties by the Methods of Nano-indentation
Obtaining of Tomograms of the Mechanical Properties by the Methods of Nano-indentation
On the example of the polymeric coatings the authors demonstrate the advantages of the high-cycle instrumental nano-indentation with a partial discharge to studying of the mechanical properties of the near-surface volume of materials.
Теги: high-cycle indentation nanodurometer research of the near-surface layers of materials tomography многоцикловое индентирование нанотвердомер приповерхностные слои материалов томографирование
One of the trends in cognition of the properties of the around world consists in a constant increase of the spatial measurements of an experiment. This completely refers to the research of the physical-mechanical properties of the materials. If the first tests were done by indentation (pricking in one point), then paths of pricks were made with construction of a profile of the mechanical properties, and the modern nanodurometers implement a lot of pricks on a rectangular grid on a surface, which allows us to create a card of the mechanical properties.
The greatest interest has always been expressed to the approaches, allowing us to look inside of an investigated object, be it the earth crust, a human body or a material. Various ways are known for determination of the mechanical properties of a material depending on the depth. So, the optical tomography allows us to obtain a spatial resolution at the level of 100 microns [1] and by means of a rather complex analysis of data to determine the value of the modulus of elasticity [2]. Measurement of the mechanical properties can be done also on the basis of nano-indentation – the modern nanodurometers implement the method of a partial discharge [3], which allows us to determine hardness and modulus of elasticity as the depth functions [4, 5]. Such measurements are interesting for studying of the mechanical properties of the multilayered functional coatings and layers on the surface of a sample or inside of it. They are also useful for research of the modified samples (for example, processed by an ion irradiation or plasma), the distribution of the surface properties of which is not uniform.
The authors of the presented article have combined the indentation with a partial discharge and mapping of the mechanical properties. On the example of an experimental research of the samples of the polymeric coatings by a joint processing of a big number of experimental curves they obtained a resultant tomogram, which is a 3-D card of distribution of the modulus of elasticity and hardness of the samples.
Measurement devices and methods
Measurements were done on NanoScan scanning nanodurometer [6-8]. This multipurpose measuring complex is intended for research of the physical-mechanical properties of the surface of materials at a submicronic scale. It integrates more than twenty measuring techniques, including instrumental indentation, scratching, power spectroscopy and high-cycle abrasion, which allow us to determine the key mechanical parameters of the materials, including roughness of a relief, hardness and modulus of elasticity (Young modulus).
The device uses the principle of a high-cycle indentation with a partial discharge. For calculation of the mechanical properties it uses a section of a curved line of discharge, just like the traditional instrumental nano-indentation [9]. Discharge is done up to a certain share of the maximal load. In each subsequent cycle a repeated loading is done up to the level, higher than in the previous cycle (fig.1). Fig.2 presents the resultant charge-discharge curve for a 15-cycle indentation with a partial unloading up to 50% of the maximal value. Software allows us to change the parameters of the tests, for example, to set the number of cycles, algorithm of a loading increase (linear, power, etc.), speed, and waiting time in the relaxation sites. Thus, the results of processing of the experimental dependence for one high-cycle indentation are equivalent to the data received in a series of indents with an increasing loading, which allows us to construct a dependence of hardness and modulus of elasticity on the depth of introduction of an indentor for the given local site of the sample.
Tomography method
Application of hifh-cycle indentation in a combination with mapping allows us to determine distribution of the mechanical properties of a material in the volume (tomogram). The range of construction of a tomogram depends on the maximal depth of an indentor in a sample. The method was tested on the samples of commercial polymeric coatings (№1 and №2), deposited on a substrate from polydimethylsiloxane and divided by a boundary zone. The material used for calibration of the form of the indentor was polycarbonate.
In the experiment the limiting depth of indentation equaled to 10 microns. Resolution of the device allowed us to begin measurement of the mechanical properties from the depths of several tens of nanometers. The lateral resolution of the tomogram was determined by the distance between the neighboring prints, which depended on their size. The area subjected to tomography was 3×3 mm in size, on which a regular grid of high-cycle pricks was done in accordance with the procedure described above. Time of measurements was 6 hours. Images of the tomograms of hardness and modulus of elasticity are presented in fig.3. The results were visualized by means of special software. For presentation of the volume data of the hardness and modulus of elasticity of the samples, a temperature color palette and also a transparency function were used. In accordance with the introduced signs, the harder sites are visible through the more transparent soft sites. With account of interpolation of the data, the resultant volume maps contain 60×60×204 pixels.
As is visible from the received numerical results, coating №1 has essentially higher hardness properties, than №2. Thus, at the depth of 1 micron the moduli of elasticity of the coatings are equal to 4 and 1.5 МPа, accordingly. The received numerical results demonstrate a triple reduction of hardness and modulus of elasticity of the coatings at the depth from 1 up to 10 microns.
Of special interest is the behavior of a material on the borderline of two coatings. The tomogram shows, that in the borderline the modulus of elasticity is higher (7 МPа at the depth of 1 micron), at that, with a depth increase its change is minimal (5 МPа at the depth of 10 microns.). As one can see in fig.3, the width of the boundary area characterized by better mechanical properties is about1 mm.
As a whole, construction of 3-D maps of distribution of the mechanical properties is a rather informative way of research of the near-surface layers of materials. A wide choice of the adjustable parameters, high speed of tests and automation of the data processing are powerful tools for studying of the physical-mechanical properties. At that, the obtained data can be presented in the form of traditional two-dimensional charts or 3-D maps by any selected spatial measurements. Thus, in research of the mechanical properties tomography opens new opportunities for studying of the latent defects, and also of the gradients of hardness and modulus of elasticity in the near-surface volume of various samples. ■
The greatest interest has always been expressed to the approaches, allowing us to look inside of an investigated object, be it the earth crust, a human body or a material. Various ways are known for determination of the mechanical properties of a material depending on the depth. So, the optical tomography allows us to obtain a spatial resolution at the level of 100 microns [1] and by means of a rather complex analysis of data to determine the value of the modulus of elasticity [2]. Measurement of the mechanical properties can be done also on the basis of nano-indentation – the modern nanodurometers implement the method of a partial discharge [3], which allows us to determine hardness and modulus of elasticity as the depth functions [4, 5]. Such measurements are interesting for studying of the mechanical properties of the multilayered functional coatings and layers on the surface of a sample or inside of it. They are also useful for research of the modified samples (for example, processed by an ion irradiation or plasma), the distribution of the surface properties of which is not uniform.
The authors of the presented article have combined the indentation with a partial discharge and mapping of the mechanical properties. On the example of an experimental research of the samples of the polymeric coatings by a joint processing of a big number of experimental curves they obtained a resultant tomogram, which is a 3-D card of distribution of the modulus of elasticity and hardness of the samples.
Measurement devices and methods
Measurements were done on NanoScan scanning nanodurometer [6-8]. This multipurpose measuring complex is intended for research of the physical-mechanical properties of the surface of materials at a submicronic scale. It integrates more than twenty measuring techniques, including instrumental indentation, scratching, power spectroscopy and high-cycle abrasion, which allow us to determine the key mechanical parameters of the materials, including roughness of a relief, hardness and modulus of elasticity (Young modulus).
The device uses the principle of a high-cycle indentation with a partial discharge. For calculation of the mechanical properties it uses a section of a curved line of discharge, just like the traditional instrumental nano-indentation [9]. Discharge is done up to a certain share of the maximal load. In each subsequent cycle a repeated loading is done up to the level, higher than in the previous cycle (fig.1). Fig.2 presents the resultant charge-discharge curve for a 15-cycle indentation with a partial unloading up to 50% of the maximal value. Software allows us to change the parameters of the tests, for example, to set the number of cycles, algorithm of a loading increase (linear, power, etc.), speed, and waiting time in the relaxation sites. Thus, the results of processing of the experimental dependence for one high-cycle indentation are equivalent to the data received in a series of indents with an increasing loading, which allows us to construct a dependence of hardness and modulus of elasticity on the depth of introduction of an indentor for the given local site of the sample.
Tomography method
Application of hifh-cycle indentation in a combination with mapping allows us to determine distribution of the mechanical properties of a material in the volume (tomogram). The range of construction of a tomogram depends on the maximal depth of an indentor in a sample. The method was tested on the samples of commercial polymeric coatings (№1 and №2), deposited on a substrate from polydimethylsiloxane and divided by a boundary zone. The material used for calibration of the form of the indentor was polycarbonate.
In the experiment the limiting depth of indentation equaled to 10 microns. Resolution of the device allowed us to begin measurement of the mechanical properties from the depths of several tens of nanometers. The lateral resolution of the tomogram was determined by the distance between the neighboring prints, which depended on their size. The area subjected to tomography was 3×3 mm in size, on which a regular grid of high-cycle pricks was done in accordance with the procedure described above. Time of measurements was 6 hours. Images of the tomograms of hardness and modulus of elasticity are presented in fig.3. The results were visualized by means of special software. For presentation of the volume data of the hardness and modulus of elasticity of the samples, a temperature color palette and also a transparency function were used. In accordance with the introduced signs, the harder sites are visible through the more transparent soft sites. With account of interpolation of the data, the resultant volume maps contain 60×60×204 pixels.
As is visible from the received numerical results, coating №1 has essentially higher hardness properties, than №2. Thus, at the depth of 1 micron the moduli of elasticity of the coatings are equal to 4 and 1.5 МPа, accordingly. The received numerical results demonstrate a triple reduction of hardness and modulus of elasticity of the coatings at the depth from 1 up to 10 microns.
Of special interest is the behavior of a material on the borderline of two coatings. The tomogram shows, that in the borderline the modulus of elasticity is higher (7 МPа at the depth of 1 micron), at that, with a depth increase its change is minimal (5 МPа at the depth of 10 microns.). As one can see in fig.3, the width of the boundary area characterized by better mechanical properties is about1 mm.
As a whole, construction of 3-D maps of distribution of the mechanical properties is a rather informative way of research of the near-surface layers of materials. A wide choice of the adjustable parameters, high speed of tests and automation of the data processing are powerful tools for studying of the physical-mechanical properties. At that, the obtained data can be presented in the form of traditional two-dimensional charts or 3-D maps by any selected spatial measurements. Thus, in research of the mechanical properties tomography opens new opportunities for studying of the latent defects, and also of the gradients of hardness and modulus of elasticity in the near-surface volume of various samples. ■
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