rus
Issue #3/2016
K.Kravchuk, A.Useinov, I.Maslenikov, S.Perfilov
Automated control of composite products using NanoScan scanning nano-hardness tester
Automated control of composite products using NanoScan scanning nano-hardness tester
The ability to automate a large volume of routine measurements is demonstrated using NanoScan scanning nano-hardness tester for control of the strength properties of composite elements of the machining tool.
Теги: automation mechanical properties nanoindentation scanning nano-hardness tester автоматизация механические свойства наноиндентирование сканирующий нанотвердомер
Composite materials – the multicomponent systems consisting of a matrix and reinforcing element (a dispersion powder or reinforcing fibers and filaments) – are widely used in the creation of a modern machining tool. The combination of components with different characteristics allows to obtain materials with unique strength properties [1]. Properties of the boundary between matrix and reinforcing element are an important factor affecting the characteristics of the composite. Control of the density distribution homogeneity of components in the working area of the finished product is also important.
Diamond-based ceramics in the form of cutting inserts, double-layer diamond-carbide plates and other elements is widely used for the processing of a various materials. For example, polycrystalline diamond (PCD), which feature is the frame of strongly coupled diamond particles, are used for drilling of hard and abrasive rocks. This frame is made by processing (sintering) of the diamond powder in the conditions of thermodynamic stability at high pressures (6 GPa or more) and temperatures (1400°C) in the presence of metal. Metal melt (usually an alloy based on cobalt) provides during sintering the diamond recrystallization with the formation of strong bonds between particles. The remains of the alloy fills the frame of the polycrystal, providing it with additional mechanical strength.
When PCD based tools are used for drilling of rocks, in some cases, the important characteristic is not only the hardness of the material, but also its young's modulus and fracture strength as an indicator of resistance to impact load [2].
The direct contact methods of measuring the hardness and elastic modulus, which are based on the interaction between the diamond tip and the material, are widely used to characterize the strength properties. In combination with the mapping methods they allow to study the distribution of properties over the sample surface.
Experiment
The instrumental indentation in accordance with
GOST R 8.748-2011 (ISO 14577-1:2015) is based on the introduction into the surface of the solid material of the tip of the specified geometry with continuous recording of the penetration depth and of the force on its edge during the entire indentation procedure [3–4]. The obtained correlation is called "load-indentation" curve (Fig.1).
Under this method, the modulus of elasticity is calculated according to the following formula:
, (1)
where Ac is the area of the imprint at the maximum applied load Pmax. The contact stiffness S is determined by the slope of the curve of unloading in the Pmax point:
. (2)
One of the advantages of instrumental indentation is high speed of measurements, as well as the possibility of curves handling and calculation of elastic modulus and hardness in the automated mode. A series of pricks in the points of coordinates map are used to obtain the maps of mechanical properties by this method.
Automated measurements according to the method of instrumental indentation are implemented in the NanoScan-4D scanning nano-hardness tester (TISNCM, Russia). NanoScan-4D is the only Russian measuring instrument, which allows to carry out complex studies of physical-mechanical properties of materials at submicron and nanometer scale of linear dimensions [5–6]. General view of the device is shown in Fig.2. NanoScan is equipped with motorized sample stage for high accuracy positioning of the indenter in the XY plane over the sample surface.
The control of properties of samples of the same type often requires the same series of tests. The software of NanoScan devices includes a macro language that allows the user to describe the algorithm of the measurements and to conduct a series of tests in automatic mode without operator intervention. An example of a sequence of macro commands for a series of tests on a square grid with a step of 10 µm is shown in Fig.3.
Software for processing of experimental data allows mapping of the hardness and elastic modulus with the given parameters, including size, step between test points, loading. The distribution maps of the elastic modulus for the elements of the machining tool with polycrystalline diamonds, which were manufactured in TISNCM, were obtained in automated mode. The studied samples were synthesized at pressure higher than 6 GPa and at temperature of about 1400°C using diamond micro powders, impregnated with cobalt based alloy.
The modulus of elasticity indirectly characterizes the fracture strength, and therefore is the most important parameter of the quality for such items, especially for PCD based products for use in the drilling tool. Fig.4 shows a distribution map of the elastic modulus with a step of 10 µm between the measuring points, which is comparable with the size of the diamond crystals. The load during indentation was 50 mN. This map shows uniform distribution of diamonds on the surface.
Thus, the mapping mode allows to evaluate the homogeneity of mechanical properties, the characteristics of the boundaries, the size of the grains or phases on the surface. The obtained data allow to monitor the synthesis of materials and the output parameters of the finished products.
The value of the modulus of elasticity of the PCD based material can also characterize the properties of the "diamond-diamond" bonds in a frame of diamond polycrystal. Its higher value may indicate the formation of stronger interparticle bonds in the sample. At indentation of the diamond particle, which has a strong bond with neighboring particles, the value of the elastic modulus approaching to one of diamond.
Conclusion
The presented paper demonstrates the possibility of automation of many routine operations. The macro language allows to conduct different measurements – a single indentation, multi-cycle indentation with partial unloading, dynamic indentation – together with the positioning and adjustment of the device. A set of commands allows to measure large surfaces, including those with a significant height difference. The resulting data is processed in a batch manner, and the results can be represented using the NanoScan software or converted in text format for further use in third party software packages. ■
The project is financially supported by the Ministry of education and science of the Russian Federation under the agreement No.14.577.21.0159 (unique identifier of project RFMEFI57715X0113).
Diamond-based ceramics in the form of cutting inserts, double-layer diamond-carbide plates and other elements is widely used for the processing of a various materials. For example, polycrystalline diamond (PCD), which feature is the frame of strongly coupled diamond particles, are used for drilling of hard and abrasive rocks. This frame is made by processing (sintering) of the diamond powder in the conditions of thermodynamic stability at high pressures (6 GPa or more) and temperatures (1400°C) in the presence of metal. Metal melt (usually an alloy based on cobalt) provides during sintering the diamond recrystallization with the formation of strong bonds between particles. The remains of the alloy fills the frame of the polycrystal, providing it with additional mechanical strength.
When PCD based tools are used for drilling of rocks, in some cases, the important characteristic is not only the hardness of the material, but also its young's modulus and fracture strength as an indicator of resistance to impact load [2].
The direct contact methods of measuring the hardness and elastic modulus, which are based on the interaction between the diamond tip and the material, are widely used to characterize the strength properties. In combination with the mapping methods they allow to study the distribution of properties over the sample surface.
Experiment
The instrumental indentation in accordance with
GOST R 8.748-2011 (ISO 14577-1:2015) is based on the introduction into the surface of the solid material of the tip of the specified geometry with continuous recording of the penetration depth and of the force on its edge during the entire indentation procedure [3–4]. The obtained correlation is called "load-indentation" curve (Fig.1).
Under this method, the modulus of elasticity is calculated according to the following formula:
, (1)
where Ac is the area of the imprint at the maximum applied load Pmax. The contact stiffness S is determined by the slope of the curve of unloading in the Pmax point:
. (2)
One of the advantages of instrumental indentation is high speed of measurements, as well as the possibility of curves handling and calculation of elastic modulus and hardness in the automated mode. A series of pricks in the points of coordinates map are used to obtain the maps of mechanical properties by this method.
Automated measurements according to the method of instrumental indentation are implemented in the NanoScan-4D scanning nano-hardness tester (TISNCM, Russia). NanoScan-4D is the only Russian measuring instrument, which allows to carry out complex studies of physical-mechanical properties of materials at submicron and nanometer scale of linear dimensions [5–6]. General view of the device is shown in Fig.2. NanoScan is equipped with motorized sample stage for high accuracy positioning of the indenter in the XY plane over the sample surface.
The control of properties of samples of the same type often requires the same series of tests. The software of NanoScan devices includes a macro language that allows the user to describe the algorithm of the measurements and to conduct a series of tests in automatic mode without operator intervention. An example of a sequence of macro commands for a series of tests on a square grid with a step of 10 µm is shown in Fig.3.
Software for processing of experimental data allows mapping of the hardness and elastic modulus with the given parameters, including size, step between test points, loading. The distribution maps of the elastic modulus for the elements of the machining tool with polycrystalline diamonds, which were manufactured in TISNCM, were obtained in automated mode. The studied samples were synthesized at pressure higher than 6 GPa and at temperature of about 1400°C using diamond micro powders, impregnated with cobalt based alloy.
The modulus of elasticity indirectly characterizes the fracture strength, and therefore is the most important parameter of the quality for such items, especially for PCD based products for use in the drilling tool. Fig.4 shows a distribution map of the elastic modulus with a step of 10 µm between the measuring points, which is comparable with the size of the diamond crystals. The load during indentation was 50 mN. This map shows uniform distribution of diamonds on the surface.
Thus, the mapping mode allows to evaluate the homogeneity of mechanical properties, the characteristics of the boundaries, the size of the grains or phases on the surface. The obtained data allow to monitor the synthesis of materials and the output parameters of the finished products.
The value of the modulus of elasticity of the PCD based material can also characterize the properties of the "diamond-diamond" bonds in a frame of diamond polycrystal. Its higher value may indicate the formation of stronger interparticle bonds in the sample. At indentation of the diamond particle, which has a strong bond with neighboring particles, the value of the elastic modulus approaching to one of diamond.
Conclusion
The presented paper demonstrates the possibility of automation of many routine operations. The macro language allows to conduct different measurements – a single indentation, multi-cycle indentation with partial unloading, dynamic indentation – together with the positioning and adjustment of the device. A set of commands allows to measure large surfaces, including those with a significant height difference. The resulting data is processed in a batch manner, and the results can be represented using the NanoScan software or converted in text format for further use in third party software packages. ■
The project is financially supported by the Ministry of education and science of the Russian Federation under the agreement No.14.577.21.0159 (unique identifier of project RFMEFI57715X0113).
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