RU2699945C1 - Method of determining viscosity of micro destruction of thin amorphous-nanocrystalline films - Google Patents

Abstract

FIELD: test technology.

SUBSTANCE: invention relates to investigation and analysis of plastic properties of thin tapes of amorphous multicomponent metal alloys after their transition from amorphous to amorphous-nanocrystalline state as a result of heat treatment. A preliminary first series of tests of one sample with different load is performed, on the basis of which the optimum indenter indentation force is determined in the sample, at which the probability of occurrence of the characteristic micro destruction pattern is maximum. Preliminary second series of tests is carried out with optimum value of load on another sample to determine minimum allowable distance of tests between points of indentation and edge of analyzed sample, at which characteristic pattern of micro destruction is manifested. A series of basic samples of a thin amorphous metal strip is made, an amorphous-nanocrystalline structure is formed in them by controlled heat treatment, placing on substrates from metal and polymer composite material, investigating viscosity of micro destruction by inducing indenter sample in form of Vickers pyramid with load, speed and time of action on sample, which enable to provoke occurrence of group of cracks in form of system of embedded squares, calculation of micro destruction viscosity based on data on average distances between two parallel cracks in group of cracks formed in sample after test.

EFFECT: possibility of reliable calculation of viscosity coefficient of micro destruction of materials at minimum number of samples and, accordingly, reducing time consumption of materials for analysis and improving accuracy of calculations.

3 cl, 4 dwg, 3 tbl

Description

The invention relates to the field of research and analysis of the plastic properties of thin ribbons of amorphous multicomponent metal alloys after their transition from an amorphous to an amorphous-nanocrystalline state as a result of heat treatment. The microfracture toughness index is important because it characterizes those properties of these materials that cannot be determined without significant costs.

Standard methods for mechanical testing of metal samples are diverse and widely used to determine the mechanical properties of metals and alloys. For example, bending samples to their destruction, sclerometry (applying scratches with constant and variable loads to the surface of samples), tensile or compression tests in the longitudinal and transverse directions, measuring indentation, impact tests for bending, multi-cycle abrasion and a number of others (1. " Metallic materials - Bending test method "GOST 14019-2003 (ISO 7438: 1985); 2. Innovative mechanical testing of metal subjected to technological deformation and heat treatment: monograph / RE Gliner, VN Du Insky, E.B. Katyukhin, V.A. Pryanichnikov, A.V. Shabin; Nizhny Novgorod State Technical University named after R.E. Alekseev - Nizhny Novgorod: NSTU, 2016 .-- 123 pp., ill., tab. ) These methods are well established in practice, provide reliable and representative data and are considered by the authors as analogues.

However, such methods are not suitable for studying thin brittle films and coatings or have a number of significant drawbacks. For example, during the heat treatment of some amorphous metal alloys near the tempering temperature, their significant embrittlement can be observed (3. Glezer A.M., Permyakova I.E., Gromov V.E., Kovalenko V.V. Mechanical behavior of amorphous alloys. - at SibGIU. - Novokuznetsk. - 2006. - 416 p.), which does not allow them to be investigated by standard methods. This is caused by the transition of a part of the material to the nanocrystalline state, in which plasticity measurements give near-zero values, which makes it impossible to study their properties in a given temperature range. The disadvantages are the inability to study local heterogeneous regions in the samples of the tape and the high consumption of samples and the time required for testing.

There is also a method of determining plasticity by microindentation on substrates (4. Ushakov I.V., Fedorov V.A., Permyakova I.E. / Determination of plasticity of metal glass by microindentation on substrates // Factory Laboratory. Diagnostics of materials. 2003. T. 69. No. 7. P. 43-47; 5. Ushakov IV, Polikarpov VM / Tests of thin ribbons of metallic glass by indenters of various geometric shapes // Factory Laboratory. Diagnostics of materials. 2007. V. 73. No. 2. C. . 68-71.). When using this method, a pre-annealed and cooled to room temperature sample of the test material is placed on a metal substrate, on which a layer of polymer composite material is applied from the side of the test sample, fixed on it, and then the tetrahedral pyramid is exposed to the test sample, selecting the force of action, the speed of contact the surface of the test material with a pyramid and the time of exposure to the sample so that at the site of exposure (penetration) p ramidki group cracks formed in the form of figures, similar to nested squares. Moreover, to determine the coefficient of plasticity using the expression:

where h is the thickness of the test sample, μm, a d is the diameter of the reduced semicircle, completed according to the measurement results of the figure formed by a group of cracks after exposure to the sample with a tetrahedral pyramid, μm. It is also possible to use empirical coefficients multiplied by the magnitude of the “step” of the indenter impression, that is, by the distance between adjacent cracks forming a figure from the enclosed squares.

The disadvantage of this method is the relatively low accuracy of calculating the coefficient of plasticity e due to errors in determining the reduced diameter of the semicircle and empirical coefficients.

Closest to the proposed invention in technical essence and the achieved result is a method for determining the plastic characteristics of films of multicomponent amorphous-nanocrystalline metal alloys (6. Patent No. 2494039, C1 Russian Federation, IPC G01N 3/42, B82Y 35/00. Method for determining the plastic characteristics of films multicomponent amorphous-nanocrystalline metal alloys / Ushakov I.V., Safronov I.S .; applicant and patent holder of FSBEI HPE “MGGU”. - No. 2012116406/28; filed April 24, 2012; published September 27, 2013), in which ohm to calculate the value of d in the expression (1) uses the following expression:

где l_сред и l_мин._сред - среднее и минимальное среднее расстояния между соседними трещинами соответствующих сторон фигуры, образованной трещинами в форме вложенных квадратов после воздействия на образец индентора, мкм. При этом учитываются только те трещины, которые относительно параллельны соответствующим сторонам квадрата и образующие характерную фигуру в виде вложенных квадратов. Расчеты l_сред производят путем измерения всех расстояний между соседними трещинами во всех сторонах образованной ими фигуры, при необходимости достраивая незамкнутые квадраты до замкнутых.

where l _environments and l _min . _medium - the average and minimum average distances between adjacent cracks of the corresponding sides of the figure formed by cracks in the form of embedded squares after exposure to the indenter sample, microns. In this case, only those cracks that are relatively parallel to the corresponding sides of the square and forming a characteristic figure in the form of nested squares are taken into account. Calculations of l _{media are} carried out by measuring all the distances between adjacent cracks on all sides of the figure formed by them, if necessary, building open squares to closed ones.

where l _a1 , l _a2 , ... l _an , l _b1 , l _b2 , ... l _bn , l _cl , l _c2 , ... l _cn , l _dl , l _d2 , ... l _dn are the distances between neighboring

cracks in each side of the figure formed by them. Similarly, l _{min medium is calculated} , but instead of all the distances between adjacent cracks, only the minimum distances between adjacent cracks in each side of the figure formed by them are taken.

This method allows to significantly improve the accuracy of determining the coefficient of plasticity and is considered by the authors as a prototype.

However, the prototype has several disadvantages. First, the difficulty in obtaining symmetrical fracture patterns that would have symmetrical imprints and cracks oriented parallel to all four faces of the indenter pyramid. In this case, it is necessary that in such symmetrical patterns parallel to each face of the indenter, three or more parallel cracks be formed. Secondly, cracks may not appear at all on the samples under investigation or asymmetric fracture patterns may form. This leads to a decrease in measurement accuracy and the need for additional tests, which in turn leads to an increase in time and other resources. It should also be noted that the coefficient s is associated with residual deformations after loading, such as slip of dislocations, twinning, and other types of fracture. Therefore, in the study of thin films, it is desirable to abandon the determination of the plasticity coefficient by replacing it with a more precise term that reflects the physical nature of the properties of these materials by the term “microdestruction viscosity”.

The technical result of the invention lies in the fact that pre-determining the optimal value of the indentation force of the indenter into the sample, at which the probability of the appearance of a characteristic microdestruction pattern is maximum, highlighting the range of allowable loads on the indenter, and determining the minimum allowable test distances between indentation points and the edge of the sample in which a characteristic pattern of microdestruction appears, we increase the probability of obtaining t on the studied samples FIR prints of the indenter, which permit a reliable calculation of the viscosity coefficient microfracture materials on a minimum number of samples and, accordingly, reduce the cost of time and materials for research and improve the accuracy of calculations.

The technical result is achieved as follows. Samples are made of a thin amorphous metal strip, amorphous-nanocrystalline structures are formed in them by controlled heat treatment, placed on substrates of metal and a polymer composite material, the microdestruction viscosity is examined by pressing an indenter in the form of a Vickers pyramid with a load, speed and time of exposure to specimen, allowing to provoke the appearance of a group of cracks in the form of a system of nested squares, the microfracture viscosity is calculated based on the data about the average distances between two parallel cracks in the group of cracks formed in the sample after the test, and before conducting the main series of tests, the first series of additional tests of one sample with different loads is carried out, based on which the optimal value of the indenter pushing force into the sample is determined, at which the probability the appearance of the characteristic microdestruction pattern is maximum, after which a second additional series of tests is carried out with the optimal load on another specimen to determine the minimum distance between the test points and the test sample indentation edge, wherein the characteristic pattern shown microfracture.

In addition, the technical result is achieved due to the fact that the number of tests in the first and second additional series is at least 20 tests for each variant of the applied load and for each variant of the distance between the indentation points and the edge of the sample, while additional series of tests are stopped after how the range of values of the indenter indentation force into the sample was revealed, in which the probability of the formation of a characteristic microdestruction pattern exceeds 0.65, and containing the optimal value of the indentation force Nia, and defined minimum distance between points of the indentation and the test sample edge.

Also, to achieve a technical result, if during testing in the central part of the specimen the cracks formed contact with the cracks formed during the previous test or do not form a characteristic microdestruction pattern, then the distance between adjacent indentation points is increased by a factor of 1.5 and the test is repeated, and the results of the previous test are not taken into account, and the distance between the indentation points is increased until a characteristic micro picture destruction.

The invention is illustrated by the drawing, where in figure 1, figure 2 and figure 3 graphs of the probability of formation of symmetrical fracture micro-patterns on the surface of the sample (P) in fractions of a unit on the load on the indenter (F) in Newtons are shown, and in figure 4 the dependence of the proportion of symmetry in fracture micrographs (W) in fractions of a unit, from the distance of the test site to the edge of the sample (L) in micrometers.

The method can be implemented as follows.

Samples of a thin tape of an amorphous metal alloy with a thickness of 30 μm and linear dimensions of 15 × 25 mm are annealed in a furnace for 10 minutes at a constant annealing temperature at which an amorphous-nanocrystalline structure is formed in this alloy. The structure of the annealed samples is fixed on a diffractometer, for example DRON-2, by means of X-ray diffraction analysis. Heat-treated samples are applied to polymer composite substrates 2 mm thick with a base in the form of metal plates 2-3 mm thick. Due to this, it is possible to achieve sufficient rigidity of the design "sample-substrate-plate". The microhardness of the samples under study is no less than 10 times the microhardness of the polyester composite. Due to this, the indenter (tetrahedral Vickers pyramid) can well penetrate through the sample into the substrate and, accordingly, it is possible to fix the destruction patterns of a thin film after loading. Samples for some time strongly pressed to the polyester compositions until they are glued, and then placed on the side of the composites on metal plates.

After that, the first series of additional tests of one specimen with a different load is carried out, on the basis of which the optimal value of the indenter indentation force into the specimen is determined and the range of allowable loads on the indenter is determined, in which the probability of the appearance of a characteristic fracture pattern exceeds 0.65. Examination of the sample begins with its central part. Why do they conduct a series of indentation series, each of 20 tests with a constant load. The step of increasing the load of each subsequent series is set in advance, based on the design of the hardness tester, and is the same for the entire series of test samples. During the tests, the number of indentation points with the required fracture pattern is revealed by visual means and the percentage of characteristic fracture patterns is determined. The series of tests is continued until a load range is found at which the probability of the appearance of a characteristic pattern of fracture exceeds a predetermined value, and necessarily includes a load that provides the maximum probability of obtaining a fingerprint from an indenter that meets the requirements of the method for calculating the microfracture viscosity.

At the second stage, the study of another sample begins from its border in the direction of the central part. To do this, several series of indentation are carried out with the previously determined optimal load on the indenter, but with different distances from the edge of the test sample to the point of application of the load. The number of tests in each series is 20, and the initial step is defined as half the distance between the load points found in the first stage. The tests are terminated after the probability of obtaining a characteristic microdestruction picture, determined in fractions of a unit, exceeds the set value. This distance is taken as the minimum allowable distance of the test from the edge of the sample.

All subsequent tests in the main series are performed on the basis of the data thus obtained. In this case, the indentation points are placed on the same line with fixed distances between them, and if during the test the cracks formed are in contact with the cracks formed during the previous test or do not form a characteristic microdestruction pattern, then the distance between adjacent indentation points is increased by one and a half times and repeat the test, and the results of the previous test are excluded, and an increase in the distance is made until a characteristic pattern of microfracture appears sheniya. This distance is taken to be the minimum between indentation points. The distances between the lines along which tests are carried out on the same specimen are taken deliberately larger than the minimum distance between the indentation points in one line in order to exclude their influence on each other.

For an example of the implementation of the proposed method, samples were taken from standardly produced rapidly quenched tapes of amorphous magnetically soft alloys AMET based on cobalt. We investigated samples made from alloys of the following grades: 82K3KHSR, 84KKhSR, 86KGSR. The chemical (elemental) compositions of these alloys are as follows: 1) 82K3KHSR - Co _71.66 Si _17.09 B _4.73 Fe _3.38 Cr _3.14 ; 2) 84KHSR - Co _81.92 Si _7.2 Fe _4.3 Cr ₄ B _2.5 Ni _1.8 C _0.05 S _0.015 P _0.015 ; 3) 86KGSR

Co _71.02 Ni _12.4 Si _6.7 Fe _5.9 B _3.8 Mn _0.1 C _0.05 S _0.015 P _0.015 . These materials are produced in the form of tapes, delivered in a non-heat-treated state and are used, including for the production of inductors in magnetic separation devices. The products formed from them require thermal or thermomagnetic treatment.

Furnace annealing is used to obtain a nanostructure that changes the properties of the material and obtain the required technical characteristics. 15 by 25 mm samples were cut from the tapes. Samples for the study were annealed for 10 minutes at the following temperatures: 1) 82K3XSR - 833 K (560 ° C); 2) 84KHSR - 863 K (590 ° C); 3) 86KGSR - 803 K (530 ° C). After that, samples of 15 by 25 mm in size were placed on substrates, as described previously (4), while to create a relatively soft layer connecting the sample and the metal substrate, we used BodiFiber polymer composites: 67/548 / EEC.

The samples prepared in this way were investigated on a PMT-3M microhardness tester, size measurements were carried out using a screw ocular micrometer MOV-1-16x. The range of loads on the indenter of this microhardness tester is from 0.0196 N to 4.9 N with manual control. As an indenter, we used a diamond tip of the tetrahedral Vickers pyramid with a square base and a vertex angle of 136 °.

Preliminary tests of the obtained samples were carried out according to the claimed method in two stages. At the first stage, the optimal load on the indenter F _{opt was} determined for each alloy under study. Ten cycles of twenty trials were conducted. As a result, the dependence of the probability P of the formation of symmetric fracture micro-pictures on the surface of the sample on the load on the indenter F, N was obtained. The test results for each alloy under study are presented in table 1 and in figures 1, 2 and 3 in the form of graphs. Figure 1 shows the data obtained when testing a sample of 82K3XSR alloy, figure 2 - of 84KXSR alloy and figure 3 - of 86KGSR alloy. In this case, in FIG. 1, FIG. 2 and FIG. 3, the abscissa axis shows the load on the indenter in Newtons, the ordinate axis shows the probability of the formation of symmetrical fracture micro-patterns on the surface of the samples from the value of the indenter load, denoted by P and expressed in fractions of a unit, and by the numbers 1 - the boundaries of the load region on the indenter, in which the likelihood of the formation of symmetrical micro pictures is greater than 0.65.

For example, samples 82K3KHSR were not destroyed by exposure to loads up to 1.96 N inclusive. At loads less than 2.45 N, symmetrical cracks do not form, or the probability of their formation is below 10%. Such loads are unsuitable for use on this 82K3XSR alloy, since low symmetry and low reproducibility of the results do not allow the collection of statistical data.

Permissible and optimal loads were experimentally established to obtain symmetrical and fracture patterns suitable for analysis. So, for material 82K3XSR, the minimum load on the indenter is F _min ≈ 2.45 N (P ≈ 0.1), the optimal load on the indenter is F _opt ≈ 3.92 N (P ≈ 0.85), and the maximum load on the indenter is F _max ≈ 4.9 N (P ≈ 0.4), the recommended load range at which the probability of the formation of symmetrical micro pictures is more than 65%, from 3.53 N to 4.51 N.

At the second stage, the minimum allowable distance L _{min was} determined _{. add.} testing from the edge of the sample. Tests for each investigated alloy were carried out according to the claimed method, starting from the edge of the sample to its center, at a previously determined optimal load on the indenter F _opt and consisted of eight series of twenty tests in each series. For each series, the proportion of symmetry in the fracture micrographs, W, was calculated. The test results are presented in table 2 and in figure 4 in the form of graphs. The abscissa shows the distance from the test site to the edge of the sample, L _gp. , μm, on the ordinate axis - the proportion of symmetry in the fracture micro-pictures in fractions of a unit, W, figure 2 shows the change in W from L _gr. ,. for alloy 82K3XSR, the number 3 is the change in W from L _gr. for alloy 84KHSR and number 4 - for alloy 86KGSR.

As can be seen from the graphs in figure 4, with increasing distance from the boundaries of the sample L _gr. micro-pictures of its destruction become more symmetrical. At a certain distance L ≈ L _{min. add.} symmetrical elements in micro pictures reach their maximum value W _max. Further removal from the boundaries of the sample did not change the attained maximum of the formation of symmetrical elements of the paintings.

Based on the results of preliminary tests, a summary table 3 was compiled for interpreting the data obtained in relation to the proposed method for determining the micro-fracture viscosity of thin amorphous-nanocrystalline films, on the basis of which it is possible to determine with high probability the optimal parameters for the indentation of samples of these alloys in the main series of tests.

From the data presented in the implementation example, it can be seen that the results obtained using the proposed method make it possible to achieve the claimed technical result, and the signs characterizing the proposed method are necessary and sufficient for its implementation.

Claims (3)

1. A method for determining the micro-fracture viscosity of thin amorphous-nanocrystalline films, including the manufacture of samples from a thin amorphous metal strip, the formation of an amorphous-nanocrystalline structure in them by controlled heat treatment, placement on substrates of metal and a polymer composite material, the study of micro-fracture viscosity by pressing it into a sample indenter in the form of a Vickers pyramid with a load, speed and time of exposure to the sample, allowing to provoke the appearance groups of cracks in the form of a system of embedded squares, calculation of the micro-fracture viscosity on the basis of data on the average distances between two parallel cracks in the group of cracks formed in the sample after the test, characterized in that before conducting the main series of tests, the first series of additional tests of one sample is carried out with different loads on the basis of which the optimal value of the indenter indentation force into the sample is determined, at which the probability of the appearance of a characteristic pattern of microdestruction max is minimum, followed by a second additional series of tests the optimum load value for another sample to determine the minimum distance between the test points and the test sample indentation edge, wherein the characteristic pattern shown microfracture. 2. The method according to p. 1, characterized in that the number of tests in the first and second additional series is at least 20 tests for each variant of the applied load and for each variant of the distance between the indentation points and the edge of the sample, while additional series of tests are stopped after that as revealed the range of values of the indenter indentation force into the sample, in which the probability of the formation of a characteristic microdestruction pattern exceeds 0.65 and containing the optimal value of the indentation force, and the minimum of allowable distance between the indentation and the test sample edge. 3. The method according to p. 1, characterized in that if during the tests in the central part of the sample the cracks formed contact with the cracks formed during the previous test or do not form a characteristic microdestruction pattern, then the distance between adjacent indentation points is increased by 1.5 times and the test is repeated, and the results of the previous test are not taken into account, and the distance between the indentation points is increased until a characteristic pattern of microfracture is manifested.

Images