CZ2013613A3 - Method of causing material microstructure for evaluation of grain size and apparatus for making the same - Google Patents

Abstract

Grain size assessment The indentographic system is based on the plastic deformation of the test material by the indentation method. The assembly comprises an indentation device (1) with a spherical indentor (2) or a toroidal indentor (3), a circular hole washer (4) or an annular groove washer (5), a test sample (6) with the surface being examined. The induction of the microstructure takes place by compressing or extruding the surface to be investigated by the indentor, thereby highlighting the grain boundaries and the sub-grains in the surface being examined. Subsequent evaluation of the grain size in the investigated surface takes place in the contact area of the indentation or in the indentation area using optical methods.

Description

Method for inducing a microstructure of a grain size evaluation material and apparatus for carrying out the method.

Technical field

The present invention relates to an indenthographic system for inducing a microstructure of a material by indenting indentors and subsequently evaluating a grain size comprising a test sample loading mechanism and a substrate.

BACKGROUND OF THE INVENTION

Determination of grain size of materials is very important in terms of understanding the development of microstructure and assessing material properties, quality control and behavioral prediction of structural elements. Grain size evaluation can be used to optimize production processes, eg during the forming and inter-annealing process, where a quick and simple method makes the entire technological process more efficient. Grain size is influenced by metallurgical processes of primary and secondary technologies - casting, thermal, mechanical and thermo-mechanical processes. Grain sizes are divided into globally recognized groups according to standards ranging from 1 (very coarse) to 10 (very fine) or more (ASTM E112, ASTM E930, ASTM E1181). In practice, the grain size is usually determined on the polished and subsequently etched surface of the material. By etching, the structure of the material is developed, which can be monitored by microscopic methods at standard magnification. Methods are known which make it possible to assess grain size indirectly on the basis of diffractive, ultrasonic or X-ray phenomena. Each type of material is distinguished by its unique chemical composition, specific processing and consequently physical and mechanical properties. These facts influence the process of metallographic preparation of specific materials and, from a practical point of view, the choice of the method of grain size determination. The approach to grain size evaluation divides these methods into direct and indirect.

The most widely used approach to the evaluation of grain size is metallographic method, which belongs in classical practice of material engineering to direct methods. Using the microscope, the surface of the test sample, the so-called cut, is observed in the polished and then

-2-etched state (EN ISO 643, EN 42 0462, CN1327151 (A) (Wen Bin) 2001-12-19, RU 2317539 C2 Lezinskaja Elena 26.08.2005). The processes for the preparation of cuts are based on the gradual abrasion of the material from the surface and subsequent polishing by means of polishing agents using abrasives of different roughness. The metallographic method is relatively simple, but may be complicated by the availability and aggressiveness of the chemicals used for etching and / or the etching process (the need for more demanding processes such as electrolytic etching, the use of elevated temperatures). The etching or erosive method of inducing material microstructure utilizes different properties of the structural components of the material under study (KRj20040099994 (A) (Lee Sang Nam) 2004-12-02, CNÍ102374962 (A) (Hongwei Zhang) 201203-14, KR20120097161 (A) (Kyung Hyun Park) ) 2012-09-03, CN102735704 (A) (Zejin Yu) 201210-17, KR20040110618 (A) (Hwang Gwang Jun) 2004-12-31, KR20040099994 (A) (Lee Sang Nam 2004-12-02). The microscopic analysis may then be based on one of the known methodologies such as comparative, linear, grain counting, Minister, etc. During microscopic evaluation, the identification of individual grains may be complicated due to specific microstructure, grain size inhomogeneity, or improperly selected etch. The fraction method of grain size evaluation uses the fracture surface of the test sample, which is monitored mainly by electron microscope (ČSN EN ISO 42 0643) or optical stereo microscope. Creating a fracture surface requires the preparation of a standard sample and the use of special equipment. It is known that fractography also deals with fracture surfaces of components that arose under operating conditions in order to determine the causes of its failure. The evaluation of grain size in the study of fracture surfaces is complicated by the impossibility to distinguish individual grains in the case of tougher materials due to plasticization of the fracture surface.

Indirect grain size evaluation methods are based on empirical and correlation dependencies between the grain size of the material and the mechanical or physical properties of the material. The response of the investigated material is evaluated in the form of a feedback signal, which is further converted into a grain parameter. The response is usually influenced by grain orientation in space and its size. To obtain a return signal, it is necessary to use a special device, which is often economically demanding and uses special software to evaluate the results. The change in the mechanical properties of the material depending on the grain size can be expressed, for example, by the Hall-Petch relationship, where the correlation dependencies will still be determined

- Necessary preparation of standard samples and use of metallographic methods. Crystallography, X-ray (X-ray), backscattered electron diffraction (EBSD), ultrasonic methods, electromagnetic methods and other indirect methods are also actively used in grain size evaluation and are based on the physical properties of the material.

Ultrasonic grain size control methods are among the most widespread non-destructive methods used in industry and are generally based on: measuring the ultrasonic field propagation rate between the surface of the material being examined and the measuring cell (JP (2010236886 (A) (Matsuda Kohei) 2010-10-21) or in surface of studied material (RU 2350944 Cl Britvin Vladimír 09.08.2007); measurement of ultrasonic field propagation velocity and attenuation (JP58195148 (A) (Kawashima Katsuhiro) 1983-11-14, J $ H77160 (A) (Ichikawa Fumihiko) 1992-06-24, JR2006284349 (A) (Nagata Yasuaki) 2006-1019, KRZ0010061641 (A) (Hong Sun Taek) 2001-07-07, ZA8200664 (A) (Vanhuffel Rene) 198212-29, JP53126991 (A) Matsuda Shiyouichi 1978-11-06, RU 2334224 Cl Pavros Sergey January 16, 2007, WO 2007/148655 Al Ohara Kazuhiro December 27, 2007, JP2006250737 (A) (Jodai Tetsushi) 2006-09-21, US 4719583 Hideo Takafuji 12.01.1988); analyzing the shape of the ultrasonic wave after interaction is investigated (JR56058659 (A) (Inouchi Tooru) 1981-05-21, JP2001343366 (A) (Hashimoto Tatsuya) 2001-12-14, JP4095870 (A), Shibata Saburo 1992-0327).

Diffraction methods to distinguish individual grains using X-ray (US4649556 (A) (Rinik Christine) 1987-03-10, US 2003/0012334 Al David S.Kurtz 16.01.2003) or optical (JF * 61079139 (A) Nakatate Suezo 1986-04 -22) rays. Optical devices are also used to measure the grain size of thin coatings based on the reflectance of a laser beam (Kf & OO10095474 (A) (Cho Hyeong Seok) 2001-11-07, KR120010095474 (A) (Cho Hyeong Seok) ¹ i

2001-11-07, .1 ^ 63238536 (A) Minami Shigeo 1988-10-04, JP / 11153419 (A) Hashimoto Kazuki 1999-06-08, US 5149978 Jon Opsal 22/09/1992, US á 91855 B1 Hamphrey J Maris! 'i I i

20.02.2001) or spectral evaluation of electrical discharge between sample and electrode (JP10300659 (A) (Yamamoto Akira) 1998-11-13, JP6242003 (A) (Sugimoto Kazumasa) 199409-02.

-4Electro-magnetic methods allow grain observation in sheet and coating material by detecting magnetic field leakage at grain boundaries (JP8-145953 (A) (Ishihara Michiaki) 1996-06-07, JP59180355 (A) (Toyoda Toshio) 1984-10-13 JP59-109859 (A) (Soy Kazuo) 1984-06-25, US 7063752 B2 Joyoung Koo 20.06.2006), by correlating the electrode potential of the coating material (JP2236402 (A) Okada Takeshi 1990-09-19) or eddy currents, and hysteresis properties of the investigated material (JR7128295 (A) (Yanai Toshiyuki) 1995-05-19). Correlation is also governed by grain size estimation according to heat (JØ7062434 (A) (Kondo Yasumitsu) 1995-03-07) and thermo-mechanical (υ5 ^ 07634 (A) (Martin Ricky L) 1995-04-18, JP52020320 ( A) Hoshino Kazuo 1977-02-16) processing.

SUMMARY OF THE INVENTION

The above drawbacks are largely overcome by an indentative grain size evaluation system based on plastic deformation of the test material by an indentation method comprising an indentation device with a spherical or toroidal indentor, a circular hole washer or an annular groove washer, sample. The induction of the microstructure is effected by squeezing or extruding the surface to be examined by the indentor, thereby enhancing grain and sub-grain boundaries in the surface of interest. The subsequent evaluation of the grain size in the surface to be examined can be carried out in the contact area of the indentation or in the vicinity of the indentation by means of a microscope.

Double indentation of the spherical indentor is the principal indentation method of the present invention which enhances the microstructure of the subsurface area of the indentation in the surface to be examined after the indentation. This is followed by a microscope evaluation of the grain size in the embossed impression. To induce a microstructure during one indentation cycle, a spherical indentor and a washer with a circular hole in the middle or an indentor of a toroidal shape with a washer with an annular groove are used. The toroidal indentor is used to increase the deformed area suitable for evaluating the microstructure of a test specimen by extrusion or indentation of the test surface. Microscope evaluation of grain size in the extruded area follows. The contact area of the indentation is also a source of information about the grain size and sub-grain, as well as the surface of the test material examined in the vicinity of the indentation.

It is known that the mechanical behavior of a grain in a material depends on its spatial orientation relative to the load axis. An important factor is the angle between the main load direction, ie the axis of the indentor and the atomic planes of the grain, which ranges between 0 and 90 °, which results in a gradient of the measured values of the mechanical properties of the individual grains. This knowledge contributes to the understanding of the basic principle of indenthographic image formation, which arises from different behavior of individual grains and grain boundaries. It is also known that bond disruption in the material is easiest along grain boundaries since these sites are most densely populated by crystal lattice defects such as dislocations, point defects, inclusions, etc. Thus, the grain gets under load, depending on its size and orientation in the space, it rotates with respect to the load axis and other grains. This change of grain orientation, accompanied by the breaking of bonds in the material, achieves the most energy-efficient state under the given load, which is manifested by the induction of structural relief. Sufficiently large area and depth of indentation, together with optimum sample thickness, give rise to a significant relief at the boundary between grains or sub-grains, formed by different height of grains or sub-grains relative to the contact surface of the indentation, or by tearing grains apart. The formation of cracks along grain boundaries is a typical manifestation of fragile materials, which is comparable to intercrystalline fracture. In the case of tougher materials, grain rotation and sliding along grain boundaries are performed. The contact area of the first indentation is further monitored for subsequent grain size determination. The indenthographic method of sample preparation for grain size evaluation makes it possible to reliably distinguish grain from sub-grain, since transcrystalline fracture does not occur in this method, since the deformation takes place at grain boundary and sub-grain slips. The test area of the tough materials after microstructure development has additional information on the character of the slip systems of the test material, which enables a more detailed understanding of the microstructure development and its mechanical behavior.

The essence of creating an indenthographic image is the movement of dislocations. Founder of contact mechanics Heirich Rudolf Hertz, in 1882 discovered that the elastic contact pressure, which is transmitted by a spherical indentor to the flat glass surface during the indentation, has an elliptical distribution and depends on the modulus of elasticity of the investigated materials. In 1717, Issac Newton observed the phenomenon of alternating dark and light concentric rings of an elliptical shape as a result of light reflection between a spherical and a flat surface

-6i »glass bodies. Later, Taylor Geoffrey Ingram, Michael Polanyi, and Egon Orowan clarified the deformation behavior of tough materials using the dislocation theory developed by Mr. Vito Volterra in 1905. The dislocation represents the boundary of the mutual displacement of the micro-volumes of material while delimiting structural features at different levels, , sub-grain, crystal. The dislocation propagation takes place by jumping to a certain discrete distance, where the final length of the jump and its speed depends on the size of the structural formation it propagates and its mechanical properties, the driving force. It follows that the geometry of concentrically arranged elliptical rings around the indentation left by the spherical shape indentor is dependent on the mechanical properties of the test material. The width of these rings corresponds to the dimensions of the structural features that make up the material under investigation and represents the distances between the areas that are most densely occupied by dislocations. The maximum distance from the indentation to which these dislocation elliptical formations extend depends on the pressure in the contact area between the indentor and the surface of the test specimen as well as the depth of the indentation. The intensity of the enhancement of the microstructure morphology around the indentation decreases with the distance from the indentation. The largest plastic deformation after indentation has the undulation area at the edge of the indentation. However, the distance between the elliptical formations in the direction from the load axis is practically constant. The deformation elliptical formations have a longer range from the load axis for harder materials, thus also contributing to more accurate grain size measurements. In the case of softer materials, elliptical formations occur only at a shorter distance, thus limiting the possibility of measuring the grain size around the indentation.

Clarification of the figures in the drawings

The invention will be described in more detail with reference to the accompanying drawings.

Giant. (a) an indenthographic assembly comprising an indentation device, a spherical indentor, a sample, and a washer with a circular orifice. Giant. 2 (b) an indenthographic system comprising an indentation device, a toroidal indentor, a sample and an annular washer. Giant. 2 (a) initial position of the spherical indentor on the test surface of the specimen. Giant. 2 (b) penetrating the spherical indentor into the test surface of the test sample and forming the first indentation. Giant. 2 (c) the initial position of the spherical indentor on the opposite side of the specimen above the first indent in the surface to be examined,

-7 which is left by the spherical indentor, the indentor axis is identical to the first indentor axis. Giant. 2 (d) penetrating the spherical indentor into the surface of the opposite side of the test sample and forming a second indentation. Giant. 3 (a) the initial position of the spherical indentor on the opposite surface of the test specimen, the test surface of the test specimen lies on a support with a circular creature, the axis of the hole being identical to the axis of the indentor. Giant. 3 (b) penetrating the spherical indentor into the surface of the opposite side of the test specimen and forming an indentation, the test surface of the test specimen is extruded into a circular hole in a washer with a circular hole. Giant. 4 (a) the initial position of the toroidal shape indentor on the opposite side of the test sample. Giant. 4 (b) penetrating the spherical indentor into the opposite side of the test specimen and forming the indentor, the test surface of the test specimen is extruded into the annular hole in the washer with the annular hole, the axis of the washer coinciding with the indentor axis. Giant. 5 (a) the initial position of the toroidal shape indentor on the sample surface to be examined. Giant. (B) penetrating the toroidal shape indentor into the test surface of the test sample and indenting it.

DETAILED DESCRIPTION OF THE INVENTION

The objects and advantages of the present invention are described in detail in the following and accompanied by a pictorial documentation. The proposed methodology for assessing grain size is based on direct grain observation, using metallographic and fractographic techniques and should be properly called indenthography. The indenthographic system of FIG. 1a comprises an indentation device 1, a spherical indentor 2, a sample 6 and a washer 4 with a circular opening. A second variant of the indenthographic system is shown in FIG. 1b, which comprises an indentation device 1, a toroidal-shaped indentor 2, a sample 6 and a washer 5 with an annular opening.

The basic principle of induction of microstructure by indenthographic method is described in Fig. 2, where the two-sided indentation of the test specimen 6 is shown. To optimize the microstructure development process, the thickness of the specimen should correspond to the depth of the plastic area below the indentor 2, which roughly corresponds to! ten times the depth of indentation after indentation. For example, if the indentation depth of the Brinell-shaped indentor 2 is equal to 0.3 mm, the optimum sample thickness 6 is 3 mm. Sample 6 is prepared by a standard metallographic process, ie cutting, grinding, polishing. To optimize the subsequent grain size evaluation process

-The impression area should be as large as possible. This is achieved by increasing the contact area between the indentor 2 and the test specimen 6 and the loading force, for example using a 10 mm diameter Brinell spherical indentor 2 and a load of 30 kN.

Microstructure development by bilateral identification - fig. 2 of the test specimen 6 proceeds in such a way that the polished surface of the specimen 6, which is in contact with the spherical shape indentor 2, FIG. 2a is identified first; FIG. 2b and the subsequent second indentation takes place from the opposite side of the specimen 6 in the axis of the first indentation; 2c. The first indent on the polished surface is then pushed back due to plastic deformation of the entire sample volume 6 between the first and second indentation. 2d. Injection of the indentor 2 takes place using the same parameters as for estimating the optimum thickness of the test specimen 6. This reverse or backward induces plastic deformation and to a certain extent forces the contact surface of the first indentation back. The polished indentation area then contains traces of plastic deformation where the resulting slips or cracks along the grain boundaries, easily identified by microscopic methods, indicate the grain size in the test material. Depending on the grain size, a stereomicroscope or electron microscope is further used for subsequent grain size assessment, thereby widening the grain size identification and reliably moving in the range of micrometer to millimeter units.

To induce a microstructure during one indentation cycle - FIG. 3, FIG. 4; FIG. 5, it is necessary to use a washer 4 with a circular opening or a washer 5 with an annular opening. When using a washer 4 with a circular hole, the surface of interest is extruded into a circular hole. 3a by means of a spherical shape indentor 2, wherein the stress acts predominantly in one direction, which is identical to the load axis - FIG. 3b. When using a washer 5 with an annular hole, the surface to be monitored is forced into the annular hole - FIG. 4a by means of a toroidal-shaped indentor 3, FIG. 4b. This is followed by observation using a microscope. The response of individual grains to the magnitude of this stress depends on their orientation and is subsequently manifested by a different displacement relative to the plane of the monitored surface. A toroidal indentor 3 is used to induce the microstructure during a single indentation cycle without having to create a special test sample 6 of optimum thickness. 5a. To determine the grain size, the plastically deformed surface area of the test sample 6, which is closed by the toroidal indentor 3, is monitored by a microscope. 5b. Use this

The inductor 3 induces a more complicated voltage state in the investigated area of the test material. Here, it is important to understand this stress state as a result of integrating the deformation action from the spherical indentor 2 along the perimeter of the common contact surface of the toroidal indentor 3 with the test specimen 6. Thus, the resulting deformation action, centered towards the load axis, layers of the test surface enclosed by the toroidal indentor 3 and is shown in the form of slip lines. The resulting slip lines surround the grains and sub-grains, creating the background of the indenthographic image, thereby highlighting the grain and sub-grain boundaries in the test area.

In FIG. 6 shows the microstructure of the test material induced by the principle described in FIG. 2. FIG. 6 clearly show the grains - closed polygonal formations, and the grain boundaries of the test material - bright closed loops around the grains in the contact area of the first indentation. In FIG. 7 shows the microstructure of the test material induced by the principle described in FIG. 3. In FIG. 7, grains and their boundaries are clearly visible with additional information about slip planes.

Industrial applicability

The device for inducing the material microstructure by indentor indentation according to the invention will find application especially in the field of material engineering, in modernization of existing obsolete hardness testers and extension of their applicability in scientific research workplaces. In the industrial sector, it can be used in product quality control and development. Depending on the equipment, the use of the equipment is possible both in combination with other available load methods and as an autonomous unit.

Claims (3)

PATENT CLAIMS Method for developing a microstructure of a grain size evaluation material, characterized in that the microstructure development is carried out by compressing or extruding the investigated surface by an indentor, to highlight grain boundaries and sub-grains in the investigated surface, and subsequently evaluating the grain size in the investigated surface the indentor indentation is double and / or backward. Device for carrying out the method according to claim 1, characterized in that it comprises an indentation device (1) with a spherical indentor (2) for producing a double-sided indentation or for extruding the surface to be examined into a circular hole in the washer (4) with an indentor (2) spherical. Device for carrying out the method according to claim 2, characterized in that it comprises an indentation device (1) with a toroidal indentor (3) for producing a double-sided indentation or for extruding the examined surface into an annular groove in the annular groove washer (5). shape using indentor