RU2140075C1 - Process investigating properties of material of article - Google Patents

Abstract

FIELD: nondestructive acoustic method of examination of physical and mechanical properties of materials. SUBSTANCE: given process includes loading of standard and tested articles with indenter with change of indentation depth by means of its movement along arc of circle, recording of signals of acoustic emission and evaluation of properties of material with the aid of comparison of signal parameters by separation criterion Ks from standard and tested articles found by dependence Ks = lg(Ec/τ²), where Ec is energy of pulses, τ is duration of pulses. EFFECT: enhanced accuracy of investigation of properties of material of article and expanded technological capabilities of process. 8 dwg, 2 tbl

Description

 The method relates to non-destructive acoustic methods for studying the (physicomechanical) properties of products, including metal-cutting tools with wear-resistant coatings, including relates to methods for identifying products (In the literature, for example, Vainberg V.E. state of the cutting tool // Defectoscopy, 1989, N 10, p.29, the term "recognition" is used, but it is more correct to use the term "identification" here).

 It is known (A. S. USSR N 1555659) a solution in which the relationship between the speed of propagation of acoustic waves and the electrical resistivity of the material of the products is found, the limits of rejection are determined, the acoustic parameters of the samples cut from the products are measured, and the products are rejected according to the measurement results. If we consider the function of sorting (sorting into suitable and unusable products) as a study of the properties and identification of products by the properties of their materials, then the disadvantage of this method is its complexity (it is necessary to study the selection of products, cut out samples from them).

 The closest according to the applicant in technical essence is (A.S. USSR N 1585728) a solution according to which a sample (made of tool steel and carbide coating or plate) is loaded with an indenter (indentation) indentation near their interface. In this case, tool steel is used as a reference, a coating as a test product. Simultaneously with loading (from the moment of indentation indentation), acoustic emission signals are recorded (the number of signals is fixed) (when the standard and the product are destroyed), properties (crack resistance) of the product material are evaluated by comparing the parameters (the ratio of the number of signals) of the signals from the standard and the product. The disadvantage of this solution is its limited capabilities (only for a soldered tool or carbide-coated steel) and relatively low accuracy (the ambiguous concept “near the interface” and “in the front crumb zone” is used) of research.

 The task of the invention is to increase the information content of acoustic emission signals on the mechanisms of destruction of the investigated materials.

 The technical result achieved in solving the problem is to expand the technological capabilities of the research method and increase the accuracy of research.

 The specified technical result is achieved through the application of loading conditions close to the actual operating conditions of the products, and the use of more informative energy parameters of acoustic emission, characterizing the accumulation of damage to the material of the product over time. In particular, not the number of acoustic emission signals was used for this, but the energy and duration of acoustic emission pulses, which make it possible to distinguish the presence of brittle and viscous mechanisms of material destruction.

Thus, the claimed object, like the prototype, includes loading the standard and the product used by introducing the indenter, simultaneously loading the acoustic emission signals, evaluating the properties of the product material by comparing the parameters of the signals from the standard and the product. However, the claimed object is characterized in that the loading is carried out with a change in the depth of penetration of the indenter by means of its movement along the arc of a circle described by the pendulum carrying the indenter, the energy E _c (b ² • s) and the duration τ (c) of pulses are taken as recorded parameters of acoustic emission properties are evaluated according to the criterion of separation of pulses, determined by the dependence K _p = logE _c / τ, including the identification of material products by comparing the values of the separation criterion. At the same time, an energy storage diagram over time is additionally obtained (built), and product identification is carried out by comparing the identity of the graphs for standards and products.

 These features are significant, new and inventive.

 In FIG. 1 shows a classification scheme (separation) of AE signals.

 Figure 2 shows a diagram of the symmetric loading of the product with a multilayer coating.

 Figure 3 shows a diagram with the edge loading of the product.

 Figure 4-8 shows examples of graphs of energy storage during exposure of the indenter to the product.

The essence of the method is based on the fact that AE signals generated during loading of the product can be classified into various types of pulses. The fewer such types of pulses, the easier it is to distinguish them from each other. Therefore, it is necessary to create such a loading scheme for the product that would not affect its performance (impact on local microvolumes), provide pulses that are easily distinguishable from each other, and at the same time, if necessary, provide information on any of the traditionally used AE parameters . From the point of view of plasticity of materials, the envelopes 1, 2 (Fig. 1) of pulses are divided into two different types A and B, which differ fundamentally. Type A (envelopes 1, 2) is characterized by a small amplitude (A ₁ and A ₂ ) with a significant pulse duration (τ ₁ and τ ₂ ). Type B - significant amplitude with a short duration. Type A is caused by the processes of microplastic deformation of the material, type B is caused by failure, i.e. formation and growth of cracks.

 Therefore, it is necessary to create such a loading scheme of products in which both of these types of signals are present. First of all, it should be microloading, i.e. load localization on minimum volumes of material. The introduction of the indenter is not suitable, since with this loading scheme the fraction of microplastic deformation is small, i.e. the fraction of type A pulses is small. Scribing (sclerometric studies) is also not very suitable, because here either microplastic deformation prevails (with a small depth of penetration of the indenter into the product material) or brittle fracture (type B with a large depth of penetration of the indenter). Such a loading scheme is necessary in which there would be a small and significant depth of penetration of the indenter, i.e. pulses of both types. This is possible when loading with a variable penetration depth.

 Such a scheme can be implemented in the case of a pendulum type of loading, when the indenter, being fixed on a pendulum rotating (swinging) around its axis, moves (motion B) along the arc of rotation of the pendulum and, therefore, loads the material of the product with a variable indenter penetration depth (this can be microns, hence the length of the cut of the indenter is localized).

The method was implemented as follows. We took products from instrumental materials (carbide inserts). They were loaded according to the described scheme (penetration depth 2-20 μm). In the process of loading, AE signals were recorded and, according to a package of special programs, were analyzed in a computer. In the process of signal analysis, the energy E _cj (b ² • s) and the duration τ (c) of the recorded sequence (from 1 to the last with intermediate j-th through the selected sampling step) of the acoustic emission signals were determined:
E _cj = ΔτΣ (ΔuA $\genfrac{}{}{0ex}{}{\text{i}}{\text{j}}$ ) ² , b ² • c (1)
τ _j = ΔτL • E _j , (2)
where Δτ is the sampling time interval; Δu is the price of the division of the discharge of the analog-to-digital converter (input sensitivity); A _i ^j - the number of bits of the analog-to-digital Converter for the i-th reference amplitude of the j-th signal; LE _j is the duration of the j-th signal in machine samples.

Then the criterion for the separation of signals (pulses) was determined:
K _p = log (E _c / τ ² ) (3)
In physical terms, it is adequate to the rate of change of energy density during loading. From the essence of the analysis of AE signals, it can be called a criterion for separating AE pulses.

 For each material, a reference product was chosen, the remaining products from this material were investigated.

Then, the products were subjected to microfractographic analysis (using an electron microscope) over the surface exposed to the indenter, and the nature (presence and number of breaks, cracks, etc.) and type (deformation, shear, delamination, etc.) were revealed by the fracture traces. destruction of microvolumes of products. We compared the results To _p and the results of the destruction of products. They judged the properties of the materials of the products and classified (divided, sorted) the products according to the value of the criterion K _p , i.e. identification of products by K _p . Additional identification was performed when analyzing the graph of energy storage over time, namely, the graphs of the standard and products were compared, and recognition was carried out by the identity of the graphs.

 The product loading diagram is shown in FIG. 2 and 3, where due to the rotation of Indenter 3 with the appropriate depth of penetration into the product, it acts on the product containing the base 4 with several 5, 6, 7, 8 or one coating layer with a symmetric (Fig. 2) or edge (Fig. 3 ) loading.

 Example 1 of the implementation of the method.

In practice, there are cases of external similarity of products in shape, color (and weight). For example, carbide inserts of metal cutting tools with wear-resistant coatings of the same size and shape are extremely difficult to distinguish. Their color is very similar, depending on the technology of preparation of the base and coating. Labeling on the products is not performed, it is performed on the packaging box (or inserted into it), as a result, errors are possible (which often happens). Moreover, the design and composition of coatings in the markings are indicated conditionally. For example, the number, order of location and thickness of the coating layers are not indicated. For the operator, this information is often important. He receives it (as a rule) on his own, for example, makes an oblique section on the product and examines it. It is difficult and time consuming. Moreover, having examined one product, there is no certainty that the other products in the package are the same. To implement the method, a series of VK8 + TiN plates were taken; BK8 + ZrN; BK8 + Ti + TiN; BK8 + Zr + ZrN; BK8 + TiC + TiCN + TiN. A control sample (reference) was taken from each series of plates (products). Examining oblique sections on them, they were convinced of the conformity of their series (inscriptions, markings). The above-described pendulum method was used to load the articles during micro cutting (with a depth of 5–20 μm) by an indenter, acoustic emission signals were recorded, and E _c , τ, K _{p was} determined for each product. They did the same with the standards. Assigned to them conditional serial numbers (in tens). The numbers were applied to the products (out of sight, i.e. they wrote the number on the back). All products (mixing the series) were mixed together. Choose a product by accident. They loaded it again under similar conditions and, according to the value of K _p, classified (identified to which series it belongs) its belonging to a particular series of products (i.e., the coating of the product was recognized). The results are shown in table 1. The denominator shows the serial numbers assigned to the products.

From the data table shows that the criterion K _p allows you to separate the product. However, due to the similarity of the properties of the materials in some cases (product number 8 from the VK8 + TiN series and number 29 from the VK8 + ZrN series), the values of the criterion K _p are close or the same for the given accuracy of calculations, which makes it difficult to recognize (recognize the material) products. There is no such coincidence of the K _p values if the design and composition of the coatings are significantly different. For example, the values of K _p for VK8 + TiN, VK8 + Zr + ZrN, VK8 + TiC + TiCN + TiN are significantly different, there are no problems with product recognition. Moreover, they are not there if the basis of the coatings is different, for example, VK8, T15 K6, TT10 K8B.

Then all (i.e., all 45 products) were mixed, several products were selected randomly. They were loaded under the same conditions, K _{p was} determined, Table 2. By the magnitude of K _p, they tried to determine a series of products (i.e., what coating was applied to VK8). In general, this succeeded (product A, B, G, I, K). But due to the very close similarity of the coatings (and the values of K _p, respectively), this cannot be definitely done (products B, D, E), i.e. doubts remain. Then (according to the value of K _p according to the numbering of products according to Table 1), they tried to guess the number previously applied to the product (second line from the bottom in table 2). Then checked the alleged numbers and valid. There were no errors. The accuracy of identification of products by the properties of the material is quite high, but with the equality of K _p for different products (products B, D, E) doubts about the accuracy of identification remain.

 Example 2 of the implementation of the method.

 We took only those products for which doubts remained from Example 1, i.e., products 14, 17, 23, 27 and standards (numbers 20 and 30) of those series to which these products could (Table 2) be assigned. Rather, a schedule of energy storage during testing was extracted (printed) from the computer for these product numbers. Such a schedule is constructed according to the program from the data of AE signals entering the computer during the testing of products.

First of all, we were convinced that the energy storage schedule (mb ² s) in time (ms) really characterizes a specific material (it is a material passport). Samples were taken from one batch of products, using available methods (by marking, hardness, microhardness, thin section testing, and coating thickness control) to verify their identity. They were subjected to loading under similar conditions, and a plot of energy storage E (mb ² s) over time τ (ms) was obtained. The similarity (identity) of the graphs was analyzed. So, figure 4 shows an example of three graphs for three identical products. The similarity of the graphs is largely, the identity is clearly visible (steps, values of E _i , E _k , E _j , Δτ). At least the type of graphs shown in FIG. 4 is significantly different from the type of graphs shown in FIG. 5 (these are graphs for two samples that are representatives of a completely different material). Here is a different number of steps, their location on the graph, Δτ, etc.

 Having ascertained that the energy storage schedule is a “passport” of the product material, we proceeded to analyze the indicated products with numbers 14, 17, 23, 27. So, comparing the graphs for products 14, 17, 23, 27 with the graphs of standards (products 20 and 30 ) it was found that the graphics of reference 20 correspond to the schedules of products 14 and 17 (for products 17 and reference 20, examples of graphs are given in Fig. 6), i.e. products 20, 14 and 17 belong to the same series and, judging by the standard 20, all these products are VK8 + Ti + TiN. Judging by table 1, this is indeed so, i.e., product recognition has taken place. It was also found that the graphics of the standard 30 correspond to the graphics of the products 23 and 27, Fig. 7, i.e. These are products from the VK8 + ZrN series, i.e. recognition took place.

 From the graphs of energy storage over time, shown in Fig.6 and Fig.7 it is clearly seen that the type of graphs on them is completely different, they can not be confused, that is, the use of graphs additionally allows to increase the information content of AE signals and, thereby, increase the recognition accuracy products.

 Example 3 of the implementation of the method.

We took one test sample (item 35) and a reference for it (item 40). Product 35 was placed along with other products (made from completely different materials). Alternately loaded products. The value of the criterion K _p separation was not determined, immediately received only the graphs of energy storage over time. The graphs are shown in FIG. 8. Of these, it is clearly visible (only by the values of E _i and E _j , and it is also possible to analyze by Δτ that only one graph corresponds to the schedule of pattern 40, namely, the pattern of product 35. From this example it follows that recognition can only be made by graphs , ie, without the value of K _p . This is so. But taking into account the value of the criterion K _p, separation is more reliable.

 The above examples show that simplification of the research, increasing the accuracy of research, expanding the capabilities of the method and ensuring the identification of the material of the products due to the choice of acoustic emission parameters that increase the information content and the loading scheme, providing local non-destructive effect of the indenter on the product.

Claims (1)

A method for studying the properties of the product material, which includes loading the standard and the test product by introducing an indenter, simultaneously recording acoustic emission signals, evaluating the properties of the material by comparing the parameters of the signals from the standard and the product, characterized in that the loading is performed with a change in the depth of introduction of the indenter by means of its movements along a circular arc described by the pendulum bearing indenter, as registered parameters _to take energy E (b ²⁾ and time- NOSTA τ (c) pulses, evaluation properties of the material produced by the criterion of separation _Kp pulses determined from the dependence of _{K p = lg (E c /} τ), the method further comprising, comparing the magnitude criterion of separation and pulse energy accumulation schedules time for standards and products, identify the material of the product.

Images