RU2138038C1 - Method testing physical and mechanical properties of articles - Google Patents

Abstract

FIELD: non-destructive testing of physical, mechanical and operational properties of articles with coats. SUBSTANCE: method includes loading of tested article with indenter, registration of parameters of signals of acoustic emission, namely, energy of pulses of acoustic emission and duration of pulse, evaluation of quality of adhesion of coat to base. Criterion of separation of pulses K_p= lg(E_c/τ²), is used as means testing properties of articles, where Ec is energy of pulses, τ - is duration of pulses. EFFECT: substantially enhanced accuracy of test of properties of articles. 3 cl, 8 dwg

Description

 The invention relates to acoustic methods of non-destructive testing of physico-mechanical and operational properties of products, mainly products with coatings, including metal cutting tools with wear-resistant coatings in terms of the adhesion quality of the coating to the base.

 A solution is known (USSR AS N1580229), which includes the creation of mechanical stresses as a result of loading the product along the base-coating interface, the simultaneous loading of acoustic emission (AE) signals, and the assessment of the adhesion strength (adhesion quality) of the adhesion of the coating to the base on mechanical stresses arising at the time of sharp growth of AE signals. The disadvantage of the solution is its limited ability (only the adhesion quality and nothing about the crack resistance of the coating or base) of application and the complexity of stress control.

 The closest in the opinion of the applicant in technical essence to the claimed object is the solution (the essence of the solution is described on pages 47-56 of the work: Kabaldin Yu.G., Mokritsky B.Ya., Semashko N.A., Taraev S.P. "Modern methods of designing, quality control and predicting the health of the cutting tool ", Vladivostok, DVU publishing house, 1990, - 122 pp., copies of these pages of the work are attached), including loading by the indenter of the products, simultaneous loading of the registration of AE signals, control of physical and mechanical properties ( crack resistance bone and adhesion quality of the coating to the base) of the product material according to the parameters of AE signals. The disadvantage of this solution is its complexity (it is necessary to record the number of AE pulses at various stages of indenter penetration, dwell and withdrawal) and the relatively low control accuracy (it is difficult to separate the pulses by the stages of indenter implantation).

 The objective of the proposed solution is to increase the accuracy of control of the physico-mechanical properties of products and simplify the control method without reducing the capabilities of the method.

 The technical result achieved in solving the problem lies in increasing the information content of AE signals by assessing the crack resistance of products and the quality of adhesion of their coatings to the base.

 The technical result is achieved by choosing such parameters of AE signals that characterize the energy indicators of the destruction of the surface layers of the products when they are loaded, namely, the energy of the AE pulses and the pulse duration, which allow using the pulse separation criterion adequate to the rate of change of energy density as a means of monitoring the properties of the products. Therefore, the accuracy of control is increased by increasing the information content of AE signals due to the use of AE signals to control the energy parameters, reflecting the physical nature of the deformation and destruction of the product material under loading.

где E_c - энергия импульса, b²•c;
τ - длительность импульса, с.Thus, the claimed object, as well as the prototype, includes loading by the indenter of the product, simultaneously with loading the registration of acoustic emission signals, control of the physical and mechanical properties of the material of the products according to the parameters of the signals. However, the inventive object is characterized in that the energy of the pulses is taken as a parameter of the signals, and the properties of the product are controlled by the criterion of separation of acoustic emission pulses, which is adequate to the rate of change of energy density and is determined by the dependence

where E _c is the pulse energy, b ² • c;
τ is the pulse duration, s.

Moreover, for a comparative assessment of the quality of adhesion of the coating to the base, a histogram of the criterion K _{p is used} from the condition: the smaller the area of the graph K _p on the histogram with an equal number of recorded signals and the value of the criterion K _p corresponding to the maximum of the envelope of the histogram, the higher the adhesion quality. With comparable and equal areas, the adhesion quality is higher for the product for which the maximum envelope corresponds to a smaller value of the criterion K _p .

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

In FIG. 2 shows a histogram of the dependence of the criterion K _p on the number N of AE signals for the item N1.

 In FIG. 3 shows the same for item N4.

 In FIG. 4 shows the same for article N5, in FIG. 5 - for item N7 (dash-dot line is the envelope of the histogram), in FIG. 6 - for product N9, in FIG. 7 - for product N10, in FIG. 8 - for product N8.

The method is implemented as follows. Products (they took instrumental hard alloys without coating and with wear-resistant coatings) were subjected to loading by an indenter (on a hardness tester, a special device) without breaking (pressing or scribing) the product. In the process of loading, acoustic emission signals were received, excited by deformation or destruction of the product material, various (by analogy, prototype and claimed object) parameters of acoustic emission signals were recorded using equipment (standard instruments, or through an analog-to-digital converter interacting with a programmable electronic computer machine). Including recorded amplitudes A _i energy E _c and duration τ ₁ envelopes of pulses of acoustic emission. From the point of view of the plasticity of the product materials, the pulse envelopes are divided into two different types A and B. The pulses of these types differ fundamentally. Type A (examples of envelopes 1 and 2 of the pulses are shown in Fig. 1) are characterized by a small amplitude (A ₁ and A ₂ ) with a significant duration (τ ₁ and τ ₂ ). Type B is characterized by significant amplitude at short duration. At least the ratio of the amplitude to the duration of type B is much larger than that of type A. The physics of the process and calibration tests show that the reasons for the difference in the pulses for these types are the essence of the destruction of the material: type A is caused by microplastic deformation processes, type B is caused by the formation and straining microcracks. In the process of growth of the formed microcracks, one or another type is present.

The recorded acoustic emission signals were analyzed in a computer (software package). During the analysis, the energy of acoustic emission signals (pulse energy) E _ci (unit of measure b ² c) and the duration τ _i (unit of measure c) of the recorded sequence (from 1 to the last with intermediate i-ths through the selected sampling step) of acoustic emission signals were determined (hereinafter AE):
E _cj = ΔτΣ (ΔuA $\genfrac{}{}{0ex}{}{\text{i}}{\text{j}}$ ) ² , b ² c, (1)
τ _j = ΔτL • E _j , c, (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 _j ⁱ - 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 we define some criterion
K _p = log (E _c / τ ² ) (3)
In the physical sense, it is adequate to the rate of change of the energy density of AE signals during loading. From the essence of the analysis of AE signals, it can be called a criterion for separating AE pulses.

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, cleavage, peeling, etc.) were revealed by the signs of fracture. ) destruction of microvolumes of products. We compared the values of K _p and the results of the destruction of the products. They judged the physicomechanical properties of the material of the products, in particular, the quality of adhesion of the coating to the substrate.

Example 1 of the implementation of the method. We took several products (carbide cutting inserts of a metal cutting tool), namely, VK8 coated material (thickness up to 10 μm) TiN. Coatings are applied according to different technologies, i.e., various physical and mechanical properties are possible. Samples were numbered, mounted on a loading device (arranged according to the pendulum principle, the product was loaded on the test surface with an indenter in the form of a standard pyramid, cone, etc.), the indenter penetration depth was set (10-12 μm, i.e., slightly more than the coating thickness , 8-10 microns - commensurate with the thickness, 5-7 microns - less than the coating thickness, in the course of research it was found that the penetration depth does not play a decisive role, but products are evaluated more accurately and faster if the depth exceeds the coating thickness), the loading signals A E, and through an analog-to-digital converter was submitted to a computer for registration and analysis. The AE signals were processed and analyzed using an application software package, the values of E _c , τ were determined in a known manner, the values of the criterion K _p were calculated, and the distribution (histogram) of the values of K _{p was} calculated based on the number N of signals. The samples were examined using microfractographic analysis of the traces of fracture by the indenter (the area of coating spalling along the trace left by the indenter, which stopped in front of the indenter in front of it, the number and area of cracks, etc.). The same samples were subjected to full-scale tests when cutting metal (heat-treated hard-to-process special cast iron) under the same cutting conditions. The physicomechanical properties of the material of the products (i.e., the quality of adhesion of the coating to the base, crack resistance of the coating, base, etc.) were evaluated by the intensity of chipping and wear of the coating at the cutting edge. It was believed, for example, that the greater the chips and wear, the lower the grip quality. Some test results are given in table. 1.

Analysis of the data in table 1 shows:
1. The criterion K _{p of} separation of signals (pulses) of acoustic emission unambiguously reflects the results of control of the physicomechanical properties of the product and arranges the products in the same order (quality level) in which they are placed by microfractographic studies and studies of working capacity during cutting.

2. The adhesion quality of the coating to the base is adequately characterized not only by the value of the criterion K _p , but also by the area of the histogram, moreover, it is more precisely characterized by the area (if the difference in the value of K _{p of} products N1 and N4 is only 0.05, then the difference in the area of the histograms, FIG. 2 and 3, these products have significantly more) histograms.

It is convenient to compare the areas of the histograms for identical conditions, i.e. at the same scale of building the histogram, with the equality of the number N _{i of} signals and the correspondence (equality) of the values of K _{pi of the} criterion K _{p to the} maximum of the histogram (envelope of the histogram). Examples of this are shown in FIG. 2 and 3, respectively, for article N1 and article N4. If they have equal N _i and K _{pi, the} area in arbitrary units (for the selected histogram scale in arbitrary mm ² ) is respectively S ₁ = 1075 and S ₄ = 1250. This shows that the accuracy of assessing the quality of adhesion of the coating to the substrate when used as the area parameter (for equal K _p ) is higher than when simply using the value of K _p .

Example 2 of the implementation of the method. They took the same products, numbered them. Subjected to all the same loading, analysis and testing conditions. Identified products with close values of K _p and areas S of histograms (for example, the penultimate and last columns of table 2).

It was believed that the quality of such products is comparable, i.e. the adhesion quality of the coating to the substrate is approximately the same. But in order to solve the question which of these products has the quality, it was better to conduct additional studies comparing histograms. The histograms were compared by the value of the criterion K _p corresponding to the maximum of the envelope (since there can be more than one maximum) of the histogram, i.e. in magnitude K _pi .

Let us analyze the data of table 2 and the histograms shown in FIG. 4 - 8. The best quality of adhesion of the coating to the base among products numbered from 6 to 10 is noted by the histogram area of product N8. He also has a smaller area of destruction. He also has a smaller value of K _p .

For products N6 and N7, the histogram areas are very close. Because of this, it is impossible to say exactly which one has higher quality. We describe the histograms as envelopes (dash-dot line). Select K _p corresponding to the maximum of the envelope. For item N6, K _p is 2.83. For the product N7 K _p = 2.8.

For products N6 and N7, the histogram areas are also close to each other. We also determine K _p from the maximum of the histograms (the envelopes are not constructed, since the position of the maximum of the histogram is obvious). For the product N9 K _p = 3.04, for the product N10 K _p = 2.97.

 To make a decision about where the adhesion quality is better (for 6 or 7 products, for 9 or 10 products) they chose (essentially this can not be done, since the area of the product No. 6 is larger (albeit insignificant) than for product No. 7, also for products 9 and 10) an additional verification method (in table 2 it is called the control method). Such a verification (control) method is adopted from the possibilities available to the applicant. It is described on pages 93-96 of the earlier work by Kabaldin Yu. G., Mokritsky B.Ya. and others and consists in laser exposure to the product. The higher the laser radiation energy is required to “peel” the coating, the higher the adhesion quality of the coating to the substrate.

Now, comparing all the lines of Table 2, we can conclude that with comparable areas of the histograms, the quality of the product (adhesion of the coating to the base) is higher, the smaller the value of K _p corresponding to the maximum of the envelope of the histogram.

 The data show that the specified technical result is achieved, the task is solved.

 However, the physicomechanical properties of materials are not limited only by the adhesion strength of the coating to the substrate. Therefore, further, to confirm the name of the invention and to fully achieve the specified technical result, information is given on yet another property - crack resistance, i.e. the ability of the material to resist the formation and growth of cracks. To do this, we use all the same data as above. We will present them as a separate example.

Example 3 of the implementation of the method. Products that were previously assigned numbers 1, 2, 9 were taken. They were loaded in the same way, AE signals were recorded, the separation criterion K _{p was} determined, tests were carried out under real cutting conditions, and the amount of wear was measured (as an indicator of the performance of the products due to the crack resistance of the products). The data are summarized in table 3. Here are the data on the comparative method. He adopted a method for the work of Naumov A.V., Kalaido V.V., Krasiko V.N. "Methodology for assessing the static crack resistance of materials" // Factory Laboratory, 1992, N7, p.22-24. This method is taken for comparison and no more, i.e. to confirm that the claimed method gives the same reliable results. We analyze table 3. Tool wear during cutting is the result of destruction. The more fracture, the worse (lower) crack resistance. According to the crack resistance of the product, they occupy the places: product N1 is the first (best) place in terms of working capacity when cutting (and by the comparative method). Product N2 - second place. Product N9 - third (last, worst) place. The same sequence of product locations when trying to use the criterion K _p (bottom row of the table) as a parameter for assessing crack resistance. This allows us to recommend the value of K _p for assessing crack resistance by the condition: the smaller the value of the criterion, the higher the crack resistance.

Example 4 implementation of the method. They took two more products. They were assigned the numbers 11 and 12. They were subjected to all the same actions as in Example 3. For item N11, the criterion K _p is 3.2, for item N12 the criterion K _p is 3.12. According to the proposed method, products N 1, 2, 9, 11 and 12 in terms of crack resistance based on the criterion K _{p are} arranged in the following row: 1 place for product N1 (since physical and mechanical properties are higher due to higher crack resistance), 2 place for product N2 , 3 place for the product N9, 4 place for the product N12, 5 place for the product N11.

 Check if this is the comparative method. It turned out that the products are located in the same sequence. This proves that the proposed method works and gives reliable results. It gives only quality information (better or worse). It does not provide quantitative information on crack resistance, i.e. does not allow to say how much worse or better. But in general, the task has been solved, because control accuracy (see tables 2 and 1) has increased.

Claims (4)

1. A method of controlling the physical and mechanical properties of products, including loading products, including loading the products with an indicator, recording acoustic emission signals simultaneously with loading, monitoring the physical and mechanical properties of the signal parameters, characterized in that the pulse energy is taken as a parameter signals, and control is carried out according to the criterion, determined by the dependence
K _p = log (E _c / τ ² ),
where E _c - pulse energy, b ² • c;
τ is the pulse duration, s.  2. The method according to claim 1, characterized in that the histogram "Cr value - number of signals" is additionally constructed, the physical and mechanical properties are controlled by the adhesion quality of the coating to the product base, the adhesion quality is judged by the condition: the smaller the histogram area when equal the number of signals and equal to the value of the criterion Kr, corresponding to the maximum of the envelope of the histogram, the higher the quality.  3. The method according to claims 1 and 2, characterized in that the adhesion quality is judged from the condition: for comparable areas of the histograms, the quality of adhesion of the coating to the base is higher for the product whose maximum histogram envelope corresponds to a smaller value of the criterion Cr.  4. The method according to p. 1, characterized in that the control of physical and mechanical properties of the material of the products is carried out according to their crack resistance from the condition: the smaller the value of the criterion Кр, the higher the crack resistance.

Images