Method of confirmation of exhaustion of protective properties of heat-resistant diffusive coatings

FIELD: measurement equipment.

SUBSTANCE: invention relates to nondestructive examination, to study of metal properties and is intended for confirmation of exhaustion of protective properties of heat-resistant diffusive coatings on details made of carboniferous heat-resistant alloys. The method of confirmation of exhaustion of protective properties of heat-resistant diffusive coatings on details made of carboniferous heat-resistant alloys by change of physical and chemical properties of the surface layer of heat-resistant diffusive coatings during operation in conditions of high temperature, comprises application of reagent on the coating surface, and the fact of exhaustion of protective properties of the heat-resistant diffusive covering is witnessed visually by change of colour of the surface of heat-resistant diffusive coating with formation of carbon and black oxides during the process of chemical reaction between carbide phases, forming in the surface layer of the heat-resistant diffusive coating at the late stages of operation, and reagent.

EFFECT: simplicity, reliability and reliability of tests is achieved.

1 ex, 5 tbl, 10 dwg

 

The invention relates to nondestructive testing, to investigate the properties of metals and is intended to confirm the exhaustion of the protective properties of heat-resistant diffusion coatings on parts made of carbon-containing superalloys.

The known method of determining the developed part of the resource, which is measured by changes in the physical properties of the material of the sensor attached to the surface of the test details [Sahm K.-F., M. Natter Dornier-fatique measuring system. "Dornier Post", 1978, No. 3, p.48-49].

The disadvantage of this method is that developed about the resource is judged by the change in reflectivity of the sensor, glued on its surface, which does not guarantee reliability of the definition elaborated by the resource due to differences in the properties of materials parts and the sensor.

The closest technical solution is a method of assessment developed resource [RF Patent №1769069 from 04.12.1990 G. / Method of evaluating the degree of fatigue damage of materials // Voropaev V. S., J. A. Svirsky, Vorobyova L. A.], namely that the sample material is subjected to cyclic loading, and determine the change in the chemical composition of the surface layer of the material from cyclic loading, which are judged on the proportion of generated resource.

The disadvantage of this method is the high complexity it is basically�Oh implement due to the necessity of special preparation of the polished test surface area of the details and complexity of the technique of electron probe x-ray analysis, requiring the creation of a high vacuum.

The problem to be solved by the claimed invention is the development of reliable and simple way of confirming the exhaustion of the protective properties of heat-resistant diffusion coatings on carbon-based heat-resistant alloys.

The technical result that can be achieved by carrying out the invention, is the possibility of transition from the operation of parts made of heat-resistant carbon-containing alloys coated with heat-resistant diffusion coatings under the assigned resource to the system operation on the technical condition.

This technical result is achieved in that in the method of confirmation of the exhaustion of the protective properties of heat-resistant diffusion coatings on parts made of carbon-containing heat-resistant alloys, the change of physico-chemical properties of the surface layer of heat-resistant diffusion coatings in the process of operation at elevated temperatures, including the application of the reagent on the surface of the heat-resistant diffusion coatings, the fact of the exhaustion of the protective properties of heat-resistant diffusion coatings are judged visually on the basis of color change of the surface heat-resistant diffusion coatings with formation of carbon oxides and black color in the course of chemical re�functions between the carbide phases, formed in the surface layer of heat-resistant diffusion coatings in the later stages of operation, and a reagent.

The inventive method is explained in Fig. 1-10 and table. 1-5, where a given phase composition of heat-resistant alloy IS (Fig. 1, tab. 1) deposited on the alloy heat-resistant diffusion coatings (Fig. 2, table. 2), the change of phase composition of the surface layer of the coating during operation at elevated temperatures (Fig. 3, 4 and 5, tab. 3, 4 and 5); the appearance of the samples coated in the process of operation at an elevated temperature until the coating protective properties (Fig. 6), at the time of exhaustion of the coating protective properties (Fig. 7) and after the coating has exhausted protective properties (Fig. 8); coating the surface of a drop of liquid reagent solution to the exhaustion of protective coating properties does not cause a chemical reaction (Fig. 9), whereas at the time of exhaustion of the coating protective properties, there are signs of a chemical reaction (Fig. 10).

Simultaneously with the exhaustion of the coating protective properties, as it follows from Fig. 4 and table. 4, in the surface coating layer formed of the carbide phase Cr23C6and'alni3C0,5. To detect them on the surface was applied an aqueous solution of sodium hypochlorite NaOCl. As a result of redox reactions between the carb�DNAME phases and sodium hypochlorite

Cr23C3+23NaOCl=6C+23NaCl+23CrO(1)
2AlNi3C0,5+12NaOCl=C+3Ni2O3+A12O3+12NaCl(2)

are the reaction products (e.g., carbon and oxides of chromium and Nickel black color) that can be detected visually (Fig. 10).

Operation of parts made of heat-resistant alloys at elevated temperatures after the exhaustion of heat-resistant diffusion coating protective properties inevitably leads to burnout coatings, the development of the process of oxidation of heat-resistant alloy and substantial violation of part geometry (Fig. 8). This fact makes non-repairable parts, which eliminates the possibility of re-use and lead to significant material losses. However, the timely withdrawal of the parts from operation to onset of burnout coating allows repeatedly to carry out the refurbishment and return the item for re-use, thus saving material. To prevent burnout of the coating, typically use a system of exploitation assigned to a resource that does not allow full use of the protective properties of heat-resistant coatings. The existence of simple objects and�guidance criterion of exhaustion of heat-resistant coating protective properties allows you to navigate to the system operation on the technical condition, that gives the opportunity to use reserves of heat-resistant coatings without the risk of burnout.

An example of a specific implementation method

Experimental cylindrical samples with a diameter of 14 mm and a height of 5 mm made of heat-resistant alloy grades GS. According to the spectral analysis conducted on the spectrograph brand PMI Master PRO, was determined the chemical composition of the alloy (weight %): C - 0,17; Cr - 5,0; With 9.2 per; W - 9,1; Mo - 1,2; Al - 5,9; Nb - 1,5; TA - 4,1; Re - 3,9; Hf - 0,03; 0,014; Y - 0,004; CE - a 0.02; Si - 0,24; Ni - basis.

Heat treatment alloy: quenching under vacuum to 1280°C after annealing for 4 hours at the same temperature.

The phase composition of the alloy and coatings as in the initial state and at different stages of operation at elevated temperatures, was determined by x-ray diffraction diffractometer brand DRON-3 using the standard software of the diffractometer; before removing the diffraction pattern of the surface of the samples was cleaned from oxide films using soft abrasive-liquid processing.

The diffraction pattern of the surface layer of the sample after heat treatment of the alloy prior to coating shown in Fig. 1; phase composition of the alloy IS after heat treatment before coating are shown in table. 1.

The samples were deposited heat-resistant diffusion coating (�Ravalomanana in vacuum, the residual pressure of 1.33·10-1PA). The coating was carried out in a powder mixture of the following composition (weight %): aluminium powder brand ASD-4 - 10%; chromium powder brand PHS - 40%; powder of aluminum oxide of the brand of the sur - 50%; ammonium chloride NH4Cl (qualification "analytical grade") of 0.5%. The temperature of formation of the coating was 1000°C, duration - 5 hours.

After coating, the samples were subjected to thermal treatment at a temperature of 1210°C for 1 hour and 15 minutes at a residual pressure of 1.33·10-1PA to relieve internal stresses and removal of gases from the surface layers.

The diffraction pattern of the surface layer of the coating before use at elevated temperatures is shown in Fig. 2; the phase composition of the surface layer of the coating before use at elevated temperatures are presented in table. 2. The carbide phase in the surface coating layer is not detected.

After coating, the samples were kept in a muffle furnace at a temperature of 1080°C.

The diffraction pattern of the surface layer of the coating after 300 hours in a muffle furnace at a temperature of 1080°C is shown in Fig. 3; phase composition of the surface layer of the same coating is shown in table. 3.

The diffraction pattern of the surface layer of the coating after 400 hours in a muffle furnace at tempera�ur 1080°C is shown in Fig. 4; phase composition of the surface layer of the same coating is shown in table. 4.

The diffraction pattern of the surface layer of the coating after 500 hours in a muffle furnace at a temperature of 1080°C is shown in Fig. 5; the phase composition of the surface layer of the same coating is shown in table. 5.

Fig. 6 shows the appearance of samples after 300 hours in a muffle furnace at a temperature of 1080°C. a Uniform gray color of the solid oxide film suggests that the coating has not exhausted its protective properties. The result of the analysis of the phase composition of the surface layer of the coating (Fig. 3, tab. 3) indicate the absence of carbide phases. Applying drops of a 4% aqueous solution of sodium hypochlorite to clean oxide films from the surface of this coating does not lead to chemical reactions (Fig. 9).

Fig. 7 shows the appearance of samples after 400 hours in a muffle furnace at a temperature of 1080°C. Uneven gray color of the oxide film caused by the appearance in its structure complex oxide NiCrO4that indicates that coverage has exhausted its protective properties and has begun the oxidation of heat-resistant alloy. The results of the analysis of the phase composition of the surface layer of the coating (Fig. 4, tab. 4) indicate the appearance of a carbide phases. Applying drops of a 4% aqueous solution� of sodium hypochlorite to clean oxide films from the surface of this sample led to the chemical reactions of type (1, 2) with the formation of carbon, chromium oxide and Nickel oxide black, which can easily be detected visually (Fig. 10).

Fig. 8 shows the appearance of samples after 500 hours in a muffle furnace at a temperature of 1080°C. On the sample surface, there are clear signs of burnout coating, which is indicative of the intensive development of the process of oxidation of heat-resistant alloy. The results of the analysis of the phase composition of the surface layer of suitable cover (Fig. 5, tab. 5) indicate the presence of carbide phases and a significant amount of various oxides.

Compared with the prior art the use of this reliable and simple method allows, without resorting to the use of expensive equipment, visually confirm the fact of exhaustion of the protective properties of heat-resistant diffusion coatings on carbon-based heat-resistant alloys.

Confirmation method of exhaustion of the protective properties of heat-resistant diffusion coatings on parts made of carbon-containing heat-resistant alloys, the change of physico-chemical properties of the surface layer of heat-resistant diffusion coatings in the process of operation �ri elevated temperature, including the application of the reagent to the surface of the coating, characterized in that on the fact of exhaustion of the protective properties of heat-resistant diffusion coatings are judged visually on the basis of color change of the surface heat-resistant diffusion coatings with formation of carbon oxides and black color in the course of chemical reaction between the carbide phases formed in the surface layer of heat-resistant diffusion coatings in the later stages of operation, and reagent.



 

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