RU2281194C1 - Method of reconditioning of machine parts - Google Patents

Abstract

FIELD: mechanical engineering.

SUBSTANCE: invention relates to method of reconditioning of parts of machine damaged in operation and it can be used at repairing different articles operating at high temperatures, constant cyclic loads and in aggressive media. Method includes removal of damaged surface layers and protective coatings of parts by irradiation of parts with high-current pulsed electron beam. Said irradiation is done by high-current pulsed electron beam of microsecond duration with density in pulse of W=45-90 J/sq.cm at energy of electrons of E=100-120 keV and number of pulses required for complete removal of surface layer damaged in operation. Then surfaces are subjected to electron beam burnishing at lower current densities of 18-45 J/sq/cm and vacuum annealing at temperatures of final thermal treatment for 2-6 h.

EFFECT: increased capacity, improved quality of surface cleaning and operating characterizing of machine parts.

2 ex, 2 tbl, 7 dwg

Description

The invention relates to a method for restoring the operational properties of machine parts damaged during operation and can be used in the repair of various products operated at high temperatures, constant cyclic loads, in aggressive environments.

The invention can be implemented in the aviation, engineering, shipbuilding, metallurgical, space and other industries.

In modern metalworking technologies, various methods are known for cleaning the surface of machine parts that have been run from impurity elements, oxide layers and oxide films, soot, etc. These methods can be divided into three groups: mechanical (cutting, vibroabrasive processing, diamond smoothing, etc.), chemical (chemical etching in liquid solvents, etching in a gas medium, electrochemical etching, plasma-chemical etching, etc.) and physical (processing by electron beams, processing by ion beams, laser processing, processing by plasma energy flows, etc.). In practice, most often, combined methods are used. In aircraft engines, for repair of high pressure compressor blades of gas turbine engines with ZrN and TiN coatings, vibroabrasive, chemical and thermal treatments are used, in some cases, high-energy vacuum plasma technology and heat treatment are used, and in the repair of turbine blades with protective condensation coating SDP-2 and VSDP -16 (vacuum diffusion coating) use sandblasting followed by chemical etching in liquid solvents or vacuum-plasma processing of high energies.

All these methods are characterized by low productivity, high complexity and their application leads to negative changes in the physicochemical state of the material in the surface layers, i.e. to the formation of microcracks, pores, inclusions, etc., and therefore to a decrease in the basic operational properties.

To clean the surface of impurity elements (most often, before applying protective coatings to the surface of parts or before carrying out the ion implantation process), ion-beam etching is used, i.e. surface treatment with continuous ion beams at energies E = 100-1000 eV and ion current densities j = 10 ^-2 -10 ² mA / cm ² in vacuum or in an inert gas (P = 0.1-1 Pa) [1]. This method, chosen as the prototype, allows to obtain a sufficiently clean surface of the part, however, the removal rate of surface layers damaged during operation does not exceed 5-7 μm / h, and due to differences in the sputtering coefficients of the phase components of the alloy, the chemical composition and structural phase state of the material change in the near-surface zone. An increase in the ion flux density allows to increase the productivity of the method, however, in this case, the part is heated to high temperatures, which can lead to a deterioration in the operational properties of the products.

It is possible to increase the productivity of the ion-beam method using powerful high-current pulsed ion beams (SIEC) of nanosecond duration with an energy density of 1-10 J / cm ² and the number of pulses 1-10 [2-4]. In this case, it is possible to remove from 0.1 to 1 μm per pulse at a pulse repetition rate of 0.1 Hz. However, in this case, due to the action of shock waves, the structural phase state changes, surface and subsurface microcracks and microcraters form, which sharply reduces the fatigue strength and corrosion resistance of the parts being repaired.

The technical result of the invention is a significant increase in the productivity of the process of removing surface layers and coatings damaged during operation, improving the quality of surface cleaning and improving the operational characteristics of the parts being repaired.

This is achieved by the fact that the repaired part is irradiated with a high-current electron beam of microsecond duration with an energy density in the pulse of W = 45-90 J / cm ² at an electron energy of E = 100-120 keV and the number of pulses necessary to completely remove the surface layer damaged during operation, followed by electron-beam smoothing of the surface at lower energy densities of 18-45 J / cm ² and vacuum annealing at temperatures of final heat treatment for 2-6 hours.

The method is implemented as follows.

Repair parts are placed in the working chamber of a high-current electronic accelerator (Fig. 1). Irradiation is realized by pulses of a duration of tens of microseconds. The required energy density in the range of 45-90 J / cm ^{2 is} achieved by changing the current density or pulse duration at a fixed electron energy of 100-120 keV.

The energy density necessary for the implementation of the method is determined by: the duration of exposure to the electron beam; target material, including thermophysical characteristics of the damaged surface layer or coating to be removed during operation; thickness of the removed layer.

Irradiation at the lower boundary of the energy density range (45 J / cm ² ) is sufficient to remove relatively volatile materials (chlorides, bromides, oxychlorides, chromium, tin, aluminum, etc.) or to remove relatively thin damaged surface layers from nitride-based materials, oxides and alloys based on Ti, Zr, Fe, Ni, with a thickness of several nanometers to several micrometers. The upper limit of this range of 90 J / cm ² provides the removal of almost all substances by the ablation mechanism [5].

The choice of irradiation modes (energy density and number of pulses) can be realized with high accuracy from the curves of the dependence of the thickness of the removed layer on the energy density, which can be obtained experimentally. Such curves are shown in FIGS. 2 and 3 for blades made of VT9 and ZhS26NK alloys coated with ZrN and NiCrAlY, as well as for blades made of steel EP866ш. These blades went through operation on the RD33 engine for 1000 hours, 600 hours and 300 hours, respectively. Parts are exposed to SIEC so many pulses, which is enough to remove all damaged during operation of the surface layer. Since the target surface after removal of the desired surface layer may have a wavy relief and contain microdefects in the form of craters (Fig. 4), the parts are re-irradiated in the melting mode at lower energy densities to reduce surface roughness. The energy density of the re-exposure in the melting mode depends on the material from which the part is made. For titanium alloys, the energy density values should be equal to 18-20 J / cm ² , for steels 20-22 J / cm ² , for nickel alloys 42-45 J / cm ² . It is with these energy densities that it is possible to obtain the surface of the part being repaired with low roughness (Fig. 5). Then the parts are placed in a vacuum oven and maintained at the temperature of their final heat treatment for 2-6 hours, in order to relieve residual tensile stresses and stabilize the structural phase state, as is the case in the serial production of repaired parts.

The differences of the proposed method are due to the physics of the processes occurring in the surface layer during two stages of electron beam and finish heat treatments: removal of surface contaminants (oxides, fuel combustion products, nitrides, carbides, etc.) at the stage of formation of the vapor-plasma cloud; melting of the material of the surface layer with a thickness of 20-30 microns and its high-speed crystallization; healing of surface microcracks and craters; removal and guidance of residual stresses during thermal impact on the surface of the part; relaxation of residual stresses, recrystallization and annealing of defects.

The occurrence of the totality of these processes leads to both high-intensity removal of contaminants and corrosion products from the surface of the part, and to hardening of the material due to structural-phase transformations.

Example 1. The blades of the first stage of a gas turbine engine made of heat-resistant nickel alloy ZhS26NK coated with SDP-2 and VSDP-16, which were run on the engine for 600 hours, were irradiated on a Geza-2 accelerator with a high-current pulsed electron beam with an energy of 110-120 keV at energy density W = 80-90 J / cm ^{2 with} nine pulses for complete removal of the coating with a thickness of 60 ± 5 microns. The appearance of the blades with the removed coating is presented in figure 4

The surface of the part after removal of the coating has a wavy relief and contains a large number of microcracks and craters. After that, the blades were irradiated on a Geza-1 accelerator with an energy of E = 110-120 keV at an energy density of W = 42-45 J / cm ² with four pulses to smooth the surface microrelief and heal surface defects (Fig. 5). Irradiated blades were annealed in a vacuum oven at a temperature of 1250 ° C for 2 hours.

The surface layers of the blades before and after electron beam treatment were studied by x-ray diffraction analysis, scanning electron microscopy and optical metallography. In addition, the roughness and microhardness of the surface of the blades, their fatigue strength and heat resistance (after applying a new coating using serial technology) were determined. The results of the studies and tests are presented in Fig.6 and table 1. From these data it directly follows that the use of SIEC for repair of turbine engine blades allows removing 60 micron NiCrAl coating in 15 minutes from the entire surface of the blade.

The ablation rate of the material reaches 7 μm per pulse. Since the duty cycle of the SIEC processing is 50 seconds, the total ablation rate reaches 500 μm / h, which is almost 2 orders of magnitude higher than the material removal rate when using the prototype and the ablation rate is an order of magnitude if the material is removed with a powerful ion beam [2-4]. In addition, the operational characteristics of the blades after repair using the proposed method (fatigue strength and heat resistance) become adequate to the characteristics of serial blades.

Example 2. The blades of the 7th stage of the rotor of a high-pressure gas turbine compressor of EP866sh steel, which were run on the engine for 260 hours, were irradiated with the Geza-2 accelerator at pulse energies of 20-22, 26-28 and 31-36 J / cm ² two pulses (Fig.7). After running, the blades contained on the surface the products of fuel combustion in various areas (carbon deposits), the thickness of this contaminated layer being from 20 to 40 microns, and also the oxide layer from 8 to 25 microns thick. In addition, some blades had traces of mechanical damage (nicks, dents, microcracks). Individual parts could not be repaired according to geometric requirements. After irradiation with an energy density of 20-22 J / cm ² with two pulses, it is possible to completely remove carbon from the surface of the blades. To remove oxide layers, irradiation was carried out at an energy density of 50-55 J / cm ² with four pulses (see the curve in Fig. 3), which allowed the oxide layers to be completely removed. Since separate craters formed on the surface of the blades being repaired, irradiation was implemented in a single mode (W = 20-22 J / cm ² ) with four pulses. After irradiation, vacuum stabilizing annealing was carried out at a temperature of 600 ± 30 ° C for 2-6 hours to relieve residual tensile stresses. The blades made in this way were studied by Auger electron spectroscopy, scanning electron microscopy, X-ray diffraction, and optical metallography. In addition, microhardness, roughness, endurance limit, heat resistance, and corrosion resistance were determined under thermal cycling conditions. The results of research and testing of blades processed according to the proposed method are presented in table 2.

Table 1.
The effect of electron beam treatment on the physicochemical state of the material in the surface layers and the properties of ZhS26NK alloy turbine blades (σ _-1 is the endurance limit at 975 ° C and a loading frequency of 3000 Hz based on 2 · 10 ⁷ cycles; h _o is the thickness of the oxidized layer after 500-hour exposure to air at 950 ° C; tests were carried out on model samples made by the technology of production of blades.) No. Part or Sample Condition Exposure mode Annealing mode R _a μm,
± 0.02 Nμ units HV ± 80 σ _-1 MPa
± 20 N _about microns
± 5 W, J / cm ²

, имп

, imp T ° C τ, hour one Original, before operation - - - - 2.60 430 250 0 2 Original, after operation - - - - 2.90 560 210 42 3 After operation, processing SIEP 88-90 9 1050 2 0.85 450 200 - four After operation,
SIEP processing and heat treatment 88-90
42-45 9
four 1050 2 0.29 420 270 - 5 After operation,
SIEP processing
heat treatment and applying a new coating 88-90
42-45
- 9
four
- 1050

1210 2

2 0.30

2.60 430

430 270

250 -

39 6 After operation,
SIEP processing
heat treatment, coating, processing SIEP 88-90
42-45
42-45 9
four
four 1050
1210
1050 2
2
2 0.29
2.65
0.25 420
430
420 270
245
265 -
40
12 7 After operation,
chemical and mechanical
treatments (serial technology) -
-
- -
1210 -
2 3.20
2.70 -
460 200
240 - 45

Table 2.
The effect of electron beam processing on the physicochemical state of the material in the surface layers and the properties of HPC blades made of EP866sh steel (σ _-1 is the fatigue limit at 600 ° C, the loading frequency is 3000 Hz based on 2 · 10 ⁷ cycles; h _o is the thickness of the oxidized layer after 600 hours of thermal exposure in air at 600 ° C, the specific weight gain of the samples after 200 cycles of heating to 600 ° C and cooling in seawater to 20 ° C). No. Part or Sample Condition Exposure mode Annealing mode R _a , μm ± 0.01 Hμ HV p = 1H ± 30 σ _-1 MPa ± 20 h _o , μm ± 5 Δm / S, mg / mm ² ± 0.03 W, J / cm ²

, имп

, imp T ° C τ, hour one Original before operation - - - - 0.24 410 380 45 1.98 2 Original after operation - - - - 1.25 690 290 65 - 3 After operation and processing of the SIEC 20-22 2 - - 0.32 470 310 fifty 2.12 four After operation,
SIEP processing and heat treatment 50-55
20-22 four
2
670
6
0.22
430
420
fifteen
0.38 5 After operation, chemical and mechanical treatments (serial technology) - - - - 0.25 400 360 45 2.01

Literature

1. Dalsky A.A., Pastukhov K.M., Strygin A.E., Yagodkin Yu.D. The formation of the surface layer of parts from nickel alloy using finish ion-beam processing // Vestnik mashinostroeniya, 1988. No. 5, p.40-44.

2. Zubarev G.I., Isakov I.F., Nochnovaya N.A., Remnev G.E. Shulov V.A. The method of restoring the operational properties of machine parts // A.S. (19) RU (11) No. 2009269 C1, Cl. 5 C 23 C 8/36, C 23 F 4/09, claimed 02/10/1992, bull. 03/15/1994, No. 5.

3. Remnev G.E. and Shulov V.A. Application of high-power ion beams for technology. J. Laser and Particle Beams. 1993. v.14, No. 4, p. 707-731.

4. Shulov V.A., Remnev G.E., Nochnovaya N.A., Lvov A.F. Kinetics of evaporation and ablation upon irradiation by high-energy ion beams of products from heat-resistant alloys with protective coatings // g. FiHOM, 2003, No. 1, pp. 22-27.

5. Yatsui K. Industrial applications of pulse power and particle beams. J. Laser and Particle Beams. 1989. v.7, No. 4, p. 733-741.

Claims (1)

A method for restoring the operational properties of machine parts, including cleaning the surface of parts with a high-current pulsed electron beam, characterized in that to remove damaged surface layers and protective coatings, a high-current electron beam of microsecond duration with an energy density of pulses W = 45-90 J / cm ^{2 is} irradiated electron energy E = 100-120 keV and the number of pulses required to completely remove the surface layer damaged during operation, after which the electron beam is produced e burnishing surface at lower energy densities of 18-45 J / cm ² and a vacuum annealing at a finish heat treatment temperatures for 2-6 hours.

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