RU2572690C2 - Method of single stage diffusion chrome aluminising of parts out of heat-resistant alloys - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: parts are heated to temperature of diffusion saturation and held in circulating halide environment created upon contact of the input gaseous environment with sources of diffusible elements, ferroaluminium and chrome are used as such elements. The diffusion saturation is performed in mixture additionally containing ammonium chloride, nickel-yttrium and aluminium oxide, at the following ratio of elements wt %: ferroaluminium 38-50, chrome 23-27, ammonium chloride 2.0-5.0, nickel-yttrium 12-19, and aluminium oxide - rest. Heating is performed initially to 1000°C with holding for 6-12 h, them temperature is increased to 1050°C with holding at it for 6-14 h, at that at each heating stage during the diffusion holding the uniform circulation of the halide environment is performed. In particular case of invention implementation at each heating stage during the diffusion holding the circulating halide environment is additionally cleaned of the reacted mixture.

EFFECT: stability of composition, and coating thickness at all treated parts of charge regardless of place of location in the reaction chamber.

2 cl, 1 dwg, 1 tbl, 1 ex

Description

The present invention relates to the field of metallurgy, in particular to the chemical-thermal treatment of metals and alloys in a circulating gas medium, and in particular to methods of diffusion saturation with several elements of the external and internal surfaces of parts, and can be used to obtain anti-corrosion, heat-resistant and erosive coatings on parts from heat-resistant alloys having internal cavities of complex configuration used in engine building and in other sectors of the national economy.

A known method of diffusion chromoalithization of parts from heat-resistant alloys, including heating the parts to a temperature of diffusion saturation and exposure in a circulating halide medium formed when the source gas comes in contact with sources of diffusing elements, which use chromium and aluminum. Saturation is carried out in stages, creating at each stage a circulating medium from only one saturating element (USSR author's certificate No. 1759957, IPC С23С 12/00, publ. 07.09.1992).

A known method of one-stage diffusion chromoalithization of parts from heat-resistant alloys, including heating the parts to a temperature of diffusion saturation and exposure to a circulating halide medium formed when the source gas comes in contact with sources of diffusing elements, which use chromium and an alloy of chromium and aluminum. Saturation is carried out in a one-stage-simultaneously with both elements, by changing the speed of movement of the circulating halide medium (RF patent for the invention No. 2270880, IPC С23С 10/14, publ. 02.27.2006).

The closest is a method of single-stage diffusion chromoalithization of parts made of heat-resistant alloys, which includes heating the parts to a temperature of diffusion saturation and exposure to a circulating halide medium formed upon contact of the source gas medium with sources of diffusing elements, which use ferroaluminium and chromium (RF patent for invention No. 2186873, IPC С23С 10/14, published on 08/10/2002).

With this method of chromo-lamination of parts, mainly blades made of heat-resistant alloys with narrow internal channels, saturation is carried out in a one-step process - simultaneously with both elements by an aluminum and iron alloy (ferroaluminium) and chromium with a periodic change not only of the speed of movement of the circulating halide medium, but also of the direction of its circulation to the opposite .

Known methods provide uniform along the entire length of the coating part on both the outer and inner cavities of each part in the cage.

The presence of a turbulent mode of circulation of the halide medium creates uneven velocities along the profile of the flow cross section: in the center above, at the walls of the muffle below, and contributes to the appearance of vortices, which leads to uneven washing of surfaces of different parts in the cage and, as a result, to the lack of stability of the coating applied to them in composition and thickness.

In addition, the quality of the coating is deteriorating due to the presence in the working zone of the reaction chamber of particles of the reacted mixture in the form of dust delivered by the circulating halide medium and deposited on the surfaces of the parts.

The technical result of the invention is to ensure the stability of the composition and thickness of the coating for all processed parts of the cage regardless of their location in the reaction chamber due to step heating while saturating ferroaluminium with ichrome and leveling the velocity field of the circulating halide medium at each heating stage.

The stepwise heating during saturation ensures the stability of the coating layer by composition, namely, the maximum saturation of the coating with aluminum and chromium for all parts of the charge regardless of their location in the reaction chamber (at its walls or in the center).

Alignment of the field (front) of the speeds of the circulating halide medium ensures the stability of the applied coating layer in thickness, namely, a uniform (uniform) thickness coating layer for all parts of the cage regardless of their location in the reaction chamber (at its walls or in the center).

The technical result is achieved by the fact that in the method of one-stage diffusion chromoalitization of parts made of heat-resistant alloys, which includes heating the parts to a temperature of diffusion saturation and holding in a circulating halide medium formed by contact of the initial gas medium with sources of diffusing elements, in which ferroaluminium and chromium are used, unlike the known diffusion saturation is carried out in a mixture additionally containing ammonium chloride, nickel-yttrium and aluminum oxide, followed by present component ratio, wt. %: ferroaluminium 38-50, chromium 23-27, ammonium chloride 2.0-5.0, nickel-yttrium 12-19 and aluminum oxide the rest, and heating is performed first to a temperature of 1000 ° C with holding for 6-12 hours , then the temperature is increased to 1050 ° C and maintained at it for 6-14 hours, while at each heating stage during the diffusion holding process, the halide medium is uniformly circulated.

To improve the quality of the coating layer at each heating stage during diffusion exposure, the particles of the reacted mixture are further purified from the circulating halide medium.

The drawing schematically shows the installation for implementing the proposed method.

The installation comprises a muffle 1 with a hermetically sealed cover 2 installed in the heating furnace 3. In the muffle 1 there is a stand 4 made in the form of a truncated cone with holes for the passage of a gas medium flow. Inside the stand 4 there are containers 5 for diffusing elements and an activator. On the stand is a reaction chamber 6, made, for example, in the form of a cylinder directing the flow of a gaseous medium. Inside the reaction chamber, a device 7 is installed for equalizing the flow rate of the flow field of a circulating halide medium having openings for its passage. The dimensions of the holes of the device and their location are chosen experimentally or by calculation in such a way as to prevent the appearance of vortices and create a mode with a constant speed over the flow cross section. The device can be made, for example, in the form of a lattice, the size of the holes of which are reduced from the center to the periphery.

Additionally, a system for cleaning the circulating medium from particles of the reacted mixture, which consists of a chimney 8 of dust particles made in the form of a conical shell, directing the flow of the halide medium of the conical diffuser 9, and a lid 10, which forms and closes, can be installed with the device 7 for equalizing flow rates cavity for the disposal of dust particles of the reacted mixture, which ensures the absence of contact of the dust mass with the surface of the parts.

Above the device 7 in the working zone of the reaction chamber 6 is placed a device 11 for installing workpieces 12, which can be made in the form of a lattice.

To increase the intensity of the chromizing process, a pressure increasing device 13 can be placed above the parts in the working zone of the reaction chamber, for example, made in the form of a lattice, while the diameters of the holes are made in such a way as to provide additional dynamic resistance to the flow and create some excess pressure in the zone of the parts to be processed .

A diffuser 14 is installed on the reaction chamber 6, providing a given direction of movement of the saturating medium. A fan 15 is mounted above the diffuser inside the muffle 1, with a drive, for example, from an electric motor 16. The muffle 1 through valve 17 communicates with a vacuum system consisting of a vacuum pump 18 connected to a filter cooler 19. The pressure inside the muffle 1 is visually monitored using pressure gauge 20.

The arrows in the drawing show the direction of movement of the circulating halide medium.

The method of one-stage diffusion chromoalitization of parts from heat-resistant alloys is as follows.

In the reaction chamber 6 set the charge of the workpiece 12 and the tank 5 with sources of diffusing elements and an activator. Ferroaluminium and chromium powder are used as diffusing elements. Saturation can be performed in a mixture additionally containing an activator, nickel-yttrium and alumina, in the following ratio of components, wt. %:

ferroaluminium - 38-50;

chrome 23-27;

activator - 0.2-0.5;

nickel-yttrium -12-19

aluminum oxide - the rest.

Ammonium chloride is used as an activator.

Muffle 1 is sealed with cover 2, and air is evacuated. The assembled muffle 1 is placed in the oven 3 and heated. The initial gas medium is created as a result of evaporation of ammonium chloride during heating. During heating, the pressure inside the muffle increases due to the sublimation of ammonium chloride. When the temperature in the muffle reaches 1000 ° C, a fan 15 is turned on for forced circulation of the gaseous medium.

Saturation is performed in one step, i.e. simultaneously ferroaluminium and chromium. Circulating medium is passed through device 7 and additionally through a system for cleaning the circulating medium from particles of the reacted mixture. This creates a dust-free circulation regime of the saturating medium uniform with a flat front of velocities, equalizing the velocities and pressures in the working zone of the reaction chamber.

In this case, the shutter speed is carried out with a step change in temperature and saturation time at each stage. Moreover, the holding temperature at the saturation stage for each step is determined taking into account the diffusion activity of saturating elements and their quantitative content in the coating, and the holding time - taking into account the required coating thickness. At a temperature of 1000 ° C, hold for 6-10 hours. Next, increase the temperature to 1050 ° C and stand at it for 6-14 hours.

At the end of the technological shutdown, the fan 15 is turned off, the muffle 3 is cooled, and the processed parts 12 are removed.

An example implementation of the method

Carried out the simultaneous saturation of chromium and aluminum from the gas phase of the outer surfaces of complex parts - turbine blades of a gas turbine engine.

Ferroaluminium (FA45) and chromium powder (PH-1C) in a mixture with ItN1 nickel-yttrium alloy, crushed to a fraction of 2-4 mm, alumina grades GN, GN-00, GK, GN-1, were used as sources of diffusing elements. GN-2, and the activator is ammonium chloride.

At the bottom of the reaction chamber, containers with a powder mixture mixed according to the technology were installed:

nickel-yttrium 1.5 kg (12%)

alumina 2 kg (14.8%)

chrome powder 2.5 kg (20%)

ferroaluminium 7 kg (53%)

ammonium chloride 0.3 kg (0.2%)

The parts were installed in the working zone of the reaction chamber from the periphery to its center. The reaction chamber with parts was loaded into the muffle and a diffuser was installed. They closed the muffle with a lid and installed a loading thermocouple in the area of the parts. The muffle was sealed. They turned on the vacuum pump, pumped air out of the muffle. The assembled muffle was moved to a preheated furnace and the heating indices were transferred to the temperature set by the technological process. During heating, the pressure inside the muffle increases due to the sublimation of ammonium chloride and reaches a positive value specified by the technological process, which, when the set value is exceeded, is discharged through the filter cooler, and if it is insufficient, it increases by feeding argon to the muffle.

When the temperature in the muffle was reached by a loading thermocouple of 1000 ° C, the fan was turned on for forced circulation of the saturating medium and the shutter speed was held for 6-10 hours with a uniform saturating medium circulation mode. Then the temperature was raised to 1050 ° C and held for 10 hours. Additionally, dust was removed from each heating stage.

At the end of technological exposure, the fan and the heating of the furnace were turned off, the muffle was cooled. The atmospheric pressure was set in the muffle, the muffle cover was removed and the reaction chamber with parts was unloaded.

The quality of the coating layer was evaluated on samples (parts of the same alloy and geometry that underwent the same heat treatment and surface preparation as the workpieces).

The results are presented in the table:

The table shows that the maximum change in the thickness of the coating along the profile of the feather blade is 0.004 mm (2%). The maximum difference in the average values of the coating thickness between the blades located in different zones of the reaction chamber is 0.0015 mm (0.75%).

The maximum difference in the content of chromium and aluminum in the coating, respectively, is Cr = 0.4%; Al = 1.9%.

Such stability of the coating parameters in composition and thickness is ensured by the stepwise heating and uniform distribution of the field of flow velocities of the saturating medium over the volume of the reaction chamber, regardless of the location of parts in the reaction chamber.

Using the proposed method allows you to control the coating process.

Thus, in comparison with the known methods, the proposed method of single-stage diffusion chromoalitization of parts made of heat-resistant alloys ensures uniformity and quality of their coating, regardless of the location of the parts in the reaction chamber.

Claims (2)

1. The method of single-stage diffusion chromoalitization of parts from heat-resistant alloys, comprising heating the parts to a temperature of diffusion saturation and exposure to a circulating halide medium formed by contact of the source gas medium with sources of diffusing elements, which use ferroaluminium and chromium, characterized in that the diffusion saturation carried out in a mixture additionally containing ammonium chloride, nickel-yttrium and alumina, in the following ratio, wt. %: ferroaluminium 38-50, chromium 23-27, ammonium chloride 2.0-5.0, nickel-yttrium 12-19 and aluminum oxide the rest, and heating is performed first to a temperature of 1000 ° C with holding for 6-12 hours , then the temperature is increased to 1050 ° C and maintained at it for 6-14 hours, while at each heating stage during the diffusion holding process, the halide medium is uniformly circulated. 2. The method according to p. 1, characterized in that at each heating stage during diffusion exposure, the circulating halide medium is further purified from particles of the reacted mixture.

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