RU2451770C2 - Method for vacuum ion-plasma coating application - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to mechanical engineering, in particular, to methods for vacuum ion-plasma coating application, and can be used for applying coating to details of a difficult configuration. The method includes creation of potential drop between a detail and a cathode, cleaning of the detail surface by ion current, lowering of the potential drop and coating application, and annealing of the coating by means of increasing potential drop. After annealing, the detail is cooled to the indoor temperature, placed into a furnace and subjected to homogenising annealing in vacuum environment. The ion current and evaporating material current coming from the cathode to the detail are exposed during cleaning. Cleaning is done by noble gas ions, after cleaning shields are withdrawn and coating is applied while the detail is rotating on its axis. Cleaning, coating application and annealing are done within one cycle, and homogenising annealing of the coating is done stepwise at T=100±5, 340±10, 730±10 and 900±50 °C in vacuum 1·10^-3 mm Hg.

EFFECT: method efficiency increases.

5 cl

Description

Technical field

The invention relates to the field of engineering, in particular to vacuum coating by the ion-plasma method, and can be used for coating parts of complex configuration, for example, on a turbine impeller made of high alloy alloys, mainly on a nickel basis.

State of the art

The known method of ion-plasma coating on the surface of a part of complex configuration (patent RU No. 2192501, IPC С23С 14/34 from 2002), made of high-alloy nickel alloy in high vacuum in the presence of an inert gas - argon. The method includes creating a high-voltage electric arc between the part and the cathode, in which a plasma stream is formed in the chamber containing inert gas (argon) ions, by which the surface of the part is cleaned, then the voltage between the part and the cathode is reduced and coating is applied, followed by annealing, moreover, in the process of coating the part is rotated around its axis, then the part is cooled to room temperature, placed in a furnace and diffusion annealing is performed in a vacuum medium, while in the process onnoy purification item shielded from the plasma stream, the evaporated cathode material, and these screens is removed after the ion cleaning. The process of cleaning the part and coating is carried out repeatedly to the required thickness.

However, in the known method, the performance of the coating process of a given thickness is low due to the need to carry out the deposition of layers on the substrate and their annealing in several cycles.

Disclosure of invention

The objective of the invention is the creation of a method for producing a coating of the required thickness, in which cleaning, coating of the required thickness and annealing are carried out in one cycle.

This problem is solved due to the fact that in the method of vacuum ion-plasma coating, including creating a difference in electric potentials between the part and the cathode, cleaning the surface of the part with an ion flow, reducing the potential difference and coating, annealing the coating by increasing the potential difference, the ion flux and the flow of evaporating material going from the cathode to the part is shielded during cleaning, and the cleaning is carried out with inert gas ions, after cleaning, the screens are diverted and coated, followed by annealing ohm, and during the coating process, the part is rotated around its axis, then the part is cooled to room temperature, placed in a furnace and diffusion annealing is performed in a vacuum medium, while cleaning, coating of the required thickness and annealing are carried out in one cycle, and diffusion annealing of the coating carried out stepwise at T = 100 ^{± 5} , 340 ^{± 10} , 730 ^{± 10} and 900 ^{± 50 °} C in a vacuum of 1 × 10 ^-3 mm RT.article

Other differences are:

- cleaning the surface of the part is carried out at a difference of electric potentials between the part and the cathode 1500-2000 V.

- the coating process is carried out at a voltage difference between the part and the cathode of 70-90 V.

- annealing of the applied coating layer is carried out at a difference of electric potentials between the part and the cathode up to 500 V.

- diffusion annealing of the coating is carried out stepwise at T = 100 ^{± 5} , 340 ^{± 10} , 730 ^{± 10} and 900 ^{± 50 °} C in a vacuum of 1 × 10 ^-3 mm Hg, while at 100 ^{± 5 the} shutter speed is 2.5 hours, at 340 ^{± 10} - ~ 5 hours, at 730 ^{± 10} - ~ 6 hours and at 900 ^{± 50 °} C - ~ 2 hours.

An example of the method

As a part, a turbine impeller with a diameter of 550 mm was used, made of a highly alloyed nickel-based alloy. Evaporators with nickel cathodes shielded from the side of the part were located in the chamber. After creating a 1 · 10 ^-5 mm Hg in the rarefaction chamber, introducing argon into it and creating the electric potential difference between the part and the cathode up to 2000 V, an ion-plasma flow was formed mainly from the ions of this gas. With this electric potential difference, the process of cleaning the surface of the part with argon ions was carried out. After cleaning, the difference in electric potentials was reduced to 70-90 V and a coating layer was sprayed with a thickness of 200-300 μm. Then, the electric potential difference was increased to 500 V, and as the temperature of the part reached no higher than 850 ° C, the coating was annealed for 60 min. The part was cooled to room temperature in the same chamber under high vacuum for 8 hours. After that, the part was placed in a vacuum furnace and diffusion annealing of the obtained coating was carried out with isothermal extracts from 3 to 12 hours at temperatures 120 ± 5 ° С, 340 ± 10 ° С, 730 ± 10 ° С and 900 ± 50 ° С and a vacuum of 1 · 10 ^-3 mmHg The parts were cooled with the furnace under the same vacuum.

Using the above technology, nickel coatings with a layer thickness of 150-250 μm on the impeller of the turbine were obtained. Tests of these products as part of power plants showed a high level of adhesive and protective properties of the coating.

The use of this technology for producing coatings on parts of complex configuration and large sizes has significantly reduced the time cycle for their production (1.5-1.75 times) and reduced the energy intensity of the entire process due to the elimination of multiple intermediate annealing, intensification of the substrate cleaning process, and part heating speed.

In the process of applying a Ni coating to a part in the presence of argon, argon atoms are always contained in the porous coating in the working chamber, starting from the coating – substrate interface. The presence of argon atoms at the interface prevents the diffusion of the Ni coating into the substrate, and their presence in the coating volume inhibits the self-diffusion of nickel coating atoms during heat treatment. Thus, in the first case, the conditions for ensuring adhesion of the nickel coating to the substrate are worsened, in the second there are limitations in the implementation of self-diffusion of nickel coating atoms, and, accordingly, the coating remains porous.

Even more threatening for the diffusion and self-diffusion processes is the free rise in temperature during heat treatment. This is explained by the fact that in the process of arbitrary heating there are many reasons for the explosive mechanism in the coating, and the bond between the nickel coating atoms and the nickel atoms with the substrate after the coating process is completed is weak - at the level of physical bonding. There is no physicochemical bond at the stage preceding the heat treatment.

One of the reasons for the explosion of the coating may be the accumulation of argon and moisture particles in the pores, which are contained in large quantities in the nickel coating, when transferring parts for heat treatment on other equipment.

Raising the temperature to 850 ° after the end of the nickel coating process and holding it for 40 ÷ 60 min allow reducing the negative effect of argon on the diffusion and self-diffusion of the nickel coating. This happens due to the onset of crystallization of the atoms of the nickel coating at this temperature (a more ordered structure of the nickel coating is created - a type of short-range order), and, accordingly, the coating becomes denser. This ensures an improvement in the self-diffusion of Ni atoms and its diffusion into the substrate.

Step annealing during slow heating of the impeller of a nickel-coated turbine starting at 100 ° C with a holding time of 2.5 hours allows even heating of the substrate and coating to be achieved at the first stage, thereby eliminating the appearance of a temperature gradient between the substrate and the coating and, accordingly, the effect of the difference thermal expansion coefficients. At the same time, laminar removal of argon atoms from the coating occurs. Evenly removed argon from the coating does not cause side "explosive" phenomena, and thereby the previously formed coating state is maintained at this temperature. In addition, such exposure at 100 ° C allows you to remove moisture particles from the coating that fall into it during the control measurements of its thickness. It is known that pore is a good capillary, and control operations are carried out in atmospheric conditions. Upon further heating to 340 ° C with a shutter speed of ~ 5 hours, favorable conditions for further coating formation remain. They are ensured by the fact that the part is heated to this temperature slowly, because the heating time is quite long and amounts to no more than 100 ° C per hour, and holding for ~ 5 hours at this temperature still further allows these conditions to be maintained. Thus, this stage allows you to completely remove residual moisture particles and reduce the content of argon atoms in the coating.

Continued heating to T = 730 ° C for ~ 6 hours and the onset of the process of recrystallization of the nickel coating and exposure to this temperature allow most of the argon atoms to be removed from the coating. This contributes to the onset of the diffusion of nickel into the substrate, the compaction of the nickel coating due to the process of self-diffusion of nickel atoms. Further heating to 900 ^{± 50} ° C and holding it for ~ 2 hours ensure the diffusion of nickel atoms into the substrate to a depth of 30-40 μm and the formation of a crystal face-centered lattice in the entire coating volume. This final stage allows to achieve high adhesion of the coating to the substrate and sufficient coating density.

Industrial applicability

The method can be used when coating parts of complex configuration, for example, on turbine impellers made of high alloy alloys, mainly on a nickel basis.

Claims (5)

1. The method of vacuum ion-plasma coating, including creating a difference in electric potentials between the part and the cathode, cleaning the surface of the part with an ion flow, reducing the potential difference and coating, annealing the coating by increasing the potential difference, while the ion flux and the flow of the evaporated material, going from the cathode to the part during screening is screened, and the cleaning is carried out with inert gas ions, after cleaning the screens are removed and coated, followed by annealing, and during application coating, the part is rotated around its axis, after annealing, the part is cooled to room temperature, placed in a furnace and diffusion annealing in a vacuum medium is performed, characterized in that cleaning, coating of the required thickness and annealing are carried out in one cycle, and diffusion annealing of the coating is carried out stepwise at T = 100 ± 5, 340 ± 10, 730 ± 10 and 900 ± 50 ° С in a vacuum of 1 · 10 ^-3 mm Hg 2. The method according to claim 1, characterized in that the surface of the part is cleaned when the difference in electric potential between the part and the cathode is 1500-2000 V. 3. The method according to claim 1, characterized in that the coating process is carried out at an electric potential difference between the part and the cathode of 70-90 V. 4. The method according to claim 1, characterized in that the annealing of the applied coating layer is carried out at a voltage difference between the part and the cathode of up to 500 V. 5. The method according to claim 1, characterized in that the diffusion annealing of the coating is carried out stepwise at T = 100 ± 5, 340 ± 10, 730 ± 10 and 900 ± 50 ° C in a vacuum of 1 · 10 ^-3 mm Hg, at 100 ± 5 ° C, the shutter speed is 2.5 hours, at 340 ± 10 ° C ~ 5 hours, at 730 ± 10 ° C ~ 6 hours and at 900 ± 50 ° C ~ 2 hours.