RU2375495C2 - Method of cermet coating receiving on details made from nickel alloy - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to cermet coating receiving field on details of complex configuration implemented from nickel alloys. Method includes application on detail at first of nickel alloy and then by method of dipping of ceramic slurry layer containing suspension of mixture of metals oxides in water. Then it is implemented drying up to total removing of moisture from the external and internal surfaces, formation of cermet coating in protective medium by means of burning and cooling of detail up to room temperature. Additionally before formation of cermet coating detail is located in container, it is pumped out air from it up to residual pressure not lower than 1·10^-1 millimetres of mercury. After what tank is located into furnaces and detail is heated up to temperature higher than boiling point of water during the period providing total warming up of all sections of detail, and detail is isolated at continuous pumping out of water vapours from tank up to total removing of residue moisture from pores of plated layers of coating.

EFFECT: exclusion of defects of distention of coating during burning and increasing of yield.

5 cl

Description

The invention relates to the field of production of ceramic-metal coatings on parts of complex configuration made of nickel-containing alloys and pre-coated with protective layers that protect their surfaces from aggressive environments under extreme operating conditions.

Parts of complex configuration under such conditions are exposed to high temperatures and pressure of an oxygen-containing gas in the presence of particles of aluminum alloy AM _g- 6, leading to erosion and ignition of the part.

To protect such parts from destruction under extreme conditions, we used the technology of applying a thick-layer (up to 300 μm) nickel coating to the surface by ion-plasma spraying, which is resistant to oxidation and fire in an oxygen-containing medium (Russian patent No. 2192501, 2000). After cooling to room temperature, the sprayed and annealed coating was subjected to heat treatment — diffusion annealing — in a vacuum furnace at a temperature of 1000–1050 ° C and a vacuum of at least 1 · 10 ^–3 mm Hg. A dense and durable coating with a sufficiently high adhesion to the surface of the part was obtained.

However, the obtained nickel coating during tests as part of the power plant showed insufficient resistance to erosion by particles of the aluminum alloy AM ₂ -6, as a result of which the nickel coating was carried away by these particles and the base metal ignited in oxygen.

To increase the degree of protection of the nickel coating from the effects of the above particles under extreme conditions, a method has been proposed for applying a cermet coating resistant to erosion on a nickel layer (US patent No. 6090191, 1999). A ceramic-metal coating on the nickel layer was applied by dipping the part into a slip containing a mixture of its components in water. The resulting layer was subjected to heat treatment by drying in a stream of hot air to completely remove moisture from inaccessible places on the outer and inner surfaces of the part. Next, the dried part was placed in a container, filled with argon, and a cermet coating was burned in a vacuum oven at a temperature of 1000-1050 ° C. The container was cooled with the oven to room temperature.

However, when applying a slip on the surface of a nickel coating, the moisture present in it penetrates into the pores of this coating and does not have time to completely evaporate during heating. As a result, high pressure of water vapor develops in micropores, which leads to swelling of some parts of the nickel layer and, as a result, the part goes into marriage.

When using thermal vacuum drying of parts, including first heating it to the required temperature and then pumping out moisture from hard-to-reach spots, complete removal of water from the micropores of the nickel coating was not achieved even after its preliminary heating in the air stream, which caused the nickel layer to swell in some areas of the coating .

The objective of the invention is the creation of a technology for the production of ceramic-metal coatings on parts of complex configuration made of high-alloyed nickel alloys and pre-coated with nickel and then metal-ceramic layers, which provides reliable protection of the resulting coating from aggressive environments in extreme conditions by increasing the degree of moisture removal from it.

The problem is solved due to the fact that in the method for producing a cermet coating on parts made of nickel alloys, including applying a nickel layer to the part first, and then dipping a slip layer containing a suspension of a mixture of metal oxides in water, drying to completely remove moisture from the external and internal surfaces, the formation of cermet coating in a protective environment by firing and cooling the part to room temperature, while before forming the cermet coating, the part is placed in a container they pump air out of it to a residual pressure of at least 1 · 10 ^-1 mm Hg, place the container in the furnace and heat the part to a temperature above the boiling point of water for a time that ensures full heating of all parts of the part, and maintain the part under continuous pumping water vapor from the container to the complete removal of residual moisture from the pores of the applied coating layers.

After evacuation of air, the container with the part is placed in a vacuum furnace previously heated to 300 ± 50 ° C.

Heating the part in the container is carried out to a temperature of 140-160 ° C for 1.0-1.5 hours.

Argon is used as a protective medium.

The formation of cermet coating is carried out by firing at a temperature of 1000-1050 ° C.

The technical result is the elimination of defects in the expansion of the coating during the firing process and increasing the yield of products.

The proposed method is as follows.

A nickel layer of a given thickness, mainly by ion-plasma spraying, is applied to the surface of a part of a complex configuration, for example, a turbine impeller, and a ceramic-metal layer is applied to it by dipping the part into a slip containing a suspension of a mixture of metal oxides in water. The coating formed on the surface of the part is subjected to heat treatment. Initially, the coated part is dried either in an oven or in a stream of hot gas, mainly air. The drying process is carried out until the moisture is completely removed from the outer and inner surfaces of the wheel. Next, the dried part is placed in a metal container, sealed with subsequent pumping of air until a vacuum of about 1-3 · 10 ^-1 mm RT.article Together with the evacuated air, part of the moisture is also removed from the relatively large pores of both layers of the coating. Before placing the container with the part in a vacuum oven, the latter is heated predominantly to a temperature of 250-350 ° C. A container is placed in a preheated oven and the part is slowly heated for a time of 1.0-1.5 hours until it reaches a temperature above the boiling point of water. Slow rise in temperature of the part allows you to completely warm up all its parts to the desired value. Upon reaching the indicated temperature, mainly 150 ± 10 ° С, and during continuous pumping of the container, isothermal exposure is performed for a time, which ensures the removal of vapors from micropores of both nickel and cermet coating layers. The isothermal exposure time depends on the technological features of the heat treatment process. After cooling the container with the part to room temperature, it is filled with an inert gas - argon - and again placed in the oven. The heating of the furnace is carried out to a temperature of 1000-1050 ° C and exposure is carried out at which the process of forming a cermet coating by firing takes place. Next, the calcined part is cooled with the furnace.

The proposed technology was applied on several details - turbine impellers of various diameters and thicknesses. Visual observation showed the absence of swelling defects on their surfaces. When testing these parts in the composition of energy devices under extreme conditions, the destruction of the coatings was not observed.

Claims (5)

1. A method of producing a ceramic-metal coating on nickel alloy parts, comprising first applying a nickel layer, and then dipping a slip layer containing a suspension of a mixture of metal oxides in water, drying to completely remove moisture from the outer and inner surfaces, forming a ceramic-metal coating protective medium by firing and cooling the part to room temperature, characterized in that before the formation of the cermet coating the part is placed in a container, pumped out of th air to a residual pressure not lower than 1 × 10 ^-1 Torr, the container is placed in an oven and heated piece to a temperature above the boiling point of water for a time that ensures complete heating of all parts of the items, and the item is kept under continuous pumping the water vapor from the container to the complete removal of residual moisture from the pores of the applied coating layers. 2. The method according to claim 1, characterized in that after evacuation of air, the container with the part is placed in a vacuum oven preheated to a temperature of 300 ± 50 ° C. 3. The method according to claim 1, characterized in that the heating of the part in the container is carried out to a temperature of 140-160 ° C for 1.0-1.5 hours 4. The method according to claim 1, characterized in that argon is used as a protective medium. 5. The method according to claim 1, characterized in that the formation of the cermet coating by firing is carried out at a temperature of 1000-1050 ° C.