RU2437963C1 - Procedure for application of nano-composite coating on surface of steel item - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: procedure consists in cleaning chamber in medium of inert gas at item cleaning, in ion etching and ion plasma nitriding whereupon there is additionally performed ion etching of item surface. Ion-plasma nitriding with successive ion etching is performed in N stages, where N is integral number, and N≥1 till saturation with nitrogen of near-surface layer of metal of depth to 500 mcm. Further, there is applied coating by the method of physical sedimentation from vapour phase by application of a micro-layer of nano layers of thickness 1-100 nm of titanium, aluminium and silicon, application of a micro-layer of nano-layers of thickness 1-100 nm of nitrides of titanium, aluminium, and silicon or application of micro-layer in form of amorphous matrix of silicon nitride with solid inclusions of nitride of titanium and aluminium with typical distances between the said inclusions 1-100 nm.

EFFECT: coating with increased service life under conditions of erosion, corrosion and high temperature.

5 cl, 2 tbl, 2 ex

Description

The invention relates to the field of engineering, in particular to methods for the formation of protective coatings on parts subject to mechanical stress, high temperatures, exposure to an aggressive working environment. The invention can be used in power engineering for the protection of turbine blades and compressors, as well as elements of shut-off and control valves from erosion, corrosion and thermal effects.

Currently, methods of applying protective coatings in a vacuum by physical deposition on a protected surface with the formation of compounds resistant to the damaging effects - mechanical, chemical, and thermal - are widely used. Such coatings are applied in several layers using electric arc or magnetron sources of sprayed material (see US Pat. No. 6033734, IPC C23C 14/06; C23C 14/24, publ. 07.03.2000).

However, the coating obtained in this way has a low service life.

The closest in technical essence to the invention is a method of processing turbomachine blades (US Pat. RU No. 2373302 IPC ⁸ , C23C 14/06, publ. 20.11.2009), which protects the method of applying nanocomposite coatings. The method consists in the fact that after machining the product and placing it in a vacuum chamber, the product and the vacuum chamber are cleaned in an inert gas medium, ion etching and ion-plasma nitriding of the product surfaces, coating by physical vapor deposition.

However, mechanical surface treatment of the product, argon cleaning, and nitriding do not provide the required quality of surface preparation, which reduces the quality of the coating and does not provide the necessary service life when the product is operated under conditions of erosion, corrosion and high temperatures.

An object of the invention is to increase the service life of the coating in conditions of erosion, corrosion and high temperatures.

The solution to this technical problem is achieved by the fact that in the known method of applying a nanocomposite coating on the surface of a steel product, including cleaning products and a vacuum chamber in an inert gas environment, ion etching and ion-plasma nitriding of product surfaces, coating by physical vapor deposition, additionally when cleaning the product, the chamber is cleaned in an inert gas medium, and after ion etching, ion-plasma nitriding is carried out, after which additionally ion etching of the surface of the article is carried out, while ion-plasma nitriding followed by ion etching is carried out in N stages, where N is an integer and N≥1, until the surface layer of the metal is saturated with nitrogen to a depth of 500 μm, while the coating is applied by physical deposition from the vapor phase is carried out by applying a microlayer of nanolayers 1-100 nm thick of titanium, aluminum and silicon, then applying a microlayer of nanolayers 1-100 nm thick of titanium, aluminum, silicon nitrides or applying a microlayer in the form of an amorphous m a matrix of silicon nitride with solid inclusions of nitrides of titanium and aluminum with typical distances between said inclusions is 1-100 nm.

In addition, before cleaning the products can carry out pre-heating of the vacuum chamber with simultaneous pumping of air.

A microlayer of nanolayers of titanium, aluminum and silicon can be applied by successive passage of the product in front of magnetron targets from these materials, and the thickness of the microlayer is 0.4-0.6 microns.

In addition, a microlayer of nanolayers of titanium, aluminum, and silicon nitrides can be applied by successive passage of the product in front of magnetron targets from these materials when nitrogen is supplied to the chamber, the thickness of the microlayer being 2.5-3 microns.

Additionally, a microlayer in the form of an amorphous matrix of silicon nitride with solid inclusions of titanium and aluminum nitrides can be applied while applying titanium, aluminum and silicon nitrides.

The method of applying nanocomposite coatings is as follows.

Products are polished, degreased in an ultrasonic bath, treated with a gasoline-alcohol mixture, and subjected to heat treatment in an oven. Products thus prepared are placed on a carousel in a vacuum chamber. Heating the vacuum chamber and pumping air out of it is carried out simultaneously. In addition to accelerating the process, the simultaneous heating of the chamber and the creation of a vacuum in it are advisable for the desorption of water vapor and working fluids of vacuum pumps, as well as solvents used to process the products previously adsorbed on the surface of the product.

The surface of the products and the vacuum chamber in a glow discharge are cleaned from adsorbed water vapor, solvents, etc., for which a voltage of 1000 to 1200 V is applied to the carousel, and an inert gas, such as argon, is introduced into the vacuum chamber. Next, ion surface etching is carried out. For etching the cleaned surface, increase the ion flux density on the product. For this, magnetrons are included, which in this case play the role of plasma generators, however, they choose such a mode of operation that the deposition rate of the atomized metal is less than the rate of its etching. Moreover, to remove the etched material from the surface of the product, the argon pressure should be low so that the mean free path of the particle is comparable with the distance from the product to the chamber wall. The most intense etching occurs when products pass between magnetrons. The use of magnetrons in the etching process avoids the application of metal droplets on the surface of the product, which is typical when using electric arc sprayers. Etching is carried out until a characteristic pattern of metal grains appears on the surface of the product, and as a result, the surface of the product is intact by mechanical and chemical treatment.

The surface of the article etched in this way is subjected to ion-plasma nitriding. Nitriding of the surface consists in the diffusion saturation with nitrogen of the surface layer of the metal with a depth of up to 500 μm, as a result of which a solution of nitrogen in the metal is formed. The surface hardness can increase four or more times from the original value, decreasing with depth to the hardness of the starting material. This is necessary to exclude a sharp change in hardness at the border "nanocomposite coating - the main material", which reduces the maximum stresses in the boundary zone of the coating materials and the base. Etching the surface before nitriding allows for the diffusion of nitrogen to a greater depth and the formation of a more uniform and saturated solution of nitrogen in the metal. Nitriding is carried out by feeding nitrogen gas into the chamber and heating the product with the support of magnetron discharge, which increases the diffusion rate of nitrogen. At the end of ion-plasma nitriding, additional ion etching is carried out to remove nitrogen compounds formed on the surface of the products, which subsequently prevent high adhesion of the nanocomposite coating material. Nitriding is carried out in N stages, where N is an integer and is selected from the condition N≥1, alternating with ion etching, since nitrogen compounds formed on the surface of the product reduce the rate of nitrogen penetration into the material. As a result, a clean metal surface with a solid surface layer is formed, ready for applying a nanocomposite coating.

The nanocomposite coating is applied by physical vapor deposition using magnetrons, sequentially alternating layers of various materials. The first is a microlayer of titanium, aluminum and silicon with a total thickness of 0.4-0.6 microns, which in turn consists of nanolayers of these materials with a thickness of 1 to 100 nm. These nanolayers are formed during the sequential passage of the product in front of magnetrons with targets from various sprayed materials - titanium, aluminum and silicon. Then a second microlayer of titanium, aluminum and silicon nitrides with a total thickness of 2.5-3 microns is applied. This microlayer also consists of nanolayers with a thickness of 1 to 100 nm and is formed by sequential passage of the product in front of magnetrons with targets made of titanium, aluminum, silicon when nitrogen is introduced into the chamber. Next, the operations are repeated, and the result is a nanocomposite protective coating with a total thickness of 5.8-7.2 microns or more. The thickness of the nanolayers is controlled by a change in the speed of rotation of the carousel and the power of the magnetron discharge. The thickness of the microlayers is controlled by the time of formation of the coating.

It has been experimentally found that the best coating characteristics are achieved in the indicated thickness ranges of micro- and nanolayers.

To study the properties of the nanocomposite coating deposited as described above, samples were made of steel 20X13. The first group (I) of samples was not subjected to processing. A nanocomposite coating consisting of Ti + Al + Si - TiN + AlN + SiN layers was applied to the surface of the samples of the second group (II), while nitriding was carried out after cleaning with argon, and the coating was applied immediately after nitriding. The processing of samples of the third group (III) was different from the processing of samples of the second group by ion etching before and after nitriding. The first group was the control, and the erosion resistance of the samples of the second and third groups was determined in relation to the erosion resistance of the samples of the first group. The study was conducted at the stand "Erosion-M" MPEI (TU), its results are shown in table 1.

Table 1 Sample Group Relative erosion resistance I 1,0 II 2.7 III 3,7

When organizing the simultaneous flow of titanium, aluminum and silicon to the surface of the product with the supply of nitrogen to the chamber, a microlayer is formed on the surface of the product in the form of a so-called amorphous matrix of silicon nitride with solid inclusions of metal nitride phases. The characteristic distances between these inclusions lie in the range of 1-100 nm. The formation of such an amorphous matrix can significantly increase the durability of the coating.

To study the properties of the nanocomposite coating, characterized by an amorphous matrix with solid inclusions, samples were made of steel 20X13. The first group (I) of samples was not subjected to processing. A nanocomposite coating consisting of silicon nitride with TiAlN grains was applied to the surface of the samples of the second group (II), while nitriding was carried out after purification with argon, and the coating was applied immediately after nitriding. The processing of samples of the third group (III) was different from the processing of samples of the second group by ion etching before and after nitriding. The first group was the control, and the erosion resistance of the samples of the second and third groups was determined in relation to the erosion resistance of the samples of the first group. The study was conducted at the stand "Erosion-M" MPEI (TU), its results are shown in table 2.

table 2 Sample Group Relative erosion resistance I 1,0 II 3,1 III 4.0

Thus, it is the inclusion in the method of applying a nanocomposite coating, characterized by an amorphous matrix with solid inclusions, the stage of ion etching of the surface before and after nitriding that allows to increase the erosion resistance of products, and hence their service life.

However, the proposed method of applying nanocomposite coatings is not limited to the above combinations of materials for applying layers. In the particular case of the implementation of the method may include the use of a target, which is a set of plates. In some cases, the surface treatment according to the proposed method can be carried out using various elements as a sprayed material, for example, Ti, Ni, Co, Cr, Al, Y, Zr, Hf, V, Ta, Mo, W, B, Si, C or any alloy based on these elements. It is possible to use nitrogen, oxygen, hydrocarbons, vapors of organosilicon liquids, as well as any mixture of these gases, as a reaction gas.

When implementing the method, it is possible to arrange magnetrons on the periphery of the vacuum chamber and / or in the center of it, which reduces the processing time of the product.

Example No. 1 of a specific implementation of the method:

- polishing the product, degreasing with ultrasound and wiping with a gasoline-alcohol mixture, drying in a cabinet at T = 60 ° C;

- placement of products on the carousel in a vacuum chamber, simultaneous heating and pumping of the vacuum chamber T = 150 ° C, P _ost = 10 ^-4 Pa;

- ion cleaning with argon, P = 1.5 Pa, t = 10 min, U _bias = 1150 V;

- ion etching, P = 0.2 Pa, t = 20 min, U _bias = 1150 V, voltage on magnetrons - 150 V each;

- nitriding, P = 2 Pa, t = 60 min, U _bias = 1150 V;

- ion etching, P = 0.2 Pa, t = 20 min, U _bias = 1150 V, voltage on magnetrons - 150 V each;

- applying a multilayer nanocomposite coating, consisting of layers of Ti + Al + Si - TiN + AlN + SiN according to the regime P = 0.2 Pa, t = 60 min, U _bias = 75 V, voltage on magnetrons - 450-500 V.

Example No. 2 of a specific implementation of the method:

- polishing the product, degreasing with ultrasound and wiping with a gasoline-alcohol mixture, drying in a cabinet at T = 60 ° C;

- placement of products on the carousel in a vacuum chamber, simultaneous heating and pumping of the vacuum chamber T = 150 ° C, P _ost = 10 ^-4 Pa;

- ion cleaning with argon, P = 1.5 Pa, t = 10 min, U _bias = 1150 V;

- ion etching, P = 0.2 Pa, t = 20 min, U _bias = 1150 V, voltage on magnetrons - 150 V each;

- nitriding, P = 2 Pa, t = 60 min, U _bias = 1150 V;

- ion etching, P = 0.2 Pa, t = 20 min, U _bias = 1150 V, voltage on magnetrons - 150 V each;

- deposition of a multilayer nanocomposite coating consisting of Ti + Al + Si layers and layers consisting of TiAlN grains surrounded by silicon nitride in the regime P = 0.15 Pa, t = 60 min, U _bias = 50 V, voltage on magnetrons - 450-500 V.

The use of the invention provides an increase in the service life of the nanocomposite coating.

Claims (5)

1. The method of applying a nanocomposite coating on the surface of a steel product, including cleaning the product and the vacuum chamber in an inert gas environment, ion etching and ion-plasma nitriding of the surface of the product, coating by physical vapor deposition, characterized in that the product is cleaned when cleaning chambers in an inert gas medium, and after ion etching, ion-plasma nitriding is carried out, after which ion etching of the product’s surface is additionally carried out, while Variable nitriding followed by ion etching is carried out in N stages, where N is an integer and N≥1, until nitrogen is saturated with the surface layer of the metal up to 500 μm deep, while coating by physical vapor deposition is carried out by applying a microlayer of nanolayers with a thickness of 1 -100 nm from titanium, aluminum and silicon, the subsequent deposition of a microlayer of nanolayers 1-100 nm thick of titanium, aluminum, silicon or the deposition of a microlayer in the form of an amorphous matrix of silicon nitride with solid inclusions of nitride titanium and aluminum in the characteristic distances between said inclusions is 1-100 nm. 2. The method according to claim 1, characterized in that before cleaning the products carry out preliminary heating of the vacuum chamber with simultaneous pumping of air. 3. The method according to claim 1, characterized in that the microlayer of nanolayers of titanium, aluminum and silicon is applied by sequential passage of the product in front of magnetron targets from these materials, and the thickness of the microlayer is 0.4-0.6 microns. 4. The method according to any one of claims 1 to 3, characterized in that the microlayer of nanolayers of titanium, aluminum, silicon nitrides is applied by sequential passage of the product in front of magnetron targets from these materials when nitrogen is fed into the chamber, and the thickness of the microlayer is 2.5-3 microns. 5. The method according to any one of claims 1 to 3, characterized in that the microlayer in the form of an amorphous matrix of silicon nitride with solid inclusions of titanium and aluminum nitrides is applied while applying titanium, aluminum and silicon nitrides.