RU2348741C2 - Nanostructured protective coating for stainless steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention concerns nano-structured coatings for stainless steel and can be used at operation of stainless steel in the capacity of materials for constructional and technological purposes of petrochemical industry. Coating contains a layer made of titanium nitride and intermediate layer made of silicon carbide of thickness from 5 till 10 nm. Layer made of titanium nitride has thickness from 25 till 50 nm, and layer made of silicon carbide - from 5 till 10 nm. Coating has total thickness 30-60 nm and total content, wt %: SiC - 16.6 and TiN - 83.4.

EFFECT: increasing of materials corrosion resistance at operating in acid environment and at higher temperature.

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Description

The invention relates to a nanocoating of stainless steel and brass containing titanium nitride and intended to protect metals from corrosion. The invention can be used primarily in the petrochemical industry to protect stainless steel and brass coil heat exchangers from corrosion, as well as for other cases of using these materials in strongly acidic environments.

Currently, several different coating options based on titanium nitride are disclosed in the patents:

DE 196000172 for cutting tools

Fr 2647271 for the protective layer of the contact element

Jp 1317963 for membrane shell

Jp 11332260 and 55112733 for cutting tools

RU 2214890 and 2214892 for cutting tools

In the above patents, titanium nitride-based coatings have a significant drawback: the presence of a pronounced interface between the metal to be protected and the nitride layer to be protected. This, when the material is operated at temperatures of 100 ° C and higher in a highly aggressive environment, leads to the start of phase formation processes at the interface, the formation of small pores and cracks and a decrease in the protective characteristics of the coating.

Since the invention proposes the use of nanostructured coatings, among these patents there are no analogues in explicit form.

Known nanostructured coating of the carrier base (Application for invention RU 2005116488), where the coating material is carbon.

The closest analogue of the present invention is described in the work (Dong Li, Xi Cnu, Snang-Cong Cneng. Et al. // Appl. Phys. Lett. 1995. Vol.67. N 2. P.202-205) composite coating, which represents a sandwich structure of alternately sputtered layers of titanium nitride and carbon nitride. For reasons that impede the achievement of the following technical result when using a material with a multilayer coating, adopted as a prototype, is that in the known material with a multilayer coating, since the coating has a micron thickness, the formation of a pronounced interface between the protected metal and the protected coating is realized, as well as between the nitride and carbide layers. This, when the material is operated at temperatures of 100 ° C and higher in a highly aggressive environment, leads to the start of phase formation processes at the interface, the formation of small pores and cracks, and a decrease in the protective (including anti-corrosion) characteristics of the coating.

In contrast to analogues, the structure of the protective nanostructured coating includes not only a nanolayer of titanium nitride, but also a nanolayer of silicon carbide, which is directly bonded to the steel surface, and a titanium nitride nanolayer is bonded to this nanolayer. Such a composition should minimize the occurrence of phase formation processes, since the ability to phase formation for a substance in the nanostate is much lower than for a substance of micron size. This will improve the protective properties of the coating located in a strongly acidic environment.

The aim of the proposed nanostructured coating on steel is to increase the corrosion resistance of petrochemical industry materials (stainless steel and brass heat exchanger coils) in a strongly acidic environment.

The goal is achieved as follows.

A nanocoating is used on the surface of stainless steel with a total thickness of 30-60 nm, with an additional layer of silicon carbide having a thickness of 5-10 nm, and a titanium nitride layer of 25-50 nm and the chemical composition of the nanocoating, wt.%: SiC 16.6 and TiN 83 ,four.

Nanocoatings are obtained by chemical surface engineering methods described, for example, in the article (V.M.Smirnov, J. General Chemistry, 2002, v. 72, No. 4, pp. 63-3-650).

Unlike analogues, the protective coating includes not only a nanostructured titanium nitride layer, but also a nanostructured silicon carbide layer, which is directly connected to the steel surface, and a titanium nitride nanolayer is connected with this nanolayer. Such a composition makes it possible to improve the protective properties of a coating located in a strongly acidic environment, since the ability to phase formation for a substance in the nanostate is much lower than for a substance of micron size.

Verification of the effectiveness of the proposed coatings was tested in comparison with micron coatings with the composition of the prototype. Since various materials are used in the apparatus and pipelines of the petrochemical industry, two of the most commonly used materials were used in the work - stainless steel (for example 12X1SH10T) and brass.

Anticorrosive nanocoatings were obtained in a batch laboratory reactor in the gas phase according to the procedure described in the article (V.M.Smirnov, J. General Chemistry, 2002, v. 72, No. 4, pp. 6333-650), and microcoatings by spraying layers of titanium nitride and nitride (Dong Li, Xi Spi, Snang-Cong Cneng. et al. // Appl. Phys. Lett. 1995. Vol.67. N 2. P.202-205).

The corrosion rate of metallic materials is determined by various methods, but the simplest and most reliable method is to evaluate the corrosion rate by the weight loss of the sample. Aggressive solution (1M HCl) was prepared by diluting 37% HCl with bidistilled water. Gravimetric measurements were carried out in a thermostated glass beaker. The volume of the solution is 100 ml. The research sample had a rectangular shape with dimensions (1.5 cm × 1.5 cm × 0.05 cm).

Results.

1. Anticorrosive properties of coatings on steel 12X18H10T

The effect of the protective effect of nanocoatings on the corrosion behavior of 12Kh18N10T steel in a 1 M HCl solution was studied by the change in weight at two temperatures (300K and 323K) after 6 hours in solution. The effectiveness of protection (E%) was determined by the formula E (%) = (1-W / W ₀ ) 100%, where W and W ₀ are corrosion rates with protective layers and without protective layers.

As can be seen from Table 1, the deposition of a protective nanolayer (SiC and TiN) and a TiN micro layer leads to a sharp decrease in the corrosion rate. The main difference in the behavior of TiN layers is that with an increase in the thickness of the deposited layer, approaching the micron layer at higher temperatures, crystallization (phase formation) processes are possible, which leads to the appearance of microdefects (cracks and other defects) and, accordingly, an increase in the corrosion rate. For nanolayers, such processes are possible only at very high temperatures. Note that the maximum anticorrosive effect is achieved even with TiN nanolayers 0.5 nm thick. This allows us to recommend for practical use of such coatings the thickness of TiN films in the range of 10-50 nm. The role of the SiC intermediate layer is that, with the same properties as TiN, the structure of SiC (bond lengths, angles) is closer to the structure of the materials taken, which makes it possible to create a dense coating with a minimum size and high thermal stability.

2. Anticorrosion properties of brass coatings

Brass are solid solutions of the copper-zinc system with a zinc content of up to 50 at.%. Products made of brass are usually operated under conditions of exposure to a humid atmosphere, and the specificity of the corrosion behavior of brass is their dezincification. Zinc passes into the corrosive medium, and copper crystallizes on the surface of brass in the form of a fine crystalline porous layer. For corrosion tests, the brass coil tubes were sawn into disks 2 mm thick with a diameter of 30 mm.

Solutions were prepared on bidistillate from reagent grade grade reagents. Corrosion tests were carried out in molybdenum glass beakers. On 1 cm ^{2 the} surface of the sample was taken 10 ml of solution. The test time is 15 days. Corrosion products were removed with a 3% HCl solution, then washed with double distillate. In the resulting solution, copper and zinc were determined. According to the loss in sample weight, the coefficients of dezincification were calculated. When studying the corrosion resistance of brass, it was found that applying a protective nano- and micro-layer of TiN and SiC allows you to get rid of the corrosion process on brass. Since the characteristic feature of brass corrosion is their dezincification to a greater extent due to oxygen depolarization, the presence of dense layers of TiN and SiC on the surface makes it possible to radically prevent the corrosion of brass. It should be noted that SiC nanolayers are more corrosion resistant, however, when choosing a composition for application, technological features of the synthesis (their peculiarity and advantages) should be taken into account. Thus, it was found in the work that refractory compounds based on titanium (carbides, nitrides) possess effective protective properties. Their coating significantly increases the corrosion resistance of structural metals and alloys.

Table 1. Weight loss of steel in 1M HCl at various thicknesses of the protective TiN layer (test temperature 300 K and 323 K, test time 6 h) Steel sample Corrosion rate, W (mg cm ^-2 h ^-1 ) The effectiveness of the protection, e (%) * 300K 323K S ₃₀₀ E ₃₂₃ Raw steel 0.661 0.894 - - with a 0.5 nm thick TiN layer 0.001 0.001 99.85 99.89 with a TiN layer 1 nm thick 0.001 0.001 99.85 99.89 with a TiN layer 1 nm thick, heated at 573 K 0.001 0.001 99.85 99.89 with a TiN layer 1 nm thick, heated at 773 K 0.001 0.001 99.85 99.89 with a 10 nm thick TiN layer 0.001 0.001 99.85 99.89 with a TiN layer 10 nm thick, heated at 573 K 0.001 0.001 99.85 99.89 with a TiN layer 10 nm thick, heated at 773 K 0.001 0.001 99.85 99.89 with a TiN layer 50 nm thick 0.001 0.001 99.85 99.89 with a TiN layer, 50 nm thick, heated at 573 K 0.001 0.001 99.85 99.89 with a TiN layer 50 nm thick, heated at 773 K 0.001 0.001 99.85 99.89 with a TiN layer 100 nm thick 0.001 0.001 99.85 99.89 with a TiN layer, 100 nm thick, heated at 573 K 0.001 0.001 99.85 99.89 with a TiN layer 100 nm thick, heated at 773 K 0.003 0.012 99.55 98.20 with a TiN layer 1000 nm thick 0.001 0.001 99.85 99.89 with a TiN layer, 1000 nm thick, heated at 573 K 0.004 0.007 99.40 98.90 with a TiN layer 1000 nm thick heated at 773 K 0.006 0.019 99.10 97.90 with TiN layer, 1 micron thick 0.001 0.001 99.85 99.89 with a TiN layer 1 μm thick, heated at 573 K 0.007 0.016 99.00 98.20 with a TiN layer 1 μm thick, heated at 773 K 0.009 0.051 98.64 94.30 * E (%) = (1-W / W ₀ ) 100%

Table 2. Corrosion rates K (g / dm ² days) and dezincification factors Z Samples 0.5N solutions NaCl Hcl H ₂ SO ₄ (NH ₄ ) ₂ SO ₄ K × 10 ³ Z K × 10 ³ Z K × 10 ³ Z K × 10 ³ Z Copper 4.3 530 37.6 46.5 α - L 70 4.3 1.8 530 1.8 42.5 1.9 40.8 1.9 (α + β) - L 62 1,1 66.8 22.0 ∞ 38,2 28,2 54,2 3.3 (α + β) - L 58 1,2 ∞ 40,0 ∞ 42.6 ∞ 54.0 3,1 α - L 70 + TiN layer 0.5 nm thick 0 0 0.001 0 0 0 0 0 α - L 70 + TiN layer 1 nm thick 0 0 0.001 0 0 0 0 0 α - L 70 + TiN layer 10 nm thick 0 0 0 0 0 0 0 0 α - L 70 + TiN layer 100 nm thick 0 0 0 0 0 0 0 0 α - L 70 + TiN layer 1000 nm thick 0 0 0 0 0 0 0 0 α - L 70 + SiC layer 0.5 nm thick 0 0 0 0 0 0 0 0 α - L 70 + SiC layer 1 nm thick 0 0 0 0 0 0 0 0 α - L 70 + SiC layer 10 nm thick 0 0 0 0 0 0 0 0 α - L 70 + SiC layer 100 nm thick 0 0 0 0 0 0 0 01 α - L 70 + SiC layer 1000 nm thick 0 0 0 0 0 0 0 0

Claims (1)

A nanostructured protective coating for stainless steel containing a titanium nitride layer, characterized in that it further comprises an intermediate layer of silicon carbide from 5 to 10 nm thick, a titanium nitride layer has a thickness of 25 to 50 nm, and the coating has a total thickness of 30 -60 nm and the total composition, wt.%: SiC 16.6 and TiN 83.4.