RU2349681C2 - Composition for receiving of coating - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention can be used for protection of details made of steel, nickel and titanium alloys against saline and fretting corrosion and contact wear. Composition for receiving of coating on details made of structural steel or of heat-resistant alloy on the basis of nickel or titanium, contains following ratio of ingredient, wt %: aluminium-chromium-phosphate binding substance - 30-35, water - 12-18, chromic anhydride - 2-3, molybdenum disilicide - the rest. Molybdenum disilicide powder has fraction till 10 micrometer. In particular cases of invention implementation compound can additionally contains 0.3-0.5 wt % of surface-active material, for instance synthanol, "ОП"-7, "ОС"-20, "АФ"-10.

EFFECT: resistance against saline and fretting corrosion, against contact wear.

3 cl, 2 tbl, 1 ex

Description

The invention relates to the field of mechanical engineering and metallurgy and can be used in aviation and energy turbine construction to protect parts from structural steels, as well as titanium and nickel alloys from salt and fretting corrosion and contact wear.

A known method and composition for obtaining a corrosion-resistant coating consisting of a first layer of a condensed coating of an alloy based on nickel containing chromium, cobalt, aluminum, yttrium, and a second layer of an alloy based on aluminum (RF patent No. 21545475).

The known composition allows to obtain on the compressor blades and other machine parts a coating resistant to salt corrosion at temperatures up to 700 ° C, not reducing the strength characteristics of these parts.

A disadvantage of the known composition is the low resistance of the coating to contact wear.

A known composition for obtaining a non-stick coating, including ingredients in the following ratio, wt.%:

Black graphite 15-25 Nepheline flame retardant 5-15 Alumochromophosphate Binder 36-48 Glycerol 1-3 Organosilicon emulsion 0.5-1.5 Water Rest

(USSR Copyright Certificate No. 1212686)

The composition allows to obtain a non-stick coating on casting molds and cores, to improve the quality of castings and to exclude marriage on burns and gas sinks.

A disadvantage of the known composition is the low resistance of the resulting coating to contact wear.

Also known is a composition for coating casting molds and cores, including ingredients in the following ratio, wt.%:

Alumochromophosphate Binder 10.0-15.0 Water 30.0-40.0 Sulphuric acid 0.8-1.0 High Alumina Cement 0.8-2.0 Dust quartz Rest

(USSR copyright certificate No. 1507507)

The composition has high technological properties - ease of application, good absorbency in the surface and increased crack resistance.

A disadvantage of the known composition is the unsatisfactory and low resistance of the coating to contact wear and fretting corrosion.

The closest analogue taken as a prototype is a composition for obtaining a non-stick coating on foundry molds and cores, including a refractory filler in the form of distensillimanite paste, alumina-chromophosphate binder, water and calcium oxide hydrate in the following ratio of ingredients, wt.%:

Refractory filler in the form of distensillimanite paste 43.0-44.0 Calcium oxide hydrate 0.5-1.0 Alumochromophosphate Binder 27.0-31.0 Water Rest

(USSR Copyright Certificate No. 1207619)

The composition allows to obtain a non-stick coating on casting molds and cores, to improve the quality of castings and reduce the complexity, both when coating the molds, and during cleaning and chipping operations.

A disadvantage of the known composition is also the low resistance of the resulting non-stick coating to salt corrosion, fretting corrosion and contact wear.

The technical task of the present invention is to provide a composition for coating on parts of machines with a working temperature of up to 600 ° C, made of structural steels and heat-resistant alloys based on nickel and titanium and working in dry friction under contact wear and fretting corrosion and salt corrosion.

This is achieved by the fact that the composition for coating on parts made of structural steels or heat-resistant alloys based on nickel or titanium, including aluminum-chromophosphate binder, filler and water, additionally contains chromic anhydride, and molybdenum disilicide powder as the filler in the following ratio of ingredients , wt.%:

Alumochromophosphate binder 30-35 Water 12-18 Chromic anhydride 2-3 Molybdenum Disilicide Rest

Molybdenum disilicide powder has a fraction of up to 10 microns.

The composition may additionally contain a surface-active substance (surfactant) "Syntanol", OP-7, OS-20, AF-10 in an amount of 0.3-0.5 wt.%.

The authors found that the use of a composition based on alumochromophosphate binder, water, chromic anhydride and a filler - molybdenum disilicide powder in the proposed quantitative ratio, provides high resistance of the coating on parts made of steels and heat-resistant alloys to salt corrosion and at the same time to contact wear and freting corrosion . Moreover, the resistance to salt corrosion is practically not inferior to the resistance of all known coatings, and the resistance to contact wear, fretting corrosion is many times higher than the resistance of known coatings.

The presence in the composition to obtain a coating of chromic anhydride in an amount of 2-3% allows to increase the resistance of the coating based on the composition to salt corrosion, and also allows to increase the shelf life of the composition by 2-3 times. The content of chromic anhydride is limited to 3 wt.% Due to the inadmissibility of a high content in hexavalent chromium. Moreover, the content of chromic anhydride of more than 3% does not increase the protective properties of the coating.

The resistance of the coating based on the proposed composition to contact wear is associated with the content in the composition of molybdenum disilicide (MoSi ₂ ) having a relatively high microhardness, reaching values of 1200 kg / mm ² , and a strong bond of MoSi ₂ powder with an AHFS based binder.

The high resistance of the coating based on the proposed composition to salt corrosion is characteristic of coatings containing AHFS, and this resistance is increased when chromic anhydride is present in the composition.

Recommended coating thickness up to 20 microns. This determines the fraction of MoSi ₂ powder up to 10 μm. Coatings up to 10 microns thick and with a powder fraction up to 5 microns can find the greatest application.

The use of a surface-active substance in an amount of 0.3-0.5 wt.% Helps to improve the technological properties of the composition upon receipt of the coating by dipping.

An example implementation. The following ingredients were used to prepare the composition:

Alumochromophosphate binder (AHFS), TU 6-18-166-83;

Distilled water, GOST 6709;

Chromic anhydride CrO ₃ , ChDA, GOST 3776-78;

Molybdenum disilicide, TU 6-09-03-395-74;

Surfactant - "Syntanol" DS-10, OP-7, TU 6-14-577-70.

The order of preparation of the composition is as follows: a portion of the aluminochromophosphate binder was diluted with water, then chromic anhydride was introduced and the aqueous solution of AHFS was thoroughly mixed until it was completely dissolved. Then, molybdenum disilicide, previously ground to 5 μm, was added to the resulting aqueous solution, and thoroughly mixed. In this form, the composition is ready for coating on machine parts. The compositions of the prepared coatings are shown in table 1. Note that compositions No. 2, 3 contain a surfactant - OP-7 in an amount of 0.3 wt.% And Sintanol DS-10 in an amount of 0.5 wt.%.

Details of the GTE compressor and samples of heat-resistant martensitic steel EP866, heat-resistant iron-chromium-nickel alloy EP718 and titanium alloy VT8 were prepared for coating. As parts of heat-resistant martensitic steel EP866, alloy EP718 and alloy VT8, compressor blades of a marine aviation gas turbine engine were used. A coating with a thickness of 8-10 μm was applied to the locking part of the blades, which undergoes contact loads during operation and is subject to salt and fretting corrosion and contact wear. The padlocks of the blades and the samples were sandblasted and then blown with compressed air, cleaned of moisture and oil. Then the composition was applied with a brush to the locks of the blades, and on the samples - by dipping them into the composition. Then, the coating was dried in air. After that, stepwise heat treatment of the blades and coated samples was carried out with heating from room temperature to 150 ° C with holding at this temperature for 30 minutes, then they were heated to 500 ° C (500 ° C is the maximum working temperature of the compressor blades from VT8 titanium alloy) and made holding at this temperature for 30 minutes, then cooled the parts and samples together with the furnace to 100 ° C, then in air.

Table 1 Ingredients The content of ingredients, wt.%, In the composition one 2 3 Alumochromophosphate Binder thirty 32,5 35 Distilled water 12 fifteen eighteen Chromic anhydride 2 2.5 3 Molybdenum Disilicide 56.0 49.7 40.5 1% aqueous surfactant solution 0.3 0.5

The thickness of the coating was determined on the samples and locks of the blades by the eddy method. The thickness varied in the range of 8.5-10 microns with an allowable thickness of 12 microns. The corrosion resistance of parts and coated samples was studied by the method of accelerated cyclic tests on flat samples of 20 × 30 × 1.5 mm according to the regime: heating to a temperature of 600 ° C and holding for 1 h, cooling in air for 2 minutes, cooling in a 3% NaCl solution , exposure for 22-24 hours in a wet chamber. Note that 10 test cycles without corrosion damage are considered satisfactory corrosion resistance. Resistance to contact wear under fretting corrosion conditions was tested on a special stand that allows loading the contacting pair and setting the displacement with a small amplitude and with a certain frequency. The test conditions for all samples were the same, the results are summarized in table 2.

table 2 Type of sample The number of cycles before the appearance of foci of corrosion, cycle Depth of wear per 100 hours of test, microns Composition 1 Composition 2 Composition Z Composition 1 Composition 2 Composition 3 EP866 coated steel 19 17 eighteen 1-1,2 <1 1.8-2.0 Coated EP718 Alloy twenty 17 eighteen 1-1.3 <1 2.0-2.2 Coated VT8 Alloy > 20 > 20 > 20 1.4-1.6 1.2-1.3 2.2-2.5 EP718 alloy without coating four 45-70 removed from the test after 12 hours. Strong wear EP718 steel coated with a prototype according to AS No. 1207619 6 60-90 removed from the test after 12 hours. Strong wear

From the results in the table it is seen that the proposed composition allows to obtain coatings with high corrosion resistance. The coating according to the prototype method based on an aqueous solution of AHFS with distene sillimanite paste, calcium oxide hydrate slightly increases the corrosion resistance of EP718 alloy. The minimum resistance to salt corrosion at a maximum test temperature of 600 ° C has a base (alloy EP718) without coating. As for contact wear in the conditions of fretting corrosion (fretting - wear), the proposed coating has one to two orders of magnitude less wear than the coating according to the prototype method and the material without coating.

Locks of compressor blades made of EP866 steel and EP718 alloy with a coating of the proposed composition have been successfully tested in a gas turbine engine. Tests have shown that a coating of the proposed composition will increase the resource of parts more than double compared to compressor blades having a serial coating.

Claims (3)

1. A composition for coating on parts made of structural steels or from heat-resistant alloys based on nickel or titanium, containing an aluminum-chromophosphate binder, a filler and water, characterized in that it additionally contains chromic anhydride, and as a filler - molybdenum disilicide powder with the following ratio of ingredients, wt.%:
Alumochromophosphate Binder 30-35 Water 12-18 Chromic anhydride 2-3 Molybdenum Disilicide Rest 2. The composition according to claim 1, characterized in that the molybdenum disilicide powder has a fraction of up to 10 microns. 3. The composition according to claim 1, characterized in that it additionally contains a surfactant Sintanol, OP-7, OS-20, AF-10 in an amount of 0.3-0.5 wt.%.