RU2270878C1 - Method of production of cast oxide material and material produced by this method - Google Patents

Abstract

FIELD: metallurgy; methods of production of cast oxide materials on silicon oxide base for production of rods of complex configuration for gas-turbine engine blades.

SUBSTANCE: proposed method includes preparation of reaction mixture of starting components containing chromium oxide VI and reductant, placing the mixture in graphite mold which is placed in reactor, local ignition of mixture at excessive pressure of inert gas for obtaining synthesis product and separation of cast oxide material. Oxide material is obtained on base of solid solution of chromium oxide in silicon oxide of amorphous structure. Silicon introduced into starting mixture in the amount of 17.0-50.0 mass-% is used as reductant. Functional layer of silicon oxide, 3 to 7 mm thick is placed between mixture and mold walls.

EFFECT: low thermal expansion coefficient of alloy and high resistance to melts of heat-resistant alloys.

6 cl, 2 tbl, 1 ex

Description

The invention relates to powder metallurgy, in particular, to methods for producing cast oxide material based on silicon oxide, which can be used in the field of aircraft engine manufacturing to produce ceramic rods of complex configuration for casting gas turbine engine blades (GTE, GTU), as well as the manufacture of other ceramic products such as molds, crucibles, etc.

A known method of producing refractory inorganic materials, in particular cast oxide material from a reaction mixture of chromium oxide VI, aluminum as a reducing agent and carbon by local ignition of the mixture under a gas pressure of 0.1 MPa (SU 617485, C 22 C 29/00, 30.07. 1978).

In the known method, the initial mixture is placed in a refractory cylindrical form, placed in a reactor and the mixture is ignited with a tungsten electric spiral under gas pressure. After the combustion process is completed, the synthesis product is cooled and recovered. The synthesis product is a cast sample, divided into two layers: the top is cast aluminum oxide (corundum), the bottom is chromium carbide.

The disadvantage of this method is the low quality of the obtained oxide material, in which the content of free carbon impurities, metal inclusions, etc. is at least 3%, which does not allow to obtain high-quality ceramic products.

The closest analogue to the claimed method is the invention (RU 2009019 C1, B 22 F 1/00, C 22 C 29/00, 03/15/1994), which describes a method for producing cast oxide material. The method includes preparing a reaction mixture of starting components containing chromium oxides VI and III, aluminum as a reducing agent and carbon, placing the mixture in a graphite form, placing it in a reactor, local ignition of the mixture under an inert gas (nitrogen) pressure of 4 MPa, in the following ratio of components , wt.%:

chromium oxide VI 32.0-40.0 chromium oxide III 24.0-36.0 aluminum 22.0-30.0 carbon 6.0-10.0

The oxide target product is a solid solution of Al ₂ O ₃ —Cr ₂ O ₃ with a Cr ₂ O ₃ content _of from 3.0 to 5.0 wt.%.

The disadvantages of the known invention are the high coefficient of thermal expansion of this material and the impossibility of dissolution in alkaline solutions, which makes it ineffective for casting GTE and GTU blades (as forming forming rods) and leads to a low yield of suitable blades.

The technical result of the claimed invention is to obtain a cast oxide material based on a solid solution of chromium oxide in silicon oxide with an amorphous structure for the manufacture of ceramic rods with a combination of unique properties: low coefficient of thermal expansion, high resistance to melts of heat-resistant alloys, with the complete removal of ceramic rods from castings in alkali solutions.

The material obtained by the proposed method is characterized by a low coefficient of thermal expansion in the range of (0.1-0.5) × 10 ^-6 1 / deg, dissolution time in an alkali solution from 30 to 120 minutes and a zone of interaction with melts of heat-resistant alloys from 0.001 up to 0.005 mm.

The technical result is achieved in that a method for producing a cast oxide material, comprising preparing a reaction mixture of starting components containing chromium VI and a reducing agent, placing the mixture in a graphite form, placing it in a reactor, local ignition of the mixture at an inert gas overpressure to obtain a synthesis product, and subsequent separation of the cast oxide material, leads to the production of oxide material based on a solid solution of chromium oxide in silicon oxide with an amorphous structure, when ohm as a reducing agent in the feed mixture is silicon in an amount of 17,0-50,0 wt.%, and between the mixture and mold walls arranged functional layer of silicon oxide 3-7 mm thick. The composition of the reaction mixture can additionally be introduced aluminum in an amount of 1-15 wt.% Or at least one lanthanum compound from the group La ₂ O ₃ , LaB ₆ in an amount of 1-20 wt.%.

Cast oxide material obtained by the proposed method is a solid solution of chromium oxide in silicon oxide with an amorphous structure, while the content of silicon oxide is up to 98 wt.%. Additionally, the cast oxide material may contain up to 20 wt.%. aluminum oxide or up to 20 wt.%. lanthanum oxide.

The synthesis product is an ingot, which consists of two layers: the upper one is a cast oxide material SiO ₂ -yCr ₂ О ₃ , which is a solid solution of chromium oxide in silicon oxide with an amorphous structure, used in the aviation industry for the manufacture of forming rods for molding GTE blades and gas turbines, and the lower - “metallic” - CrSi _x , which is used to obtain heat-resistant protective coatings by plasma spraying and surfacing.

Additions of Al and lanthanum compounds to the initial charge lead to the formation of an oxide solid solution of Al ₂ O ₃ and La ₂ O ₃ in SiO ₂ -yCr ₂ O ₃ .

It should be noted that LaB ₆ introduced into the mixture decomposes into La and B during combustion. Lanthanum oxidizes to La ₂ O ₃ and forms a solution of SiO ₂ -yCr ₂ O ₃ -La ₂ O ₃ (upper layer), and boron forms a compound with chromium and silicon Cr-Si-B (lower layer).

Placed between the initial mixture and the inner surface of the graphite mold, a functional layer of 3–7 mm thick made of silicon oxide eliminates the contact of the melt of the target product with the mold material and reduces the cooling rate of the melt, acting as a heat-insulating layer. In general, the presence of a functional layer leads to an increase in the “life” time of the melt and a decrease in the content of impurities in the target oxide material (the content of carbon and inclusions of the metal phase in the target product is no more than 0.1%).

The combination of features claimed in the formula makes it possible to obtain a cast oxide material based on silicon oxide, with a SiO ₂ content _of the target product in the amount of 70-98 wt.%, Having a high degree of purity, low coefficient of thermal expansion, high resistance to interaction with melts of high-temperature alloys, quick and complete dissolution in alkali solutions. Cores of complex configuration for casting blades of gas turbine engines (GTE, GTU) made of this material do not interact with melts of heat-resistant alloys and are quickly and completely removed by alkali solutions.

The essence of the method is confirmed by examples.

Example 1

Prepare a reaction mixture of the starting components in the following ratio, wt.%: Chromium oxide VI (CrO ₃ ) - 50.0, silicon - 50.0.

Preliminarily, a thin-walled cylinder of non-ferrous metal or thick paper with a gap of 3 mm from its wall to the inner surface of the graphite form is installed in the graphite form. The reaction mixture is poured into the cylinder, and a functional layer of SiO _{2 is} poured into the gap between the cylinder and the mold. The cylinder is removed, and the curb form from the reaction mixture and the functional layer with a thickness of 3 mm is placed in the reactor. An inert gas (nitrogen) pressure of 4.0 MPa is created in the reactor, after which the reaction mixture is ignited by an electric spiral.

After completion of the combustion process, the synthesis product is cooled and recovered from the reactor. The synthesis product consists of two layers: the upper one is the cast oxide target material SiO ₂ -yCr ₂ О ₃ and the lower one is CrSi _x , which are easily separated from each other. The content of chromium oxide in the target product is 2.0 wt.%, And silicon oxide 98 wt.%. A forming core made of the obtained material practically does not interact with melts of heat-resistant nickel-based alloys (for example, with ZhS-6U, the interaction zone (S) does not exceed 0.005 mm), has a KTP of 0.5 × 10 ^-6 1 / deg, and the time of complete dissolution of the rod in alkali is 30 minutes.

The results of examples of the method are presented in table 1.

The properties of the target material by examples are presented in table 2.

As can be seen from the presented data, the target material, as well as the forming rods made from the obtained material, practically do not interact with the melts of heat-resistant nickel-based alloys (for example, with ZhS-6U, the interaction zone (S) does not exceed 0.005 mm, have KTP (0.1 -0.5) × 10 ^-6 1 / deg, and the time of complete dissolution of the rods in a solution of alkalis is 30-120 minutes). The proposed cast oxide material was given the technical name PLAMTIKAST (fused material like quartz with an amorphous structure).

The method of producing cast material based on SiO _{2 is} high-performance, low-energy, environmentally friendly, since the synthesis products do not contain gaseous substances that pollute the atmosphere; it is technologically advanced because the graphite form is used repeatedly and eliminates the use of potassium bifluoride (poison) at the stage of removal of the rod from the blade existing technology.

Table 1 No., example Layer thickness mm The composition of the reaction mixture of components, wt.% The composition of the oxide material, wt.% CrO ₃ Si Al La ₂ o ₃ LaB ₆ one 3 fifty fifty - - - SiO ₂ -98, Cr ₂ O ₃ -2 2 3 83 17 - - - SiO ₂ -85, Cr ₂ O ₃ -15 3 four 82 17 one - - SiO ₂ -84, Cr ₂ O ₃ -14, Al ₂ O ₃ -2 four four 65 twenty fifteen - - SiO ₂ -70, Cr ₂ O ₃ -10, Al ₂ O ₃ -20 5 5 70 29th - one - SiO ₂ -84, Cr ₂ O ₃ -14, La ₂ O ₃ -2 6 5 60 twenty - twenty - SiO ₂ -70, Cr ₂ O ₃ -10, La ₂ O ₃ -20 7 7 70 29th - - one SiO ₂ -84, Cr ₂ O ₃ -14, La ₂ O ₃ -2 8 7 60 twenty - - twenty SiO ₂ -70, Cr ₂ O ₃ -10, La ₂ O ₃ -20 table 2 Example No. Characteristics of the target oxide material Coefficient of thermal expansion, 1 / deg The time of dissolution of the rod in an alkali solution (min) Interaction zone S *, mm one 0.5 × 10 ^-6 thirty 0.005 2 0.1 × 10 ^-6 40 0.001 3 0.1 × 10 ^-6 45 0.003 four 0.5 × 10 ^-6 120 0.001 5 0.2 × 10 ^-6 40 0.002 6 0.4 × 10 ^-6 thirty 0.001 7 0.2 × 10 ^-6 40 0.002 8 0.4 × 10 ^-6 thirty 0.001

Claims (6)

1. A method of producing a cast oxide material, including preparing a reaction mixture of the starting components containing chromium VI and a reducing agent, placing the mixture in a graphite form, placing it in a reactor, local ignition of the mixture at an inert gas overpressure to obtain a synthesis product, and then separating the cast oxide material, characterized in that the oxide material is obtained on the basis of a solid solution of chromium oxide in silicon oxide with an amorphous structure, while as a reducing agent in odnuyu mixture is silicon in an amount of 17,0-50,0 wt.%, and between the mixture and mold walls arranged functional layer of silicon oxide 3-7 mm thick. 2. The method according to claim 1, characterized in that the composition of the reaction mixture is additionally introduced aluminum in an amount of 1.0-15.0 wt.%. 3. The method according to claim 1, characterized in that at least one lanthanum compound from the group La ₂ O ₃ , LaB ₆ is added to the composition of the reaction mixture in an amount of 1.0-20.0 wt.%. 4. Cast oxide material, characterized in that it is obtained by the method according to any one of claims 1 to 3 and is a solid solution of chromium oxide in silicon oxide with an amorphous structure, while the content of silicon oxide is up to 98 wt.%. 5. Cast oxide material according to claim 4, characterized in that it further comprises up to 20.0 wt.% Alumina. 6. Cast oxide material according to claim 4, characterized in that it further comprises up to 20.0 wt.% Lanthanum oxide.