RU2461530C1 - METHOD OF PRODUCING Al2O3-Al COMPOSITE MATERIAL - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to the technology of composite materials - cermets, and can be used in producing wear-resistant articles used in tribocouplings. To produce an Al₂O₃ - Al cermet, aluminium powder with stearic coating on plate-like particles was mixed with aqueous solution of liquid glass with its content in the mixture of 1.0-2.5 wt % with respect to dry residue of substance. The mixture was held at room temperature until completion of the process of formation of sodium stearate and glycerine and then granulated by forcing through a sieve with cell size of 1.5-3.0 mm and then dried. A workpiece was pressed from the mixture at pressure 100-500 MPa and then heat treated in air at temperature 250-300°C for 2.5-10 hours. The workpiece was then heated with an air heat carrier to temperature 550-600°C in order to initiate self-propagating high-temperature synthesis (SHS) and maintaining that temperature for 45-60 minutes. At the end of isothermic holding, the article was cooled on air to room temperature. The composite material has density of 2.1-2.35 g/cm³, impact-bending strength of 10.7·10³-12.0·10³ J/m², coefficient of sliding friction (counterface - SHX-15 steel, normal load - 1SH) on a "rod-disc" scheme 0.13-0.17.

EFFECT: high resistance of the material to destruction due to impact load and lower coefficient of sliding friction.

3 cl, 3 ex, 1 tbl

Description

The invention relates to the technology of composite cermet materials and can be used to obtain durable, wear-resistant products operating in tribological conjugation under the influence of static and dynamic loads.

A known method of producing a composite material Al ₂ O ₃ - Al [1], including the preparation of a mixture by mixing aluminum powder PAP-2, consisting of lamellar particles with a stearin coating, with an aqueous solution of polyvinyl alcohol, drying it to a predetermined residual moisture content (3- 10%), pressing the workpiece under pressure of 1.25 · 10 ^-2 -2.5 · 10 ^-2 MPa, burning out it in air organic binder, an additional pressing the workpiece under pressure 520-600 MPa and initiating the process of self-propagating high-temperature synthesis way heating the workpiece to an air-cooled temperature of 550-600 ° C, followed by cooling due to its exposure to air at room temperature.

The disadvantage of this method is its high complexity associated with the need to implement a sufficiently large number of technological operations. In addition, the material obtained by this method demonstrates a relatively high coefficient of friction in tribological conjugations with a steel counterbody, as well as insufficiently high resistance to fracture when exposed to impact.

The closest to the claimed technical essence and the achieved effect is a method of producing a composite material Al ₂ O ₃ - Al [2], (adopted as a prototype), including heat treatment in air (220-250 ° C) of aluminum powder PAP-2, consisting of lamellar particles with a stearin coating, the preparation of the mixture by mixing it with an aqueous solution of liquid glass in an amount of 3-15% of the mass, calculated on the dry residue of the substance, drying the mixture in air at a temperature of 20-60 ° C until complete removal of moisture, pressing from it blanks for d pressure of 620-700 MPa, the initiation of the process of self-propagating high-temperature synthesis by heating the workpiece with an air coolant to a temperature of 610-650 ° C followed by isothermal exposure for 1-5 hours and cooling by holding the heated product in air at room temperature. In this case, heat treatment of PAP-2 powder in air is carried out in order to remove stearin from the surface of its particles.

The disadvantage of the prototype method is the relatively high coefficient of friction inherent in the resulting material in a pair of friction with a steel counterbody, as well as insufficient strength under shock impact of the load.

An object of the present invention is to reduce the coefficient of friction during tribological conjugation of a material with a steel counterbody, as well as to increase its strength upon impact.

To accomplish the task in a method for producing a composite material Al ₂ O ₃ - Al, which includes preparing a mixture by mixing an aluminum powder consisting of plate-shaped particles with an aqueous solution of liquid glass, drying the mixture, pressing the preform, initiating the process of self-propagating high-temperature synthesis by heating the preform with air coolant and cooling due to exposure of a heated product in air at room temperature, aluminum powder, a plate is used for mixing The particles of which contain a stearin coating, and an aqueous solution of water glass is added in an amount of 1.0-2.5 wt.%, calculated on the dry residue of the substance, before drying, the mixture is kept at room temperature until the formation of sodium stearate and glycerol is completed, then it granulated by pressing through a sieve with a mesh size of 1.5-3.0 mm, before initiating the process of self-propagating high-temperature synthesis, the pressed preform is heat treated in air at a temperature of 250-300 ° C for 2.5-10 hours.

In addition, in the proposed method, the pressing of the preform is carried out under a pressure of 100-500 MPa, and its heating with an air coolant, to initiate self-propagating high-temperature synthesis, is carried out to a temperature of 550-600 ° C with an isothermal exposure time of 45-60 minutes.

To obtain the material according to the claimed method, aluminum powder of the PAP-2 grade (GOST-5494-95), consisting of lamellar particles (prevailing particle sizes: 10-100 μm in length, 5-50 μm in width, according to 0.5-1.0 μm thick). Particles of powder, as a product of industrial supply, are coated with a thin layer of stearin (3.0 wt.%), Introduced as a fat additive at the stage of their grinding in a ball mill.

To prepare the charge, the calculated volume of an aqueous solution of water glass — sodium hydrosilicate (nNa ₂ O ₃ · mSiO ₂ · SiO ₂ · xH ₂ O, where m / n is the module of water glass, varying from 1 to 4, the value of x varies from 1 to 14).

Mixing of the charge components was carried out continuously using a propeller mixer. The mixture was kept at room temperature for the time required to complete the chemical reaction of the formation of sodium stearate and glycerol on the surface of the particles of PAP-2 powder. This reaction:

characterized by certain isothermal kinetics and at room temperature (18-25 ° C), in accordance with experimental data, it takes from 0.5 to 1.0 hours to complete it. After the end of reaction (1), proceeding in a thin layer on the surface of plate aluminum particles, a plastic mass is formed that resembles wet clay (clay-like mass). In this reaction, alkali (NaOH) is the product of hydrolysis of sodium silicate.

When the content of liquid glass in the mixture (C) is less than 1.0 wt.% (In terms of the dry residue of the substance), the plasticity of the resulting mass is insufficient for the operation of granulating it by forcing through a sieve. An increase in C of more than 2.5 wt.% Is not advisable, since the tribotechnical properties of the sintered material are reduced (the friction coefficient paired with a steel counterbody increases sharply due to the increased content of sodium silicates in the material).

Granulation of the mass is quite efficiently ensured by its forcing through sieve cells. The use of a sieve with a mesh size (N) of less than 1.5 mm makes it impossible to carry out the granulation operation due to the excessively high resistance to bursting of the mass. The use of sieves with an N value of more than 3.0 mm is not advisable due to the destruction of the granules.

The wet mixture (a set of granules obtained by pressing through a sieve) was dried to completely remove moisture and pressed to produce blanks. Pressing pressure (P) of less than 100 MPa led to a decrease in impact strength, an increase of P of more than 500 MPa gave the effect of the formation of “repressive cracks”.

Before initiating the process of self-propagating high-temperature synthesis (SHS), the pressed billet was heat treated in air to partially decompose a mixture of sodium stearate with glycerin and remove gaseous decomposition products in accordance with chemical reactions:

The final decomposition of the mixture of sodium stearate with glycerin is completed during the course of the SHS process, and its preliminary, partial decomposition, according to reactions 2 and 3, is aimed at the slow removal of a larger proportion of gaseous products from the workpiece. If the specified heat treatment is not preliminarily carried out, then upon initiation of the SHS, gaseous products create increased pressure inside the sintered billet ”, which leads to its destruction.

A decrease in the heat treatment temperature (T ₁ ) of less than 250 ° C and the time of isothermal exposure (τ ₁ ) of less than 2.5 hours is not possible, since in this case a sufficient removal of gaseous reaction products from the workpiece is not provided. An increase in T ₁ and τ _{1 of} more than 300 ° C and 10 hours (respectively) is not advisable, since at these temperature-time parameters a slow removal of the main portion of the gaseous reaction products (1) is achieved and no subsequent destruction of the sintered billet was observed upon subsequent initiation of the SHS.

The initiation of the SHS process was achieved by heating the workpiece with an air coolant to a predetermined temperature (T ₂ ). A decrease in T _{2 of} less than 550 ° C did not lead to the initiation of SHS, and an excess of T _{2 of} more than 600 ° C is impossible, since an emission of aluminum melt from the workpiece was observed. The isothermal exposure time (τ ₂ ) of less than 45 minutes (at a temperature of T ₂ ) did not provide a satisfactory level of the strength properties of the sintered billet, an increase of τ _{2 of} more than 60 minutes is not justified, since no improvement in the mechanical and tribological properties of the sintered material was observed.

After initiating the SHS process, filtration combustion of the preform is observed, the mechanism of which coincides with the mechanism implemented in the prototype method {2]. After completion of filtration combustion, sintering of the material and the formation of its final phase composition are achieved. By the method of x-ray phase analysis it was found that the following crystalline phases were synthesized in the volume of sintered material — Si, Al ₂ O ₃ , Na ₂ Si ₂ O _5, C, distributed in an aluminum matrix. The formation of these crystalline phases is associated with the occurrence of the following chemical reactions:

Chemical reactions (4) - (10) provide the formation of solid crystalline silicon, aluminum oxide and sodium silicate inclusions in a plastic aluminum matrix. These inclusions increase the hardness and wear resistance of the material. These reactions are also implemented in the prototype method [2]. In the claimed method, in comparison with the prototype, there are additionally reactions of thermal decomposition of sodium stearate (2) and glycerol (3) with the formation of a carbon residue in the form of thin molecular layers on the surface of plate aluminum particles that compose the structure of the sintered product.

The obtained carbon residue performs the function of a solid lubricant capable of significantly reducing the friction coefficient in tribological conjugations. In addition, when exposed to impact, ”due to the optimal local weakening of the interface between the lamellar particles, a very energy-intensive fracture mechanism was recorded. It is associated with the involvement in the destruction of a significant amount of material, accompanied by a shift of the layers relative to each other and their breakout. Moreover, the high work of destruction is provided by overcoming the frictional forces between the plate particles in an extended fracture zone.

Thanks to these effects, a solution to the technical problem of the invention is achieved.

Examples of the implementation of the claimed method

Example 1. In order to prepare the mixture, 100 grams of aluminum powder (grade PAP-2) was mixed with a solution of liquid glass (GOST 13078-81). To ensure the content of liquid glass in the charge in the amount of (C _o ) 2.5% (in terms of the dry residue of the substance), the initial liquid product was diluted with distilled water (95.31 cm ^{3 of} water was added to 4.69 cm ^{3 of} liquid glass), dilution was ~ 1: 20 (1 part liquid glass to 20 parts water). The components were mixed for 30 minutes in a porcelain container using a propeller stirrer. After distribution of the diluted aqueous solution of water glass in the volume of the powder, stirring was stopped. The mixture was kept until the formation of sodium stearate and glycerol was completed (30 minutes). A sign of the end of the synthesis of sodium stearate and glycerol on the surface of plate aluminum particles is the transformation of the initial powder mixture into a clay-like viscous mass.

It was granulated by forcing through a sieve with a mesh size (N) of 3.0 mm. After drying the obtained granules in air (to zero humidity at a temperature of 60 ° C), a granular charge was obtained. The billet was pressed by applying a pressure (P) of 500 MPa to the filling of granules in a steel mold on a P-50 hydraulic press.

The pressed billet was heat-treated in an oven in air at a temperature (T ₁ ) of 300 ° C for a time (τ ₁ ) of 2.5 hours.

After that, the preform was placed in a muffle furnace and heated in air to a temperature (T ₂ ) of 600 ° C. As a result, the SHS process was initiated. Its beginning was visually recorded by the glow of the workpiece, which was kept in the furnace space at T ₂ for a time (τ ₂ ) of 60 minutes. Upon completion of exposure, the sintered product was removed from the furnace and cooled at room temperature.

According to the XRD data, the main phase composition of the sintered material was as follows (vol.%): Al - 80%, γ-Al ₂ O ₃ - 10%, α-Na ₂ Si ₂ O ₅ - 6%, Si - 2%, C - 2%

Example 2. All technological operations and their sequence coincide with those described in example 1.

100 grams of aluminum powder PAP-2 was mixed with an aqueous solution of liquid glass (1.87 cm of liquid glass + 98.13 cm ^{3 of} water), the dilution was ~ 1: 52 (1 part of liquid glass to 52 parts of water). The value of C _about was 1.0%.

The resulting mixture was granulated by forcing it through a sieve with a mesh size (N) of 1.5 mm. The workpiece was pressed at P equal to 100 MPa. The pressed billet was heat treated in an air oven (T ₁ = 250 ° C, τ ₁ = 10 hours).

The SHS process was initiated at T ₂ equal to 550 ° C, the subsequent exposure of the sintered billet in the furnace space was carried out at τ ₂ equal to 45 minutes.

According to the XRD data, the main phase composition of the sintered material was as follows (vol.%): Al - 73%, γ-Al ₂ O ₃ - 15%, α-Na ₂ Si ₂ O ₅ - 7%, Si - 4%, C - one%.

Example 3. All technological operations and their sequence coincide with those described in example 1.

100 grams of aluminum powder PAP-2 was mixed with an aqueous solution of liquid glass (3.28 cm ^{3 of} liquid glass + 96.72 cm ^{3 of} water), the dilution was ~ 1: 29 (1 part of liquid glass to 29 parts of water). The value of C _o was 1.75%.

The resulting mixture was granulated by forcing it through a sieve with a mesh size (N) of 2.0 mm. The workpiece was pressed at P equal to 300 MPa. The pressed billet was heat treated in an air oven (T ₁ = 275 ° C, τ ₁ = 6.25 hours).

The SHS process was initiated at T ₂ equal to 575 ° C, the subsequent exposure of the sintered billet in the furnace space was carried out at τ ₂ equal to 53 minutes.

According to the XRD data, the main phase composition of the sintered material was as follows (vol.%): Al - 78%, γ-Al ₂ O ₃ - 12%, α-Na ₂ Si ₂ O ₅ - 6.5%, Si - 2%, C - 1.5%.

The table shows the test results of the material obtained by the claimed method, in comparison with materials manufactured by the method similar to the prototype method.

The sliding friction coefficient was determined according to the "rod-disk" scheme on a Tribometer, CSM Instr. A ball with a diameter of 3 mm made of ShKh-15 steel was used as a counterbody. The normal load was 1 N, and the linear velocity of the counterbody relative to the disk (diameter - 20 mm, height - 8 mm) - 10 cm / sec.

Impact bending strength [3] was determined using a pendulum driver on prismatic samples with dimensions of 7 × 7 × 50 mm, and the distance between the supports was 32 mm. The velocity of the shock disk is 5 m / s.

As can be seen from the data in the table, an improvement is achieved in the mechanical characteristics of the material obtained by the proposed method in comparison with the material manufactured by the prototype method (the strength under shock bending increases by 1.6-2.0 times, and the average value of the coefficient of friction slip decreases 1.73 times).

Thus, the technical task of the present invention has been achieved - an increase in strength under shock bending and a decrease in the sliding friction coefficient of the composite material Al ₂ O ₃ - Al have been achieved.

Table Properties of the composite material Al ₂ O ₃ - Al Material
The properties Density ρ, g / cm ³ Strength in impact bending a _N · 10 ³ , J / m ² Coef. friction K _c According to the claimed method ^* No. C ₀ , wt.% N mm R, MPa T ₁ , ° C τ _1, hour T ₂ ° C τ ₂ , hour one 2.5 3.0 500 300 2.5 600 60 2,35 12.0 0.13 2 1,0 1,5 one hundred 250 10 550 45 2.10 8.0 0.17 3 1.75 2.0 300 275 6.25 575 53 2,30 10.7 0.15 According to the prototype method [2] 2.15-2.50 5.0-6.0 0.23-0.30 By the method analogue [1] 2.40-2.53 6.0-7.2 0.51-0.76 ^* here: С ₀ - dry residue of liquid glass, N - sieve mesh size, Р - pressure of the workpiece pressing, T ₁ and τ ₁ - temperature and time of heat treatment of the workpiece in air, T ₂ - temperature of the air coolant to initiate SHS, τ ₂ - isothermal exposure time at a temperature of T ₂ .

Information sources

1. RF patent No. 2266270 "Method for producing composite material Al ₂ O ₃ - Al", C04B 35/65, B22F 3/23, publ. 12/20/05, bull. No. 35.

2. RF patent 2319678 "Method for the production of composite material Al ₂ O ₃ - Al", C04B 35/65, C04B 35/00, B22F 3/23, publ. 03/20/08, bull. No. 8 (prototype).

3. Workshop on the technology of ceramics and refractories / ed. D.N. Poluboyarinova and R.Ya. Popilsky. M .: publishing house of construction literature, 1972, 351 pp.

Claims (3)

1. A method of producing a composite material Al ₂ O ₃ -Al, including the preparation of a mixture by mixing an aluminum powder consisting of plate-shaped particles with an aqueous solution of liquid glass, drying the mixture, pressing the billet, initiating the process of self-propagating high-temperature synthesis by heating the billet with an air heat carrier and cooling due to exposure of the heated product in air at room temperature, characterized in that aluminum powder, lamellar particles are used for mixing It contains a stearin coating, and an aqueous solution of water glass is added in an amount of 1.0-2.5 wt.%, calculated on the dry residue of the substance, before drying, the mixture is kept at room temperature until the formation of sodium stearate and glycerol is completed, then it is granulated by pressing through a sieve with a mesh size of 1.5-3.0 mm, before initiating the process of self-propagating high-temperature synthesis, the pressed preform is heat treated in air at a temperature of 250-300 ° C for 2.5-10 hours. 2. The method according to claim 1, characterized in that the pressing of the workpiece is carried out under a pressure of 100-500 MPa. 3. The method according to claim 1, characterized in that the preform is heated with an air coolant to initiate self-propagating high-temperature synthesis, carried out to a temperature of 550-600 ° C with an isothermal exposure time of 45-60 minutes