Method of making wear-proof antifriction self-lubricating apply

FIELD: process engineering.

SUBSTANCE: invention relates to powder metallurgy, particularly, to production of wear-proof antifriction self-lubricating alloy with larger amount of alloy. Pulverised powders of Al-40Sn-composition are pelletised and sintered in inert atmosphere at 590-615°C for 90-30 min. Sintered pellet is subjected to equal-channel angular extrusion at invariable position of deformation plane.

EFFECT: high mechanical and tribotechnical properties at steel friction in the absence of lubrication.

7 dwg

 

The invention relates to metallurgy, and more specifically to methods of producing wear-resistant antifriction self-lubricating alloy with a high content of tin.

When the load bearing made of alloys of Al-Sn contained in them tin can be squeezed out on the friction surface and dispersed in the form of a film between the sliding bodies. Eliminating direct contact between the steel shaft and aluminum bearing, this film reduces the probability of formation of burrs and increases the wear resistance of the friction pair. For the formation of a solid film in the role of a solid lubricant, the proportion of tin should be high and evenly distributed alloy Al-Sn. This condition satisfies the distribution of tin, for example, in the form of bulk continuous mesh with small cells [1].

However, the high content of soft tin, especially in the form of a continuous mesh on the boundaries of the aluminum grains, leads to a significant reduction of mechanical strength of two-phase alloys, reduces the threshold allowable load bearing, made of such materials [2]. For this reason, the maximum content of tin in the modern alloys does not exceed 40% of the weight. While in the materials on the basis of Al used in the manufacture of industrial self-lubricating bearings casting method, the proportion of tin does not exceed 20 weight and only in the experimental products reaches to 40% weight [3].

In the latter case, the purpose of hardening alloys with a high content of tin them additionally alloyed elements dissolved in the aluminum matrix [3-5], and enter the insoluble solid particles or elements forming with aluminum solids [3-6]. Since alloying elements this will inevitably strengthen and tin phase, then, to restore its lubricating properties, the alloys Al-Sn additionally alloyed with substances such as Pb, Sb, In, forming with tin Logoplaste phase [3, 7]. Thus, to improve antiaging properties of alloys of the system Al-Sn usually resort to an increase in their concentration of tin, which, in turn, requires additional alloying of reinforcing elements, that is, improving their tribological properties is achieved by the complexity of the composition and technology of obtaining products.

The density of tin is much higher, and the temperature of crystallization is significantly lower than that of aluminum, so the alloys of the system Al-Sn prone to the formation of segregation and stratification, the more noticeable the higher the tin content and the lower the cooling rate of the melt. Massive castings of them are inhomogeneous gradient distribution of phases, which complicates the formation of optimal friction patterns described in [1]. To increase the value of the homogeneity of the structure of cast alloys due to the rapid crystallization of their bottled in the form of a thin rapidly cooling strips. For such a thin strip can be used in bearings, connect them with a solid substrate, or the melt immediately pour on a strong and solid substrate and then the bimetallic product gauge in thickness.

When creating a bearing materials such technology cannot be used for large deformations with the purpose of hardening the deposited layer due to its low thickness and low plasticity adjacent to the solid substrate layer. Therefore, a comprehensive doping remains virtually the only method of hardening alloys with a high content of tin. However, when spraying the melt in the form of fine powders of the rate of cooling increases, and therefore, it becomes possible to obtain materials with crushed structure. Such structural hardening allows you to maintain a given level of strength without adding in the alloys Al-Sn large number of hardening alloy elements. The strength of a two-phase composite alloy of a given composition is higher, the smaller the grain size of the matrix and the size of the tin inclusions.

The obtained fine powder is then sprayed on the solid substrate with preservation of the fine structure of the material [8]. However, with the increase of the thickness of the deposited layer increases its porosity and deteriorating relationship between the powder particles. Similar Raza is Tatu leads and magnetron deposition of the alloy on a metal substrate [9]. Obtained by spraying the bimetal is subjected to rolling for compaction of the applied layer and improve its relationship with the substrate. The result is compression formed layered structure, where the connection between the parallel surface friction layers of tin no. This structure does not meet the above-mentioned [1] the most favorable for self-lubricating antifriction material type structure. So, for example, despite high hardness (~70 HV) deposited and laminated on 75% Al alloy-20 (% vol.) Sn, its tribological properties in dry contact with steel is not very high, even when testing with a small amplitude of friction (fretting test): the friction coefficient is equal to 0.7 to 0.9, and the wear rate equal to 18.2·10-5mm3/N·m [8].

Known another way structural hardening alloys Al-Sn due to the homogeneous distribution of the phases. He is in the grinding mixture of powders of tin and aluminum to description size by mechanical grind them in attritor, followed by sintering [10]. But in this case, despite the strong dispersion hardening alloy Al-Sn (HV=85), the coefficient of friction it in pair with steel without lubrication amounted to 0.95 when the wear rate of 23.5·10-5mm3/N·m. Here, as in the previous example, there is provided a fast and efficient formation of a continuous, separating the aluminum matrix and the social counterbody antibodies film due to insufficient capacity (as sources of solid lubricants) communicating with the surface friction of small discontinuous inclusions tin. That is, the degree of connectivity of tin inclusions is an important factor determining the performance of the bearing aluminum alloys.

The above-described methods of powder metallurgy in combination with intensive plastic processing allows to obtain materials with a high content of particles of the second phase and even distribution of different high strength. This approach for this purpose also applies to the materials composition of the Al-Sn with a high content of tin [8-11]. However, these measures do not provide a good self-lubrication materials in friction as a result of its intensive plastic handle tin inclusions or torn into small isolated fragments, not able to put on the friction surface of the required amount of tin, or the orientation of the fiber or flat tin inclusions becomes unfavorable for this purpose. In addition, at high strain samples heavily thinned, and the possibility of their practical use as blanks for bearings severely limited.

The problem to which the invention is directed, is to develop technologies (way) obtain durable solid samples with a uniform distribution of large amounts of tin, and this technology should allow not the only to expose the self-lubricating bearing materials large plastic deformation with the purpose of hardening, but still keep the high efficiency of tin inclusions as sources of solid lubricants on the friction surface.

The technical result is achieved due to the fact that the sprayed powders of alloy Al-Sn pressed into briquette, which then is sintered in a furnace with an inert atmosphere and then subjected to repeated severe plastic deformation by the method of equal-channel angular pressing (pressing). When this pressing is carried out by the route, usually called the route "A"at which the sample is rotated between its successive passages through the mold [12].

Sintering the briquette is carried out to form a solid continuous frame made of aluminium matrix. Raw briquette such a frame is missing. The presence of the frame prevents the localization of deformation in the form of narrow strips only within the soft phase and ensures uniform distribution of the compressed volume of the sample.

Pressing as a method of severe plastic deformation [12], [13] differs in that it allows you to preserve the original section of the sample at any intensity imposed deformation, and the route of pressing, called "route A", provides in the course of this processing, the formation of in-plane deformation (flow) of the layered structure with a small distance between the lamellar inclusions of tin. the ri, despite a significant change in the original form of tin inclusions, their initial volume as sources of solid lubricant is retained. Other routes pressing change the shape of the inclusions slightly.

These procedures allow to obtain a material with reinforced aluminum phase and a high content of tin layers which periodically come to the surface friction and provide uniform lubrication embossed tin under dry and boundary friction. Provision of surface friction tin leads to a significant decrease in the magnitude of the friction coefficient and the wear rate of the bearing alloys Al-Sn.

Further, the essence of the claimed invention is illustrated by examples of its implementation with the involvement of graphic materials.

Figure 1 - the shape, size and structure (inset) of raw powder with a composition of Al-40Sn.

Figure 2 - cracks in the sintered sample Al-40Sn with weak aluminum matrix, processed pressing.

3 - microstructure of alloy Al-40Sn after sintering (box) and three processing pressing.

Figure 4 - structure region of turbulence in the alloy Al-40Sn after four processing pressing.

Figure 5 - effect of sintering parameters on the machinability pressure powder alloy Al-40Sn (table 1).

6 - influence of the number of pressovanii on the structure and mechanical properties of sintered alloy Al-40Sn (table 2).

7 - influence of the number of pressovanii on the friction coefficient and wear rate of the alloy Al-40Sn during dry friction on steel 45 (50 HRc) (table 3).

In one example implementation, the powder to obtain the alloy Al-40Sn, the structure of which is shown in figure 1, extruded into pellets with dimensions of 10×10×60, and specaly in a vacuum oven at various temperatures and exposure times. The sintered pellets were subjected to severe plastic deformation by the method of pressing with intensity γ=2 in one pass. The number of pressovanii reached five. The pressing was carried out on a route that is different from the other routes pressing the fact that the sample between pressovaniya not rotated around its longitudinal axis [12].

The results of the above experiment showed that raw or sintered at temperatures below 590°C material has a high porosity due to poor wetting of the aluminum tin and partial bleed the last of compaction. Cervical sintering between the particles of the aluminum phase grow slowly. Obtained by sintering in the specified temperature range samples is not strong enough and are destroyed when pressing.

Aged less than 90 minutes at a temperature of 590°C briquette turns thick, but still has a fairly sturdy aluminum frame and is destroyed during the first, second or third pressing. Destruction, as in the above PR is least occurs on the plane of the pair of channels of the mold (Figure 2).

Sintering of any duration at 620°C and above leads to the loss of briquettes their initial shape due to the formation of a significant amount of the liquid phase by dissolving aluminum in the molten tin. The duration of sintering at temperatures below 620°C set depending on the intensity of the processes of stratification of very different density components (Al and Sn) alloy and coarsening of the structure, deteriorating the uniformity of the soft phase in the volume of the sintered samples. For this reason, the higher the sintering temperature, the shorter ought to be its duration, however, the duration should be sufficient for formation between particles of aluminum sturdy necks sintering, which is formed by diffusion. Therefore, sintering at 590°C for 90 minutes or sintering at 615°C for 30 minutes are modes that allow you to save the form compacts of powders of alloy Al-40Sn, relatively uniform distribution of tin in the amount of pressing and simultaneously to ensure the formation of durable aluminum matrix. The intermediate sintering temperature must be suitable duration, for example, sintering at 600°C for 60 minutes gives satisfactory results and allows to generate mater the al with the set of structural parameters, capable of withstanding four times the pressing method for pressing, as shown in Table 1 (Figure 5).

The study of the structure and measurement of the hardness of the deformed samples was carried out on the plane deformations. Measurement of the structure parameters of two-phase Al-40Sn alloy was carried out according to the method of clipping. It was found that with increasing number of passes (degree of deformation) of the sample, the thickness of the tin layers and the distance between them is reduced, but the magnitude of these reductions is becoming smaller with increasing number of pressovanii (see Table 2 - 6).

This is the essential difference between pressing a selected route from the usual methods of deformation of the rolling or extrusion, in which the refinement phase layers and the sample is always in proportion to the magnitude of the tested strain. When the fourth and subsequent pressovaniya rectilinear shape and the periodic arrangement of tin inclusions, established after the third passage (Figure 3), begin to be broken, and, above all, in the Central regions of the sample. This is because of the mutual overlapping above and below the mid-plane of the sample zones of homogeneous deformation as the result of the manifestation of the "trailing" effect when pressing. Inhomogeneous deformation (flow) of material in the specified area of the sample is accompanied by the emergence of nesp is ochesta on the limits of the phases (Figure 4).

From mid deformed by the method of pressing sintered blanks cut four rectangular sample for mechanical and tribological tests. It was found that, despite a constant (γ=2) tested material macroscopic deformation during each passage of the sample through the mold, the rate of increase of compressive strength and hardness of the alloy Al-40Sn decrease with increase in the number of pressovanii (see Table 2 - 6). The changing nature of deformation of a material with a homogeneous to a heterogeneous when the fourth pressing (Figure 4) causes additional hardening of the alloy, however, this is accompanied by the occurrence of micro-cracks at the boundaries of the phases, which in the subsequent fifth pressing merge into macro-cracking, which weakens the material.

The part cut from the pressings of the samples was tested for friction without lubrication on a "thumb-drive". The disk was made of steel grade 45, hardened to 50 HRc. Before the test, the surface was polished fine-grained emery paper, and then polished on a cloth with diamond paste particle size of 5-7 μm to a mirror finish. The polished surface was cleaned with alcohol. The friction surface of the samples coincided with the plane of deformation of the material during pressing, and before the test has also been cleaned with alcohol. The grinding of the samples was conducted in accordance with the Institute of 1 MPa for 20 minutes. The pressure in the friction process was changed stepwise, and was 5 MPa sliding speed was varied in the range of 0.07-0.6 m/s the value of the coefficient of friction was determined automatically using the built-in processor. The wear rate of the samples was determined from the change in their height and counted in units of [mm3/N·m], which allowed the results to compare with literature data.

From the data obtained by friction, it follows that to reduce the intensity of wear of sintered or once extruded alloy requires relatively high pressure through friction. This is because the thickness of the separating tin include aluminum layers is large, and to cover them with tin foil requires a large amount of pressed tin. However, after the third pressing the inclusion of tin in the alloy Al-40Sn take an elongated shape, and the distance between them is reduced so that even at low pressure extruded from the sample volume to surface friction tin is enough to cover the surface of the aluminum matrix and to separate it from the steel counterface. Accordingly, the wear rate of three and four extruded alloy is practically not dependent on the amount of pressure on the friction surface in the range of measured values.

Because tin is formed is eplacem metal, the value of the coefficient of friction and the wear rate of the alloys Al-Sn paired with the steel has a noticeable effect sliding speed, because it affects the temperature of the friction surface, and therefore, the tensile shear tin and they formed a surface film. Thus, while maintaining the other conditions, the increase in sliding velocity from 0.07 to 0.6 m/s resulted in a marked reduction in the magnitude of the coefficient of friction, and a very strong decrease in the intensity of wear of Al alloy-40Sn. Moreover, the values of the friction coefficient of the three - and four-pressed samples is approximately the same, however, the wear resistance of the latter at low speeds better.

The results of tribological tests of alloy Al-40Sn are shown in Table 3 (Fig.7). Here are data from the literature and data on comparative tests of pure aluminum and tin. It is seen that in the aggregate tribological properties of Al alloy-40Sn received on the proposed technology, after three or four pressing significantly superior properties not only pure metals and alloys on their basis, obtained by traditional methods.

From the totality of the presented results indicate that the proposed method of obtaining antifriction bearing alloys can significantly improve the mechanical and tribological characteristics of alloys sist what we Al-Sn in friction against steel in the absence of liquid lubricant.

The effect is achieved by forming a sintered alloy by severe plastic processing special patterns, contributing to the reduction of the friction coefficient and the wear rate.

Have known from the literature alloys of similar composition but obtained by other technologies, these parameters are much higher. To achieve a noticeable improvement in the tribological properties of Al alloy-40Sn enough to subject him three or four times pressing method for pressing a route, preserving the original orientation of the compression of the sample relative to the working channel of the mold. Increasing the number of passes this route to further grinding patterns and increase the mechanical and tribological properties of sintered alloys of the Al-Sn requires special measures to prevent inhomogeneity of plastic deformation of a deformable material.

In another embodiment, implementation of the proposed method, the powders of the alloy Al-40Sn have merged into briquette, which was then specaly in a vacuum furnace at 600°C for one hour. Sintered briquettes were subjected to four-pressing method for pressing on the route, keeping the position of the plane strain compression of the material.

The resulting material showed a high hardness and strength. During dry friction on his steel nagruzke is 5 MPa and a sliding velocity of 0.6 m/s the friction coefficient was 0,46, and the wear rate was 6,9·10-5mm3/N·m

Given the relative simplicity of the implementation process of the proposed method and the unique values of the friction coefficient and the wear rate of the resulting alloy, the invention may find wide application in mechanical engineering.

LINKS

[1] F. Masahito, Y. Yukio. Al-Sn bearing alloy material / JP 6093360 (A). - 1994-04-05.

[2] - A. A. Bataev, VA Bataev, N.G. Kuz'min, K.G. Ryzhankov. Antifrictional alloy of aluminum base / EN 2329321 C2. - 2007-11-27.

[3] - T. Tanaka, M. Sakamoto, K. Yamamoto, Y. Sato, T. Kato. Aluminum-based bearing alloy with excellent fatigue resistance and anti-seizure property / US 5162100. - 1992-10-10.

[4] F. Masahito, O. And Akira, S. Takeshi, O. Toshihisa, O.Takeshi. Al-Sn-Pb bearing alloy / JP 2077549 (A). - 1990-03-16.

[5] F. Masahito, Akira O., S.Takeshi, O.Toshihisa, O.Takeshi. Al-Sn-Pb series bearing alloy / JP 3047934 (A). - 1991-02-28.

[6] F. Masahito, O. And Akira, S. Takeshi, O. Toshihisa, O. Takeshi. Al-Sn-Pb series bearing alloy / JP 3047935 (A). - 1991-02-28.

[7] F. Masahito, Akira O., S.Takeshi, O. Toshihisa, O. Takeshi. Al-Sn-Pb series bearing alloy / JP 3047936 (A). - 1991-02-28.

[8] - M.R. Tripathy, B.V.M. Kumar, B. Basu, R.K. Dube, S.C. Koria. Tribological behaviour of steel backed Al-Sn strip prepared via spray atomization-deposition-rolling route / Materials science and technology, 2007, Vol.23. No.1. pp.15-22.

[9] - C. Perrin. Forming a plan bearing lining / US 6416877 B1. - 2002-07-09.

[10] X. Liu, M.Q. Zeng, Y. Ma, M. Zhu. Wear behavior of Al-Sn alloys with different distribution of Sn dipersoids manipulated by mechanical alloying and sintering / Wear, 2008, Vol.265, pp.1857-1863.

[11] - K. Xu, A.M. Russell. Texture-strength relationships in a deformation processed Al-Sn metal-metal composite / Materials science and engineering, 2004, Vol.373A, pp.99-106.

[12] - V.M. Segal, R.E. Gofbrth, K.T. Hartwig. Apparatus and method for deformation processing of metals, ceramics, plastics and other mateials / US 5400633 (A). - 1995-03-28.

[13]. Hemandez, G. Gonzalez. Microstructural and mechanical behavior of highly part of Al-Sn alloys / Materials characterization, 2008, Vol.59, pp.534-541.

A method of obtaining a wear-resistant antifriction self-lubricating alloy, characterized in that the sprayed powders of composition Al-40Sn pressed into briquettes, is sintered in an inert atmosphere at a temperature of 590-615°C for 90-30 min and then subjected to equal-channel angular pressing at maintaining the position of the plane strain compression of the material unchanged.



 

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4 cl, 4 tbl, 2 ex

FIELD: metallurgy.

SUBSTANCE: aluminium-based alloy with lower density is designed for making deformed semi-finished products, including sheets used in aircraft building. The alloy contains the following components, wt %: magnesium 4.2-5.0; zinc 3,2-3.9; copper 0.4-1.0; scandium 0.17-0.30; zirconium 0.07-0.14; titanium 0.01-0.05; berillium 0.0001-0.005; hydrogen 0.05-0.35 cm3/100 g of metal; manganese < 0.25; chrome <0.10; iron <0.30; silicon <0.20; aluminium - balance, with the ratio of magnesium content and zinc content - 1.3. The method for processing of alloy includes homogenisation is carried out at 400-430°C for 6-15 hours, hot deformation - at temperature of 380-430°C, and cold deformation to the final size - at the total extent of hot and cold deformation of less than 80%.

EFFECT: alloy has higher strength in combination with lower density.

2 cl, 5 tbl

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy, particularly, to producing articles from aluminium or magnesium alloys with nano- and sub micro crystalline structure, and articles made thereof. Proposed method comprises preliminary equal-channel angular pressing and subsequent strain-forming of articles thereof. Said equal-channel angular pressing is performed at deformation temperature and rate selected subject to alloy composition by preset relation while strain-forming is carried out by extrusion at room temperature and deformation rate selected subject to alloy composition by preset relation.

EFFECT: better manufacturability, higher strength and ductility.

9 cl, 2 dwg, 1 tbl

FIELD: metallurgy.

SUBSTANCE: method involves casting of an ingot and obtaining of workpiece from it using equal-channel annular pressing with back pressure. Reduction of duration of shape-generating operations performed in the mode of high-speed superplasticity, as well as reduction of the workpiece heating time is provided due to the fact that prior to the ingot casting, the molten metal is heated up to 760-800°C and exposed at that temperature during 0.5-1.0 h; ingot is cast by means of semi-continuous casting to sliding crystalliser; cast ingot is annealed at temperature of 360-380°C during 3-8 h; workpiece of rectangular section, which is square in plan view, is obtained from ingot with ratio of thickness to width of 0.17 to 0.33; deformation of workpiece obtained from the ingot by pressing is performed at crossing angle channels of 90° at temperature of 305-325°C with number of passes of 4 to 8, which corresponds to true deformation of ~4 to ~8, with back pressure value equal to 30-40% of the value of applied pressure, with rotation of workpiece after each pass through 90° relative to the axis perpendicular to large edge of workpiece and passing through the centre of workpiece; then, workpiece is subject to rolling at temperature of previous pressing with total swaging of 80-95% at temperature of working rolls of rolling mill, which is equal to rolling temperature.

EFFECT: optimisation of superplastic shaping process of products of irregular shape.

1 tbl, 1 ex

FIELD: physics.

SUBSTANCE: invention relates to a method of making a permanent magnet, which involves: placing evaporating metallic material (v), which contains at least one of dysprosium and terbium, and a sintered magnet (S) into a treatment box; placing said treatment box into a vacuum chamber; heating the treatment box to a given temperature in a rarefied atmosphere to evaporate the evaporating metallic material and depositing vapour onto the sintered magnet; and a step for diffusing the deposited dysprosium and/or terbium metal atoms into the boundaries of crystal grains and/or the boundary phase of crystal grains of the sintered magnet to obtain a high-performance magnet. Even if the sintered magnet is placed near the evaporating metallic material, the present method ensures increase or restoration of magnetisation force or coercitive force, which is very desirable during mass production of permanent magnets. During the period over which the evaporating metallic material evaporates, an inert gas is fed into the working chamber (70) in which the sintered magnet is placed, and before feeding the inert gas, pressure in the working chamber is maintained at about 0.1 Pa or less.

EFFECT: improved method.

9 cl, 12 dwg

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