RU2256003C2 - Material for applying anitifriction coatings and material preparation process - Google Patents

Abstract

FIELD: powder metallurgy, namely antifriction powder materials, possibly application of coatings on steel parts, for example in machine engineering.

SUBSTANCE: material for applying antifriction coatings of mechanically alloyed alloy in the form of powder contains, mass %: lead, 4 -22; copper, 0.4 - 1.0; aluminum, the balance at next relation of fraction sizes: 1 - 50 micrometers, 5 - 30%; 51 - 160 micrometers, 70 - 95 %. At preparation of such material, mixture of powders of aluminum, lead, copper or their alloys is blended for 0.5 - 2 h while using aluminum pellets 5 - 20 mm as working bodies. Then charge is subjected to mechanical working in high-power mill at power content 3 -30 kWt/kg for 0.5 -10 h.

EFFECT: enhanced wear resistance, lowered friction factor of coating.

3 cl, 2 tbl, 1 ex

Description

The invention relates to the field of powder metallurgy. A more specific area is materials for applying anti-friction coatings and methods for producing powders of anti-friction aluminum alloys for coating steel parts in mechanical engineering, for example, on bearings of heavily loaded bearings of engines of various types.

The materials widely used in industry are known - babbits, cast aluminum alloys Al-Cu-Si and Al-Sb-Pb-Mg for the manufacture of bearing shells by centrifugal melt casting. The disadvantages of these materials are their scarcity, high cost and high consumption.

It is economically more profitable to manufacture bearing shells or rubbing parts of steel with special anti-friction coatings applied to them.

Known powder material for applying antifriction coatings, consisting of a mixture of powders of 30-50% tin-lead and 50-70% aluminum bronzes, which allows to obtain coatings with high antifriction properties, however, its disadvantage is the multi-stage and complexity of its manufacturing technology, high cost and scarcity of raw materials , the difficulty of obtaining a homogeneous structure.

Also known is a powder for applying an antifriction coating from a sprayed alloy containing aluminum, tin and copper (Patent No. 2111280, 1998, RF). The powder allows to obtain coatings with high antifriction properties, but its drawback is the complexity of the manufacturing technology - the need for spraying the alloy, the high cost of the starting materials.

A known method of producing antifriction material by mixing dissimilar powders - aluminum, magnesium and lead (Application No. 59-89737, Japan) and a method for producing aluminum-lead powder (Patent DE 3925973) by co-grinding aluminum and lead powders in a grinding device. These methods do not provide the necessary uniformity of the structure of the mechanically alloyed alloy, since during their implementation the mixing and consolidation of particles proceed simultaneously, as a result of which the combination of particles vigorously proceeds to the necessary averaging of the charge. The uncertainty of the energy saturation value of the crushing zone does not guarantee mechanical activation of the surface of the processed particles, which reduces the strength and tribological characteristics of the material.

As a prototype, we made a well-known solution (Patent No. 2111280, 1998, RF), the main disadvantages of which are the high cost of the initial components (tin), the complexity and high cost of manufacturing the material by high-temperature spraying of the alloy.

An object of the invention is a material for applying antifriction coatings by plasma, gas thermal or detonation spraying methods, which has high antifriction qualities and a method for producing it.

This goal is achieved in that the material for applying an antifriction coating of an alloy containing aluminum, lead and copper, contains a mechanically alloyed alloy in the form of a powder, with the following components, wt.%:

lead 4-22,

copper 0.4-1.0,

aluminum - the rest;

and the following ratio of fractions:

1-50 microns - 5-30%,

51-160 microns - 70-95%,

Material for applying anti-friction coatings is obtained by averaging and machining in a ball mill a mixture of powders of aluminum, lead, copper or their alloys, and the process of averaging the charge is carried out in the mixer before machining for 0.5-2.0 hours using aluminum as working fluids granules with a particle size of 5-20 mm, and machining is carried out in a high-energy mill with an energy load of 3-30 kW / kg for 0.5-10 hours, while up to 1% stearic acid is introduced into the mixture to prevent cold welding of pores shka.

Such a powder after spraying provides the creation of a more durable and high-quality anti-friction coating. Fine particles of lead fill the pores, eliminate porosity, and the presence of copper in the range of 0.4-1.0% strengthens the aluminum matrix. An increase in copper content above 1% leads to brittleness of the coating, an increase in lead content in excess of 22% reduces fatigue strength, and a decrease in it below 4% does not provide the necessary tribological characteristics, and increases the friction coefficient.

The established limits for the content of lead (4-22%) and copper (0.4-1.0%) in the powder allow one to widely vary the properties of coatings, choosing the optimal conditions for specific conditions.

The Al-Pb-Cu system has an extensive monotectic region, which occupies a significant part of the concentration triangle. The solubility of lead in liquid aluminum increases with temperature and reaches about 4.0% at 800 ° C and 22% at 1100 ° C.

Obtaining a homogeneous Al-Pb alloy powder by melt spraying is inefficient and technologically difficult. It was experimentally established that the production of such an alloy with a homogeneous structure is possible only by the method of mechanochemistry in high-energy mills with an energy load of 3-30 kW / kg. To obtain a powder alloy Al-Pb-Cu, a mixture of the starting powders of aluminum, copper and lead is loaded and averaged in a mixer. The use of aluminum granules with a particle size of 5-20 mm, having the same density as the main component of the charge — aluminum — during averaging in the mixer allows to increase the efficiency and speed of averaging without deformation of particles and contamination of the charge with foreign material. The duration of the averaging operation is 0.5-2 hours. When averaging over less than 0.5 hours, the mixture is not uniform, more than 2 hours is not economically feasible, because material uniformity does not improve.

When mechanically doping in a ball mill, only 2-3% of the useful energy is spent on dispersion, and 97-98% is spent on structural changes in the lattice of a solid, and deformation of the crystal lattice, an increase in the number of dislocations, breaking or weakening of the bonds of the inner layers of the substance surface atoms, shear deformations. In other words, processing in grinding machines is not only a method of obtaining substances in a finely dispersed state, but also a method of generating various kinds of structural defects in the volume and active states on the crystal surface, facilitating the diffusion and incorporation of inclusions during alloy formation. For mutual diffusion to occur, it is necessary to bring the atoms closer to the distance of interatomic forces, and also to tell them the energy at which the distribution of the electron density of atoms is favorable for the alloy formation process. The very fact of the destruction of particles contributes to the processes of mutual diffusion and alloy formation, since on the freshly formed surface all atoms as a result of bond breaking are briefly activated.

Depending on the intensity and duration of the machining, a certain stress field is formed in the contact zone of the batch particles, the direction of the process depends on the magnitude and rate of change of it. At low values of the energy saturation of the grinding unit (0.1-2.0 kW / kg), the conversion of mechanical energy into heat is decisive, as a result of which thermal processes are activated, in particular chemical synthesis. This mode is typical for ball, rod, centrifugal mills. In the intermediate zone (3-10 kW / kg), dispersion processes develop. This is characteristic of vibration, attritor, planetary, magnetic-vortex mills. A further increase in energy supply (energy-loaded zone) dramatically increases the reactivity of particles, accelerates diffusion and alloy formation. Disintegrators, disintegrators, hammer, jet, impact and rotor mills have a high energy load. However, due to the short duration of the impact on the material in these mills, alloy formation is difficult or even impossible.

To obtain a homogeneous alloy, it is necessary to simultaneously ensure the flow of two processes: acceleration of mutual diffusion and grinding of diffusing components. After completion of the alloying process, it is necessary to ensure aggregation and coarsening of particles due to their “cold” welding. The most successful combination of these two processes occurs in the zone of transition from medium to high degree of energy load of 3-30 kW / kg, for example, in attritors of vibration and planetary mills. In this interval of energy intensity, regardless of the type of grinding apparatus, a change in the size and structure of particles during grinding proceeds in four stages. The first stage corresponds to a progressive decrease in the size of individual particles with time and their activation. The second stage is an alternation of acts of destruction and association of particles due to the “cold” welding of dissimilar particles with the formation of particles with a characteristic layered structure. At the third stage, the newly formed complex “riveted” particles are destroyed and the particles of the initial powders completely turn into particles of a pseudo-alloy with a layered structure. The fourth stage is characterized by the establishment of equilibrium between the processes of grinding and aggregation, the uniformity (homogeneity) of particles increases, the layers of heterogeneous components become thinner and crushed. During this period, the particle size does not change with time.

During mechanical alloying, up to 1% stearic acid was introduced into the charge to slow down the process of cold welding of alloy particles, which allowed to extend the grinding stage and to quickly control the size of the material obtained.

An example of obtaining anti-friction material.

The averaging of the charge was carried out in a rotating drum with a capacity of 2.5 l, which was loaded with 1 kg of aluminum granules, 5-20 mm in size. As initial components, aluminum powder with a particle size of less than 50 microns, PMS-1 copper powder (-100 μm) and lead powder with a particle size of less than 63 microns were used. The mass of the charge was 0.5-1.0 kg Averaging time 1 h.

Mechanical alloying was carried out in an attritor with a capacity of 15 l, a vibration mill with an oscillation frequency of 8-16 Hz at an amplitude of 90 mm, and in a rotating ball mill with a volume of 5 l. The working bodies in the attritor and vibration mill were steel balls with a diameter of 5-9 mm, in a ball mill - balls with a diameter of 15-46 mm. The results of mechanical alloying are presented in table 1.

Plasma spraying of the powder of the -160 μm fraction was performed on samples with a diameter of 42 mm and a width of 20 mm. Argon and air were used as the plasma-forming gas.

The samples were tested on a friction machine with a conjugated pair of steel 45 and 18X9H4M. The tests were carried out in M14 oil (6 drops / min). Running-in was carried out for 3 hours. The load at run-in from 25 to 200 kg, with a change every 15 minutes. The test load was 200 kg and the rotation speed was 200 rpm.

At the same time, tests were conducted of a coating of an analogue material: Al-20Sn-1Cu alloy powder obtained by spraying the melt with compressed nitrogen with an oxygen content of less than 1%. The analog powder had a spherical shape. The test results are shown in table 2.

table 2
Tribological characteristics of sprayed coatings Arr. Plasma-forming gas The velocity of the jet, m / s Coeff. friction in a pair of _St45 / _Steel18H9N4M Depreciation (mm) in a pair of _St45 / _Steel18H9N4M atomized analog, Al-20Sn-1Cu alloy powder air 800 0.06 / 0.08 0,06 / 0,1 1 argon 500 0,03 / 0,04 0.01 / 0.01 2 air 800 0.04 / 0.04 0.04 / 0.06 3 air 800 0,03 / 0,04 0.01 / 0.02 4* argon 500 0,07 / 0,08 0.20 / 0.10 5* argon 500 0.06 / 0.08 0.10 / 0.10 Note. * - during the test, peeling of the sprayed coating was observed.

Tests have shown that mechanically alloyed Al-Pb-Cu alloy provided an increase in wear resistance by 2-5 times, reduced the friction coefficient by 2 times.

Claims (3)

1. Material for applying antifriction coatings from an alloy containing copper and aluminum, characterized in that the alloy additionally contains lead in the following ratio of components, wt.%: Lead 4-22 Copper 0.4-1.0 Aluminum Else and the material contains a mechanically alloyed alloy in the form of a powder in the following ratio of fractions: Fraction 1-50 microns 5-30% Fraction 51-160 microns 70-95% 2. A method of obtaining a material for applying anti-friction coatings from an alloy containing aluminum, characterized in that the mixture containing powders of copper, lead and aluminum is averaged in the mixer for 0.5-2.0 hours using aluminum granules as working fluids fineness of 5-20 mm, after which the charge is machined in a high-energy mill with an energy load of 3-30 kW / kg for 0.5-10 hours 3. The method according to claim 2, characterized in that before machining, up to 1% of stearic acid is introduced into the charge.