A boron nitride interface assembly decorated foam metal-polytetrafluoroethylene interpenetrating phase lubricating material and a preparation method thereof

Abstract

The application provides a boron nitride interface assembly modified foam metal-polytetrafluoroethylene interpenetrating phase lubricating material and a preparation method thereof, which is prepared by boron nitride interface assembly, emulsion impregnation and high-temperature sintering with polytetrafluoroethylene emulsion as a main raw material, three-dimensional connected foam metal as a reinforcing framework and two-dimensional sheet boron nitride as an interface assembly material. The application improves the interface separation of the foam metal and the polytetrafluoroethylene matrix caused by the thermal sintering process by assembling boron carbide on the three-dimensional continuous interface of the foam metal. On this basis, the same two-dimensional sheet boron nitride is introduced into the polytetrafluoroethylene matrix as a reinforcing filler to further improve the thermal conductivity and the friction and wear performance of the composite material. In combination with the regulation of the impregnation and sintering process and parameters, the compactness of the composite material is further improved, the metal framework integrity and mechanical strength are maintained, and thus the load capacity, wear resistance and thermal conductivity of the lubricating material are improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lubricating materials, and relates to a preparation method of interpenetrating phase lubricating materials, in particular to a preparation method of interfacial assembly modified foam metal-polytetrafluoroethylene interpenetrating phase lubricating materials. BACKGROUND

[0002] Polymer materials are used as solid lubricating materials due to their small density, high specific strength, fatigue resistance, good self-lubricating property and foreign object compatibility. Among them, polytetrafluoroethylene is widely used in friction components such as mechanical seals, bearings and gaskets due to its low friction, corrosion resistance, excellent chemical stability and high thermal stability. However, polytetrafluoroethylene has low thermal conductivity, poor wear resistance and creep resistance, and often fails to lubricate due to thermal deformation, pressure deformation and wear during friction. The common method is to use zero-dimensional, one-dimensional or two-dimensional functional fillers for composite modification to improve the wear resistance, thermal conductivity, mechanical strength and creep resistance of polytetrafluoroethylene resin. However, in traditional polytetrafluoroethylene composites, the low content of functional fillers is often insufficient to form a continuous phase, and the reinforcing effect on polytetrafluoroethylene is limited by the interface size scale. That is, polytetrafluoroethylene is still the only continuous phase in the composite, which greatly limits the thermal conductivity, mechanical strength and lubrication performance of polytetrafluoroethylene.

[0003] Interpenetrating phase composites are a new type of material in which two or more constituent phases are three-dimensionally topologically connected in the microstructure. In recent years, interpenetrating metal-polymer composites have been designed and applied in the field of friction and wear due to their dual-phase advantages of foam metal and polymer. Among them, three-dimensionally connected foam metal and polytetrafluoroethylene are combined to construct interpenetrating phase composites, which can break through the bottleneck problem of the interface size scale limitation of traditional filler reinforcement and comprehensively improve the comprehensive performance of the composite material. CN101906549A discloses an embedded solid self-lubricating material based on porous foam metal, which fills the solid lubricant into the skeleton of the foam metal with an organic suspension liquid, and is prepared into a shape after air drying and cold pressing sintering. The prepared composite material has the characteristics of light weight and high thermal conductivity of foam metal, and excellent lubrication performance and foreign object compatibility of polymer base. However, due to the poor dispersibility of the organic suspension liquid, there are many unfilled pores in the dual-continuous phase composite, which has a high water absorption rate in water environment, resulting in poor friction and wear performance; at the same time, the strength of the metal skeleton is easily damaged during the process of pressing into the molten resin, resulting in insufficient mechanical strength.

[0004] For the interpenetrating phase composite material with polytetrafluoroethylene as the matrix, the main weakness is that the temperature required for sintering and melting of polytetrafluoroethylene to form a continuous phase is high, usually above 330℃. Because the linear expansion coefficient of metal materials such as copper, aluminum, nickel, and iron is much smaller than that of polytetrafluoroethylene, there is often a large interfacial gap between the two when melting and cooling. Therefore, in the absence of interface protection, the transfer of stress and heat between the metal skeleton and polytetrafluoroethylene is limited, making it difficult to fully improve their load-carrying capacity, wear resistance, and thermal conductivity.

[0005] Based on this, the present application provides an interface assembly modified foam metal-polytetrafluoroethylene interpenetrating phase lubricating material and its preparation method. In the metal skeleton / polytetrafluoroethylene interpenetrating phase composite system, boron nitride is assembled and constructed on the three-dimensional continuous interface of the metal skeleton / polytetrafluoroethylene, improving the interface bonding between the two. On this basis, boron nitride is used as an increasing reinforcing filler to modify the polytetrafluoroethylene matrix, further improving its load-carrying capacity, wear resistance, and thermal conductivity. The prepared boron nitride interface assembly modified foam metal-polytetrafluoroethylene bicontinuous phase material has the characteristics of high thermal conductivity, high wear resistance, and high load-carrying capacity, and can be used for high-temperature lubricating materials under oil-free lubrication conditions. It can also be widely used in the manufacture of bearings, seals, thrust washers, and other moving parts that serve in corrosive media environments. SUMMARY

[0006] The purpose of the present application is to address the problem of poor comprehensive performance of commonly used composite modified polytetrafluoroethylene lubricating materials, and to provide an interface assembly modified foam metal-polytetrafluoroethylene interpenetrating phase lubricating material and its preparation method. By introducing a three-dimensional continuous foam metal skeleton, the thermal conductivity and load-carrying capacity of the polytetrafluoroethylene composite material are greatly improved. Then, through the interface assembly and construction of boron nitride, the interface bonding is improved, and the transfer and dissipation of stress and friction heat during friction and wear are promoted. Furthermore, by modifying the polytetrafluoroethylene matrix with boron nitride, the thermal conductivity and friction and wear performance of the composite material are comprehensively improved, resulting in an interpenetrating phase lubricating material with a unique three-dimensional continuous metal skeleton-boron nitride-polytetrafluoroethylene interface structure and high thermal conductivity, high wear resistance, and high load-carrying comprehensive performance advantages.

[0007] I. Preparation of the interpenetrating phase lubricating material

[0008] 1) Interface assembly: Add boron nitride to the polytetrafluoroethylene emulsion and disperse uniformly to prepare an assembly liquid; immerse the foam metal in the assembly liquid under vacuum for 5-20min, then take it out and dry it at 70-110℃ for 5-20min to remove the solvent; repeat the immersion-drying steps several times;

[0009] 2) matrix immersion: take boron nitride into deionized water, disperse uniformly, get boron nitride dispersion liquid; then add boron nitride dispersion liquid into polytetrafluoroethylene emulsion, disperse uniformly, prepare matrix liquid; under vacuum, immerse the foam metal assembled in interface in the matrix liquid for 10-60 min, take out, place in 80-120℃ environment to dry for 30-120 min to remove the solvent; repeat the immersion-drying step for several times;

[0010] 3) place the composite material obtained in step 2) in a sintering furnace, heat to 330-390℃ and sinter for 60-390 min, take out after the furnace cools down, get boron nitride interface assembled modified foam metal-polytetrafluoroethylene interpenetrating phase lubricating material.

[0011] In the above steps 1) to 3), the particle size of the boron nitride is 2-15 μm, the thermal conductivity is 150-800 W / (m·K); the mass concentration of the polytetrafluoroethylene emulsion is 35%-65%, the particle size of the polytetrafluoroethylene in the emulsion is 60-500 nm; the foam metal is one or more of nickel, copper, iron or iron-nickel alloy, the porosity is 90-99%, and the number of openings per inch (PPI) is 10-110.

[0012] The solid-liquid mass ratio of boron nitride to polytetrafluoroethylene emulsion in the assembly liquid is 5:1-2:1.

[0013] The mass ratio of boron nitride to polytetrafluoroethylene in the matrix liquid is 1%-10%, and the concentration of the boron nitride dispersion liquid is 0.5-5%.

[0014] II. Structure characterization of the interpenetrating phase lubricating material

[0015] The surface structure, interface structure and wear morphology of the prepared interpenetrating phase composite material are observed by optical fiber microscope, scanning electron microscope and X-ray energy spectrometer. The results are shown in the following figures. Figures 1-3

[0016] Figure 1 The figure is the surface morphology of the boron nitride interface assembled modified foam metal-polytetrafluoroethylene interpenetrating phase lubricating material of the application. As shown in the figure, the metal skeleton in the prepared interpenetrating phase composite material is tightly embedded in polytetrafluoroethylene, the surface is smooth and dense, and no obvious pores or cracks are seen.

[0017] Figure 2 The figure is the interface structure of the boron nitride interface assembled modified foam metal-polytetrafluoroethylene interpenetrating phase lubricating material of the application. As shown in the figure, the lamellar boron nitride can be assembled and constructed on the surface of the metal skeleton after being dispersed in the polytetrafluoroethylene emulsion. The fluorine element on the surface of the metal skeleton belongs to polytetrafluoroethylene, which is replaced by nitrogen and boron elements, proving the existence of boron nitride.

[0018] Figure 3 ​is the wear morphology of the boron nitride interface assembly modified foam metal-polytetrafluoroethylene interpenetrating phase composite material. Only the friction furrow along the horizontal sliding direction can be seen, and the interface between the metal skeleton and the polytetrafluoroethylene is still tightly combined.

[0019] III. Performance evaluation of the interpenetrating phase lubricating material

[0020] 1. Thermal conductivity test

[0021] The samples prepared in Examples 1-3 were machined into φ12.7 mm x 2 mm round plates, and tested on a thermal conductivity tester according to GJB / T1201.1-91. The data are listed in Table 1.

[0022] 2. Friction and wear performance

[0023] The samples prepared in Examples 1-3 were machined into long rectangular thin sheets with a length of 30 mm, a width of 15 mm and different thicknesses, and the friction and wear performance was tested using a UMT friction and wear tester. The test environment temperature was 23±5℃. The upper test piece was a 316 stainless steel flat pin with a hardness of HRC56 and a diameter of 4.8 mm. Reciprocating motion was performed under a load of 100N and a frequency of 8Hz, with a single stroke of 5mm and a total stroke of 300m. The data are listed in Table 1.

[0024] Table 1. Performance of the interpenetrating phase lubricating material prepared in Examples 1-3

[0025]

[0026] As can be seen from Table 1, the thermal conductivity of the boron nitride interface assembly modified foam metal-polytetrafluoroethylene interpenetrating phase lubricating material prepared by the present application is 0.72-2.60 W / (m·K), the friction coefficient is 0.09-0.15, and the wear rate is (1.0-4.3) x 10 - 5 mm 3 / Nm. It can be seen that the boron nitride interface assembly modified foam metal-polytetrafluoroethylene interpenetrating phase lubricating material has better thermal conductivity and friction and wear performance than the polytetrafluoroethylene / foam metal composite material without interface assembly, and the thermal conductivity is much higher, and has excellent lubrication and wear resistance. As a comparison, the lowest wear rate obtained in CN101906549A is 2.05 x 10 -5 mm / N·m, which is converted to the volume wear rate as 37 x 10 -5 mm 3 N·m, which is 1 order of magnitude higher than the wear rate of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1The surface morphology of the boron nitride interfacial assembly modified foam metal-polytetrafluoroethylene interpenetrating phase lubricating material is prepared.

[0028] Figure 2 The interface structure of the boron nitride interfacial assembly modified foam metal-polytetrafluoroethylene interpenetrating phase lubricating material is prepared.

[0029] Figure 3 The wear morphology of the boron nitride interfacial assembly modified foam metal-polytetrafluoroethylene interpenetrating phase lubricating material is prepared. DETAILED DESCRIPTION

[0030] Example 1

[0031] Take boron nitride 55 g (size 5 μm, thermal conductivity 400 W / (m·K)), foam nickel 60 g (porosity 96%, number of openings per inch 60) and excess polytetrafluoroethylene emulsion 500 g (polytetrafluoroethylene particle size 50 nm, mass percentage 50%).

[0032] 1) Interfacial assembly

[0033] 50 g of boron nitride is added to 20 g of polytetrafluoroethylene emulsion and dispersed by magnetic stirring at 50 rpm for 2 h to prepare an assembly liquid with a boron nitride to polytetrafluoroethylene ratio of 5:1. The metal skeleton is immersed in the assembly liquid for 5 min under a vacuum degree of -0.10 MPa, then taken out and placed in an oven to dry at 80°C for 5 min to remove the solvent. The above-mentioned immersion-drying steps are repeated 2 times.

[0034] 2) Matrix immersion

[0035] 5 g of boron nitride is uniformly dispersed in 95 g of deionized water. Then 100 g of the water dispersion of boron nitride is added to 200 g of polytetrafluoroethylene emulsion (boron nitride to polytetrafluoroethylene ratio of 5%), and dispersed by magnetic stirring at 150 rpm for 5 h to prepare a matrix liquid. The foam metal skeleton after interfacial assembly is immersed in the matrix liquid for 10 min under a vacuum degree of -0.12 MPa, then taken out and placed in an oven to dry at 100°C for 15 min to remove the solvent. The above-mentioned immersion-drying steps are repeated 3 times.

[0036] 3) Sintering

[0037] The composite material is placed in a polytetrafluoroethylene special high-temperature sintering furnace and sintered at a temperature of 375°C for 100 min. After cooling, the boron nitride interfacial assembly modified foam metal-polytetrafluoroethylene interpenetrating phase lubricating material is obtained, and its performance is shown in Table 1, and its structure is shown in Figures 1-3 .

[0038] Example 2

[0039] Take boron nitride 36 g (size 10 pm, thermal conductivity of 600 W / (m K)), foam nickel 25 g (porosity of 88%, 100 openings per inch), and excess polytetrafluoroethylene emulsion 400 g (polytetrafluoroethylene particle size 80 nm, mass percentage of 40%).

[0040] 1) Interface assembly

[0041] 30 g of boron nitride was added to 7.5 g of polytetrafluoroethylene emulsion and dispersed by magnetic stirring at 100 rpm for 1 h to prepare an assembly solution with a boron nitride to polytetrafluoroethylene ratio of 10:1. The metal skeleton was immersed in the assembly solution for 8 min under a vacuum of-0.04 MPa, then taken out and placed in an oven to dry at 75°C for 15 min to remove the solvent. The above immersion-drying step was repeated 1 time.

[0042] 2) Matrix immersion

[0043] 6 g of boron nitride was uniformly dispersed in 194 g of deionized water. Then 200 g of the water dispersion of boron nitride was added to 300 g of polytetrafluoroethylene emulsion (boron nitride to polytetrafluoroethylene ratio of 5%), and dispersed by magnetic stirring at 150 rpm for 5 h to prepare a matrix solution. The foam metal skeleton after interface assembly was immersed in the matrix solution for 60 min under a vacuum of-0.05 MPa, then taken out and placed in an oven to dry at 120°C for 120 min to remove the solvent. The above immersion-drying step was repeated 4 times.

[0044] 3) Sintering

[0045] The composite material was placed in a polytetrafluoroethylene special high-temperature sintering furnace and sintered at a temperature of 345°C for 240 min. After cooling, a boron nitride interface assembly modified foam metal-polytetrafluoroethylene interpenetrating phase lubricating material was obtained, and its performance is shown in Table 1.

[0046] Example 3

[0047] Take boron nitride 30 g (size 15 pm, thermal conductivity of 750 W / (m K)), foam nickel 50 g (porosity of 90%, 20 openings per inch), and excess polytetrafluoroethylene emulsion 1000 g (polytetrafluoroethylene particle size 200 nm, mass percentage of 60%).

[0048] 1) Interface assembly

[0049] A dispersion solution of boron nitride and polytetrafluoroethylene was prepared by adding 27 g of boron nitride into 7.5 g of polytetrafluoroethylene emulsion and stirring magnetically at 250 rpm for 10 h until fully dispersed, with a ratio of boron nitride to polytetrafluoroethylene of 6:1. The metal skeleton was immersed in the dispersion solution for 15 min under a vacuum of -0.03 MPa, then taken out and placed in an oven to dry at 110°C for 12 min to remove the solvent. The above immersion-drying step was repeated 3 times.

[0050] 2) Matrix immersion

[0051] A dispersion solution of boron nitride and polytetrafluoroethylene was prepared by adding 27 g of boron nitride into 7.5 g of polytetrafluoroethylene emulsion and stirring magnetically at 250 rpm for 10 h until fully dispersed, with a ratio of boron nitride to polytetrafluoroethylene of 6:1. The metal skeleton was immersed in the dispersion solution for 15 min under a vacuum of -0.03 MPa, then taken out and placed in an oven to dry at 110°C for 12 min to remove the solvent. The above immersion-drying step was repeated 3 times.

[0052] 3) Sintering

[0053] The composite material was placed in a high-temperature sintering furnace specially designed for polytetrafluoroethylene and sintered at a temperature of 350°C for 300 min, and after cooling, the boron nitride interfacial assembly modified foam metal-polytetrafluoroethylene interpenetrating phase lubricating material was obtained, with the performance shown in Table 1.

Claims

1. A method of preparing a boron nitride interface assembled decorated foam metal- polytetrafluoroethylene interphase lubricating material, characterized by, The method comprises the following steps: 1) interface assembly: adding boron nitride into a polytetrafluoroethylene emulsion, uniformly dispersing, and preparing an assembly liquid; immersing the foamed metal in the assembly liquid for 5-20 min under vacuum, taking it out, and drying it at 70-110 ℃ for 5-20 min to remove the solvent; repeating the immersing-drying step for several times; wherein the solid-liquid mass ratio of boron nitride to the polytetrafluoroethylene emulsion is 5:1-2:1; 2) substrate immersion: additionally taking boron nitride and adding it into deionized water, uniformly dispersing, and obtaining a boron nitride dispersion liquid; then adding the boron nitride dispersion liquid into the polytetrafluoroethylene emulsion, uniformly dispersing, and preparing a substrate liquid; immersing the foamed metal after the interface assembly in the substrate liquid for 10-60 min under vacuum, taking it out, and drying it at 80-120 ℃ for 30-120 min to remove the solvent; repeating the immersing-drying step for several times; wherein the concentration of the boron nitride dispersion liquid is 0.5-5%, and the mass ratio of boron nitride to polytetrafluoroethylene in the substrate liquid is 1%-10%; 3) placing the composite material obtained in step 2) in a sintering furnace, sintering it at 330-390 ℃ for 60-390 min, taking it out after the furnace is cooled, and obtaining a boron nitride interface assembly modified foamed metal-polytetrafluoroethylene interpenetrating phase lubricating material; In the above preparation steps, the mass concentration of the polytetrafluoroethylene emulsion is 35%-65%, and the particle size of the polytetrafluoroethylene in the emulsion is 60-500 nm.

2. The method of claim 1, wherein the boron nitride interface assembly modified foam metal-polytetrafluoroethylene interphase lubricant is prepared by the steps of: In steps 1) and 2), the particle size of the boron nitride is 2-15 μm, and the thermal conductivity coefficient is 150-800 W / (m·K).

3. The method of claim 1, wherein the boron nitride interface assembly modified foam metal-polytetrafluoroethylene interphase lubricant is prepared by the steps of: In steps 1) and 2), the foamed metal is one or more of nickel, copper, iron, or iron-nickel alloy, the porosity is 90-99%, and the number of openings per inch is 10-110.

4. A boron nitride interface assembly modified foamed metal-polytetrafluoroethylene interpenetrating phase lubricating material prepared by the method according to claim 1.

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