A NbSe2-LaF3 composite lubricating film for 50~300K vacuum environment and its preparation method

Abstract

The present invention relates to a NbSe2-LaF3 composite lubricating film for a 50-300K vacuum environment and a preparation method thereof, which is characterized in that the resistivity of superconducting materials is reduced at low temperatures, thereby reducing the contribution of electrons to friction, and a NbSe2-LaF3 composite film is prepared by unbalanced magnetron sputtering technology. First, a method of mixing and pressing metal Ti and LaF3 into a target is used to solve the problem that the rare earth compound LaF3 is difficult to sputter due to excessive resistance; secondly, the effect of the rare earth compound LaF3 in refining grains is used to improve the compactness of the NbSe2 film, thereby further reducing the resistance of the NbSe2 film at low temperatures, reducing the contribution of electrons to friction, and making the film have excellent lubrication performance and load-bearing capacity at low temperatures. The technology of the present invention can be applied to the surface lubrication treatment of low-temperature moving contact parts such as superconducting coils, rocket engines, and deep space exploration telescopes.

Description

Technical Field

[0001] The invention belongs to the technical field of functional films, and in particular relates to a NbSe2-LaF3 composite lubricating film for a 50-300K vacuum environment and a preparation method thereof. Background Art

[0002] Efficient lubrication of various types of machinery under extremely low temperature conditions is a key technical commanding height for the development of current and future advanced equipment. Equipment ranging from ships, boats, fighter jets serving in polar regions to advanced spacecraft are subject to the harsh environment challenges of extremely low temperatures, and this extreme temperature often changes dynamically. Therefore, the service temperature range of the equipment continues to expand, and the service form changes from static temperature to dynamic continuous operation. Currently, most lubricating materials need to work within the temperature range of 50~300K, but the understanding of the lubrication mechanism of materials in this temperature range is still not in-depth. Currently, common space lubricating materials are PTFE, PEEK, MoS2, DLC and other materials. Most of the selection of low-temperature lubricating materials directly uses the above materials, and there is a lack of theoretical design guidance. In addition, polymers such as PTFE have a high friction coefficient (10 -1 The existing materials are difficult to meet the lubrication requirements of precision parts. Although MoS2 has excellent lubrication performance in a vacuum environment, its friction coefficient increases at ultra-low temperatures, which greatly reduces its lifespan. DLC faces the problem of short lifespan in a vacuum environment. Therefore, it is difficult for existing materials to meet the lubrication requirements of this temperature range.

[0003] Friction is an energy dissipation process, which is mainly divided into electron dissipation and phonon dissipation. The movement of molecules and electrons will be inhibited at ultra-low temperatures, thus affecting energy dissipation. Based on this, ultra-low friction is expected to be achieved by suppressing electron or phonon dissipation at ultra-low temperatures. NbSe2 with a layered structure has excellent lubrication properties and is also a new type of superconducting material. Its resistivity gradually decreases with decreasing temperature, resulting in a reduction in the effect of electrons on friction, thereby significantly reducing the friction coefficient. However, the superconducting transition temperature of pure NbSe2 film is as low as 5K, and most low-temperature working conditions are above 50K, which makes it difficult for the lubrication performance improvement brought by the superconducting effect to play a role in this temperature range. Further reducing the resistivity of NbSe2 film by doping modification is expected to reduce the effect of electrons on friction in the temperature range of 50 to 300K and obtain an extremely low friction coefficient. Summary of the invention

[0004] The present invention aims to disclose a NbSe2-LaF3 composite lubricating film for a 50-300K vacuum environment and a preparation method thereof, wherein the superconducting material NbSe2 is doped with the rare earth compound LaF3, and the influence of electrons on friction is reduced by increasing the superconducting transition temperature, thereby achieving ultra-low friction.

[0005] 1. Preparation of NbSe2-LaF3 composite lubricating film

[0006] 1) Preparation of LaF3-Ti composite target

[0007] According to the mass ratio of LaF3:Ti=5%~25%, rare earth compound LaF3 powder and metal Ti powder are ball-milled for 4~8h, and then LaF3-Ti composite target is pressed by hot isostatic pressing;

[0008] Among them, the process parameters of the hot isostatic pressing method are: vacuum degree ≤1.33Pa, temperature 500℃~1000℃, pressure 50~150MPa, and insulation time 3~8h; the particle size of the rare earth compound LaF3 powder is 50~400 mesh, and the purity is ≥95%; the particle size of the metal Ti powder is 200~700 mesh, and the purity is ≥98%.

[0009] 2) Preparation of NbSe2-LaF3 composite lubricating film

[0010] The magnetron sputtering method was used to prepare NbSe2-LaF3 composite film on the substrate surface with LaF3-Ti composite target and NbSe2 target as sputtering targets. During sputtering, the LaF3-Ti composite target and NbSe2 target were turned on at the same time. The substrate bias voltage was -40~-120V. The sputtering power of LaF3-Ti composite target ranged from 0.4 to 2W / cm 2 ; The sputtering power of NbSe2 target is 0.2~1 W / cm 2 .

[0011] The substrate of the present invention may be any metal substrate, such as 304 stainless steel, 9Cr18, 2A14, TC4, aluminum or copper.

[0012] The present invention utilizes the superconducting transition effect at low temperature to reduce the resistivity of the film, thereby reducing the effect of electrons on friction, and selects the superconducting material NbSe2 as the main phase of lubrication to achieve low friction in a vacuum low-temperature environment. At the same time, the rare earth compound LaF3 with special activity is doped to further significantly improve the compactness of the pure NbSe2 film, reduce the resistance of the NbSe2 film, and further reduce the friction coefficient of the film at low temperatures. In addition, the rare earth compound LaF3 is mixed with metal Ti and pressed into a block by hot isostatic pressing. The strong conductivity of metal Ti is used to bombard the rare earth compound from the target surface during the sputtering process, solving the problem that the rare earth compound is difficult to perform magnetron sputtering. Finally, the prepared NbSe2-LaF3 composite film can have an ultra-low friction coefficient and a long lubrication life in the vacuum temperature range of 50~300K.

[0013] 2. Structural Characterization of NbSe2-LaF3 Composite Lubricating Films

[0014] The structure of the prepared NbSe2-LaF3 composite film was characterized by high-resolution transmission electron microscopy to observe its crystal orientation and crystallinity (see Figure 1 The prepared NbSe2-LaF3 composite film has an amorphous structure with a small amount of (002) oriented nanocrystals.

[0015] 3. Performance evaluation of NbSe2-LaF3 composite lubricating films

[0016] Compared with the pure NbSe2 lubricating film, the resistivity of the NbSe2-LaF3 composite lubricating film prepared by the present invention is reduced by one order of magnitude. When the temperature is reduced to 50K, the resistivity of the pure NbSe2 lubricating film is 2.1×10 -7 Ω·m, while the resistivity of NbSe2-LaF3 composite lubricating film is 3.2×10 -8 Ω·m. Compared with the MoS2 film, which is currently the most widely used in space applications, the resistivity has dropped by 9 orders of magnitude, and has an extremely low resistivity (see Table 1 below).

[0017] The friction coefficient of the traditional MoS2 film gradually increases with the decrease of temperature, from 0.024 at 300K to 0.10 at 50K; although the friction coefficient of the pure NbSe2 film is very stable in the temperature range of 50~300K, it is also maintained at about 0.05; the NbSe2-LaF3 composite lubricating film prepared by doping LaF3 further reduces the friction coefficient from 0.035 at 300K to 0.02 at 50K, which can achieve low friction in the temperature range of 50~300K (see Figure 2 ). Test method: vacuum low temperature friction tester, vacuum degree 8.0×10 -5 Pa, ball-disk contact rotation motion mode, the upper sample is a GCr15 commercial steel ball with a diameter of 6 mm, and the lower sample is a flat 9Cr18 specimen coated with NbSe2-LaF3 lubricating film, MoS2 film and NbSe2 film of equal thickness, respectively. The normal load is 5 N, the rotation radius is 5 mm, and the sampling frequency is 50 Hz.

[0018] Based on the above excellent properties, the NbSe2-LaF3 composite lubricating film of the present invention is expected to be used for surface lubrication treatment of low-temperature moving contact parts such as superconducting coils, rocket engines, deep space exploration telescopes, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a high-resolution transmission electron microscope photograph of the NbSe2-LaF3 composite lubricating film prepared by the present invention.

[0020] Figure 2This is a comparison chart of the vacuum friction coefficients of the NbSe2-LaF3 composite film prepared by the present invention and MoS2 and NbSe2 films at different temperatures. DETAILED DESCRIPTION

[0021] The present invention is further explained below with reference to specific embodiments.

[0022] Example 1

[0023] (1) Preparation of LaF3-Ti composite target: Select rare earth compound LaF3 powder with a purity of 95% and a particle size of 50 mesh and metal Ti powder with a purity of 98% and a particle size of 200 mesh, dope the two powders with a mass ratio of LaF3:Ti=5%, and mix the two powders in a ball mill for 4 hours. Press by hot isostatic pressing: vacuum degree 1.33 Pa, heating temperature 500 ℃, pressure 50MPa, holding time 3 h.

[0024] (2) Preparation of NbSe2-LaF3 composite lubricating film: The chamber was evacuated and ionized Ar + Bombard the substrate surface and deposit a certain thickness of Ti transition layer; then turn on the LaF3-Ti and NbSe2 target sputtering power at the same time, adjust the substrate bias to -40 V, and adjust the LaF3-Ti composite target sputtering power to 0.4 W / cm 2 The sputtering power of NbSe2 target is 0.2 W / cm 2 After depositing a thickness of 1 μm, turn off all target sputtering power supplies, and when the temperature of the prepared film drops to room temperature, open the chamber and take out the sample.

[0025] Example 2

[0026] (1) Preparation of LaF3-Ti composite target: Select rare earth compound LaF3 powder with a purity of 97% and a particle size of 200 mesh and metal Ti powder with a purity of 99% and a particle size of 500 mesh, dope the two powders with a mass ratio of LaF3:Ti=15%, and mix the two powders in a ball mill for 6 hours. Press by hot isostatic pressing: vacuum degree 1.21 Pa, heating temperature 800 ℃, pressure 100 MPa, and holding time 5 h.

[0027] (2) Preparation of NbSe2-LaF3 composite lubricating film: The chamber was evacuated and ionized Ar + Bombard the substrate surface and deposit a certain thickness of Ti transition layer; then turn on the LaF3-Ti and NbSe2 target sputtering power at the same time, adjust the substrate bias to -80 V, and adjust the LaF3-Ti composite target sputtering power to 1 W / cm 2 The sputtering power of NbSe2 target is 0.5 W / cm 2After depositing a thickness of 3 μm, turn off all target sputtering power supplies, and when the temperature of the prepared film drops to room temperature, open the chamber and take out the sample.

[0028] Example 3

[0029] (1) Preparation of LaF3-Ti composite target: Select rare earth compound LaF3 powder with a purity of 99% and a particle size of 400 mesh and metal Ti powder with a purity of 99.5% and a particle size of 700 mesh, dope the two powders with a mass ratio of LaF3:Ti=25%, and mix the two powders in a ball mill for 8 hours. Use hot isostatic pressing method to press, when the vacuum degree is 1.12 Pa, the heating temperature is 1000℃, the pressure is 150 MPa, and the holding time is 8 hours.

[0030] (2) Preparation of NbSe2-LaF3 composite lubricating film: The chamber was evacuated and ionized Ar + Bombard the substrate surface and deposit a certain thickness of Ti transition layer; then turn on the LaF3-Ti and NbSe2 target sputtering power at the same time, adjust the substrate bias to -120 V; adjust the LaF3-Ti composite target sputtering power to 2 W / cm 2 The sputtering power of NbSe2 target is 1 W / cm 2 After depositing a thickness of 5 μm, turn off all target sputtering power supplies, and when the temperature of the prepared film drops to room temperature, open the chamber and take out the sample.

[0031] In the above embodiments 1-3, the substrate can be made of any material such as 304 stainless steel, 9Cr18, 2A14, TC4, aluminum, copper, etc.

[0032] After testing, the friction coefficients of the NbSe2-LaF3 composite films prepared in the above Examples 1-3 at different temperatures are shown in Table 1 below:

[0033] Table 1 Friction coefficients of NbSe2-LaF3 composite films prepared in Examples 1-3 at different temperatures

[0034]

[0035] It can be seen from Table 1 that the friction coefficient of the NbSe2-LaF3 composite film (1-5 μm) prepared by the present invention is maintained in the range of 0.035-0.02 at 300K to 50K, and low friction can be achieved in the temperature range of 50-300K.

[0036] In addition, MoS2 and NbSe2 films of the same thickness as those in Example 3 of the present invention were prepared by magnetron sputtering, and the resistivity of the NbSe2-LaF3 composite film and the MoS2 and NbSe2 films at different temperatures was measured. The results are shown in Table 2 below:

[0037] Table 2 Resistivity of NbSe2-LaF3 composite film, MoS2 and NbSe2 film at different temperatures

[0038]

[0039] It can be seen from Table 2 that the resistivity of the NbSe2-LaF3 composite film prepared by the present invention is significantly lower than that of the traditional MoS2 and NbSe2 films, which reduces the influence of electrons on friction and achieves ultra-low friction.

Claims

1. A NbSe2-LaF3 composite lubricating film for use in a 50-300K vacuum environment, characterized in that: The thickness of the composite lubricating film is 1~5μm.

2. A method for preparing a NbSe2-LaF3 composite lubricating film for a 50-300K vacuum environment, characterized in that: The following steps are involved: 1) Preparation of LaF3-Ti composite target According to the mass ratio of LaF3:Ti=5%~25%, rare earth compound LaF3 powder and metal Ti powder are ball-milled for 4~8h, and then LaF3-Ti composite target is pressed by hot isostatic pressing; The process parameters of hot isostatic pressing are: vacuum degree ≤ 1.33Pa, temperature 500℃~1000℃, pressure 50~150MPa, and holding time 3~8h; 2) Preparation of NbSe2-LaF3 composite lubricating film The magnetron sputtering method was used to prepare NbSe2-LaF3 composite film on the substrate surface with LaF3-Ti composite target and NbSe2 target as sputtering targets. During sputtering, the LaF3-Ti composite target and NbSe2 target were turned on at the same time. The substrate bias voltage was -40~-120V. The sputtering power of LaF3-Ti composite target ranged from 0.4 to 2W / cm 2 ; The sputtering power of NbSe2 target is 0.2~1 W / cm 2 .

3. A method for preparing a NbSe2-LaF3 composite lubricating film for a 50-300K vacuum environment as claimed in claim 2, characterized in that: In step 1), the particle size of the rare earth compound LaF3 powder is 50-400 mesh, and the purity is ≥95%; the particle size of the metal Ti powder is 200-700 mesh, and the purity is ≥98%.

Images