CN109338287B

CN109338287B - Textured Ta/Ag wide-temperature-zone self-lubricating coating and preparation method thereof

Info

Publication number: CN109338287B
Application number: CN201810930269.8A
Authority: CN
Inventors: 李建亮; 张夏菲; 王俊; 李航; 熊党生
Original assignee: Nanjing University of Science and Technology
Current assignee: Nanjing University of Science and Technology
Priority date: 2018-08-15
Filing date: 2018-08-15
Publication date: 2021-02-26
Anticipated expiration: 2038-08-15
Also published as: CN109338287A

Abstract

The invention discloses a preparation method of a textured Ta/Ag wide-temperature-area self-lubricating coating, which comprises the following steps: 1) pretreating a base material; 2) sputtering and depositing a Ta transition layer; 3) and surface texturing treatment: 4) and sputtering and depositing an Ag lubricating phase to obtain the textured Ta/Ag wide-temperature-area self-lubricating coating. In the laser texturing process of the preparation method of the textured Ta/Ag wide-temperature-area self-lubricating coating, the heat affected zone of the Ta coating is small, the chemical property is stable, the roughness of the hole edge is low, and the low roughness is beneficial to spreading of a lubricating film and prolonging of the lubricating life. Ta is used as a transition layer, so that the bonding capability between the matrix and the Ag lubricating film is improved, and an excellent bearing effect can be achieved; the texture micropores can store silver abrasive dust particles in the friction process, and the service life of a surface lubricating film is prolonged; the depth of the micropores is far greater than the thickness of the Ta transition layer, and the holes penetrating through the transition layer can effectively eliminate stress in hole machining.

Description

Textured Ta/Ag wide-temperature-zone self-lubricating coating and preparation method thereof

Technical Field

The invention belongs to the technical field of preparation of solid lubricating films, and relates to a textured Ta/Ag wide-temperature-zone self-lubricating coating and a preparation method thereof.

Background

Silver is a typical solid lubricant material that provides lubrication through low shear within the film for critical part surface tribological modification. Under severe friction conditions such as vacuum, high temperature, high load and the like, silver has higher wear rate at high temperature as a solid lubricating coating; in addition, the bonding performance between the silver film and the surface of the steel substrate is poor, and the steel substrate is easily oxidized to generate hard iron oxide abrasive grains in the friction process, so that the silver lubricating film is damaged.

In recent years, the surface texturing technology of the coating is used for improving the tribological performance of a contact interface, and the texture array can be used as a reservoir of a lubricating material and can also play a role in capturing abrasive dust. The chemical silvering is reported on the outer surface of a textured piston ring, but the surface quality after direct texturing treatment is poor, an upward convex heat affected zone exists around the micro texture, and the larger surface roughness is not beneficial to the deposition and adhesion of a subsequent lubricating film. The texturing of the coating surface can cause the coating to crack and peel due to the thermal stress generated by laser, and can also have the influence of phase change and the like on a metastable coating. In view of both of the above, it is desirable to deposit a suitable transition layer between the steel substrate and the Ag coating.

There are related research reports that Cr and Ni are used as a transition layer between an Ag coating and a steel substrate, and the friction coefficient of the Ag coating on the textured Cr or Ni transition layer is lower and more stable, and the wear rate is reduced by one order of magnitude compared with the Ag coating on textured steel without the transition layer. Tantalum has a high melting point, excellent ductility and corrosion resistance, and is widely used in many fields such as electronics, biomedicine, barrel protection, and the like. The tantalum intermediate layer improves the bonding performance of the Ag film and the steel matrix to a certain extent, and prevents the formation of oxide abrasive grains on the surface of the steel; when texturing is performed on the Ta hard layer, the range of the surface heat affected zone is small due to the high temperature resistance of tantalum, and the surface roughness is low.

Therefore, the textured Ta/Ag wide-temperature-zone self-lubricating coating and the preparation method thereof are provided for solving the problems.

Disclosure of Invention

The invention aims to solve the problems and provide a textured Ta/Ag wide-temperature-zone self-lubricating coating and a preparation method thereof.

The invention realizes the purpose through the following technical scheme:

a preparation method of a textured Ta/Ag wide-temperature-zone self-lubricating coating comprises the following steps:

1) and (3) pretreating the base material: grinding with sand paper to remove rust layer and oxide layer, polishing to mirror surface, cleaning, and oven drying to obtain pretreated substrate;

2) and sputtering and depositing a Ta transition layer: sputtering a layer of Ta as a transition layer on the surface of the pretreated substrate obtained in the step 1) by adopting a first direct current magnetron sputtering method;

3) and surface texturing treatment: etching micropores on the Ta transition layer in the step (2) by using an Nd (yttrium aluminum garnet) pulse laser to obtain a textured Ta transition layer;

4) sputtering deposition of Ag lubricating phase: sputtering Ag on the surface of the textured Ta transition layer obtained in the step 3) as a lubricant by adopting a second direct current magnetron sputtering method to obtain the textured Ta/Ag wide-temperature-zone self-lubricating coating.

Further, the base material in the step 1) is 45 steel.

Furthermore, the first direct current magnetron sputtering method in the step 2) adopts the following process parameters: vacuum degree of back bottom is lower than 5.5 x 10^-3Pa, the target base distance is 60mm, the working air pressure is 0.1-0.4Pa, the argon flow is 40-60sccm, the sputtering power is 40-70W, and the sputtering time is 1-2 h.

Further, the thickness of the Ta transition layer in the step 2) is 500nm-2 μm.

Furthermore, in the step 3), the wavelength of the Nd-YAG pulse laser is 1064nm, the pulse energy is 30 muJ/pulse, the pulse width is 450 ns-500 ns, and the frequency range is 1-100 Hz.

Further, the diameter of the micropores in step 3) is 200um, and the micropores are arranged in an equilateral triangle.

Further, the texture density in the step 3) is 2-8%.

Furthermore, the second direct current magnetron sputtering method in the step 4) adopts the following process parameters: vacuum degree of back bottom is lower than 5.5 x 10^-3Pa, the target base distance is 60mm, the working air pressure is 0.1-0.4Pa, the argon flow is 40-60sccm, the sputtering power is 50-70W, and the sputtering time is 30-60 min.

Further, the thickness of the Ag lubricating layer in step 4) was 10 μm.

Furthermore, the step 1) of removing the surface rust layer and the oxide layer by sanding is to remove the surface rust layer and the oxide layer by sanding step by using 180#, 400 #, 600 # and 800# sandpaper.

The preparation method of the textured Ta/Ag wide-temperature-zone self-lubricating coating has the following beneficial effects:

in the laser texturing process of the preparation method of the textured Ta/Ag wide-temperature-area self-lubricating coating, the heat affected zone of the Ta coating is small, the chemical property is stable, the roughness of the hole edge is low, and the low roughness is beneficial to spreading of a lubricating film and prolonging of the lubricating life. Ta is used as a transition layer, so that the bonding capability between the matrix and the Ag lubricating film is improved, and an excellent bearing effect can be achieved; the texture micropores can store silver abrasive dust particles in the friction process, and the service life of a surface lubricating film is prolonged; the depth of the micropores is far greater than the thickness of the Ta transition layer, and the holes penetrating through the transition layer can effectively eliminate stress in hole machining.

Drawings

FIG. 1 is a three-dimensional topographical view of textured dimples from example 1;

FIG. 2 is a schematic representation of textured dimples from example 1;

FIG. 3 is a SEM image of a cross section of a Ta coating layer in example 1;

FIG. 4 is a three-dimensional topography of a surface textured array of the Ta coating in example 1;

FIG. 5 is a SEM image of the cross section of the composite coating in example 1;

FIG. 6 is a schematic cross-sectional view of a composite coating;

FIG. 7 is a graph of the 600 ℃ coefficient of friction of the composite coating in example 2;

FIG. 8 shows the three-dimensional morphology of the wear scar of the composite coating at 600 ℃ in example 2;

FIG. 9 is a Raman spectrum of a 600 ℃ wear scar in example 2.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The invention relates to a preparation method of a textured Ta/Ag wide-temperature-area self-lubricating coating, which comprises the following steps:

step 1, pretreatment of a base material: grinding with 180#, 400 #, 600 # and 800# sandpaper to remove surface rust layer and oxide layer, polishing to obtain mirror surface, ultrasonic cleaning the substrate with acetone and alcohol for 15min before sputtering, and oven drying; in step 1, the substrate is 45 steel.

Step 2, sputtering and depositing a Ta transition layer: sputtering a Ta layer as a transition layer on the surface of the pretreated substrate by adopting a direct current magnetron sputtering method, wherein the specific process parameters of the direct current magnetron sputtering method are as follows: vacuum degree of back bottom is lower than 5.5 x 10^-3Pa, the target base distance is 60mm, the working air pressure is 0.1-0.4Pa, the argon flow is 40-60sccm, the sputtering power is 40-70W, and the sputtering time is controlled to be 1-2 h; preferably, the thickness of the Ta transition layer is 500nm-2 μm;

step 3, surface texturing treatment: etching regular micropores with the diameter of 200um, arranged in an equilateral triangle array and the texture density of 2-8% on the Ta transition layer in the step 2 by using an Nd-YAG pulse laser with the wavelength of 1064nm, the pulse energy of 30 muJ/pulse, the pulse width of 450-500 ns and the frequency range of 1-100 Hz;

step 4, sputtering and depositing an Ag lubricating phase: sputtering Ag on the surface of the textured Ta transition layer by adopting a direct current magnetron sputtering method as a lubricant, wherein the direct current magnetron sputtering method comprises the following specific process parameters: vacuum degree of back bottom is lower than 5.5 x 10^-3Pa, the target base distance is 60mm, the working air pressure is 0.1-0.4Pa, the argon flow is 40-60sccm, the sputtering power is 50-70W, and the sputtering time is controlled to be 30-60 min. Preferably, the thickness of the Ag lubricating layer is 10 μm.

The principle of the prior art of the direct current magnetron sputtering method is as follows: in magnetron sputtering, because moving electrons are subjected to Lorentz force in a magnetic field, the moving tracks of the moving electrons can bend and even generate spiral motion, the moving path of the moving electrons is lengthened, the number of times of collision with working gas molecules is increased, the plasma density is increased, the magnetron sputtering rate is greatly improved, and the moving electrons can work under lower sputtering voltage and lower pressure to reduce the tendency of film pollution; on the other hand, the energy of atoms incident on the surface of the substrate is also increased, so that the quality of the film can be improved to a great extent. Meanwhile, electrons that lose energy through multiple collisions reach the anode become low-energy electrons, so that the substrate is not overheated. Therefore, the magnetron sputtering method has the advantages of high speed and low temperature. The method has the defects that an insulator film cannot be prepared, and the target material can be obviously and unevenly etched due to the uneven magnetic field adopted in the magnetic control electrode, so that the utilization rate of the target material is low and is generally only 20-30%.

The textured Ag/Ta composite coating with excellent lubricating property is obtained by combining a texturing treatment technology and a soft/hard composite coating, can keep a low friction coefficient at medium and low temperature, even at medium and high temperature regions, and is a self-adaptive solid lubricating coating.

Compared with the prior art, the invention has the following advantages:

(1) and selecting a spherical pit with optimal friction performance from various texture micro-models, and optimizing the depth-diameter ratio of the pit.

(2) In the laser texturing process, the heat affected zone of the Ta coating is small, the chemical property is stable, the hole edge roughness is low, and the low roughness is beneficial to spreading of a lubricating film and prolonging of the lubricating life.

(3) Ta is used as a transition layer, so that the bonding capability between the matrix and the Ag lubricating film is improved, and an excellent bearing effect can be achieved; the texture micropores can store silver abrasive dust particles in the friction process, and the service life of a surface lubricating film is prolonged; the depth of the micropores is far greater than the thickness of the Ta transition layer, and the holes penetrating through the transition layer can effectively eliminate stress in hole machining.

Example 1:

(1) pretreatment of the substrate: a45 steel disc with the diameter of 45mm and the thickness of 1.5mm is taken, 180#, 400 #, 600 # and 800# sandpaper is adopted to polish and remove a surface rust layer and an oxidation layer step by step, and then diamond grinding pastes of W3.5 and W1 are used for polishing. And (3) putting the polished base material into a small beaker, adding absolute ethyl alcohol, carrying out ultrasonic cleaning for 15min, and drying the base material.

(2) Preparing a Ta transition layer: sputtering a layer of Ta as a transition layer on the surface of the pretreated substrate by adopting a direct current magnetron sputtering method, wherein the purity of the used Ta target is 99.95%, and the specific process parameters of the direct current magnetron sputtering method are as follows: the target base distance is 60cm, the vacuum degree of the back bottom is lower than 5.5*10^-3Pa, the working pressure is 0.2Pa, the argon flow is 40sccm, the sputtering power is 70W, and the sputtering time is controlled to be 2 h;

(3) surface texturing treatment: etching regular micropores on the Ta transition layer in the step 2 by using an Nd: YAG pulse laser with the wavelength of 1064nm, the pulse energy of 30 muJ/pulse, the pulse width of 450 ns-500 ns and the frequency range of 1-100Hz, and arranging the micropores in an equilateral triangle array with the texture density of 8%;

(4) sputtering deposition of Ag lubricating phase: sputtering a layer of Ag as a lubricant on the surface of the textured Ta transition layer by adopting a direct current magnetron sputtering method, wherein the purity of the used Ag target is 99.95%, and the specific process parameters of the direct current magnetron sputtering method are as follows: the target base distance is 60cm, the vacuum degree of the back bottom is lower than 5.5 x 10 < -3 > Pa, the working pressure is 0.2Pa, the argon flow is 40sccm, the sputtering power is 65W, and the sputtering time is controlled to be 30 min.

The three-dimensional topography of the textured pits in this example 1 is shown in fig. 1 and 2, and the pits have a diameter of 200 μm and a depth of about 80 μm. The thickness of the prepared Ta transition layer is about 2 mu m (see figure 3), the whole interface combination is good, no gap or crack exists between the Ta layer and the substrate, the surface of the coating is smooth, and the obtained nanocrystalline alpha-Ta phase with excellent mechanical property is obtained. FIG. 4 is a three-dimensional shape of a textured Ta coating, micropores are regularly arranged in an equilateral triangular array, a heat affected zone around the micropores is small, surface roughness is low, and texturing density is 8%. FIGS. 5 and 6 are sectional morphology diagrams of the textured Ag/Ta composite coating finally prepared, wherein Ag completely covers the surface of the Ta transition layer, the content of the Ag is up to 96.89 wt%, and the thickness of the Ag film is about 10 μm. The textured composite coating effectively reduces the friction coefficient and the wear rate of the friction surface. Under the condition of room temperature, the friction coefficient of the composite coating with the texture density of 8% is reduced by about 20% from 0.5 to 0.4; at 600 ℃, the friction coefficient is reduced by 63 percent, and the wear rate is reduced by about 68 percent.

Example 2:

(1) pretreatment of the substrate: the same as example 1;

(2) preparing a Ta transition layer: sputtering a layer of Ta as a transition layer on the surface of the pretreated substrate by adopting a direct-current magnetron sputtering method, wherein the purity of the used Ta target99.95 percent, the specific technological parameters of the direct current magnetron sputtering method are as follows: target base distance 60cm, back vacuum degree lower than 5.5 x 10^-3Pa, the working pressure is 0.2Pa, the argon flow is 40sccm, the sputtering power is 50W, and the sputtering time is controlled to be 2 h;

(3) surface texturing treatment: and (3) etching regular micropores on the Ta transition layer in the step (2) by using an Nd: YAG pulse laser with the wavelength of 1064nm, the pulse energy of 30 muJ/pulse, the pulse width of 450 ns-500 ns and the frequency range of 1-100Hz, and arranging the regular micropores in an equilateral triangle array with the texture density of 6%.

(4) Sputtering deposition of Ag lubricating phase: the same as in example 1.

In this example, the sputtering power of Ta was 50w, and the Ta film was dense and smooth with a flat surface and a hardness of 9.47 GPa. The friction curve of the finally prepared composite coating at 600 ℃ is shown in figure 7 under the friction conditions of 2N load, 5mm friction radius and 300r/min rotation speed, and the average friction coefficient is kept at a lower level (about 0.2), is reduced by 81 percent compared with the friction coefficient of a 45 steel matrix, and is reduced by 75 percent compared with the friction coefficient of an untextured sample. After 30min friction test, the three-dimensional shape (figure 8) of the grinding mark shows that the grinding mark is shallow, the depth of the grinding mark is only 3 mu m, and the calculated wear rate is 54 x 10^-6mm³N^-1m^-1The abrasion life is increased by more than 3 times. At the moment, the micropores play the roles of capturing abrasive particles and storing lubricant Ag, so that the abrasion is reduced, and the friction chemical reaction is generated at the grinding mark at high temperature to generate Ta₂O₅(see fig. 9), the new lubricant phase works in concert with the Ag particles, resulting in a reduced coefficient of friction and an extended coating life.

Claims

1. A preparation method of a textured Ta/Ag wide-temperature-zone self-lubricating coating is characterized by comprising the following steps:

1) and (3) pretreating the base material: grinding with sand paper to remove rust layer and oxide layer, polishing to mirror surface, cleaning, and oven drying to obtain pretreated substrate; the base material in the step 1) is 45 steel; in the step 1), the surface rust layer and the oxide layer are removed by polishing with sand paper, namely, the surface rust layer and the oxide layer are removed by polishing with 180#, 400 #, 600 # and 800# sand paper step by step;

2) and sputtering and depositing a Ta transition layer: sputtering a layer of Ta as a transition layer on the surface of the pretreated substrate obtained in the step 1) by adopting a first direct current magnetron sputtering method; the first direct current magnetron sputtering method in the step 2) adopts the following process parameters: vacuum degree of the back bottom is lower than 5.5 multiplied by 10^-3Pa, the target base distance is 60mm, the working air pressure is 0.1-0.4Pa, the argon flow is 40-60sccm, the sputtering power is 40-70W, and the sputtering time is 1-2 h; the thickness of the Ta transition layer in the step 2) is 500nm-2 mu m;

3) and surface texturing treatment: etching micropores on the Ta transition layer in the step 2) by using an Nd (yttrium aluminum garnet) pulse laser to obtain a textured Ta transition layer; in the step 3), the wavelength of the Nd-YAG pulse laser is 1064nm, the pulse energy is 30 muJ/pulse, the pulse width is 450 ns-500 ns, and the frequency range is 1-100 Hz; in the step 3), the diameter of the micropores is 200um, and the micropores are arranged in an equilateral triangle; in the step 3), the texture density is 2-8%;

4) sputtering deposition of Ag lubricating phase: sputtering Ag on the surface of the textured Ta transition layer obtained in the step 3) as a lubricant by adopting a second direct-current magnetron sputtering method to obtain a textured Ta/Ag wide-temperature-zone self-lubricating coating;

the second direct current magnetron sputtering method in the step 4) adopts the following technological parameters: vacuum degree of the back bottom is lower than 5.5 multiplied by 10^-3Pa, the target base distance is 60mm, the working air pressure is 0.1-0.4Pa, the argon flow is 40-60sccm, the sputtering power is 50-70W, and the sputtering time is 30-60 min; the thickness of the Ag lubricating layer in the step 4) is 10 μm.