阅读说明：本技术 一种应用于铜基刹车片的复合涂层及其制备方法 (composite coating applied to copper-based brake pad and preparation method thereof ) 是由 黄亚平 薛艳 王莹 田进军 于 2019-09-25 设计创作，主要内容包括：本发明涉及摩擦材料及其制备技术,具体为一种应用于铜基刹车片在高速制动条件下增加其稳定性的复合涂层及其制备方法。该复合涂层包括两层表面涂层,其中：内层涂层的制备为金属或者合金涂层,包括镍、铬、钛等能够在室温和高温下形成钝化层的金属或者合金涂层；外层涂层为高分子及陶瓷复合涂层,包括聚酰亚胺、聚四氟乙烯、聚醚醚酮等具有高温稳定性、憎水性,并且具有较好的耐磨性能的高分子涂层,并可能含有氧化铝、碳化硅、二氧化硅等陶瓷添加剂。本发明铜基刹车片在非摩擦面的涂层厚度大于25微米,具有两层涂层,分别为金属或合金涂层和高分子或者陶瓷涂层,X射线荧光光谱等检测手段表面铜的质量分数含量小于1％。(The invention relates to a friction material and a preparation technology thereof, in particular to a composite coating applied to a copper-based brake pad for improving the stability of the copper-based brake pad under a high-speed braking condition and a preparation method thereof. The composite coating comprises two surface coatings, wherein: the inner layer coating is prepared into a metal or alloy coating, and comprises nickel, chromium, titanium and other metal or alloy coatings which can form a passivation layer at room temperature and high temperature; the outer coating is a polymer and ceramic composite coating, comprises polyimide, polytetrafluoroethylene, polyether ether ketone and other polymer coatings with high temperature stability, hydrophobicity and better wear resistance, and may contain ceramic additives such as alumina, silicon carbide, silicon dioxide and the like. The thickness of the coating on the non-friction surface of the copper-based brake pad is more than 25 microns, the copper-based brake pad is provided with two layers of coatings, namely a metal or alloy coating and a polymer or ceramic coating, and the mass fraction content of copper on the surface is less than 1% by detection means such as X-ray fluorescence spectroscopy.)

1. a composite coating applied to a copper-based brake pad, which is characterized by comprising two surface coatings of an inner coating and an outer coating, wherein: the inner layer coating is a metal or alloy coating capable of forming a passivation layer at room temperature or high temperature; the outer coating is a polymer and ceramic composite coating, and the polymer coating with high temperature stability, hydrophobicity and wear resistance contains a ceramic additive.

2. the composite coating applied to the copper-based brake pad according to claim 1, wherein the inner coating comprises one or more metals or alloys of nickel, chromium or titanium, the content of the metal or alloy is 60-99 wt%, and the thickness of the inner coating is 1 micrometer-1 millimeter.

3. The composite coating applied to the copper-based brake pad according to claim 1, wherein in the outer coating, the polymer material is one or more than two of polyimide, polytetrafluoroethylene and polyether ether ketone, the content of the polymer material is 50-99 wt%, the rest is one or more than two of alumina, silicon carbide and silicon dioxide, and the thickness of the outer coating is 1-200 microns.

4. The composite coating applied to the copper-based brake pad according to claim 1, wherein a surface modification layer is arranged between the inner layer coating and the copper-based brake pad, and the thickness of the surface modification layer is 10 nanometers to 1 micrometer; a bonding layer is arranged between the inner coating and the outer coating, and the thickness of the bonding layer is 10 nanometers to 1 micrometer.

5. the composite coating applied to a copper-based brake pad according to claim 1, wherein the composite coating preferably has a total thickness of 25 μm to 1 mm.

6. A preparation method of the composite coating applied to the copper-based brake pad as claimed in any one of claims 1 to 5, characterized by comprising the following steps:

(1) The surface of the copper-based brake pad is polished by sand paper, and the sand paper is 120#, 400#, and 800# in sequence;

(2) Washing the copper-based brake pad with water and wiping the copper-based brake pad to dry;

(3) Cleaning the copper-based brake pad by using normal hexane, and wiping the copper-based brake pad to dry;

(4) preparing a surface modification layer on the surface of the copper-based brake pad;

(5) Placing the copper-based brake pad in a chemical plating solution to prepare a chemical plating layer;

(6) Placing the copper-based brake pad in a surface modification solution to prepare an adhesive layer;

(7) and (3) putting the copper-based brake pad into the high polymer coating to prepare a surface high polymer layer.

7. The method for preparing a composite coating applied to a copper-based brake pad according to claim 6, wherein in the step (4), the surface modification layer is prepared by one of the following processes:

A. placing the copper-based brake pad into a solution formed by mixing 20-40 wt% of n-propanol, 20-40 wt% of isopropanol, 5-15 wt% of phosphoric acid and the balance of water, soaking for 1-10 minutes, taking out, and naturally drying;

B. placing the copper-based brake pad in a hydrochloric acid solution of stannous chloride, soaking for 5-15 minutes, and taking out; wherein, the hydrochloric acid solution of stannous chloride is: 0.4-0.6 wt% of stannous chloride, 0.4-0.6 wt% of hydrochloric acid with the concentration of 37 wt%, and the balance of water; then placing the mixture into hydrochloric acid solution of palladium chloride for soaking for 5-15 minutes, and naturally drying; wherein, the hydrochloric acid solution of the palladium chloride is as follows: 0.2 to 0.3 weight percent of palladium chloride, 0.2 to 0.3 weight percent of hydrochloric acid with the concentration of 37 weight percent, and the balance of water;

C. and (3) placing the copper-based brake pad in a sulfuric acid solution with the concentration of 10 wt%, soaking for 1-10 minutes, taking out, and naturally drying.

8. the method for preparing a composite coating applied to a copper-based brake pad according to claim 6, wherein in the step (5), the electroless plating layer is prepared by one of the following processes:

A. The chemical plating solution comprises the following components: 10-30 wt% of nickel sulfate, 0.4-0.6 wt% of ammonium citrate, 4-6 wt% of thiourea, 0.4-0.6 wt% of disodium ethylenediamine tetraacetic acid, 10-30 wt% of sodium hypophosphite, 4-6 wt% of ethanol, 0.5-1.5 wt% of boric acid and the balance of water; heating to 80-90 ℃, keeping for 0.5-2 hours, and taking out the copper-based brake pad;

B. the chemical plating solution comprises the following components: 20-40 wt% of chromium trioxide, 0.2-0.4 wt% of boric acid, 0.4-0.6 wt% of fluosilicic acid and the balance of water; heating to 80-90 ℃, keeping for 0.5-2 hours, and taking out the copper-based brake pad.

9. The method for preparing a composite coating applied to a copper-based brake pad according to claim 6, wherein in the step (6), the adhesive layer is prepared by one of the following processes:

A. Placing the taken copper-based brake pad in a surface modification solution, and heating to 70-80 ℃ for 4-6 minutes; wherein the surface modification solution is: 0.5-2 wt% of aminopropyltriethoxysilane, 0.05-0.2 wt% of boric acid and the balance of ethanol;

B. placing the taken copper-based brake pad in a surface modification solution, and keeping the temperature at room temperature for 5-15 minutes; wherein the surface modification solution is: 0.5-2 wt% of dopamine, 0.5-2 wt% of hydrochloric acid with the concentration of 37 wt%, and the balance of water;

C. Placing the taken copper-based brake pad in a surface modification solution, and keeping the temperature at room temperature for 4-6 minutes; wherein the surface modification solution is: 0.4-0.6 wt% of aminopropyltriethoxysilane, and the balance of N, N-dimethylformamide.

10. The method for preparing a composite coating applied to a copper-based brake pad according to claim 6, wherein in the step (7), the surface polymer layer is prepared by one of the following processes:

A. putting the copper-based brake pad into the high polymer coating while the copper-based brake pad is hot, directly taking out, airing, putting into a 300-400 ℃ drying oven, keeping the temperature for 20-40 minutes, taking out, and cooling at room temperature; the high polymer coating comprises 5-15 wt% of polytetrafluoroethylene emulsion, 0.05-0.2 wt% of fumed silica, 0.05-0.2 wt% of nano aluminum oxide, 0.05-0.2 wt% of nano silicon carbide, 0.05-0.2 wt% of polyvinylpyrrolidone and the balance of a mixed solution of water and ethanol, wherein the weight ratio of the water to the ethanol is 1: 8-10;

B. Putting the copper-based brake pad into the high polymer coating, directly taking out, airing, placing in a drying oven at 400-500 ℃ for keeping the temperature for 10-30 minutes, taking out, and cooling at room temperature; wherein the high polymer coating comprises 5-15 wt% of polyether-ether-ketone, 4-6 wt% of sodium silicate, 0.05-0.2 wt% of nano aluminum oxide, 0.05-0.2 wt% of nano silicon carbide and the balance of water;

C. putting the copper-based brake pad into the high polymer coating, directly taking out, airing, putting into a vacuum oven at 200-400 ℃, keeping the temperature for 1-3 h, taking out, and cooling at room temperature; wherein the high molecular coating comprises 4-6 wt% of polyamic acid, 0.05-0.2 wt% of fumed silica, 0.05-0.2 wt% of nano alumina, 0.05-0.2 wt% of nano silicon carbide, 0.05-0.2 wt% of polyvinylpyrrolidone and the balance of dimethylformamide.

Technical Field

the invention relates to a friction material and a preparation technology thereof, in particular to a composite coating applied to a copper-based brake pad for improving the stability of the copper-based brake pad under a high-speed braking condition and a preparation method thereof, belonging to the field of high-speed rail industry.

background art:

High-speed trains are becoming a popular vehicle, and friction braking is one of the core components of the vehicle, and is an important guarantee for safe train stop. An ideal friction brake material should have good stability and high braking reliability. However, with the increase of the train speed, the volume temperature of the braking unit on the train exceeding 200km/h is greatly changed and can reach over 500 ℃, and the flash point temperature reaches about 1000 ℃. Within the larger temperature range, the brake pad is easy to cause unstable friction performance, aggravated abrasion and high-temperature failure under the condition of high-speed braking. Brake pads conventionally used in high-speed rails at present are copper-based alloys prepared by powder metallurgy. The copper-based alloy prepared by powder metallurgy can still maintain good mechanical property and stable components in the service temperature range and has good braking performance, but the friction performance is unstable due to the damage of a lubricating film on the surface of the copper-based alloy, the plastic deformation of a subsurface layer of the material, oxidation and the like at high temperature.

The copper-based powder alloy has already started to be oxidized at the temperature exceeding 100 ℃ due to the fact that the main component of the copper-based powder alloy is copper, and is easier to be oxidized in a humid environment, so that the friction stability and the long-term mechanical property stability of the copper-based brake pad can be influenced, the friction condition of the copper-based brake pad is changed, and the long-term friction stability of the copper-based brake pad is influenced. In order to increase the thermal stability of copper, CN1050051 adopts a multi-solid co-infiltration method of chromium, aluminum, silicon and the like to form a protective layer with the thickness of 1-3.5 mm on the surface of the copper wire to improve the stability of the copper wire, CN202816443U adopts polyimide coated on the surface of the copper wire to improve the stability of the copper wire, and CN103390445A improves the high temperature resistance of the copper wire by spraying silver on the surface of pure copper, then winding glass fiber and carbon fiber, and adding polyvinyl chloride on the outside. CN105219987A strengthens copper alloy through titanium diboride and the like, thereby improving the high temperature resistance of the copper alloy. These methods all use copper covering the bare surface to increase its stability.

the invention content is as follows:

Aiming at the principle that high temperature and friction coefficient requirements are met in the high-speed braking process of the copper-based brake pad, the invention aims to provide the composite coating applied to the copper-based brake pad and the preparation method thereof, and the composite coating has better mechanical property stability and friction property stability during high-speed braking.

In order to achieve the above effects, the invention is realized by the following technical scheme:

a composite coating applied to a copper-based brake pad, the composite coating comprising two surface coatings of an inner coating and an outer coating in combination, wherein: the inner layer coating is a metal or alloy coating capable of forming a passivation layer at room temperature or high temperature; the outer coating is a polymer and ceramic composite coating, and the polymer coating with high temperature stability, hydrophobicity and wear resistance contains a ceramic additive.

the composite coating applied to the copper-based brake pad comprises one or more than two metals or alloys of nickel, chromium or titanium in an inner coating, wherein the content of the metal or the alloy is 60-99 wt%, and the thickness of the inner coating is 1 micrometer-1 millimeter.

In the composite coating applied to the copper-based brake pad, the outer coating is made of one or more than two of polyimide, polytetrafluoroethylene and polyether ether ketone, the content of the polymer material is 50-99 wt%, the balance is one or more than two of alumina, silicon carbide and silicon dioxide, and the thickness of the outer coating is 1-200 microns.

The composite coating applied to the copper-based brake pad is characterized in that a surface modification layer is arranged between the inner layer coating and the copper-based brake pad, and the thickness of the surface modification layer is 10 nanometers to 1 micrometer; a bonding layer is arranged between the inner coating and the outer coating, and the thickness of the bonding layer is 10 nanometers to 1 micrometer.

The composite coating applied to the copper-based brake pad preferably has the total thickness of 25 mu m-1 mm.

the preparation method of the composite coating applied to the copper-based brake pad comprises the following steps:

(1) the surface of the copper-based brake pad is polished by sand paper, and the sand paper is 120#, 400#, and 800# in sequence;

(2) Washing the copper-based brake pad with water and wiping the copper-based brake pad to dry;

(3) Cleaning the copper-based brake pad by using normal hexane, and wiping the copper-based brake pad to dry;

(4) Preparing a surface modification layer on the surface of the copper-based brake pad;

(5) placing the copper-based brake pad in a chemical plating solution to prepare a chemical plating layer;

(6) Placing the copper-based brake pad in a surface modification solution to prepare an adhesive layer;

(7) and (3) putting the copper-based brake pad into the high polymer coating to prepare a surface high polymer layer.

in the preparation method of the composite coating applied to the copper-based brake pad, in the step (4), the preparation of the surface modification layer adopts one of the following processes:

A. Placing the copper-based brake pad into a solution formed by mixing 20-40 wt% of n-propanol, 20-40 wt% of isopropanol, 5-15 wt% of phosphoric acid and the balance of water, soaking for 1-10 minutes, taking out, and naturally drying;

B. Placing the copper-based brake pad in a hydrochloric acid solution of stannous chloride, soaking for 5-15 minutes, and taking out; wherein, the hydrochloric acid solution of stannous chloride is: 0.4-0.6 wt% of stannous chloride, 0.4-0.6 wt% of hydrochloric acid with the concentration of 37 wt%, and the balance of water; then placing the mixture into hydrochloric acid solution of palladium chloride for soaking for 5-15 minutes, and naturally drying; wherein, the hydrochloric acid solution of the palladium chloride is as follows: 0.2 to 0.3 weight percent of palladium chloride, 0.2 to 0.3 weight percent of hydrochloric acid with the concentration of 37 weight percent, and the balance of water;

C. And (3) placing the copper-based brake pad in a sulfuric acid solution with the concentration of 10 wt%, soaking for 1-10 minutes, taking out, and naturally drying.

in the step (5), the chemical plating layer is prepared by one of the following processes:

A. the chemical plating solution comprises the following components: 10-30 wt% of nickel sulfate, 0.4-0.6 wt% of ammonium citrate, 4-6 wt% of thiourea, 0.4-0.6 wt% of disodium ethylenediamine tetraacetic acid, 10-30 wt% of sodium hypophosphite, 4-6 wt% of ethanol, 0.5-1.5 wt% of boric acid and the balance of water; heating to 80-90 ℃, keeping for 0.5-2 hours, and taking out the copper-based brake pad;

B. the chemical plating solution comprises the following components: 20-40 wt% of chromium trioxide, 0.2-0.4 wt% of boric acid, 0.4-0.6 wt% of fluosilicic acid and the balance of water; heating to 80-90 ℃, keeping for 0.5-2 hours, and taking out the copper-based brake pad.

In the preparation method of the composite coating applied to the copper-based brake pad, in the step (6), the preparation of the bonding layer adopts one of the following processes:

A. placing the taken copper-based brake pad in a surface modification solution, and heating to 70-80 ℃ for 4-6 minutes; wherein the surface modification solution is: 0.5-2 wt% of aminopropyltriethoxysilane, 0.05-0.2 wt% of boric acid and the balance of ethanol;

B. placing the taken copper-based brake pad in a surface modification solution, and keeping the temperature at room temperature for 5-15 minutes; wherein the surface modification solution is: 0.5-2 wt% of dopamine, 0.5-2 wt% of hydrochloric acid with the concentration of 37 wt%, and the balance of water;

C. placing the taken copper-based brake pad in a surface modification solution, and keeping the temperature at room temperature for 4-6 minutes; wherein the surface modification solution is: 0.4-0.6 wt% of aminopropyltriethoxysilane, and the balance of N, N-dimethylformamide.

In the preparation method of the composite coating applied to the copper-based brake pad, in the step (7), the preparation of the surface polymer layer adopts one of the following processes:

A. putting the copper-based brake pad into the high polymer coating while the copper-based brake pad is hot, directly taking out, airing, putting into a 300-400 ℃ drying oven, keeping the temperature for 20-40 minutes, taking out, and cooling at room temperature; the high polymer coating comprises 5-15 wt% of polytetrafluoroethylene emulsion, 0.05-0.2 wt% of fumed silica, 0.05-0.2 wt% of nano aluminum oxide, 0.05-0.2 wt% of nano silicon carbide, 0.05-0.2 wt% of polyvinylpyrrolidone and the balance of a mixed solution of water and ethanol, wherein the weight ratio of the water to the ethanol is 1: 8-10;

B. putting the copper-based brake pad into the high polymer coating, directly taking out, airing, placing in a drying oven at 400-500 ℃ for keeping the temperature for 10-30 minutes, taking out, and cooling at room temperature; wherein the high polymer coating comprises 5-15 wt% of polyether-ether-ketone, 4-6 wt% of sodium silicate, 0.05-0.2 wt% of nano aluminum oxide, 0.05-0.2 wt% of nano silicon carbide and the balance of water;

C. Putting the copper-based brake pad into the high polymer coating, directly taking out, airing, putting into a vacuum oven at 200-400 ℃, keeping the temperature for 1-3 h, taking out, and cooling at room temperature; wherein the high molecular coating comprises 4-6 wt% of polyamic acid, 0.05-0.2 wt% of fumed silica, 0.05-0.2 wt% of nano alumina, 0.05-0.2 wt% of nano silicon carbide, 0.05-0.2 wt% of polyvinylpyrrolidone and the balance of dimethylformamide.

the design idea of the invention is as follows:

The main component of the copper-based brake pad is copper, the copper-based brake pad is prepared by a high-temperature high-pressure powder metallurgy manufacturing method, and the main component is copper powder, graphite powder and other components. In this process, the temperature rises sharply due to the generation of a great amount of heat during the rubbing process, so that the corrosion behavior thereof is intensified, thereby affecting the rubbing performance thereof. On one hand, the corrosion behavior at high temperature is unstable due to copper, and on the other hand, the electrochemical corrosion is intensified due to the transfer of electrons into graphite due to the electric conduction of graphite. In order to prevent the two factors which cause the unstable composition of the copper-based brake pad, the invention designs two layers of coatings to protect the copper-based brake pad, the inner coating mainly protects the copper powder which is the main component of the copper-based brake pad from being damaged, and the outer coating mainly utilizes a non-conductive high polymer material to prevent electron transfer and can form the functions of hydrophobic protection, friction coefficient stabilization and the like.

in the design of the inner coating, in order to realize the high-temperature stability of the copper-based brake pad, the invention adopts coatings of nickel, titanium, chromium and the like. The metal coating can increase the high-temperature stability of the copper-based brake pad through passivation reaction to stabilize the composition stability of the copper-based brake pad. In the design of the outer coating, the functions of hydrophobic protection and barrier protection are required to be considered at the same time, and the conductivity is considered to prevent electron transfer at the same time.

The invention has the advantages and beneficial effects that:

1. The invention relates to a composite coating applied to a copper-based brake pad, which mainly comprises the following raw materials: the inner layer is a nickel, chromium or titanium coating, and the outer layer is a polyimide, polytetrafluoroethylene or polyether-ether-ketone coating. According to the scheme, the main components in the inner layer coating are respectively nickel, chromium or titanium, the main components in the outer layer coating are respectively polyimide, polytetrafluoroethylene and polyether ether ketone, and the outer layer coating further contains alumina, silicon carbide, graphite and the like. The invention has the advantages of reduced surface porosity, reduced surface defects and stable mechanical properties of the copper-based brake pad.

2. the surface hydrophobic modification reduces the influence of humidity on the copper-based brake pad, and stabilizes the performance of the copper-based brake pad in dry and humid environments.

3. the metal passive film on the surface of the brake pad reduces the influence of temperature on the copper-based brake pad and stabilizes the influence of temperature change of the copper-based brake pad after multiple times of braking on the copper-based brake pad.

description of the drawings:

FIG. 1 is a schematic diagram of a copper-based brake pad coating. In the figure, 1 a copper-based brake pad, 2 a copper-based brake pad surface modification layer, 3 an electroless plating layer, 4 an adhesive layer and 5a surface macromolecule layer.

FIG. 2 is a state diagram of a copper-based brake pad with and without a coating at high temperature; fig. 2(a) shows an uncoated state, and fig. 2(b) shows a coated state.

FIG. 3 is a state diagram of a copper-based brake pad with and without a coating in a wet environment; fig. 2(a) shows an uncoated state, and fig. 2(b) shows a coated state.

FIG. 4 is a state diagram of the copper-based brake pad containing the coating during friction.

The specific implementation mode is as follows:

in the specific implementation process, the composite coating applied to the copper-based brake pad is a composite coating consisting of two surface coatings. The inner layer coating is prepared into a metal or alloy coating, and comprises a metal or alloy coating which can form a passivation layer at room temperature and high temperature, such as nickel, chromium, titanium and the like; the outer coating is a polymer and ceramic composite coating, comprises polyimide, polytetrafluoroethylene, polyether ether ketone and other polymer coatings with high temperature stability, hydrophobicity and better friction performance, and may contain ceramic additives such as alumina, silicon carbide, silicon dioxide and the like.

the present invention will be explained in further detail below by way of examples and figures.