CN111850453A

CN111850453A - Chromium oxide-based antifriction coating and preparation method thereof

Info

Publication number: CN111850453A
Application number: CN201910363585.6A
Authority: CN
Inventors: 牛亚然; 涂文华; 李红; 洪督; 石旻昊; 钟鑫; 郑学斌
Original assignee: Shanghai Institute of Ceramics of CAS; University of Shanghai for Science and Technology
Current assignee: Shanghai Institute of Ceramics of CAS; University of Shanghai for Science and Technology
Priority date: 2019-04-30
Filing date: 2019-04-30
Publication date: 2020-10-30

Abstract

The invention relates to a chromium oxide-based antifriction coating and a preparation method thereof, and the chromium oxide-based antifriction coating comprises Cr₂O₃A main phase and Cr dispersed in the above-mentioned₂O₃And the h-BN second phase in the main phase contains 1-10 wt.%, preferably 1-7 wt.%.

Description

Chromium oxide-based antifriction coating and preparation method thereof

Technical Field

The invention relates to a chromium oxide-based antifriction coating and a preparation method thereof, belonging to the field of wear-resistant coatings.

Background

In recent years, with the rapid development of science and technology, the requirement of a severe working environment on a wear-resistant coating is gradually increased, and oil-free self-lubrication is difficult to realize by a single-phase ceramic coating under the service condition that lubricating oil cannot be used partially or the lubricating oil fails at high temperature (such as between a piston and a sleeve of an internal combustion engine), so that the design of the wear-resistant coating with excellent wear resistance and low friction coefficient under the dry friction condition is necessary. Comparative analysis of plasma sprayed hard coatings WC-Mo, Cr has been reported₃C₂-Mo, TiC-Mo and Al₂O₃-TiO₂In the wear performance under the dry friction condition, the friction coefficient and the wear rate of the coatings are high no matter at 25 ℃, 425 ℃ or 725 ℃, and the coatings cannot be practically applied. And Cr ₂O₃Exhibit good Wear resistance under certain conditions (reference 1B. Q. Wang, R.S. Zheng, Sliding Wear of thermal-sprayed chromium coatings, Wear,1990,138: 93-110.). Cr (chromium) component₂O₃As a traditional wear-resistant coating, the ceramic coating is widely applied to the fields of maritime affairs, chemical engineering, automobiles and the like due to the excellent comprehensive properties of the ceramic coating, such as high melting point, high hardness, excellent wear resistance, high-temperature chemical stability and the like. J.H.Ouyang et al use in Cr₂O₃Self-lubricating phase CaF is introduced into coating₂And Ag₂O, at room temperature to 800 ℃ with Al₂O₃The results of the ball-on-ball grinding study on the tribological properties of the coating show that the friction coefficient of the composite coating is very high (0.75-0.82) at room temperature, and gradually decreases with increasing temperature (document 2j.h.ouyang, s.sasaki, Effects of differential additives on microstructural and high-temperature tribological properties of plasma-layer)d Cr₂O₃ceramifications, Wear,2001,249: 56-67.). Middle CaF₂There is little lubrication effect at low temperatures. As a solid lubricant, hexagonal boron nitride (h-BN) has a layered crystal structure similar to graphite, does not bring black pollution like graphite, and has the oxidation resistance temperature in the air as high as 900 ℃ which is obviously superior to that of graphite (450 ℃) and MoS ₂(400 ℃), the using temperature of nitrogen or inert atmosphere is as high as 2800 ℃, and the lubricating effect is more obvious under the high-temperature condition, and the application prospect is wide.

Among various thermal spraying techniques, the atmospheric plasma spraying technique has the characteristics of high plasma flame flow temperature, high powder deposition efficiency, wide spraying material range and the like, is most widely applied, and is particularly suitable for spraying high-melting-point coating materials.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a chromium oxide-based composite coating with self-lubricating and antifriction characteristics and a preparation method thereof.

In one aspect, the present invention provides a chromium oxide based friction reducing coating comprising a composition comprising Cr₂O₃A main phase and Cr dispersed in the above-mentioned₂O₃And a second h-BN phase in the main phase, wherein the content of the h-BN in the second h-BN phase is 1-10 wt.%, preferably 1-7 wt.%.

The chromium oxide-based composite coating provided by the invention is made of Cr₂O₃As a main phase, and dispersed in the Cr₂O₃The main phase is an h-BN second phase with self-lubricating property. Has high hardness, good chemical stability and wear resistance. The h-BN crystal structure with self-lubricating property is similar to graphite, solid lubrication can be performed on the surface of the coating in the friction and wear process, the friction coefficient is reduced, meanwhile, the friction heat generated in the friction and wear process causes the scattered point temperature of the surface of the coating to rise, and BN generates oxidation reaction to generate B ₂O₃，B₂O₃Covering the surface of the coating to protect the coating from further wear and thereby serving to reduce the coefficient of friction and the rate of wear. The chromium oxide-based antifriction coating provided by the invention is in frictionB is generated by the oxidation reaction of the h-BN second phase in the rubbing abrasion process (simulation environment test at room temperature)₂O₃The friction film as the main component is covered on the surface of the coating.

Preferably, the thickness of the chromium oxide-based antifriction coating is 100-500 μm, and preferably 200-400 μm.

On the other hand, the invention also provides a preparation method of the chromium oxide-based antifriction coating, and Cr is selected₂O₃Preparing the chromium oxide-based antifriction coating on the surface of the matrix by using atmospheric plasma spraying technology by taking BN composite powder as a raw material; the parameters of the atmospheric plasma spraying process are as follows: the flow of Ar of the plasma gas is 30-50 slpm; plasma gas H₂The flow rate is 5-20 slpm; powder feeding carrier gas Ar: 2-7 slpm; powder feeding rate of raw materials: 10-25 rpm; spraying distance: 100-150 mm; the spraying power is as follows: 30-55 kW.

Preferably, the Cr is₂O₃The particle size distribution range of the-BN composite powder is 20-100 mu m.

Preferably, the Cr is₂O₃the-BN composite powder contains Cr₂O₃The preparation method of the composite powder of the powder and the h-BN powder comprises the following steps: mixing Cr ₂O₃Adding a solvent and a binder into the powder and the h-BN powder to obtain slurry;

spray granulating and drying the obtained slurry to obtain the Cr-containing slurry₂O₃Powder and h-BN powder.

Preferably, the Cr is₂O₃The particle size distribution range of the powder is 1-8 mu m; the particle size distribution range of the h-BN powder is 1-8 mu m.

Preferably, the substrate is a metal substrate, an alloy substrate, a graphite substrate or a carbon/carbon composite substrate.

In addition, when the substrate is a metal substrate or an alloy substrate, the surface of the substrate is preferably provided with a NiCr transition layer; when the matrix is a graphite matrix or a carbon/carbon composite material matrix, the surface of the matrix is provided with a SiC transition layer.

Also, preferably, the surface of the substrate is subjected to a pretreatment including ultrasonic cleaning and sand blast roughening.

In the invention, the chromium oxide-based antifriction coating is made of pure Cr₂O₃The coating is prepared by further modifying the coating, and the frictional wear performance of the coating is improved. Moreover, the self-lubricating phase (second phase) in the obtained coating can play a role in lubricating and reducing the friction coefficient on the surface of the coating in the friction and wear process, and has good friction and wear resistance.

Drawings

FIG. 1 shows Cr prepared in example 1₂O₃-a microstructure map (a) and an EDS map (b) of 5 wt.% BN composite powder;

FIG. 2 shows Cr prepared in example 1₂O₃-a surface topography map of 5 wt.% BN composite coating;

FIG. 3 shows Cr prepared in example 1₂O₃-a cross-sectional topography of 5 wt.% BN composite coating;

FIG. 4 shows Cr prepared in example 1₂

O

₃5 wt.% BN composite coating with pure Cr prepared in comparative example 1₂O₃The average friction coefficient (a) and the wear rate (b) of the coating at 50N load are respectively compared with the average friction coefficient (a) and the wear rate (b) of a WC-Co friction pair;

FIG. 5 shows Cr prepared in example 1₂O₃The cross-sectional morphology (a) of a friction film generated by the abraded surface of the 5 wt.% BN composite coating and the WC-Co friction pair and the corresponding element distribution maps (O element and B element);

FIG. 6 shows Cr prepared in example 2₂

O

₃10 wt.% BN composite coating with Cr prepared in example 1₂

O

₃5 wt.% BN composite coating and pure Cr prepared in comparative example 1₂O₃The average friction coefficient (a) and the wear rate (b) of the coating at 50N load are respectively compared with the average friction coefficient (a) and the wear rate (b) of a WC-Co friction pair;

FIG. 7 shows pure Cr prepared in comparative example 1₂O₃Surface topography (a) and cross-sectional topography (b) of the coating.

Detailed Description

The present invention is further illustrated by the following examples, which are to be understood as merely illustrative and not restrictive.

In this disclosure, the chromium oxide based friction reducing coating (also called self-lubricating friction reducing coating) is Cr₂O₃Using Cr as a main phase₂O₃The coating has high hardness and excellent wear resistance, so that the coating has good wear resistance; meanwhile, h-BN is used as a second phase (the content of the h-BN accounts for 1-10 wt.%), and the self-lubricating property of the h-BN can further reduce the friction coefficient and the wear rate of the coating, so that the coating has the wear-reducing property, and the service life of the coating is prolonged.

In an alternative embodiment, the h-BN content may be 1 to 7 wt.%. If the content of the BN is excessive, agglomeration phenomenon may exist in the coating, and due to the fact that the hardness of the BN is low, micro cracks are prone to appear in a BN enrichment area under the condition of high load and the coating is prone to be peeled off in the subsequent abrasion process, the abrasion rate of the coating is increased; meanwhile, the surface roughness of the coating is increased due to the peeling of the coating, so that the friction coefficient of the coating is easily increased.

In an alternative embodiment, the thickness of the chromium oxide-based friction reducing coating may be 100 to 500 μm, preferably 200 to 400 μm.

In the disclosure, the chromium oxide-based antifriction coating (also called self-lubricating antifriction coating) can be prepared into Cr by adopting a spray granulation method₂O₃Preparing a chromium oxide-based antifriction coating (namely, Cr) on the surface of a substrate by adopting an atmospheric plasma spraying technology ₂O₃-BN composite coating). As an example, Cr is prepared by introducing a self-lubricating phase hexagonal boron nitride into a chromium oxide powder₂O₃-BN composite powder, which is sprayed on the surface of the pretreated substrate by adopting a plasma spraying technology to prepare Cr₂O₃-a BN composite coating. The following specifically describes the preparation method of the chromium oxide-based antifriction coating provided by the invention.

Cr₂O₃Preparing BN composite powder. The Cr is₂O₃the-BN composite powder is prepared by a spray granulation method. Weighing a certain proportion of Cr₂O₃Adding solvent and binder into powder and BN powder to prepare slurryAnd (5) feeding. Wherein the solvent can be water, alcohol, etc. The binder may be polyvinyl alcohol, polyvinyl butyral, or the like. The binder may be added in an amount of Cr₂O₃15-20 wt% of the total mass of the powder and the BN powder. Then the slurry and zirconia balls are put into a ball milling tank together, and are ball milled in a planetary ball mill for a period of time (for example, the ball milling speed is 300r/min, and the ball milling time is 20 min). And finally, taking out the slurry, conveying the slurry into a spray granulator for spray treatment and drying to prepare the composite powder. Wherein, Cr₂O₃The particle size of the powder and the BN powder can be 1-8 mu m. Spray granulation process parameters may include: the inlet temperature is 200-240 ℃; the outlet temperature is 100-140 ℃; the feeding speed is 25-35 rpm; the rotor speed is 15000-18000 rpm. Obtained Cr ₂O₃The particle size range of the/h-BN composite powder can be 20-100 mu m.

A substrate is prepared. The substrate may be a metal or alloy with a NiCr transition layer, or a graphite or carbon/carbon composite with a SiC transition layer. Preferably, the substrate is first subjected to a pretreatment including grit blasting roughening, ultrasonic cleaning and drying. When metal or alloy is adopted as a substrate, the NiCr transition layer is prepared by spraying NiCr powder on the surface of the treated metal or alloy by a plasma spraying technology. When graphite or a carbon/carbon composite material is used as a matrix, a Si coating is prepared on the surface of the pretreated graphite or carbon-carbon composite material by a plasma spraying technology, and the graphite or carbon/carbon composite material added with the Si coating is subjected to high-temperature heat treatment under the protection of inert atmosphere (such as argon) to form a SiC transition layer. Alternatively, the SiC coating can be obtained by an embedding method using Si powder, C powder, or the like as a raw material, and then performing reaction heat treatment under the protection of an inert atmosphere (such as argon). Alternatively, the SiC coating may be deposited directly by a CVD process.

And preparing the chromium oxide-based antifriction coating. Preparing Cr on the surface of a substrate by adopting an atmospheric plasma spraying technology₂O₃-a BN composite coating. For example, the composite coating is prepared by spraying the composite powder on the surface of the C/C composite material by using an atmospheric plasma spraying technology. Wherein, the plasma spraying process parameters can include: the flow rate of the plasma gas Ar is 30-50 slpm, Preferably 35-45 slpm; plasma gas H₂The flow rate is 5-20 slpm, and preferably 7-15 slpm; the powder feeding carrier gas Ar is 2-7 slpm; powder feeding rate: 10-25 rpm; spraying distance: 100-150 mm; the spraying power is as follows: 30-55 kW, the slpm refers to standard liter/min, and the rpm refers to revolution/min.

The composite coating prepared by the invention has excellent wear-reducing and wear-resisting properties, can obviously improve the wear resistance of the high-purity chromium oxide coating and reduce the friction coefficient, and can be applied to the fields of chemical industry, maritime affairs, metallurgy and the like to prolong the service life of parts. The preparation method has the advantages of low cost, high efficiency, simple process, large-scale production and the like.

The present invention will be described in detail by way of examples. It is also to be understood that the following examples are illustrative of the present invention and are not to be construed as limiting the scope of the invention, and that certain insubstantial modifications and adaptations of the invention by those skilled in the art may be made in light of the above teachings. The specific process parameters and the like of the following examples are also only one example of suitable ranges, i.e., those skilled in the art can select the appropriate ranges through the description herein, and are not limited to the specific values exemplified below.

Example 1:

preparation of Cr on surface of carbon/carbon composite material with SiC transition layer₂O₃-BN composite coating consisting of Cr₂O₃As the main phase, h-BN as the second phase.

The preparation steps of the coating are as follows:

step 1): weighing a certain proportion of Cr₂O₃Powder and h-BN powder, the Cr₂O₃The particle size of the powder and BN powder can be 1-8 mu m, wherein the second phase h-BN accounts for 5 wt% of the total mass of the powder, water and a binder are stirred and mixed to prepare slurry, the slurry and zirconia balls are put into a ball milling tank to be ball milled for 20min in a planetary ball mill, the slurry is taken out and conveyed into a spray granulator to be spray-dried to obtain Cr₂O₃-BN composite raw material powder for standby. Spray granulation process parametersSee table 1.

Table 1 shows the technological parameters for preparing Cr2O3-BN composite powder by spray granulation:

inlet temperature	Outlet temperature	Feed rate	Rotor speed
				220℃	100℃	35rpm	15000rpm

Step 2): and ultrasonically cleaning the carbon/carbon composite material matrix with the SiC transition layer for 3 times, 10min each time, and drying in a drying oven at 100 ℃ for later use.

Step 3): spraying the composite powder on the surface of a carbon/carbon composite material with a SiC transition layer by adopting a plasma spraying system (A-2000, Sulzer Metco AG, Switzerland), wherein the thickness of the coating is 300 mu m; the spray process parameters are seen in table 2.

Table 2 shows the process parameters of the atmospheric plasma spraying of the Cr2O3-BN composite coating:

plasma gas Ar	40slpm	Distance of spraying	110mm
				Plasma gas H₂	11slpm	Powder feeding rate	18rpm
Spraying power	45kW	Powder carrier gas Ar	3.5slpm

Slpm: standard liters per minute.

FIG. 1 shows Cr₂O₃-surface and cross-section scanning electron micrographs of the BN composite powder. The composite powder has good sphericity and good powder fluidity, and is suitable for plasma spraying. FIG. 2 and FIG. 3 are each Cr₂O₃Scanning electron micrographs of the surface and the cross section of the BN composite coating, it can be seen that the thickness of the resulting composite coating is 200 μm. The flatness of the particles on the surface of the coating is high, the molten state is good, and the coating and the matrix in the cross section are tightly combined.

Calculating the friction coefficient by a self-contained formula of a friction and wear instrument system, and directly reading the friction coefficient through an instrument display; measuring the cross section of a grinding crack by using a contourgraph, and calculating the wear rate W of the coating by using a formula 1: w ═ 2 pi RS/DN);

in the formula: r-radius of gyration upon wear; s, grinding scar sectional area; d, friction stroke; N-Friction test load. The samples were measured three times and averaged.

Using a friction and wear meter to measure Cr₂O₃The friction and wear performance of the BN composite coating is evaluated, and the evaluation conditions are as follows: the surface of the coating was polished and the sample was then ground by ball-disk abrasion under a 50N load at 0.5m/s speed for 30min against a WC-Co cermet friction pair.

FIG. 4 shows pure Cr₂O₃Coating and Cr₂O₃The friction coefficient (a) and wear rate (b) of the WC-Co friction pair counter-wear at 50N load are plotted against 5 wt.% BN composite coating, respectively. Pure Cr₂O₃The average friction coefficient of the coating to WC-Co is 0.54 + -0.08, while Cr₂O₃The average friction coefficient of the-BN composite coating and WC-Co is 0.38 +/-0.01, and the average friction coefficient of the coating is reduced by about 30% due to the introduction of the self-lubricating phase h-BN. It can also be seen from the comparison of the wear rates in FIG. 4 (b) that with the introduction of h-BN, the wear rate of the coating is greatly reduced, pure Cr₂O₃The wear rate of the coating was (34. + -. 10). times.10^-6mm³/Nm, the wear rate of the composite coating is (5.6 +/-0.9) multiplied by 10^-6mm³In Nm, the wear rate is reduced by about 83%. Obviously, the introduction of the self-lubricating phase h-BN obviously reduces the friction coefficient and the wear rate of the coating and improves the pure Cr₂O₃Frictional wear properties of the coating. The coating system designed by the invention has good antifriction and wear-resistant performance. FIG. 5 shows Cr₂O₃And (b) generating a friction film cross-sectional morphology (a) and a corresponding element distribution diagram by oppositely rubbing the 5 wt.% BN composite coating and the WC-Co friction pair on the abraded surface. As can be seen from (a) in FIG. 5, a dense friction film is formed on the surface of the composite coating, the thickness is about 1 μm to 2.56 μm, and the friction film is mainly composed of B and O elements in combination with the corresponding element distribution diagram of the friction film, when the composite coating is rubbed with WC-Co with higher hardness under high load, the temperature of the friction contact area is correspondingly increased along with the increase of friction heat in the abrasion process, and BN is oxidized to form B ₂O₃(4BN+O₂＝2B₂O₃+2N₂). With B₂O₃The friction film which is the main component uniformly covers the surface of the coating, protects the coating from further abrasion and plays a role in reducing the friction coefficient and the abrasion rate at the same time.

Example 2

Preparation of Cr on surface of carbon/carbon composite material with SiC transition layer₂O₃-BN composite coating consisting of Cr₂O₃As the main phase, h-BN as the second phase, see example 1 for a specific preparation procedure, except that 10 wt.% of h-BN is added.

The frictional wear performance of the composite coating obtained in the example 2 was evaluated under the same conditions as in the example 1, and the specific parameters include: the wear is in the form of ball-and-disc wear; the friction pair is a WC-Co cermet material; the load is 50N; the speed is 0.5 m/s; the abrasion time was 30 min.

FIG. 6 shows Cr₂O₃10 wt.% BN composite coating with Cr₂O₃-5 wt.% BN composite coating and pure Cr₂O₃The coating was plotted against the mean friction coefficient (a) and wear rate (b) of WC-Co on-mill at 50N load, respectively. By comparison, it was found that although the addition of 10 wt.% BN resulted in pure Cr₂O₃The friction coefficient and the wear rate of the coating and the WC-Co friction pair are obviously reduced, but the wear reducing effect is not as good as that of the Cr prepared in the example 1₂O₃-5 wt.% BN composite coating. And Cr₂O₃Higher BN addition than 5 wt.% BN composite coating, Cr ₂O₃5 wt.% BN composite coating exhibiting an increased friction coefficient and wear rate, Cr₂O₃-5 wt.% BN composite coating increasing the coefficient of friction from 0.38 ± 0.01 to 0.41 ± 0.03; the wear rate is from (5.6 +/-0.9) multiplied by 10^- ⁶mm³Increase in/Nm to (9.0. + -. 3.8). times.10^-6mm³in/Nm. The wear resistance of the coating was compared to that of Cr prepared in example 1₂O₃The reduction in-5 wt.% BN composite coating was due to the increased amount of h-BN added.

Comparative example 1:

pure Cr is prepared on the surface of the carbon/carbon composite material with the SiC transition layer by adopting the same plasma spraying process conditions in the example 1₂O₃And (4) coating.

Pure Cr was treated under the same conditions as in example 1₂O₃And (5) evaluating the frictional wear performance of the coating.

FIG. 7 shows pure Cr₂O₃The surface (a) and the section (b) of the coating are shown in the shape and figure, and the observation shows that more unmelted and semi-melted particles exist on the surface of the coating, and the melting state of the surface of the coating is not as good as that of the Cr prepared in the example 1₂

O

₃5 wt.% BN composite coating (see fig. 2).

Claims

1. A chromium oxide-based friction reducing coating is characterized in that the composition of the chromium oxide-based friction reducing coating comprises Cr₂O₃A main phase and Cr dispersed in the above-mentioned₂O₃And the h-BN second phase in the main phase contains 1-10 wt.%, preferably 1-7 wt.%.

2. A chromium oxide based friction reducing coating according to claim 1, characterized in that the thickness of the chromium oxide based friction reducing coating is 100 to 500 μm, preferably 200 to 400 μm.

3. A method for producing a chromium oxide based friction reducing coating according to claim 1 or 2, characterized in that Cr is selected₂O₃Preparing the chromium oxide-based antifriction coating on the surface of the matrix by using atmospheric plasma spraying technology by taking BN composite powder as a raw material; the parameters of the atmospheric plasma spraying process are as follows: the flow of Ar of the plasma gas is 30-50 slpm; plasma gas H₂The flow rate is 5-20 slpm; powder feeding carrier gas Ar: 2-7 slpm; powder feeding rate of raw materials: 10-25 rpm; spraying distance: 100-150 mm; the spraying power is as follows: 30-55 kW.

4. The method according to claim 3, wherein the Cr is₂O₃The particle size distribution range of the-BN composite powder is 20-100 mu m.

5. The method according to claim 3 or 4, wherein the Cr is present in an amount of₂O₃the-BN composite powder contains Cr₂O₃The preparation method of the composite powder of the powder and the h-BN powder comprises the following steps: mixing Cr₂O₃Adding a solvent and a binder into the powder and the h-BN powder to obtain slurry;

6. The method for preparing the compound of claim 5, wherein the process parameters of the spray granulation comprise: the inlet temperature is 200-240 ℃; the outlet temperature is 100-140 ℃; the feeding speed is 25-35 rpm; the rotor speed is 15000-18000 rpm.

7. The method according to claim 5 or 6, wherein the Cr is present in an amount of₂O₃The particle size distribution range of the powder is 1-8 mu m; the particle size distribution range of the h-BN powder is 1-8 mu m.

8. The method of any one of claims 3-7, wherein the substrate is a metal substrate, an alloy substrate, a graphite substrate, or a carbon/carbon composite substrate.

9. The method for preparing the alloy of any one of claim 8, wherein when the substrate is a metal substrate or an alloy substrate, the surface of the substrate is provided with a NiCr transition layer; when the matrix is a graphite matrix or a carbon/carbon composite material matrix, the surface of the matrix is provided with a SiC transition layer.