CN103422047A - Preparation method for boron carbide-molybdenum composite coating layer - Google Patents

Abstract

The invention discloses a method for preparing a boron carbide-molybdenum composite coating. The method is to spray B ₄ C-Mo composite powder on a metal substrate by adopting vacuum plasma spraying technology. Compared with the prior art, the coefficient of friction of the boron carbide-molybdenum composite coating prepared by the method of the invention is significantly lower than that of the pure _B4C coating, and the wear resistance has been significantly improved; moreover, the preparation method of the invention is simple , can produce a coating with a thickness of more than 200 μm, which can meet the wide application requirements in the field of friction and wear resistance, and has practical value.

Description

A kind of method for preparing boron carbide-molybdenum composite coating

technical field

The invention relates to a method for preparing a boron carbide coating, in particular to a method for preparing a boron carbide-molybdenum composite coating, and belongs to the technical field of wear-resistant materials.

Background technique

Ceramic-metal composite coatings, such as WC-Co, Cr ₃ C ₂ -Mo, Mo ₂ C-Mo, etc., have received more and more attention in recent years. The emergence of these composite coatings provides a possibility to improve the structure of ceramic coatings, and all of them show better wear resistance than pure ceramic coatings. Boron carbide is a non-oxide ceramic with extremely strong covalent bonds and extremely high hardness, second only to diamond and cubic boron nitride. It is a coating material that is expected to be widely used in the field of anti-friction and wear. Metal molybdenum has excellent properties such as high hardness, good wear resistance, corrosion resistance, adhesion resistance and corrosion resistance to molten copper and iron, and its high thermal conductivity, low expansion coefficient and excellent thermal shock resistance make it a One of the important materials of modern industry. Molybdenum coating has excellent resistance to adhesive wear, but the wear resistance of the coating is poor under high load; while boron carbide has high hardness and has excellent wear resistance. Combining molybdenum with boron carbide can improve the anti-adhesive wear ability of boron carbide pure coating, and at the same time, it can meet the requirements of the coating under high load. In addition, the thermal conductivity of molybdenum is higher than that of boron carbide. The introduction of molybdenum will facilitate the diffusion of heat during the friction process and further improve the wear resistance of the coating. But so far there is no technical report on how to prepare boron carbide-molybdenum composite coating.

Contents of the invention

In view of the above problems in the prior art, the object of the present invention is to provide a method for preparing a boron carbide-molybdenum composite coating, so as to realize the application of the boron carbide-molybdenum composite coating in the field of friction and wear resistance.

For realizing above-mentioned purpose of the invention, the technical scheme that the present invention adopts is as follows:

A method for preparing a boron carbide-molybdenum composite coating is to spray B ₄ C-Mo composite powder on a metal substrate by using a vacuum plasma spraying technology.

As a preferred solution, the metal substrate is stainless steel.

As a preferred solution, the process parameters for vacuum plasma spraying are as follows: the flow rate of plasma gas Ar is 35 to 50 standard liters/minute; the flow rate of plasma gas _H is 8 to 18 standard liters/minute; the flow rate of powder carrier gas Ar is The spraying distance is 120-250 mm; the spraying current is 600-700 amps; the spraying pressure is 300-600 mbar; the feeding rate is 15-30 rpm.

As a preferred solution, the molybdenum content in the B ₄ C-Mo composite powder is 5-15 vol% (volume percent).

As a preferred solution, the B ₄ C-Mo composite powder is prepared from boron carbide powder and molybdenum powder by mechanical ball milling.

As a further preferred solution, the particle size of the boron carbide powder is -325 to +1600 mesh, and the particle size of the molybdenum powder is -200 to +400 mesh.

Compared with the prior art, the coefficient of friction of the boron carbide-molybdenum composite coating prepared by the method of the invention is significantly lower than that of the pure _B4C coating, and the wear resistance has been significantly improved; moreover, the preparation method of the invention is simple , can produce a coating with a thickness of more than 200 μm, which can meet the wide application requirements in the field of friction and wear resistance, and has practical value.

Description of drawings

Figure 1 is the XRD pattern of the B ₄ C-Mo composite powder prepared in Example 1 before and after forming the coating, in the figure: a represents the XRD pattern of the powder before forming the coating; b represents the coating after forming the coating The XRD pattern.

Fig. 2 is a scanning electron micrograph of the cross-sectional morphology of the B ₄ C-Mo composite coating prepared in Example 1.

Fig. 3 is a scanning electron micrograph of the surface morphology of the B ₄ C-Mo composite coating prepared in Example 1.

Fig. 4 is the friction coefficient curve of the B ₄ C-Mo composite coating prepared in Example 1 and the pure B ₄ C coating under different loads, in the figure: a represents the friction coefficient of the pure B ₄ C coating and the relationship between the load Relationship curve; b represents the relationship curve between friction coefficient and load of B ₄ C-Mo composite coating.

Detailed ways

The present invention will be further described in detail and completely through the embodiments and accompanying drawings below.

Example 1

a) Preparation of B ₄ C-Mo composite powder

According to the molybdenum volume content of 10%, respectively weigh boron carbide powder with a particle size of -325 ~ +1600 mesh and molybdenum powder with a particle size of -200 ~ +400 mesh, and mechanically mix them in a rotary vibrating ball mill. The rotation speed of the ball mill tank is set The speed is 400rpm, and the ball-to-material ratio (mass ratio) is 2:1. After ball milling for 48 hours, the ball mill jar was removed, the composite powder was sieved through 400 mesh, dried in a drying oven at 70°C, and set aside.

b) Preparation of coating

1) Pretreatment of the stainless steel substrate: place the stainless steel disc substrate (Φ50mm×Φ6.5mm×7mm) treated by sandblasting (sandblasting pressure 0.2MPa) in an anhydrous ethanol solution for 5 minutes, Dry at 100°C for 1 hour for later use;

2) Vacuum plasma spraying technology was used to prepare a coating on the treated stainless steel wafer substrate; the process parameters for vacuum plasma spraying were as follows: the flow rate of plasma gas Ar was 42 standard liters/minute; the flow rate of plasma gas _H2 The powder carrier gas Ar flow rate is 3 standard liters/minute; the spraying distance is 200 mm; the spraying current is 650 amperes; the spraying pressure is 400 mbar; the feeding rate is 22 rpm; the sprayed powder The body is the B ₄ C-Mo composite powder prepared in step a).

The pure B ₄ C coating was prepared by spraying B ₄ C powder on the treated stainless steel wafer substrate according to the above-mentioned vacuum plasma spraying process parameters.

Figure 1 is the XRD pattern of the B ₄ C-Mo composite powder prepared in this example before and after forming the coating, in the figure: a represents the XRD pattern of the powder before forming the coating; b represents the coating after forming the coating The XRD pattern of the coating; it can be seen from Figure 1 that the composition and structure of the coating after spraying have not changed significantly compared with the original powder.

Figure 2 is a scanning electron micrograph of the cross-sectional morphology of the B ₄ C-Mo composite coating prepared in this example; it can be seen from Figure 2 that the prepared B ₄ C-Mo composite coating has a typical layered structure, and the Mo The distribution near the substrate is more than that near the surface, which may be due to the higher density of Mo than B ₄ C.

Fig. 3 is the scanning electron micrograph of the surface morphology of the B ₄ C-Mo composite coating prepared in this example; it can be seen from Fig. 3 that the B ₄ C-Mo composite powder has been melted well during the spraying process, and the molten droplets Spread more fully on the coating surface.

After a series of grinding and polishing processes (the surface roughness is about 0.2μm), the coated friction disc is combined with a Φ9.525mm WC-Co cemented carbide ball (hardness HRC92) to form a ball-disc (Ball -on-disk) contact grinding. The wear test equipment is the UMT-3 multifunctional friction and wear tester of the American CETR company. The wear test conditions are: load 20N, 30N, 40N and 50N, line speed 0.5m/s, friction time 1800s.

Fig. 4 is the friction coefficient curve of the B ₄ C-Mo composite coating prepared in this example and the pure B ₄ C coating under different loads, in the figure: a represents the friction coefficient and the load of the pure B ₄ C coating Relationship curve; b represents the relationship curve between friction coefficient and load of B ₄ C-Mo composite coating. It can be seen from Figure 4 that the friction coefficient of the prepared B ₄ C-Mo composite coating under different loads is lower than that of the pure B ₄ C coating, and the wear resistance is more excellent.

Example 2

The difference between this example and Example 1 is that the boron carbide powder with a particle size of -325 to +1600 mesh and the molybdenum powder with a particle size of -200 to +400 mesh are respectively weighed according to the molybdenum volume content of 5%, and the mechanical The B ₄ C-Mo composite powder was prepared by ball milling; the vacuum plasma spraying process parameters for spraying the prepared B ₄ C-Mo composite powder on the treated stainless steel wafer substrate are as follows: plasma gas Ar flow rate The flow rate of plasma gas _H2 is 10 standard liters/minute; the flow rate of powder carrier gas Ar is 2 standard liters/minute; the spraying distance is 220 mm; the spraying current is 600 amperes; the spraying pressure is 400 mbar ; The feed rate is 15 rpm.

The rest of the content is the same as described in Example 1.

The friction coefficients of the prepared B ₄ C-Mo composite coatings under different loads are shown in Table 1.

Example 3

The difference between this example and Example 1 is that the boron carbide powder with a particle size of -325 to +1600 mesh and the molybdenum powder with a particle size of -200 to +400 mesh are respectively weighed according to the molybdenum volume content of 15%; The vacuum plasma spraying process parameters of the prepared B ₄ C-Mo composite powder sprayed on the treated stainless steel wafer substrate are as follows: the flow rate of plasma gas Ar is 40 standard liters/minute; the flow rate of plasma gas H ₂ is 15 Standard liters per minute; powder carrier gas Ar flow rate of 4 standard liters per minute; spraying distance of 180 mm; spraying current of 700 amperes; spraying pressure of 400 mbar; feed rate of 30 revolutions per minute.

The rest of the content is the same as described in Example 1.

The friction coefficients of the prepared B ₄ C-Mo composite coatings under different loads are shown in Table 1.

Table 1 Friction coefficients of various coatings under different loads

Coating samples 20N 30N 40N 50N Pure B ₄ C Coating 0.330 0.260 0.232 0.227 Example 2 0.315 0.235 0.213 0.210 Example 3 0.165 0.170 0.195 0.215

It can be seen from Table 1 that the friction coefficient of the prepared B ₄ C-Mo composite coating under different loads is lower than that of the pure B ₄ C coating, indicating that the B ₄ C-Mo composite coating with excellent wear resistance can be obtained by the method of the present invention. Mo composite coating.

Finally, it is necessary to point out that: the above examples are only used to further describe the technical solutions of the present invention in detail, and should not be interpreted as limiting the protection scope of the present invention. Essential improvements and adjustments all belong to the protection scope of the present invention.

Claims (6)

1. A method for preparing a boron carbide-molybdenum composite coating, characterized in that: a vacuum plasma spraying technique is used to spray B ₄ C-Mo composite powder on a metal substrate. 2. The method for preparing boron carbide-molybdenum composite coating according to claim 1, characterized in that: the metal substrate is stainless steel. 3. the method for preparing boron carbide-molybdenum composite coating according to claim 1, is characterized in that, the process parameter that carries out vacuum plasma spraying is as follows: plasma gas Ar flow rate is 35～50 standard liters/minute; The gas _H2 flow rate is 8-18 standard liters/minute; the powder carrier gas Ar flow rate is 2-4 standard liters/minute; the spraying distance is 120-250 mm; the spraying current is 600-700 amperes; the spraying pressure is 300-600 mm bar; the feeding rate is 15-30 rpm. 4 . The method for preparing a boron carbide-molybdenum composite coating according to claim 1 , wherein the content of molybdenum in the B ₄ C-Mo composite powder is 5-15 vol%. 5. The method for preparing a boron carbide-molybdenum composite coating according to claim 1, characterized in that: the B ₄ C-Mo composite powder is prepared by mechanical ball milling of boron carbide powder and molybdenum powder And get. 6. The method for preparing a boron carbide-molybdenum composite coating according to claim 5, characterized in that: the particle size of the boron carbide powder is -325 to +1600 mesh, and the particle size of the molybdenum powder is - 200～+400 mesh.

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