A method for producing a multilayer composite structure WC-based coating resistant to impact wear

Abstract

The application relates to a preparation method of a multilayer composite structure WC-based coating resistant to impact wear, belonging to the technical field of cermet coatings. High-hardness and high-toughness WC-Co coatings are alternately deposited on a base material by a thermal spraying process; under the premise of considering processing efficiency and cost, internal stress of the coating under external load is maximally reduced by controlling the number of layers and the thickness of each layer, so that the service life of the whole coating under the combined action of high-speed impact and repeated friction and the like is improved.

Description

TECHNICAL FIELD

[0001] The application relates to a preparation method of a multilayer composite structure WC-based coating with excellent impact wear resistance, and belongs to the technical field of cermet coatings. BACKGROUND

[0002] The thermal spraying WC-Co coating has the advantages of high bonding strength, high hardness, high wear resistance and the like, is widely applied to the fields of aerospace, petrochemical industry, metallurgical machinery and the like, and provides surface wear-resistant protection for metal parts. However, in some application fields, such as oil and gas exploitation and hard rock crushing, due to the combined action of high-speed impact and repeated friction and the like on the workpiece, the material peeling caused by wear and fracture of the existing single-layer homogeneous WC-based coating will be significantly accelerated. The main reason for the above result is that the single-layer homogeneous coating has a single composition, and it is usually difficult to take into account both high hardness and high toughness, when a microcrack is formed due to local high stress, the crack will rapidly expand to cause large material peeling. How to protect the base material under the combined action of impact and wear to make the service life of the workpiece longer has become a technical problem to be broken through in many engineering applications of the WC-based coating.

[0003] In view of the shortcomings of the single-layer homogeneous WC-based coating, the application proposes the idea of constructing a multilayer composite structure WC-based coating, that is, the multilayer composite structure coating is formed by alternately growing WC-based coatings with two or more different Co contents. By reasonably designing the composition and thickness of each layer, the internal stress of the coating can be effectively reduced, the crack initiation under the action of impact load can be reduced, and then the impact toughness and wear resistance of the coating can be simultaneously improved. SUMMARY

[0004] The process flow and principle of the preparation method provided by the application are as follows: high hardness and high toughness WC-Co coatings are alternately deposited on the base material by using a thermal spraying process, under the premise of considering the processing efficiency and cost, the internal stress of the coating under the action of external load is maximally reduced by controlling the number of layers and the thickness of each layer, so that the service life of the whole coating under the combined action of high-speed impact and repeated friction and the like is improved.

[0005] The preparation method of the multilayer composite structure WC-based coating with excellent impact wear resistance provided by the application is characterized by comprising the following steps:

[0006] (1) WC-Co composite powder with an average particle size of 0.2-0.5 mu m and a mass fraction of Co of 10% to 12% is mixed with polyethylene glycol and deionized water in proportion to prepare a slurry, and then WC-Co spraying powder with a particle size distribution of 15-45 mu m is prepared through spray granulation, heat treatment and screening;

[0007] (2) using the process of step (1), agglomerating WC-Co composite powder with an average particle size of 0.5-1.0 μm and a mass fraction of Co of 17%-20% into WC-Co spraying powder with a particle size distribution of 15-45 μm;

[0008] (3) performing oil removal, rust removal and sand blasting treatment on the surface of the workpiece to be sprayed, and using the above-mentioned powder to spray by using the supersonic flame spraying process, and using the spraying powder of step (1) and step (2) to alternately deposit WC-Co coatings with different Co contents on the surface of the workpiece after sand blasting, the total thickness of the coating is 200-300 μm, the number of layers is set to 2-4 layers, the thickness ratio of the low-Co layer and the high-Co layer is 3-4, and the outermost layer is the low-Co layer, so that a multilayer composite structure WC-based coating with excellent impact wear resistance is obtained after the coating is cooled.

[0009] The technical features and advantages of the method of the present application mainly include:

[0010] (1) an innovative method for preparing a multilayer structure WC-based coating based on thermal spraying technology is proposed, the composition structure and the total number of layers are arbitrarily adjustable without considering the process efficiency and cost, and the method has universality for the design and preparation of ceramic matrix composites requiring impact wear resistance; (2) the synergistic effect of the high-hardness low-Co layer and the good toughness high-Co layer can solve the bottleneck problem that a single homogeneous coating is difficult to balance high hardness and high toughness; (3) the optimal ratio of the thickness of the low-Co layer and the high-Co layer is determined based on theoretical calculation and experimental determination, which can maximize the reduction of internal stress and the initiation of cracks under impact load, thereby simultaneously improving the impact toughness and wear resistance of the coating; (4) the present application develops a coating material with stronger impact wear resistance through innovative design of the organizational structure, and the method is simple and easy to implement, and has outstanding popularization and application value. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 The maximum internal stress and deformation of the double-layer structure composite coating prepared in Example 1 and other thickness ratios of double-layer structure composite coatings, and the single-layer homogeneous coating under the same external load;

[0012] Figure 2 The maximum internal stress and deformation of the four-layer structure composite coating prepared in Example 2 and Example 3 and other thickness ratios of four-layer structure composite coatings under the same external load. DETAILED DESCRIPTION

[0013] The present application will be further described below in conjunction with examples, but the present application is not limited to the following examples.

[0014] Example 1

[0015] WC-Co composite powder with average particle size of 0.3 μm and Co mass fraction of 12% is mixed with polyethylene glycol and deionized water in proportion to form a slurry, the mass fraction of composite powder in the slurry is 65%, and the mass fraction of polyethylene glycol is 3%, then WC-Co spraying powder with particle size distribution of 15-45 μm is prepared by spray granulation, heat treatment and screening; WC-Co composite powder with average particle size of 1.0 μm and Co mass fraction of 17% is agglomerated into WC-Co spraying powder with particle size distribution of 15-45 μm according to the above process; the surface of the workpiece to be sprayed is treated by oil removal, rust removal and sand blasting, the above powder is sprayed by using the ultra-high velocity oxygen fuel spraying process, WC-Co coatings with different Co contents are alternately deposited on the surface of the workpiece after sand blasting, the spraying parameters are as follows: kerosene flow rate 26 L / h, oxygen flow rate 940 L / min, spraying distance 350 mm, powder feeding rate 80 g / min, total coating thickness 260 μm, layer number 2, thickness ratio of low Co layer to high Co layer 3.3, and the outermost layer is the low Co layer, after the coating is cooled, a multilayer composite structure WC-based coating with excellent impact wear resistance is obtained. After a sphere with mass of 224 g, diameter of 3.7 cm and speed of 4.2 m / s freely falls from a height of 0.9 m on the coating, the maximum internal stress of the coating is measured, and the comparison with the maximum internal stress of the coating prepared under other conditions (different thickness ratios of low Co layer to high Co layer) is shown in Table 1. Figure 1

[0016] Example 2

[0017] WC-Co composite powder with average particle size of 0.3 μm and Co mass fraction of 12% is mixed with polyethylene glycol and deionized water in proportion to form a slurry, the mass fraction of composite powder in the slurry is 65%, and the mass fraction of polyethylene glycol is 3%, then WC-Co spraying powder with particle size distribution of 15-45 μm is prepared by spray granulation, heat treatment and screening; WC-Co composite powder with average particle size of 1.0 μm and Co mass fraction of 17% is agglomerated into WC-Co spraying powder with particle size distribution of 15-45 μm according to the above process; the surface of the workpiece to be sprayed is treated by oil removal, rust removal and sand blasting, the above powder is sprayed by using the ultra-high velocity oxygen fuel spraying process, WC-Co coatings with different Co contents are alternately deposited on the surface of the workpiece after sand blasting, the spraying parameters are as follows: kerosene flow rate 26 L / h, oxygen flow rate 940 L / min, spraying distance 350 mm, powder feeding rate 80 g / min, total coating thickness 260 μm, layer number 2, thickness ratio of low Co layer to high Co layer 3.3, and the outermost layer is the low Co layer, after the coating is cooled, a multilayer composite structure WC-based coating with excellent impact wear resistance is obtained. After a sphere with mass of 224 g, diameter of 3.7 cm and speed of 4.2 m / s freely falls from a height of 0.9 m on the coating, the maximum internal stress of the coating is measured, and the comparison with the maximum internal stress of the coating prepared under other conditions (different thickness ratios of low Co layer to high Co layer) is shown in Table 1. Figure 2 ​shown.

[0018] Example 3

[0019] A WC-Co composite powder with an average particle size of 0.3 μm and a mass fraction of Co of 12% is mixed with polyethylene glycol and deionized water in a proportion to form a slurry, the mass of the composite powder in the slurry accounting for 65%, the mass fraction of polyethylene glycol accounting for 3%, and then a WC-Co spraying powder with a particle size distribution of 15-45 μm is prepared by spray granulation, heat treatment and screening. A WC-Co composite powder with an average particle size of 1.0 μm and a mass fraction of Co of 17% is agglomerated to a WC-Co spraying powder with a particle size distribution of 15-45 μm according to the above process. The surface of a workpiece to be sprayed is subjected to oil removal, rust removal and sand blasting treatment, and the above powder is sprayed by using a supersonic flame spraying process, the spraying parameters being kerosene flow 26 L / h, oxygen flow 940 L / min, spraying distance 350 mm, and powder feeding rate 80 g / min. Different Co content WC-Co coatings are alternately deposited on the surface of the workpiece after sand blasting, the total thickness of the coating being 260 μm, the number of layers being set to 4, the thickness ratio of the low Co layer to the high Co layer being 3.3, and the outermost layer being the low Co layer. After the coating is cooled, a multilayer composite structure WC-based coating with excellent impact wear resistance is obtained. After a sphere with a mass of 224 g, a diameter of 3.7 cm and a speed of 4.2 m / s freely falls from a height of 0.9 m on the coating, the maximum internal stress of the coating is measured as shown in the table. Figure 2 shown.

Claims

1. A method for producing a multilayer composite structure WC-based coating with excellent impact wear resistance, characterized in that, The method comprises the following steps: (1) mixing WC-Co composite powder with average particle size of 0.2-0.5 μm and Co mass fraction of 10%-12% with polyethylene glycol and deionized water in proportion to prepare a slurry, and then preparing WC-Co spraying powder with particle size distribution of 15-45 μm through spray granulation, heat treatment and screening; (2) agglomerating WC-Co composite powder with average particle size of 0.5-1.0 μm and Co mass fraction of 17%-20% into WC-Co spraying powder with particle size distribution of 15-45 μm according to the process of step (1); (3) performing oil removal, rust removal and sand blasting treatment on the surface of the workpiece to be sprayed, and spraying the above-mentioned powder by using the supersonic flame spraying process, and alternately depositing WC-Co coatings with different Co contents on the surface of the workpiece after sand blasting by using the spraying powder of step (1) and step (2), the total thickness of the coating is 200-300 μm, the number of layers is set to 2-4 layers, the thickness ratio of the low-Co layer and the high-Co layer is 3-4, and the outermost layer is the low-Co layer, and the multi-layer composite structure WC-based coating with excellent impact wear resistance is obtained after the coating is cooled.

2. The multi-layer composite structure WC-based coating prepared by the preparation method of claim 1.

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