CN114990541A

CN114990541A - High-hardness material coating structure and preparation method thereof

Info

Publication number: CN114990541A
Application number: CN202210605175.XA
Authority: CN
Inventors: 单光存; 张吉亮; 石灿鸿; 李鑫
Original assignee: Beihang University
Current assignee: Beihang University
Priority date: 2020-06-30
Filing date: 2020-06-30
Publication date: 2022-09-02
Anticipated expiration: 2040-06-30
Also published as: CN111763938A; CN114990541B

Abstract

A high-hardness material coating structure and a preparation method thereof are provided, the high-hardness material coating structure comprises: using amorphous alloy as a substrate or a transition layer; and spraying high-hardness material powder on the amorphous alloy substrate or the transition layer by adopting a cold spraying process to obtain a high-hardness material compact coating on the amorphous alloy substrate or the transition layer. The amorphous alloy allows larger local shear deformation, high-hardness material powder is impacted on an amorphous alloy substrate or a transition layer at a speed exceeding a critical deposition speed in a cold spraying process, the impact process causes large shear deformation and shear softening of an amorphous surface, and the low temperature of cold spraying does not cause amorphous crystallization, so that the bonding strength between the amorphous alloy substrate or the transition layer and sprayed particles is effectively enhanced, the falling of the particles is obviously inhibited, and a compact and high-hardness coating can be prepared.

Description

High-hardness material coating structure and preparation method thereof

The application is a divisional application of Chinese invention patent application with application number 202010616217.0 (application date: 30/6/2020; invention name: high-hardness material coating structure and preparation method thereof).

Technical Field

The disclosure belongs to the technical field of alloy materials and surface cold spraying, and relates to a high-hardness material coating structure and a preparation method thereof.

Background

The cold spraying technology is a low-temperature spraying technology which takes preheated compressed gas (nitrogen, ammonia, air or mixed gas) as an accelerating medium to drive metal particles to impact a workpiece matrix at a very high speed in a solid state and deposit the metal particles on the surface of the matrix to form a coating in a mode of strong plastic deformation of the particles. Cold spraying differs most from thermal spraying in that the particles are heated to a different extent resulting in a different state before they impact the surface of the workpiece. The three hot-trip temperatures of the traditional thermal spraying technology are respectively as follows: burning flame, wherein the temperature is higher than 2000 ℃; arc, the temperature reaches more than 5000 ℃; plasma, such as palladium plasma, has a temperature as high as 16000 deg.c, so that the thermally sprayed particles melt during deposition and are accompanied by metallurgical processes such as droplet impingement, welding, cooling, solidification, phase transformation, etc., whereas the cold sprayed particles do not melt during deposition, and the solid particles undergo adiabatic shear destabilization under conditions of extremely high strain and strain rate, thereby causing plastic rheology and forming mechanical occlusion.

The cold spray particle deposition process has a critical deposition speed, and only when the flight speed of the particles exceeds the critical deposition speed, the erosion effect of the particles on the substrate can be converted into a perforation effect, so that the coating is deposited. Generally, the higher the hardness of the particles, the higher the critical deposition rate, i.e., the harder the powder particles are to deposit, and therefore, high hardness alloys are not suitable for effective deposition of coatings using cold spray techniques. The low-hardness pure metal or alloy can be used for preparing the coating by utilizing a cold spraying technology, but the wear-resisting property of the coating often cannot meet the use requirement. Since the cold spray technology relies on high pressure gas flow to make the flight velocity of the particles exceed the critical deposition velocity to obtain a coating, increasing the flight velocity of the particles is critical to the preparation of high performance coatings. The flight velocity of the particles is primarily related to the carrier gas and the carrier gas preheat temperature. The accelerating effect of ammonia in common carrier gas is optimal, but the cost is too high; nitrogen is the most economical, but the acceleration effect is poor. The preheating temperature of the carrier gas is mainly used for enhancing the expansion effect of gas molecules at the contraction section of the nozzle, so that the flow velocity of the gas flow at the expansion section is maximized, but the preheating temperature of the carrier gas is limited by deposition materials and equipment, the structure of the nozzle is improved no matter how the equipment is upgraded, technological parameters are optimized, a single cold spraying technology cannot be used for depositing and preparing an alloy material coating with higher hardness, and the popularization of the spraying technology is greatly restricted.

Most studies at present improve the deposition effect of the high-hardness alloy material coating mainly by adjusting the process parameters of cold spraying, such as carrier gas preheating temperature and carrier gas pressure. Some researches repeatedly impact the prepared spherical powder on a substrate with surface protrusions of corresponding specifications at a high speed to form pits on the surface of the metal powder, inhibit the occurrence of flow separation by improving the surface morphology of the powder, improve the flight rate of the powder in the spraying process and achieve the effect of improving the density of a coating.

Therefore, it is necessary to provide a method for preparing a dense coating of high hardness alloy.

Disclosure of Invention

Technical problem to be solved

The present disclosure provides a high hardness material coating structure and a method for preparing the same to at least partially solve the technical problems set forth above.

(II) technical scheme

According to an aspect of the present disclosure, there is provided a method for preparing a coating structure of a high hardness material, including: using amorphous alloy as a substrate or a transition layer; and spraying high-hardness material powder on the amorphous alloy substrate or the transition layer by adopting a cold spraying process to obtain a high-hardness material compact coating on the amorphous alloy substrate or the transition layer.

In an embodiment of the present disclosure, the amorphous alloy is a metallic glass.

In an embodiment of the present disclosure, the high-hardness material powder is a tungsten carbide alloy powder, wherein the mass ratio of tungsten to carbon is 10: 1, and the purity of the tungsten carbide alloy powder is greater than 99.9%;

the characteristic size of the powder particles of the high-hardness material powder is 0.7-2 mu m;

the size of the particles in the high-hardness material coating is 1-5 mu m.

In an embodiment of the present disclosure, in the tungsten carbide alloy powder, the content of carbon is 6.1% to 6.18%, the content of simple substance carbon impurities is less than 0.05%, the mass percentage of Fe is 0.01% to 0.02%, and the mass percentage of Mo is less than 0.01%.

In an embodiment of the present disclosure, the spraying of the high hardness material powder on the amorphous alloy substrate or the transition layer by using the cold spraying process includes: feeding high-hardness material powder into a powder feeder or a convergence-diffusion spray gun for spraying;

wherein, nitrogen or compressed air is used as spraying gas, and the air pressure is 100-200 atmospheric pressures; the pressure of the powder feeder is set to be 50 atmospheres greater than the pressure of a main gas flow including a spray gas carrying a powder of a high-hardness material;

preferably, the pressure of the compressed air is 15 atmospheres or more.

In an embodiment of the present disclosure, the high-hardness material powder is a tungsten carbide alloy powder, and the preparation method of the tungsten carbide alloy powder includes: putting raw materials of carbon and tungsten into a vacuum induction furnace according to preset components for smelting, respectively carrying out deslagging, refining, homogenizing and atomizing, and then drying and sieving to obtain a tungsten carbide alloy powder crude product; carrying out solution treatment on the tungsten carbide alloy powder crude product, and then carrying out water quenching to room temperature; and (3) carrying out hydrogen reduction on the crude product of the tungsten carbide alloy powder after water quenching to obtain the tungsten carbide alloy powder.

In one embodiment of the present disclosure, the temperature of the smelting is 1400 ℃ to 1550 ℃; and/or the presence of a gas in the gas,

the temperature of the hydrogen reduction is 200-300 ℃, and the reduction time is 1-3 h; and/or the presence of a gas in the gas,

the temperature of the solution treatment is 1050-1100 ℃; the heat preservation time is lh-2 h.

In an embodiment of the present disclosure, the atomization method is a vacuum atomization method or a plasma rotating electrode method.

In one embodiment of the present disclosure, the crude tungsten carbide alloy powder is spherical or spheroidal and has a particle size of less than 5 μm.

In an embodiment of the present disclosure, the hardness of the tungsten carbide alloy powder is 170 to 200.

In an embodiment of the present disclosure, the tungsten carbide alloy powder has a spherical, near-spherical, or polygonal shape.

According to another aspect of the present disclosure, there is provided a high-hardness material coating structure including: an amorphous alloy substrate or transition layer; and a high-hardness material coating formed on the amorphous alloy substrate or the transition layer.

In one embodiment of the present disclosure, a high-hardness material dense coating is formed by spraying high-hardness material powder on an amorphous alloy substrate or a transition layer by using a cold spraying process;

optionally, the amorphous alloy is a nanocrystalline alloy or metallic glass;

optionally, the high-hardness material powder is tungsten carbide alloy powder, wherein the mass ratio of tungsten to carbon is 10: 1, the purity of the tungsten carbide alloy powder is more than 99.9 percent;

optionally, in the tungsten carbide alloy powder, the carbon content is 6.1-6.18%, the content of simple substance carbon impurities is less than 0.05%, the mass percent of Fe is 0.01-0.02%, and the mass percent of Mo is less than 0.01%;

optionally, the hardness of the tungsten carbide alloy powder is 170-200;

optionally, the tungsten carbide alloy powder is spherical, near-spherical or polygonal in shape.

(III) advantageous effects

According to the technical scheme, the high-hardness material coating structure and the preparation method thereof have the following beneficial effects:

the amorphous alloy is used as a substrate or a transition layer, and the high-hardness material powder is sprayed on the amorphous alloy substrate or the transition layer by adopting a cold spraying process, because the amorphous alloy allows larger local shear deformation, the high-hardness material powder impacts the amorphous alloy substrate or the transition layer at a speed exceeding a critical deposition speed in the cold spraying process, the impact process causes large shear deformation and shear softening of the amorphous surface, and the low temperature of the cold spraying does not cause amorphous crystallization, so that the bonding strength between the amorphous alloy substrate or the transition layer and the sprayed particles is effectively enhanced, the falling of the particles is obviously inhibited, and the compact and high-hardness coating can be prepared.

Drawings

Fig. 1 is a schematic view illustrating a method for preparing a coating layer of a high hardness material according to an embodiment of the present disclosure.

Fig. 2 is a flow chart of a method for preparing a coating of a high hardness material according to an embodiment of the present disclosure.

Fig. 3 is a surface topography SEM image of the high-hardness material coating prepared by the method for preparing a high-hardness material coating shown in the embodiment of the present disclosure.

FIG. 4 is a graph of gas velocity versus axial position within a lance according to an embodiment of the disclosure.

FIG. 5 is a graph of particle axial velocity versus particle size according to an embodiment of the present disclosure.

Fig. 6 is a photographic schematic of a high hardness material coating sample according to an embodiment of the present disclosure, wherein (a) is a photograph of sample a, (B) is a photograph of sample B, (C) is a photograph of sample C, and (D) is a photograph of sample D.

Fig. 7 is an SEM image of the surface topography of the high hardness material coating sample as shown in fig. 6, wherein (a) is an SEM image of sample a, (B) is an SEM image of sample B, (C) is an SEM image of sample C, and (D) is an SEM image of sample D.

FIG. 8 is the microstructure of the high hardness material coating sample shown in FIG. 6 in secondary electron mode, (a1) is the microstructure of sample A; (a2) is the microstructure of sample a at a higher magnification; (b1) is the microstructure of sample B; (b2) is the microstructure of sample B at a higher magnification; (c1) is the microstructure of sample C; (c2) the microstructure of sample C at higher magnification; (d1) is the microstructure of sample D; (d2) the microstructure of sample D at a higher magnification.

Fig. 9 is an SEM image of a cross-section of the high-hardness material coating sample shown in fig. 6 in a background electron mode, wherein (a) is an SEM image of sample a, (B) is an SEM image of sample B, (C) is an SEM image of sample C, and (D) is an SEM image of sample D.

Detailed Description

The amorphous alloy is used as a substrate or a transition layer, and the high-hardness material powder is sprayed on the amorphous alloy substrate or the transition layer by adopting a cold spraying process.

For the purpose of promoting a better understanding of the objects, aspects and advantages of the present disclosure, reference is made to the following detailed description taken in conjunction with the accompanying drawings.

In a first exemplary embodiment of the present disclosure, a method of preparing a coating structure of a high hardness material is provided.

Fig. 1 is a schematic view illustrating a method for preparing a coating layer of a high hardness material according to an embodiment of the present disclosure. Fig. 2 is a flow chart of a method for preparing a coating of a high hardness material according to an embodiment of the present disclosure.

In this embodiment, the apparatus implementing the manufacturing method of the embodiments of the present disclosure may be a commercial cold-powered spray system. Referring to fig. 1, a cold power spray system includes: powder feeder, gas supply device, gas heating device and spray gun. Wherein the spray gun comprises two input ends and an output end. The powder feeder is connected with one input end of the spray gun, and the gas heating device is connected with the other input end of the spray gun. The gas supply device is connected with the gas heating device, and the spraying gas supplied by the gas supply device is heated by the gas heating device and then is sent into the spray gun. Powder supplied from a powder feeder is also fed into the spray gun.

Referring to fig. 1, the pressure and temperature of the main air flow from the nozzle are mainly regulated during spraying. The main gas flow comprises powder entrained in the spray gas. The high durometer material coating of the disclosed embodiments may be made with the pressure of the main gas flow during the manufacturing process being adjustable, for example, the pressure of the main gas flow may be 100psi, 200psi, or any value between 100psi and 200psi, such as 150 psi. The pressure of the powder feeder is also adjustable. In one embodiment, the pressure of the powder feeder may be set to 50psi greater than the pressure of the main gas flow. In a preferred embodiment, the main gas stream has a pressure of 100psi to 200psi and a temperature in the range of 250K to 500K.

In an embodiment of the present disclosure, the spray gun is a converging-diverging spray gun for accelerating powder entrained in the spray gas. In the cold kinetic spray system described above, the converging-diverging spray gun is movable to progressively approach the substrate to be sprayed. The moving speed of the nozzle is adjustable, and an exemplary moving speed of the nozzle may be 1 cm/s. The path of the spray can be programmed.

Referring to fig. 1, in the present embodiment, the substrate to be sprayed is an amorphous alloy substrate/transition layer (meaning amorphous alloy as the substrate or amorphous alloy as the transition layer), and the distance between the converging-diverging spray gun and the amorphous alloy substrate/transition layer is adjustable. In one embodiment, for example, the distance (in the left-right direction in FIG. 1) between the converging-diverging torch and the amorphous alloy substrate/transition layer is any value from 8mm to 15mm, for example, the distance may be 10 mm.

Referring to fig. 2, a method for preparing a coating structure of a high hardness material according to the present disclosure includes: step S11 and step S12.

In step S11, an amorphous alloy is used as a substrate or transition layer.

In step S12, high-hardness material powder is sprayed on the amorphous alloy substrate or the transition layer by using a cold spraying process, so as to obtain a dense coating of the high-hardness material on the amorphous alloy substrate or the transition layer.

In this embodiment, in step S11, the amorphous alloy is a nanocrystalline alloy or a metallic glass. In the present disclosure, the shape of the amorphous alloy substrate or the transition layer for spraying is not limited, and in the present embodiment, a disk shape is exemplified, and the diameter of the disk is, for example, 8mm, and the thickness of the disk is 4 mm. It is necessary to polish the surface of the amorphous alloy substrate or the transition layer for spraying the powder before starting spraying. The specific parameter settings for spraying the high-hardness material powder using the cold spray process in step S12 can be preliminarily evaluated based on a one-dimensional model of the particle velocity. Specific parameters include the pressure and temperature of the primary gas flow.

In one embodiment, the high-hardness material powder is a tungsten carbide alloy powder, wherein the mass ratio of tungsten to carbon is 10: 1, and the purity of the tungsten carbide alloy powder is more than 99.9%.

In one embodiment, the tungsten carbide alloy powder contains 6.1-6.18% of carbon, less than 0.05% of simple substance carbon impurities, 0.01-0.02% of Fe by mass and less than 0.01% of Mo by mass.

In one embodiment, the high hardness material powder may be an industrial or commercial spray powder, such as an industrial tungsten carbide powder.

In one embodiment, the characteristic size of the powder particles of the high-hardness material powder is 0.7 μm to 2 μm.

In one embodiment, the size of the particles in the coating of high hardness material is 1 μm to 5 μm.

In an embodiment of the present disclosure, referring to fig. 1 and 2, the step S12 of spraying the high hardness material powder on the amorphous alloy substrate or the transition layer by using a cold spraying process includes: the powder of the high hardness material is fed into a powder feeder or a converging-diverging spray gun for spraying. Wherein, nitrogen or compressed air is used as spraying gas, and the air pressure is 100 or 200 atmospheric pressures; the pressure of the powder feeder was set to 50 atmospheres greater than the pressure of the main gas flow including the spray gas carrying the high-hardness material powder.

In one embodiment, the compressed air has an air pressure above 15 atmospheres.

In one embodiment, four samples, sample a, sample B, sample C and sample D, were prepared using steps S11, S12 and the pressure and temperature condition parameters for spray application in table 1. In this example, the spray time for each of the four samples was 4 seconds.

Table 1 examples of pressure and temperature parameters for each sample

After the spray coating was completed, a series of characterizations were performed on the above samples. Estimating the particle velocity through a one-dimensional model; characterizing the topographical features of the coating by a digital camera, optical microscope and Scanning Electron Microscope (SEM); the mechanical properties of the WC coatings were investigated by means of a vickers hardness tester.

Referring to fig. 3, the size of particles in the coating layer using the high hardness material shown in the embodiment of the present disclosure generally falls within a range of 1 μm to 3 μm.

The velocity of the gas in the lance can be expressed as the following equation based on the isentropic gas-fluid model:

wherein v is _g Is the gas velocity; m is a Mach constant; γ is the ratio of specific heat capacities; r is a gas constant; t is the temperature of the spraying gas; m _W Is the molecular weight of the gas.

FIG. 4 is a graph of gas velocity versus axial position within a lance according to an embodiment of the disclosure. The gas velocity estimates corresponding to the samples a-D calculated by the above formula (1) are shown in fig. 4, where the axial direction refers to the direction along the axial direction of the spray gun, and along the left and right directions in fig. 1, the gas velocity curves of the sample a and the sample C coincide, the gas velocity curves of the sample B and the sample D coincide, and the gas velocities of the sample B and the sample D corresponding to a certain position along the axial direction are both higher than those of the sample a and the sample C, so that it can be seen that the gas velocity can be significantly increased by increasing the sprayed gas temperature.

Further, in order to estimate the velocity of particles (granules, both meaning the same throughout) along the axial direction, it is first assumed that these powder carried by the spraying gas are spherical particles. According to a one-dimensional particle dynamics model, the particle axial velocity v _p The following formula can be used for calculation:

wherein D is the particle diameter; x is the axial position of the particle; ρ is a unit of a gradient _p Is the particle density; p ₀ Is a static pressure.

FIG. 5 is a graph of particle axial velocity versus particle size according to an embodiment of the present disclosure. The relationship between the particle axial velocity and the particle diameter calculated by the above formula (2) is shown in fig. 5, and the result shows that the gas temperature has little influence on the particle axial velocity.

However, heating the gas can increase the temperature of the particles and even the matrix, thereby increasing their plasticity. In practice, the working particles are not spherical, but irregular. From an aerodynamic point of view, the drag coefficient of non-spherical particles is greater than that of spherical particles, so that the irregular shape of the particles facilitates the acceleration of the particles. The first cold spray coating on the substrate surface is not only related to the particle velocity but also to the difference in properties between the particles and the substrate. Therefore, the theoretical prediction of the first layer has certain difficulties in practical applications. The formation of subsequent layers is effectively envisioned.

According to the existing theory, the influence of the process and material parameters on the critical speed is summarized as the following expression:

V _cri ＝667-0.014ρ _p +0.08T _m +10 ^-7 σ _μ -0.4T (3)

wherein, T _m Is the melting temperature of the granules (unit:. degree. C.); sigma _μ Is the ultimate tensile strength or tensile strength of the particles; t is the temperature of the pellets just after ejection from the lance.

The critical velocity for coating formation (coating) between WC and WC is 660m/s, i.e. the velocity at which tungsten carbide undergoes plastic deformation large enough to form a coating on a tungsten carbide substrate. In the disclosed embodiments, the critical speed for forming a dense coating on an amorphous alloy substrate is significantly less than 660 m/s.

The process can be optimized by analyzing with reference to the samples A to D obtained by actual preparation.

Referring to fig. 6 (a), in sample a, only half of the surface area is covered with the coating. It can be seen from the analysis that since the particle velocity of sample a is low, only half of the surface area is coated, and the arrangement of each particle in the coating is loose. As the gas temperature increased, a non-uniform coating was formed on the substrate surface, but since the axial velocity of the particles along the axial direction was also relatively low, similar to that of sample a, the substrate edge was still bare and uncovered, as shown in fig. 6 (b). When the spraying speed reached a critical value, a uniform and dense coating was obtained, as shown in fig. 6 (c). However, once the velocity exceeds a critical value, the coating is eroded by the following particles and a number of craters appear, as shown in fig. 6 (d).

Fig. 7 is an SEM image of the surface topography of the high-hardness material coating sample as shown in fig. 6, wherein (a) is an SEM image of sample a, (B) is an SEM image of sample B, (C) is an SEM image of sample C, and (D) is an SEM image of sample D. In FIG. 7, the scale size is 100 μm.

Further details were studied by using light microscopy. There is a distinct boundary in the center of sample a, as shown by the dashed line in fig. 7 (a). A sludge coating is formed on the left side and some large particles are inserted into the matrix on the right side. As the gas temperature increases, a relatively dense but non-uniform coating is formed on the surface of the substrate, but several large particles remain on the coating, as shown in fig. 7 (b). Once the spray velocity reaches a critical value, a uniform coating can be produced without significant defects, as shown in fig. 7 (c). However, as the speed is further increased and exceeds the critical value for erosion of the formed coating, many cavities exceeding 200 μm are generated, as shown with reference to (d) in FIG. 7.

FIG. 8 is the microstructure of the high hardness material coating sample shown in FIG. 6 in secondary electron mode, (a1) is the microstructure of sample A; (a2) is the microstructure of sample a at a higher magnification; (b1) is the microstructure of sample B; (b2) the microstructure of sample B at a higher magnification; (c1) is the microstructure of sample C; (c2) the microstructure of sample C at higher magnification; (d1) is the microstructure of sample D; (d2) the microstructure of sample D at a higher magnification.

Comparing (a2), (B2), and (C2) in fig. 8, it can be seen that although the low velocity during spraying resulted in some weak areas in the coating, as shown by the dark areas in (a1) in fig. 8, the coating formed in sample a was much denser than the coating formed in samples B and C, i.e., sample a was more dense than samples B and C. The coating in sample C appeared more uniform than the other coatings and the coating was not as dense as samples a and D, but it contained very few pores, as shown by comparison with (C1) and (C2) in fig. 8 with (a1), (a2), (D1), and (D2) in fig. 8. The coating of sample D was the most dense, but exhibited many large particles and cavities, as shown with reference to (D1) and (D2) in FIG. 8.

Fig. 9 is an SEM image of a cross-section of the high hardness material coating sample shown in fig. 6 in a background electron mode, wherein (a) is an SEM image of sample a, (B) is an SEM image of sample B, (C) is an SEM image of sample C, and (D) is an SEM image of sample D.

Referring to fig. 9 (a) to (d), all samples had a particle layer thickness of less than 1 μm, which is consistent with the calculation results. As can be seen from fig. 9 (a), the base of sample a underwent very little deformation, with only very fine particles covering the substrate. This facilitates the formation of a coating by attaching fine particles to the substrate in sample a. Referring to fig. 9 (B), the density and uniformity of sample B are inferior compared to samples a and C. The uniformity and density of the coating in sample C can be determined from the cross-sectional view shown in fig. 9 (C), which is more uniform than the other sample A, B, D, but less dense than sample a. Referring to (D) in fig. 9, the substrate in sample D undergoes large deformation due to high particle velocity, but does not form a dense and uniform coating due to erosion of large particles. Referring to (C) of fig. 9, the substrate in sample C still suffered greater deformation than the substrate in sample B despite the low particle velocity. In addition to the particle velocity, the gas temperature for each sample was also different. Considering the presence of the superplastic region in the metallic glass substrate, it is believed that the combination of kinetic energy and gas temperature results in a temperature increase and enhances large deformation of sample C. Thus, based on the above, the pressure of the main gas stream is preferably 130psi to 250psi, and the temperature is preferably 250K to 500K, such as 280K, 300K, 320K, 350K, 380K, 400K, 420K, 450K, and the like, inclusive. The spraying time is generally used to increase the thickness of the coating, and generally, the thickness is difficult to increase after the dense coating is formed, so that the meaning of prolonging the spraying time after the dense coating is formed is not great, and the spraying time for forming the coating can be adjusted in advance according to the actual spraying process.

In addition, sample C was characterized for hardness. The mechanical properties of the coating in sample C were tested by a vickers hardness tester. A hardness test was conducted for 10 times for each of 500gf and 1000gf of load for a period of 10 seconds. The hardness values for the substrate, powder and coating are all listed in table 2. The hardness of the monolithic Bulk Metallic Glass (BMG) substrate showed a stability of about 530HV in these tests. In addition, in the above test, the corresponding coating is a single-layer coating with a spraying time of 4s, so as to illustrate the influence of different spraying conditions on the density and uniformity of the coating.

TABLE 2 hardness of substrate, tungsten carbide powder, coating

In addition, an example of the disclosure also compares the preparation method of the amorphous alloy as the substrate or the transition layer of the embodiment of the disclosure with the coating obtained by the conventional preparation process, under the same experimental conditions, except that the substrates are different, other parameter conditions including temperature, pressure of air flow, spraying time and the like are the same, the spraying on the stainless steel substrate correspondingly generates the depression with the particle size, the sprayed particles fall off, the coating appearance shows that the coating is sparse, and the hardness of the coating is not high; the coating prepared by spraying on the amorphous alloy substrate of the embodiment of the disclosure has better density and hardness.

In an embodiment of the present disclosure, the high-hardness material powder is a tungsten carbide alloy powder, and the method for producing the tungsten carbide alloy powder includes the following steps (a) to (c).

And (a) smelting raw materials of carbon and tungsten in a vacuum induction furnace according to preset components, respectively carrying out deslagging, refining, homogenizing and atomizing, and drying and sieving to obtain a tungsten carbide alloy powder crude product.

In an embodiment of the present disclosure, the temperature of the melting is 1400 ℃ to 1550 ℃, for example 1500 ℃.

And (b) carrying out solution treatment on the tungsten carbide alloy powder crude product, and then carrying out water quenching to room temperature. The temperature of the solution treatment is 1050-1100 ℃, including the endpoint value, such as 1080 ℃; the time of heat preservation by the solution treatment is lh to 2 h.

And (c) carrying out hydrogen reduction on the water-quenched tungsten carbide alloy powder crude product to obtain tungsten carbide alloy powder.

In one embodiment of the present disclosure, the temperature for hydrogen reduction is any number of 200 ℃ to 300 ℃, such as 220 ℃, 240 ℃, 250 ℃, and the like. The reduction time is 1 to 3 hours, and may be, for example, 1 hour, 2 hours or 3 hours.

In an embodiment of the present disclosure, the atomization process is performed by a vacuum atomization method or a plasma rotating electrode method.

In one embodiment of the present disclosure, the crude tungsten carbide alloy powder is spherical or spheroidal with a particle size of less than 5 μm.

In a second exemplary embodiment of the present disclosure, a high-hardness material coating structure is provided. The high-hardness material coating structure comprises: an amorphous alloy substrate or transition layer; and a high-hardness material coating formed on the amorphous alloy substrate or the transition layer.

In one embodiment of the present disclosure, the high-hardness material dense coating is formed by spraying high-hardness material powder on the amorphous alloy substrate or the transition layer using a cold spray process.

In one embodiment, the amorphous alloy is a nanocrystalline alloy or a metallic glass.

In this embodiment, the high-hardness material powder is a tungsten carbide alloy powder, in which the mass ratio of tungsten to carbon is 10: 1, and the purity of the tungsten carbide alloy powder is greater than 99.9%. In one embodiment, the tungsten carbide alloy powder contains 6.1-6.18% of carbon, less than 0.05% of simple substance carbon impurities, 0.01-0.02% of Fe by mass and less than 0.01% of Mo by mass.

In the present embodiment, the hardness of the tungsten carbide alloy powder is 170 to 200.

In the present embodiment, the tungsten carbide alloy powder has a spherical, nearly spherical, or polygonal shape.

In summary, the present disclosure provides a high-hardness material coating structure and a preparation method thereof, wherein an amorphous alloy is used as a substrate or a transition layer, and a cold spraying process is adopted to spray high-hardness material powder on the amorphous alloy substrate or the transition layer, because the amorphous alloy allows a larger local shear deformation, the high-hardness material powder impacts the amorphous alloy substrate or the transition layer at a speed exceeding a critical deposition speed in the cold spraying process, and the impact process causes a large shear deformation and shear softening of an amorphous surface, so that the bonding strength between the amorphous alloy substrate or the transition layer and the sprayed particles is effectively enhanced, the falling of the particles is obviously inhibited, and a compact and high-hardness coating is formed.

Unless otherwise indicated, the numerical parameters set forth in the specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by the present disclosure. In particular, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term "about". Generally, the expression is meant to encompass variations of ± 10% in some embodiments, 5% in some embodiments, 1% in some embodiments, 0.5% in some embodiments by the specified amount.

The above-mentioned embodiments, objects, technical solutions and advantages of the present disclosure are further described in detail, it should be understood that the above-mentioned embodiments are only examples of the present disclosure, and should not be construed as limiting the present disclosure, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present disclosure should be included in the protection scope of the present disclosure.

Claims

1. A preparation method of a high-hardness material coating structure is characterized by comprising the following steps:

using amorphous alloy as a substrate or a transition layer;

spraying high-hardness material powder on the amorphous alloy substrate or the transition layer by adopting a cold spraying process to obtain a high-hardness material compact coating on the amorphous alloy substrate or the transition layer,

the amorphous alloy is metallic glass, and the step of spraying high-hardness material powder on the amorphous alloy substrate or the transition layer by adopting a cold spraying process comprises the following steps:

feeding high-hardness material powder into a powder feeder, and spraying by a convergence-diffusion spray gun;

the method comprises the following steps of (1) taking nitrogen or compressed air as spraying gas, wherein the main gas flow comprises the spraying gas carrying high-hardness material powder, and the gas pressure of the main gas flow is 100-200 atmospheric pressures; the pressure of the powder feeder is set to be 50 atmospheres greater than the pressure of the main air flow, the temperature of the main air flow is 250K to 500K, and the pressure of the compressed air is 15 atmospheres or more.

2. The method of claim 1, wherein the primary gas stream pressure is 130 to 250 atmospheres.

3. The manufacturing method according to claim 1, wherein the distance from the convergent-divergent spray gun to the amorphous alloy substrate or the transition layer when spraying is performed is 8mm to 15 mm.

4. The production method according to claim 3, wherein the distance from the convergent-divergent spray gun to the amorphous alloy substrate or the transition layer when spraying is performed is 10 mm.

5. The production method according to claim 1,

the high-hardness material powder is tungsten carbide alloy powder, wherein the mass ratio of tungsten to carbon is 10: 1, and the purity of the tungsten carbide alloy powder is more than 99.9%;

the size of the particles in the high-hardness material coating is 1-5 mu m.

6. The preparation method according to claim 5, wherein the tungsten carbide alloy powder contains 6.1-6.18% of carbon, less than 0.05% of simple substance carbon impurities, 0.01-0.02% of Fe by mass and less than 0.01% of Mo by mass.

7. The production method according to claim 5, wherein the tungsten carbide alloy powder has a spherical, nearly spherical or polygonal shape.

8. A high-hardness material coating structure, comprising:

an amorphous alloy substrate or transition layer; and

a high-hardness material compact coating formed on the amorphous alloy substrate or the transition layer,

the amorphous alloy is metallic glass, and the high-hardness material coating is prepared by the preparation method of any one of claims 1 to 7.