CN112591753B - Rare earth doped tungsten carbide composite powder and preparation method thereof, and wear-resistant coating and preparation method thereof - Google Patents
Rare earth doped tungsten carbide composite powder and preparation method thereof, and wear-resistant coating and preparation method thereof Download PDFInfo
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Abstract
The invention relates to the technical field of wear-resistant coatings, and provides rare earth doped tungsten carbide composite powder and a preparation method thereof, and a wear-resistant coating and a preparation method thereof. According to the invention, water-soluble rare earth salt, water-soluble tungsten salt, a water-soluble organic carbon source and water are mixed, the obtained mixed feed liquid is directly prepared into the rare earth-doped tungsten carbide composite powder through spray drying and two-step calcination, the tungsten carbide powder does not need to be prepared first and then ball-milled with the rare earth oxide, and the rare earth oxide is dispersed and distributed in the grain boundary of tungsten carbide in a molecular level, so that the components of the composite powder reach an almost ideal uniform state, cracks in the coating can be effectively inhibited, and the structure and the performance of the coating are improved. The rare earth doped tungsten carbide wear-resistant coating prepared by the plasma cladding method is flat and uniform, has large thickness which can reach millimeter level, is controllable in coating thickness, is metallurgically combined with a matrix, and has higher hardness and better wear resistance compared with the coating prepared by the traditional rare earth doped tungsten carbide composite powder.
Description
Technical Field
The invention relates to the technical field of wear-resistant coatings, in particular to rare earth doped tungsten carbide composite powder and a preparation method thereof, and a wear-resistant coating and a preparation method thereof.
Background
Tungsten carbide (WC) has the characteristics of high microhardness, high wear resistance, low oxide content and the like, is widely applied to the industrial fields of energy, petroleum, chemical engineering, metallurgy, machinery and the like, and is used as an important surface modification material for carrying out wear-resistant protection on the surfaces of parts of key friction kinematic pairs of equipment. At present, common tungsten carbide powder in the market belongs to micron-sized materials, although the tungsten carbide powder has good fluidity, the tungsten carbide coating has the defects of low binding force with a matrix, high internal stress of the coating, poor tissue uniformity and the like due to the relatively large particle size, and the application range of the coating is limited to a great extent.
The research shows that: the addition of a proper amount of rare earth into the tungsten carbide alloy powder can effectively improve the structure and performance of the coating, reduce the problem of tungsten carbide decomposition during surface strengthening modification, effectively inhibit cracks in the coating and improve the microhardness and toughness of the coating. The traditional production process of the rare earth doped tungsten carbide composite powder comprises the following steps: and performing solid-solid ball milling and mixing on the tungsten carbide powder and the rare earth powder to obtain the rare earth doped tungsten carbide composite powder. Because the specific gravity of the rare earth is greatly different from that of the tungsten carbide powder, the method is difficult to ensure uniform mixing, so that the prepared coating has better hardness and wear resistance.
In addition, the rare earth doped tungsten carbide composite powder prepared by the ball milling method has poor sphericity, so that the powder has poor flowability, can be prepared only by an electroplating method or a spraying method when a coating is prepared, has a thin thickness (less than 300 micrometers), has low bonding force with a matrix, is difficult to adapt to occasions such as heavy-load impact abrasive wear and the like, and is easy to generate fatigue spalling in working occasions such as fatigue load, impact load, cold-heat cycle, abrasive wear and the like.
Disclosure of Invention
In view of this, the invention provides a rare earth doped tungsten carbide composite powder and a preparation method thereof, and a wear-resistant coating and a preparation method thereof. The rare earth doped tungsten carbide composite powder provided by the invention has uniform components and good fluidity, is suitable for preparing a wear-resistant coating by adopting a plasma cladding method, and has the advantages of large thickness, strong binding force with a matrix, high hardness and good wear resistance.
In order to achieve the above object, the present invention provides the following technical solutions:
a preparation method of rare earth doped tungsten carbide composite powder comprises the following steps:
(1) mixing water-soluble rare earth salt, water-soluble tungsten salt, a water-soluble organic carbon source and water to obtain mixed feed liquid;
(2) spray drying the mixed feed liquid to obtain a rare earth doped tungsten-carbon composite;
(3) sequentially carrying out first calcination and second calcination on the rare earth doped tungsten-carbon composite to obtain rare earth doped tungsten carbide composite powder; the first calcination is carried out in an inert atmosphere, the calcination temperature is 450-650 ℃, the second calcination is carried out in a reducing atmosphere, and the calcination temperature is 1000-1350 ℃.
Preferably, the water-soluble rare earth salt comprises one or more of rare earth nitrate, rare earth chloride and rare earth sulfate, and the rare earth element in the water-soluble rare earth salt is lanthanum or cerium; the water-soluble tungsten salt comprises one or more of ammonium metatungstate, ammonium tungstate and ammonium paratungstate; the water-soluble organic carbon source comprises one or more of glucose, sucrose and fructose.
Preferably, the molar ratio of the rare earth element in the water-soluble rare earth salt to the tungsten element in the water-soluble tungsten salt is (0.01-0.1): 1; the mass ratio of the tungsten element in the water-soluble tungsten salt to the carbon element in the water-soluble organic carbon source is (5-6): 1.
Preferably, the spray drying conditions include: the air inlet temperature is 150-260 ℃, the feeding amount is 80-200 mL/min, and the spraying pressure is 0.5-2 Mpa.
Preferably, the thickness of the first calcined material layer is 10-30 mm, and the calcining time is 20-60 min; the thickness of the material layer subjected to the second calcination is 10-30 mm, and the calcination time is 40-120 min; the reducing atmosphere is hydrogen.
The invention provides rare earth doped tungsten carbide composite powder prepared by the preparation method in the scheme, which comprises tungsten carbide and rare earth oxide doped in the tungsten carbide, wherein the rare earth oxide is dispersed in a grain boundary of the tungsten carbide in a molecular level manner, and the average sphericity of the rare earth doped tungsten carbide composite powder is not less than 95%.
The invention also provides a preparation method of the rare earth doped tungsten carbide wear-resistant coating, which comprises the following steps:
and (3) directly carrying out plasma cladding on the surface of the matrix by using the rare earth doped tungsten carbide composite powder in the scheme to obtain the rare earth doped tungsten carbide wear-resistant coating.
Preferably, the plasma cladding conditions include: the plasma beam output power is 12-15 kW, the working current is 250-350A, the ionized gas flow is 0.8-1.2 m3/h, the powder conveying gas flow is 0.8-1.2 m3/h, the shielding gas is argon, the shielding gas flow is 1.5-2 m3/h, the scanning speed of the plasma beam is 600-900 mm/min, and the distance between a nozzle and a workpiece is 25-32 mm.
Preferably, the thickness of the wear-resistant coating is 1-10 mm, and the hardness is 80-90 HRA.
The invention provides a preparation method of rare earth doped tungsten carbide composite powder, which comprises the following steps: (1) mixing water-soluble rare earth salt, water-soluble tungsten salt, a water-soluble organic carbon source and water to obtain mixed feed liquid; (2) spray drying the mixed feed liquid to obtain a rare earth doped tungsten-carbon composite; (3) and sequentially carrying out first calcination and second calcination on the rare earth doped tungsten-carbon composite to obtain the rare earth doped tungsten carbide composite powder. In the solution, rare earth and tungsten salt are uniformly mixed in an ionic form, uniform solid composite powder (rare earth-doped tungsten-carbon composite) is formed after spray drying, then the rare earth-doped tungsten-carbon composite is calcined twice, wherein the first calcination is carried out in an inert atmosphere, the tungsten salt is calcined at 450-650 ℃ to generate tungsten oxide, meanwhile, the rare earth salt is calcined to generate rare earth oxide, the second calcination is carried out in a reducing atmosphere, under the combined action of the reducing atmosphere and a carbon source, the tungsten oxide is firstly reduced into tungsten and then carbonized into tungsten carbide, and the rare earth elements are more active and can not be reduced and exist in the form of oxide; in the two-step calcining stage of the invention, the composite powder is subjected to in-situ reaction, the rare earth salt is heated to generate the oxide of the stable rare earth, the tungsten salt is gradually converted into the tungsten carbide, and no reaction can occur between the tungsten carbide and the rare earth oxide, so that the rare earth oxide is uniformly dispersed at the crystal boundary of the tungsten carbide. The preparation method provided by the invention directly prepares the rare earth doped tungsten carbide composite powder from the solution, does not need to prepare the tungsten carbide powder and then ball mill the tungsten carbide powder with the rare earth oxide, and has simple steps and easy operation.
In addition, the invention adopts the spray drying method to directly prepare the composite powder from the solution, and in the spray drying process, the solution is sprayed out through a nozzle of the atomizer by utilizing high pressure, a large amount of small droplets are formed in a drying chamber and are quickly dried, and the composite powder has higher sphericity after being dried due to the action of the surface tension of the liquid composite solution.
The invention also provides the rare earth doped tungsten carbide composite powder prepared by the preparation method in the scheme. The rare earth doped tungsten carbide composite powder prepared by the invention has high sphericity and good fluidity, is particularly suitable for automatic powder feeding, and is suitable for preparing a coating by adopting a plasma cladding method.
The invention also provides a preparation method of the rare earth doped tungsten carbide wear-resistant coating. The rare earth doped tungsten carbide wear-resistant coating is prepared by adopting a plasma cladding method, the coating can be directly prepared on the surface of a base material which is not subjected to sand blasting or acid washing by adopting the method, a pretreatment process is not needed, the obtained coating is flat and uniform, the thickness is large and can reach a millimeter level, the coating thickness is controllable, the coating is metallurgically bonded with a matrix, and the coating has better bonding force compared with a coating prepared by an electroplating method, can adapt to occasions such as heavy-load impact abrasive wear and the like, is not easy to generate fatigue spalling in working occasions such as fatigue load, impact load, cold-heat cycle, abrasive wear and the like, and has higher hardness and better wear resistance compared with a coating prepared by the traditional rare earth doped tungsten carbide composite powder.
Drawings
FIG. 1 is a scanning electron microscope image of the rare earth-doped tungsten carbide composite powder obtained in example 1;
FIG. 2 is a microstructure diagram of the interface between the rare earth doped tungsten carbide wear-resistant coating and the substrate obtained in example 1;
FIG. 3 is a surface topography of the rare earth doped tungsten carbide wear-resistant coating obtained in example 1;
FIG. 4 is a surface topography diagram of a low-carbon alloy steel test piece (left) and a 16Mn steel test piece (right) provided with a rare earth doped tungsten carbide wear-resistant coating after being worn.
Detailed Description
The invention provides a preparation method of rare earth doped tungsten carbide composite powder, which comprises the following steps:
(1) mixing water-soluble rare earth salt, water-soluble tungsten salt, a water-soluble organic carbon source and water to obtain mixed feed liquid;
(2) spray drying the mixed liquid to obtain a rare earth doped tungsten-carbon composite;
(3) sequentially carrying out first calcination and second calcination on the rare earth doped tungsten-carbon composite to obtain rare earth doped tungsten carbide composite powder; the first calcination is carried out in an inert atmosphere, the calcination temperature is 450-650 ℃, the second calcination is carried out in a reducing atmosphere, and the calcination temperature is 1000-1350 ℃.
According to the invention, water-soluble rare earth salt, water-soluble tungsten salt, water-soluble organic carbon source and water are mixed to obtain mixed feed liquid. In the present invention, the water-soluble rare earth salt includes one or more of rare earth nitrate, rare earth chloride and rare earth sulfate, the rare earth element in the water-soluble rare earth salt is lanthanum or cerium, in a specific embodiment of the present invention, the water-soluble rare earth salt is specifically one or more of lanthanum nitrate, cerium nitrate, lanthanum chloride, cerium chloride, lanthanum sulfate and cerium sulfate, in a specific embodiment of the present invention, the water-soluble rare earth salt is preferably a hydrated rare earth salt, specifically cerium nitrate hexahydrate; the water-soluble tungsten salt comprises one or more of ammonium metatungstate, ammonium tungstate and ammonium paratungstate; the water-soluble organic carbon source comprises one or more of glucose, sucrose and fructose. In the invention, the molar ratio of the rare earth element in the water-soluble rare earth salt to the tungsten element in the water-soluble tungsten salt is preferably (0.01-0.1): 1, and more preferably (0.03-0.05): 1; the mass ratio of the tungsten element in the water-soluble tungsten salt to the carbon element in the water-soluble organic carbon source is preferably (5-6): 1, and more preferably (5.3-5.5): 1.
In the specific embodiment of the present invention, preferably, the water-soluble rare earth salt and the water-soluble tungsten salt are dissolved in water, then the water-soluble organic carbon source is added, the mixture is stirred until the water-soluble organic carbon source is completely dissolved, and then the mixture is left standing for 24 hours to obtain a clear mixed feed liquid.
After the mixed material liquid is obtained, the mixed material liquid is subjected to spray drying to obtain the rare earth doped tungsten-carbon composite. In the present invention, the conditions of the spray drying preferably include: the air inlet temperature is 150-260 ℃, the more preferable temperature is 180-240 ℃, the feeding amount is 80-200 mL/min, the more preferable temperature is 100-150 mL/min, the spraying pressure is 0.5-2 MPa, the more preferable pressure is 1-1.5 MPa, the air outlet temperature is preferably 100-150 ℃, and the more preferable temperature is 120-130 ℃.
After the rare earth doped tungsten-carbon composite is obtained, the rare earth doped tungsten-carbon composite is sequentially subjected to first calcination and second calcination to obtain the rare earth doped tungsten carbide composite powder. In the invention, the first calcination is carried out in an inert atmosphere, the calcination temperature is 450-650 ℃, the preferred calcination temperature is 500-600 ℃, the preferred material layer thickness is 10-30 mm, the more preferred calcination time is 15-25 mm, the preferred calcination time is 20-60 min, and the more preferred calcination time is 30-50 min; the inert atmosphere is preferably argon or nitrogen. In the first calcination process, the tungsten salt is calcined to produce tungsten oxide and the rare earth salt is calcined to produce rare earth oxide.
In the invention, the second calcination is carried out in a reducing atmosphere, the calcination temperature is 1000-1350 ℃, the calcination temperature is 1050-1300 ℃, the material layer thickness is preferably 10-30 mm, the calcination time is preferably 15-25 mm, the calcination time is preferably 40-120 min, the calcination time is preferably 60-100 min, and the reducing atmosphere is preferably hydrogen. In the second calcining process, the tungsten oxide is reduced into tungsten firstly and then carbonized to generate tungsten carbide, while the rare earth elements are active and can not be reduced and exist in the form of rare earth oxide, and the rare earth oxide is dispersed and distributed at the grain boundary of the tungsten carbide, so that the rare earth oxide and the tungsten carbide in the obtained composite material reach an almost ideal uniform state.
The invention also provides the rare earth doped tungsten carbide composite powder prepared by the preparation method in the scheme, which is characterized by comprising tungsten carbide and the rare earth oxide doped in the tungsten carbide, wherein the rare earth oxide is dispersed in the grain boundary of the tungsten carbide in a molecular level; the content of the rare earth oxide in the rare earth-doped tungsten carbide composite powder is preferably 0.8-7.4%, more preferably 1-6%, and the average sphericity of the rare earth-doped tungsten carbide composite powder is preferably not less than 95%, more preferably 96-99%. The rare earth doped tungsten carbide composite powder provided by the invention has good sphericity and good powder fluidity, is particularly suitable for automatic powder feeding, and can meet the requirement of plasma cladding.
The invention also provides a preparation method of the rare earth doped tungsten carbide wear-resistant coating, which comprises the following steps:
and (3) directly carrying out plasma cladding on the surface of the matrix by using the rare earth doped tungsten carbide composite powder to obtain the rare earth doped tungsten carbide wear-resistant coating.
The substrate does not have special requirements, and the substrate needing surface strengthening treatment in the field can be any substrate.
The invention has no special requirements on the surface of the matrix, and can directly carry out plasma cladding on the surface of the matrix without carrying out pretreatment such as sand blasting, acid washing and the like on the matrix.
In the present invention, the plasma cladding conditions preferably include: the output power of the plasma beam is 12-15 kW, more preferably 13-14 kW, the working current is 250-350A, more preferably 280-320A, and the flow rate of the ionized gas is 0.8-1.2 m 3 More preferably 1 to 1.1 m/h 3 The flow rate of powder feeding gas is 0.8-1.2 m 3 H, more preferably 1 to 1.1m 3 The preferred shielding gas is argon, and the flow of the shielding gas is 1.5-2 m 3 More preferably 1.6 to 1.8 m/h 3 The scanning speed of the plasma beam is 600-900 mm/min, more preferably 700-800 mm/min, and the distance between the nozzle and the workpiece is 25-32 mm, more preferably 26-30 mm; the protective gas is blown into the molten pool, so that the oxidation and burning loss of the alloy elements can be prevented.
After the plasma cladding is finished, the obtained coating is preferably polished to obtain the rare earth doped tungsten carbide wear-resistant coating. In the present invention, the polishing treatment is preferably performed using a wire brush.
The invention also provides the rare earth doped tungsten carbide wear-resistant coating prepared by the preparation method in the scheme. In the invention, the thickness of the wear-resistant coating is 1-10 mm, preferably 2-8 mm, and the hardness is 80-90 HRA. The coating provided by the invention is metallurgically bonded with the substrate, and has the advantages of large and adjustable thickness, high hardness and good wear resistance.
The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention.
Example 1
(1) According to the proportion that the molar ratio of the rare earth element to the tungsten element is 0.05:1, 1488 g of ammonium metatungstate and 130.3 g of cerous nitrate hexahydrate are respectively weighed and dissolved by deionized water, and then according to the mass ratio of the W element to the C element of 5:1, adding glucose, fully stirring, and standing for 24 hours after the powder is dissolved to obtain clear mixed feed liquid;
(2) and (3) carrying out spray drying crystallization on the mixed feed liquid in a spray drying tower to obtain a uniformly mixed rare earth doped tungsten-carbon composite, wherein the spray drying parameters are as follows: the air inlet temperature is 230 ℃, the air outlet temperature is 100 ℃, the feeding amount is 100mL/min, and the spraying pressure is 0.8 Mpa;
(3) and sequentially carrying out first calcination and second calcination on the rare earth doped tungsten-carbon composite precursor, wherein the first calcination is carried out in an argon atmosphere, the thickness of a material layer is 10mm, the calcination temperature is 450 ℃, the calcination time is 20min, the second calcination is carried out in a hydrogen atmosphere, the thickness of the material layer is 10mm, the calcination temperature is 1000 ℃, the calcination time is 40min, and the rare earth oxide doped tungsten carbide powder is obtained after the two-step calcination.
FIG. 1 is a scanning electron microscope image of the rare earth-doped tungsten carbide composite powder obtained in example 1, wherein the left side of FIG. 1 is a scanning electron microscope image with a magnification of 5000 times, and the right side is a scanning electron microscope image with a magnification of 50000 times. As can be seen from fig. 1, the rare earth-doped tungsten carbide composite powder prepared in this example is spherical or nearly spherical, has high sphericity and good powder fluidity, and is particularly suitable for automatic powder feeding during plasma cladding.
The sphericity of the rare earth-doped tungsten carbide composite powder obtained in example 1 was measured, and the result showed that the average sphericity of the composite powder was 98.89%.
Example 2
The rare earth oxide doped tungsten carbide powder raw material prepared in the step 1 is used for preparing a rare earth doped tungsten carbide wear-resistant coating on the surface of low-carbon alloy steel (Q235 low-carbon steel) by adopting a plasma cladding technology, and the plasma cladding process parameters are as follows: the output power of the plasma beam is 12kW, the working current is 250A, and the flow rate of ionized gas is 0.8m 3 H, powder feeding gas flow rate is 0.8m 3 And h, blowing argon gas into a molten pool for protection in the coating preparation process to prevent the oxidation and burning loss of alloy elements, wherein the flow of protective gas is 1.5m 3 H, the scanning speed of the plasma beam is 600mm/min, and the distance between a nozzle and the workpiece is 30 mm; after the plasma cladding was completed, the resulting coating was polished with a wire brush.
FIG. 2 is a microstructure diagram of the interface between the rare earth doped tungsten carbide wear-resistant coating and the substrate obtained in example 2. As can be seen from FIG. 2, the coating and the substrate are metallurgically bonded, and the bonding force is strong.
FIG. 3 is a surface topography map of the rare earth doped tungsten carbide wear-resistant coating obtained in example 2. As can be seen from figure 3, the coating has compact structure, the rare earth composite powder is fine and is uniformly distributed in the matrix, the coating has good microstructure structure, better wear resistance can be obtained, and the thickness of the coating is more than 1.5 mm.
And (3) wear resistance test: the method is carried out on an MLS-225 type wet rubber wheel abrasive wear testing machine, and comprises the following specific steps: the grinding material is a mixture of 1000 g of water and 1500 g of quartz sand (the granularity of the quartz sand is 200-300 microns), the sample to be tested is the low-carbon alloy steel sample provided with the rare earth-doped tungsten carbide wear-resistant coating prepared in example 2, and the comparison sample is a 16Mn steel sample (not provided with a coating) with better wear resistance. Before the abrasion test, the surface of the coating to be abraded is abraded to make the whole abrasion surface have the same abrasion condition. Formal wear tests are carried out under the conditions of 70N normal load and 100rpm rotation speed, wear is carried out for 4000 revolutions, the surface appearance is observed after the wear is cleaned, the surface appearance is weighed by an electronic balance with the precision of 0.1mg, the proportion of the weight loss to the original weight is analyzed, the more the weight loss is, the poorer the wear resistance is, and the obtained results are listed in table 1.
FIG. 4 is a surface topography diagram of a low-carbon alloy steel test piece (left) and a 16Mn steel test piece (right) provided with a rare earth-doped tungsten carbide wear-resistant coating after wear. As can be seen from fig. 4, the wear of the rare earth doped tungsten carbide wear-resistant coating prepared in this example is less, which indicates that it has good wear-resistant performance.
And (3) hardness testing: the hardness of the rare earth doped tungsten carbide wear-resistant coating is obtained by adopting 60Kg load and diamond cone pressing. The results obtained are shown in Table 1.
Fold test of increase in lifetime:
by taking an uncoated low-carbon alloy steel test piece (Q235 low-carbon steel) as a reference, the service life increase times of the low-carbon alloy steel piece provided with the rare earth doped modified tungsten carbide wear-resistant coating relative to the uncoated low-carbon alloy steel test piece in the temperature environments of 100 ℃, 200 ℃ and 250 ℃ are tested, and the test method comprises the following steps: estimating the service life of a test piece by adopting a friction and wear experiment, and comparing the weight loss of the wear of the test piece with/without a coating in unit time under the same grinding medium to deduce the increase multiple of the service life, wherein the grinding medium used in the experiment is a mixture of water and quartz sand (the granularity of the quartz sand is 200-300 microns), the load is 70N, the rotating speed is 100rpm, and the increase multiple of the service life is calculated according to the following formula:
life increase times-uncoated specimen weight loss per unit time/coated specimen weight loss per unit time
The test results are listed in table 1.
Example 3
(1) The method comprises the following steps of proportioning 1220 g of ammonium tungstate and 207.8 g of lanthanum nitrate hexahydrate according to the molar ratio of the rare earth element to the tungsten element of 0.1:1, dissolving the ammonium tungstate and the lanthanum nitrate hexahydrate in deionized water, and mixing the materials according to the equivalent mass ratio of the W element to the C element of 5.5: 1, adding cane sugar, fully stirring, standing for 24 hours after the powder is dissolved to obtain clear mixed feed liquid;
(2) and (3) carrying out spray drying crystallization on the mixed feed liquid in a spray drying tower to obtain a uniformly mixed rare earth doped tungsten-carbon composite, wherein the spray drying parameters are as follows: the air inlet temperature is 240 ℃, the air outlet temperature is 110 ℃, the feeding amount is 120mL/min, and the spraying pressure is 1.0 Mpa;
(3) and sequentially carrying out first calcination and second calcination on the rare earth doped tungsten-carbon composite precursor, wherein the first calcination is carried out in a nitrogen atmosphere, the thickness of a material layer is 20mm, the calcination temperature is 550 ℃, the calcination time is 40min, the second calcination is carried out in a hydrogen atmosphere, the thickness of the material layer is 20mm, the calcination temperature is 1100 ℃, the calcination time is 80min, and the rare earth oxide doped tungsten carbide powder is obtained after the two-step calcination.
Scanning electron microscope observation is carried out on the rare earth doped tungsten carbide composite powder obtained in the example 3, and the result shows that the obtained composite powder is spherical or nearly spherical.
The sphericity of the composite powder obtained in example 3 was measured, and the result showed that the average sphericity of the composite powder was 98.3%.
The crystal phase test of the rare earth-doped tungsten carbide composite powder obtained in example 3 showed that the rare earth oxide is dispersed at the grain boundary of tungsten carbide in molecular level.
Example 4
The rare earth oxide doped tungsten carbide powder raw material prepared in the embodiment 3 is used for preparing the rare earth doped tungsten carbide wear-resistant coating on the surface of the low-carbon alloy steel by adopting a plasma cladding technology, and the plasma cladding process parameters are as follows: the output power of the plasma beam is 13kW, the working current is 300A, and the flow rate of ionized gas is 1.0m 3 H, powder feeding gas flow rate is 1.0m 3 And h, blowing argon gas into a molten pool for protection in the coating preparation process to prevent the oxidation and burning loss of alloy elements, wherein the flow of protective gas is 1.5m 3 The scanning speed of the plasma beam is 700mm/min, and the distance between a nozzle and the workpiece is 30 mm; after the plasma cladding was completed, the resulting coating was polished with a wire brush.
The microstructure at the bonding interface of the rare earth doped tungsten carbide wear-resistant coating obtained in the example 4 and the substrate is observed, and the result shows that the coating and the substrate are metallurgically bonded.
The surface morphology of the rare earth doped tungsten carbide wear-resistant coating obtained in example 4 was observed, and the result showed that the coating thickness was 2 mm.
The wear resistance, hardness and life time increase factor of the rare earth doped tungsten carbide wear-resistant coating obtained in example 4 were measured in the manner as in example 2, and the results are shown in table 1.
Example 5
(1) According to the molar ratio of the rare earth element to the tungsten element of 0.1:1, respectively weighing 1420 g of ammonium paratungstate and 13 g of cerium chloride, dissolving the ammonium paratungstate and the cerium chloride in deionized water, and then according to the mass ratio of the W element to the C element of 6: 1, adding fructose, fully stirring, standing for 24 hours after the powder is dissolved to obtain clear mixed feed liquid;
(2) and (3) carrying out spray drying crystallization on the mixed feed liquid in a spray drying tower to obtain a uniformly mixed rare earth doped tungsten-carbon composite, wherein the spray drying parameters are as follows: the air inlet temperature is 250 ℃, the air outlet temperature is 120 ℃, the feeding amount is 140mL/min, and the spraying pressure is 1.2 Mpa;
(3) and sequentially carrying out first calcination and second calcination on the rare earth doped tungsten-carbon composite precursor, wherein the first calcination is carried out in a nitrogen atmosphere, the thickness of a material layer is 30mm, the calcination temperature is 650 ℃, the calcination time is 60min, the second calcination is carried out in a hydrogen atmosphere, the thickness of the material layer is 30mm, the calcination temperature is 1200 ℃, the calcination time is 120min, and the rare earth oxide doped tungsten carbide powder is obtained after the two-step calcination is completed.
Scanning electron microscope observation is carried out on the rare earth doped tungsten carbide composite powder obtained in the example 5, and the result shows that the obtained composite powder is spherical or nearly spherical.
The sphericity of the composite powder obtained in example 5 was measured, and the result showed that the average sphericity of the composite powder was 96.6%.
The crystal phase test of the rare earth-doped tungsten carbide composite powder obtained in example 5 showed that the rare earth oxide is dispersed at the grain boundary of tungsten carbide in molecular level.
Example 6
Doping with rare earth oxide prepared in example 5Preparing a rare earth doped tungsten carbide wear-resistant coating on the surface of low-carbon alloy steel by using a plasma cladding technology, wherein the plasma cladding process parameters are as follows: the output power of the plasma beam is 13kW, the working current is 320A, and the flow rate of the ionized gas is 1.0m 3 H, powder feeding gas flow rate of 1.0m 3 H, blowing argon into a molten pool in the coating preparation process for protection to prevent the oxidation and burning loss of alloy elements, wherein the flow of protective gas is 1.5m 3 H, the scanning speed of the plasma beam is 800mm/min, and the distance between a nozzle and the workpiece is 30 mm; after the plasma cladding was completed, the resulting coating was polished with a wire brush.
The microstructure at the bonding interface of the rare earth doped tungsten carbide wear-resistant coating obtained in the example 6 and the substrate is observed, and the result shows that the coating and the substrate are metallurgically bonded.
The surface morphology of the rare earth doped tungsten carbide wear-resistant coating obtained in example 6 was observed, and the result showed that the coating thickness was 2 mm.
The wear resistance, hardness and life time increase factor of the rare earth doped tungsten carbide wear-resistant coating obtained in example 6 were measured in the manner as in example 2, and the results are shown in table 1.
Example 7
(1) According to the molar ratio of the rare earth element to the tungsten element of 0.05:1, respectively weighing 1785 g of ammonium metatungstate, 78.6 g of cerous nitrate hexahydrate and 78.4 g of lanthanum nitrate hexahydrate, dissolving the materials in deionized water, and then, according to the mass ratio of the W element to the C element of 5:1, adding glucose, fully stirring, and standing for 24 hours after the powder is dissolved to obtain clear mixed feed liquid;
(2) and (3) carrying out spray drying crystallization on the mixed feed liquid in a spray drying tower to obtain the uniformly mixed rare earth doped tungsten-carbon composite, wherein the spray drying parameters are as follows: the air inlet temperature is 240 ℃, the air outlet temperature is 110 ℃, the feeding amount is 100mL/min, and the spraying pressure is 1.4 Mpa;
(3) and sequentially carrying out first calcination and second calcination on the rare earth doped tungsten-carbon composite precursor, wherein the first calcination is carried out in an argon atmosphere, the material layer thickness is 20mm, the calcination temperature is 550 ℃, the calcination time is 40min, the second calcination is carried out in a hydrogen atmosphere, the material layer thickness is 20mm, the calcination temperature is 1100 ℃, the calcination time is 80min, and the rare earth oxide doped tungsten carbide powder is obtained after the two-step calcination is completed.
Scanning electron microscope observation is carried out on the rare earth doped tungsten carbide composite powder obtained in the example 7, and the result shows that the obtained composite powder is spherical or nearly spherical.
The sphericity of the composite powder obtained in example 7 was measured, and the result showed that the average sphericity of the composite powder was 97.2%.
The crystal phase test of the rare earth-doped tungsten carbide composite powder obtained in example 7 showed that the rare earth oxide is dispersed in the grain boundary of tungsten carbide in molecular level.
Example 8
The rare earth oxide doped tungsten carbide powder prepared in the embodiment 7 is used as a raw material, a plasma cladding technology is adopted to prepare the rare earth doped tungsten carbide wear-resistant coating on the surface of the low-carbon alloy steel, and the plasma cladding process parameters are as follows: the output power of the plasma beam is 15kW, the working current is 350A, and the flow rate of ionized gas is 1.0m 3 H, powder feeding gas flow rate is 1.0m 3 And h, blowing argon gas into a molten pool for protection in the coating preparation process to prevent the oxidation and burning loss of alloy elements, wherein the flow of protective gas is 1.5m 3 H, the scanning speed of the plasma beam is 900mm/min, and the distance between a nozzle and the workpiece is 30 mm; and after the plasma cladding is finished, polishing the obtained coating by using a steel wire brush.
The microstructure at the bonding interface of the rare earth doped tungsten carbide wear-resistant coating obtained in the example 8 and the substrate is observed, and the result shows that the coating and the substrate are metallurgically bonded.
The surface morphology of the rare earth-doped tungsten carbide wear-resistant coating obtained in example 8 was observed, and the result showed that the coating thickness was 3 mm.
The wear resistance, hardness and life time increase factor of the rare earth doped tungsten carbide wear resistant coating obtained in example 8 were measured in the manner as in example 2, and the results are shown in table 1.
Table 1 results of hardness, abrasion resistance and life increase factor test of abrasion resistant coatings obtained in examples 2, 4, 6 and 8
| Test experiment | Example 2 | Example 4 | Example 6 | Example 8 | Comparative example |
| HRA hardness | 90 | 88 | 86 | 83 | 70 |
| Abrasion resistance test (loss of weight ratio) | 4～5％ | 5～6％ | 5.5～6.5％ | 7～8％ | 12～15％ |
| Increase in lifetime at 100 DEG C | 7.5 | 7 | 6.5 | 6 | — |
| Life increase factor at 200 DEG C | 5.5 | 5 | 4.5 | 4 | — |
| Life increase factor at 250 DEG C | 3.5 | 3.2 | 3.2 | 3 | — |
According to the data in table 1, it can be seen that the rare earth doped modified tungsten carbide wear-resistant coating prepared by the invention can obviously improve the hardness and wear resistance of a workpiece and prolong the service life of the workpiece at high temperature, wherein the hardness and wear resistance of the coating obtained in example 1 are the best.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and amendments can be made without departing from the principle of the present invention, and these modifications and amendments should also be considered as the protection scope of the present invention.
Claims (9)
1. The preparation method of the rare earth doped tungsten carbide composite powder is characterized by comprising the following steps:
(1) mixing water-soluble rare earth salt, water-soluble tungsten salt, a water-soluble organic carbon source and water to obtain mixed feed liquid; the water-soluble organic carbon source comprises one or more of glucose, sucrose and fructose;
(2) spray drying the mixed feed liquid to obtain a rare earth doped tungsten-carbon composite;
(3) sequentially carrying out first calcination and second calcination on the rare earth doped tungsten-carbon composite to obtain rare earth doped tungsten carbide composite powder; the first calcination is carried out in an inert atmosphere, the calcination temperature is 450-650 ℃, the second calcination is carried out in a reducing atmosphere, and the calcination temperature is 1000-1350 ℃; the rare earth-doped tungsten carbide composite powder comprises tungsten carbide and rare earth oxide doped in the tungsten carbide, the rare earth oxide is dispersed in the grain boundary of the tungsten carbide in a molecular level, and the average sphericity of the rare earth-doped tungsten carbide composite powder is more than or equal to 95%.
2. The preparation method of claim 1, wherein the water-soluble rare earth salt comprises one or more of rare earth nitrate, rare earth chloride and rare earth sulfate, and the rare earth element in the water-soluble rare earth salt is lanthanum or cerium; the water-soluble tungsten salt comprises one or more of ammonium metatungstate, ammonium tungstate and ammonium paratungstate.
3. The method according to claim 1 or 2, wherein the water-soluble rare earth salt contains a rare earth element and
the molar ratio of the tungsten element in the water-soluble tungsten salt is (0.01-0.1): 1; the mass ratio of the tungsten element in the water-soluble tungsten salt to the carbon element in the water-soluble organic carbon source is (5-6): 1.
4. The method of claim 1, wherein the spray-drying conditions comprise: the air inlet temperature is 150-260 ℃, the feeding amount is 80-200 mL/min, and the spraying pressure is 0.5-2 Mpa.
5. The preparation method according to claim 1, wherein the thickness of the first calcined material layer is 10-30 mm, and the calcination time is 20-60 min; the thickness of the material layer subjected to the second calcination is 10-30 mm, and the calcination time is 40-120 min; the reducing atmosphere is hydrogen.
6. The rare earth-doped tungsten carbide composite powder prepared by the preparation method of any one of claims 1 to 5, which is characterized by comprising tungsten carbide and rare earth oxide doped in the tungsten carbide, wherein the rare earth oxide is dispersed in a grain boundary of the tungsten carbide in a molecular level manner, and the average sphericity of the rare earth-doped tungsten carbide composite powder is not less than 95%.
7. The preparation method of the rare earth doped tungsten carbide wear-resistant coating is characterized by comprising the following steps:
the rare earth doped tungsten carbide composite powder of claim 6 is directly coated on the surface of a substrate by plasma cladding to obtain the rare earth doped tungsten carbide wear-resistant coating.
8. The method of claim 7, wherein the plasma cladding conditions include: the output power of the plasma beam is 12-15 kW, the working current is 250-350A, and the flow rate of the ionized gas is 0.8-1.2 m 3 Per hour, the flow of powder feeding gas is 0.8-1.2 m 3 H, the protective gas is argon, and the flow of the protective gas is 1.5-2 m 3 The scanning speed of the plasma beam is 600-900 mm/min, and the distance between the nozzle and the workpiece is 25-32 mm.
9. The preparation method according to claim 7 or 8, wherein the wear-resistant coating has a thickness of 1-10 mm and a hardness of 80-90 HRA.
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