Preparation of ultra-high-speed laser cladding Al2O3 metal ceramic composite coating

Abstract

The invention relates to the field of metal materials, in particular to a preparation method of an ultra-high-speed laser cladding Al2O3 metal ceramic coating. The method comprises the following steps that iron-based metal powder, aluminum oxide ceramic powder and silicon powder are prepared according to the design proportion, the iron-based metal powder, the aluminum oxide ceramic powder and the silicon powder are evenly mixed and then subjected to ultra-high-speed laser cladding, the mass percent of aluminum oxide in the obtained composite powder is 6-10%, the mass percent of silicon powder in the obtained composite powder is 0.5-5%, and when ultra-high-speed laser cladding is carried out, the thickness of the composite powder ranges from 0.5 mm to 5 mm; the laser power ranges from 1500 W to 2400 W, the scanning speed ranges from 12 m / min to 20 m / min, the defocusing amount is + 1 mm, the powder feeding amount ranges from 22 g / min to 30 g / min, the lap joint rate ranges from 60% to 65%, and powder feeding and protective gas is argon. The component design is reasonable, the cost is low, and the obtained product is high in hardness, resistant to corrosion and convenient for industrial application.

Description

Technical Field

[0001] The present invention relates to the field of metal materials, and particularly to a method for preparing an ultra-high speed laser cladding Al2O3 metal ceramic coating. Background Art

[0002] During the use of steel materials, local wear and surface corrosion are likely to occur. Overall replacement of materials in industry will cause huge economic pressure. Therefore, coating protection is the most effective and economical measure in actual industrial production. Metal ceramic coatings are usually composed of metal alloys and ceramic reinforcing phases. They have both the high plasticity, toughness and high strength of metals and the high hardness, high wear resistance, high melting point and other advantages of ceramic phases, and are considered to be the most potential coatings. Among various ceramic materials, alumina ceramics have low cost. Mixing it with iron-based metal powders to prepare metal ceramic coatings has high economic value and application value.

[0003] From the currently disclosed information (such as patent CN111627503A), during the preparation process of alumina coatings, due to the characteristics of ultra-high speed laser cladding processing, the heating and cooling rates are extremely fast. This will result in a large temperature gradient on the same processed workpiece, with different temperatures at different parts, leading to asynchronous melting and solidification at different parts of the workpiece, and thus thermal stress will be generated. Some parts with large temperature differences will be in different phases, and the phase changes are asynchronous. The specific volumes between different phases are also different, and the expansion and contraction are mutually restricted, resulting in stress, which causes a large number of cracks and voids and other defects on the surface of the alumina ceramic coating. At the same time, alumina has a small density. When the powder particle size is small, its fluidity is very poor, which is not conducive to laser cladding. In addition, alumina also has a high laser reflectivity, which greatly reduces the laser absorption rate of the powder. Therefore, in the current related research on the surface preparation of alumina ceramic coatings, the alumina ceramic phase has always been used as the main additive phase, and rare earth or other precious metal oxides are doped and cladded to prepare composite coatings [1-3] , but such high costs are obviously not conducive to wide industrial promotion and application.

[0004] Element Si is beneficial to corrosion resistance, abundant in the earth's crust and cheap. Element Si can form eutectics with most metal elements (such as Fe, Co, Ni, etc.) at high temperatures, greatly reducing the melting point of the alloy. Then, under the action of laser energy, metal powders containing a certain amount of Si can form a molten pool earlier. During the process of the molten metal continuing to heat up and turn into a plasma state, the viscosity of the molten pool rapidly decreases, and the fluidity is improved. In addition, during the laser cladding process, although protected by an inert atmosphere, oxidation is still inevitable. Due to thermodynamic reasons, when most silicon-containing alloys are oxidized, element Si reacts first to form SiO2, and these SiO2 will accumulate on the surface of the molten pool, hindering subsequent oxidation.

[0005] [1]Su H J, Liu H F, Jiang H, et al. One-step preparation of melt-grown Al2O3 / GdAlO3 / ZrO2 eutectic ceramics with large size and irregular shapeby directed energy deposition[J]. Additive manufacturing, 2023, 70: 103563.

[0006] [2]Seyed H M, Masoud M, Mansour R, et al. Reaction behavior and wearproperties of in-situ air plasma-sprayed Al2O3-TiB2 composite coatings[J].Journal of the European Ceramic Society, 2023, 43(13): 6482-6492.

[0007] [3]Aghajani H, Valefi Z, Zamani P. Phase composition, microstructure,mechanical properties, and wear performance of nanostructured Al2O3 and Al2O3-Y2O3 coatings deposited by plasma spraying[J]. Applied Surface Science, 2022,585: 152754. Summary of the Invention

[0008] In view of the problems of oxidation, cracks, etc. that occur when alumina powder is added to metal powder with a large mass ratio / volume ratio as a reinforcing phase, which greatly affect the performance and application of the coating, and the laser reflectivity of alumina powder is greater than 90%, which will greatly reduce the utilization rate of laser during laser cladding. Based on Patent 2024104331261, a technology for preparing a composite coating by mixing appropriate amounts of iron-based metal powder, alumina powder and silicon powder is proposed, so as to improve and solve the problems of low laser efficiency of alumina ceramic powder and oxidation and cracks in the metal ceramic coating containing alumina powder with a large mass ratio / volume ratio.

[0009] A preparation method of an ultra-high speed laser cladding Al2O3 metal ceramic coating according to the present invention includes the following steps:

[0010] Step 1

[0011] Weigh iron-based metal powder, alumina powder and silicon powder according to the designed ratio; mix the three evenly to obtain a mixed powder for standby. In the mixed powder, the mass percentage content of alumina powder is 6-10%, the mass percentage content of silicon powder is 0.5-5%, and the balance is iron-based metal powder.

[0012] Step 2

[0013] Take the substrate with a clean and dry surface as the treatment object, and use the mixed powder obtained in Step 1 as the coating raw material. Adopt the ultra-high speed laser cladding technology to prepare an Al2O3 metal ceramic composite coating on the surface of the substrate; when performing ultra-high speed laser cladding, control the laser power at 1500-2400W, the scanning speed at 12-20m / min, the defocus amount at +1mm, the powder feeding amount at 22-30g / min, and the overlapping rate at 60-65%. The powder feeding gas and the protective gas are both argon; the substrate is a steel material.

[0014] Preferably, in the mixed powder, the mass percentage content of alumina powder is 7-9%, further preferably 8%, the mass percentage content of silicon powder is 0.5-3.5%, further preferably 0.7-1.2%, and even more preferably 0.9-1.1%, and the balance is iron-based metal powder.

[0015] Preferably, the substrate is selected from one of 45 steel and 40Cr steel.

[0016] Preferably, in Step 2, when performing ultra-high speed laser cladding, control the laser power at 2100W, the scanning speed at 12m / min, the defocus amount at +1mm, the powder feeding amount at 26g / min, and the overlapping rate at 60%. The powder feeding gas and the protective gas are both argon, and the substrate bar is one of 45 steel and 40Cr steel.

[0017] During the ultra-high speed laser cladding process, the fast laser scanning speed effectively reduces the material loss and improves the material utilization rate. At the same time, due to the high scanning speed, the cooling speed of the coating is fast, and a finer and more uniform grain structure can be obtained, which helps to improve the hardness and wear resistance of the coating.

[0018] In order to obtain a substrate with a clean and dry surface, the present invention adopts a process including: removing impurities and oil stains on its surface.

[0019] When the base material is a rod, a lathe can be used to machine the rod-shaped base material, remove any impurities and oil stains that may remain on the surface, wipe the base rod with alcohol, and after the surface is clean, wrap it with plastic wrap to prevent new scratches and oxidation on the surface.

[0020] In the present invention, the powder raw materials used in ultra-high-speed laser cladding include iron-based metal powder, Al2O3 ceramic powder, and Si powder.

[0021] In the iron-based metal powder of the present invention, the content of each element and its mass percentage are as follows: Cr: 16 - 20%, Ni: 9 - 13%, Mo: 1 - 2%, B: 0.5 - 2%, Si: 0 - 1%, and the balance is Fe; the purity of both the Al2O3 ceramic powder and the Si powder is greater than 99.99%.

[0022] As a further preference, in the iron-based metal powder of the present invention, the content of each element and its mass percentage are as follows: Cr: 18%, Ni: 11%, Mo: 2%, B: 1%, Si: 0 - 1%, and the balance is Fe. In the present invention, the sphericity of the iron-based powder is ≥90%, and the particle size distribution range is 70 - 100 μm; the sphericity of the Al2O3 powder is ≥90%, and the particle size distribution range is 50 - 70 μm; the Si powder is irregular in shape, and the particle size distribution range is 1 - 5 μm.

[0023] In the present invention, the alumina powder, iron-based metal powder, and silicon powder are mixed in proportion and loaded into a powder tank. When the ball-to-material mass ratio is 1 - 2:1, preferably 1:1, it is placed on a horizontal mixer and uniformly mixed at a speed of 120 revolutions per minute for 4 - 10 h, preferably 7 - 9 h. The obtained powder is dried in a drying oven before use, the drying temperature is 60 - 85 °C, and the time is 30 - 150 min.

[0024] In industrial production applications, when the base is 40Cr steel, before ultra-high-speed laser cladding, the pretreated rod-shaped base material is fixed in the coordinate system of the equipment using a fixture and wiped with alcohol to ensure that there is no impurity residue on the surface. During ultra-high-speed laser cladding, powder feeding is carried out in a coaxial powder feeding manner.

[0025] The coated rods obtained in the present invention are used directly or subjected to cutting treatment; after cutting treatment, they are polished successively with sandpapers of 400, 800, 1200, and 2000 meshes, and then polished.

[0026] In the present invention, by selecting appropriate powder components and laser cladding process parameters, metallurgical bonding between the base and the coating can be achieved, and the average microhardness of the coating is greater than 600 HV 0.2 , without macroscopic cracks and defects, and the self-corrosion current is about 1.3×10 -7 A / cm 2 , and the self-corrosion potential is about -0.47 VSCE The friction coefficient of the coating is about 0.56.

[0027] Principle and advantages

[0028] The present invention uses an appropriate amount of Si to improve and solve the poor bonding and fluidity between the Al2O3 ceramic phase and the metal matrix, and avoids the oxidation problem of metal alloy elements (such as Fe, Cr, Ni, etc.). Under the synergistic effect of appropriate printing parameters, not only the risk of cracking of the Al2O3 ceramic composite coating is greatly reduced, but also the wear and corrosion resistance of the Al2O3 ceramic composite coating is improved. Compared with other methods, the cost is lower, the surface flatness of the obtained cermet coating is high, there are no obvious defects such as oxidation and pores, the grains are fine, the thickness is uniform, a good metallurgical bond is formed with the matrix, the hardness is high, the wear resistance is good, the corrosion resistance is good, and the process cycle is short and the material waste is less. Description of the drawings

[0029] Figure 1 Macrographs of the coatings obtained in Example 1, Example 4 and Example 5;

[0030] Figure 2 Physical drawing coatings obtained by cutting the square openings in Example 4 and Comparative Example 1;

[0031] Figure 3 (a) and (b) are respectively the cross-sectional micrographs of the coatings in Comparative Example 1 and Example 1;

[0032] Figure 4 Potentiodynamic polarization curves of Example 1, Example 2, Example 3, Comparative Example 1 and Comparative Example 2;

[0033] Figure 5 Friction coefficient curves of Example 1, Example 2, Example 3 and Comparative Example 1;

[0034] Figure 6 Cross-sectional micrograph of the coating in Comparative Example 5. Detailed implementation manners

[0035] In the embodiments and comparative examples of the present invention, a Shimadzu HMV-2T hardness tester was used to measure the microhardness of the coating cross-section. Among them, the load was 1.96 N and the loading time was 10 s; a Multi Autolab / M204 electrochemical workstation was used to measure the polarization curve of the coating. The workstation consisted of three electrodes. Among them, the counter electrode was a platinum electrode, the reference electrode was a saturated calomel electrode (SCE), and the working medium was a 3.5 wt.% NaCl solution. The test range of the polarization curve was ±300 mv near the open circuit potential, and the scanning speed was 5 mv / s; a UMT-3 reciprocating friction and wear tester was used to conduct friction and wear experiments. The wear conditions were dry friction at room temperature. The grinding ball was a Si3N4 ceramic ball, the load was 30 N, the frequency was 30 Hz, and the time was 40 min.

[0036] Example 1

[0037] Weigh a certain amount of iron-based metal powder (Cr: 18%, Ni: 11%, Mo: 1.5%, B: 1.25%, Si: 1%, the balance is Fe), alumina ceramic powder and silicon powder with a balance. Among them, the mass percentages of alumina powder and silicon powder are 8% and 1%, respectively, and the rest is iron-based metal powder.

[0038] The sphericity of the iron-based powder is ≥90%, and the particle size distribution range is 70~100μm; the sphericity of the Al2O3 powder is ≥90%, and the particle size distribution range is 50~70μm; the Si powder is irregular in shape, and the particle size distribution range is 1~5μm.

[0039] Put the weighed mixed powder into a horizontal mixer, select a ball-to-material mass ratio of 1:1, put it on the horizontal mixer, and mix it evenly at a speed of 120 rpm for 8 h.

[0040] Screen the ball-milled composite powder, and select the composite powder with a particle size range of 38~75μm.

[0041] Use the above iron-based metal ceramic composite powder for ultra-high-speed laser cladding to strengthen and repair the surface of the substrate. The specific steps are as follows:

[0042] Machine the surface of the substrate (40Cr steel) to remove the surface oxide film;

[0043] Wipe the surface of the substrate with anhydrous ethanol to remove the residual surface grease after machining;

[0044] Dry the powder, control the temperature at 80°C and the time at 60 min;

[0045] Ultra-high-speed laser cladding is carried out with the following cladding process parameters: the laser defocus amount is +1 mm, the laser power is 2100 W, the laser scanning speed is 12 m / min, the powder feeding speed is 26 g / min, the overlap rate between tracks is 60%, and both the powder feeding gas and the shielding gas are argon.

[0046] The obtained coating shows no obvious oxidation. The hardness of the coating is detected using a micro-Vickers hardness tester, and the average hardness can reach 620 HV. 0.2 The self-corrosion voltage measured using an electrochemical workstation is -0.46 V, and the self-corrosion current is 1.3×10 -6 A / cm 2 After entering the stable wear stage, the friction coefficient stabilizes at 0.56, and the volumetric wear amount is 4.76×10 -3 mm 3 .

[0047] The Vickers hardness of the substrate 40Cr steel is 350 HV. 0.2 , the self-corrosion voltage is -0.612 V. SCE , the self-corrosion current is 2.04×10 -5 A / cm 2 , and the coating performance is significantly better than that of the substrate.

[0048] Comparative Example 1

[0049] Other conditions are the same as those in Example 1, except that: no silicon powder is added, the mass percentage of alumina powder in the composite powder is the same as that in Example 1, and the balance is iron-based metal powder; the performance of the obtained coating is: there is a metallurgical bond between the substrate and the coating, there is a certain degree of oxidation on the coating surface, and its average microhardness is 556 HV. 0.2 , the self-corrosion voltage measured using an electrochemical workstation is -0.55 V, and the self-corrosion current is 7.9×10 -6 A / cm 2 . Due to the presence of pores, the friction coefficient of this coating is not stable and shows a slow increasing trend. The volumetric wear amount of the coating is 5.41×10 -3 mm 3 .

[0050] Comparative Example 2

[0051] Other conditions are the same as those in Example 1, except that: the cladding process parameters are: the laser defocus amount is -1 mm, the laser power is 2100 W, the laser scanning speed is 0.9 m / min, the powder feeding amount is 8.7 g / s, the overlap rate between tracks is 60%, and both the powder feeding gas and the shielding gas are argon.

[0052] The average microhardness of the coating is 590 HV. 0.2, the self - corrosion voltage measured by an electrochemical workstation is - 0.55V, and the self - corrosion current is 5.6×10 -6 A / cm 2 . After entering the stable wear stage, the friction coefficient stabilizes at 0.8, and the volumetric wear amount is 6.36×10 -3 mm 3 .

[0053] Example 2

[0054] Other conditions are the same as those in Example 1, except that: the mass percentage of silicon powder in the mixed powder is 0.5%; the average micro - hardness of the obtained coating is 550 HV 0.2 , the self - corrosion voltage measured by an electrochemical workstation is - 0.56V, and the self - corrosion current is 9.6×10 -6 A / cm 2 . It can be seen from Example 1, Example 2 and Comparative Example 1 that the scheme of adding 0.5% silicon powder is only better than that of the substrate, and its effect is actually inferior to the scheme of only adding an appropriate amount of alumina.

[0055] Example 3

[0056] Other conditions are the same as those in Example 1, except that: the mass percentage of silicon powder in the mixed powder is 2%; the average micro - hardness of the obtained coating is 480 HV 0.2 , the self - corrosion voltage measured by an electrochemical workstation is - 0.59V, and the self - corrosion current is 12.5×10 -6 A / cm 2 . It can be seen from Example 1, Example 3 and Comparative Example 1 that the scheme of adding 2.0% silicon powder is only better than that of the substrate, and its effect is actually inferior to the scheme of only adding an appropriate amount of alumina. It can be seen from Example 1, Example 2 and Example 3 that to obtain the best effect, the addition amount of silicon powder must be strictly controlled, such as 1%.

[0057] Example 4

[0058] Other conditions are the same as those in Example 1, except that: when performing ultra - high - speed laser cladding, the laser power is adjusted to 2400W; the average micro - hardness of the obtained coating is 585HV 0.2 , the self - corrosion voltage measured by an electrochemical workstation is - 0.55V, and the self - corrosion current is 8.6×10 -6 A / cm 2 .

[0059] It can be seen from Example 1, Example 4 and Comparative Example 2 that the printing parameters have a great impact on the product.

[0060] Example 5

[0061] Other conditions are the same as those in Example 1, except that: during ultra-high-speed laser cladding, the scanning speed is 15 m / min; the average microhardness of the obtained coating is 610 HV 0.2 , and the self-corrosion voltage measured using an electrochemical workstation is -0.58 V, and the self-corrosion current is 8.5×10 -6 A / cm 2 .

[0062] It can be seen from Example 1, Example 5 and Comparative Example 2 that the printing parameters have a great influence on the product.

[0063] Example 6

[0064] Other conditions are the same as those in Example 1, except that: during ultra-high-speed laser cladding, the powder feeding speed is 30 g / min; the average microhardness of the obtained coating is 574 HV 0.2 , and the self-corrosion voltage measured using an electrochemical workstation is -0.52 V, and the self-corrosion current is 4.7×10 -6 A / cm 2 .

[0065] It can be seen from Example 1, Example 6 and Comparative Example 2 that the printing parameters have a great influence on the product.

[0066] Comparative Example 3

[0067] Other conditions are the same as those in Example 1, except that: during ultra-high-speed laser cladding, the overlapping rate is 80%, the surface of the obtained coating is severely oxidized, and there will be pits of different sizes on the surface of the coating after slightly polishing with sandpaper, and the surface quality is very poor.

[0068] Comparative Example 4

[0069] Other conditions are the same as those in Example 1, except that: the cladding process parameters are: the laser defocus amount is -1 mm, the laser power is 1750 W, the laser scanning speed is 9.6 m / min, the powder feeding rate is 8.7 g / s, the overlapping rate between tracks is 70%, and both the powder feeding gas and the shielding gas are argon.

[0070] The average microhardness of the coating is 600 HV 0.2 , and the self-corrosion voltage measured using an electrochemical workstation is -0.58 V, and the self-corrosion current is 7.2×10 -6 A / cm 2 . After entering the stable wear stage, the friction coefficient stabilizes at 0.7, and the volumetric wear amount is 5.84×10 -3 mm 3 .

[0071] Comparative Example 5

[0072] Other conditions are consistent with Example 1, except that: by mass ratio, stainless steel 316L powder: alumina powder = 8:2, weigh stainless steel 316L powder (particle size 30~50μm) and 60~80μm alumina powder; put them into a powder tank, put them into a twin-shaft mixer at a ball-to-material mass ratio of 1:1, and mix them evenly at a speed of 120 rpm for 8 hours to obtain Al2O3-316L mixed powder, and dry the powder in a drying oven before use, at a drying temperature of 150°C and a time of 1 hour. Al2O3-316L mixed powder was used to replace the powder used for printing in the example, and printing was performed according to the printing parameters of Example 1, and the coating was obviously cracked.

Claims

1. A method for preparing Al2O3 metal ceramic composite coating by ultra-high speed laser cladding, characterized in that: The steps include: Step 1 Preparing iron-based metal powder, aluminum oxide powder and silicon powder according to the designed proportion; mixing the three evenly to obtain a mixed powder for standby use, wherein the mass percentage of aluminum oxide powder is 6-10%, the mass percentage of silicon powder is 0.5-5%, and the balance is iron-based metal powder; Step 2 A substrate with a clean and dry surface is taken as the treatment object, the mixed powder obtained in step 1 is taken as the coating raw material, and the Al2O3 metal ceramic composite coating is prepared on the surface of the substrate by adopting ultra-high-speed laser cladding technology; when performing ultra-high-speed laser cladding, the laser power is controlled to be 1500~2400W, the scanning speed is 12~20m / min, the defocus amount is +1mm, the powder feeding amount is 22~30g / s, the overlap rate is 60~65%, and the powder feeding gas and the protective gas are both argon; the substrate is a steel material.

2. The method for preparing Al2O3 metal-ceramic composite coating by ultra-high-speed laser cladding according to claim 1, characterized in that: In the mixed powder, the mass percentage of aluminum oxide powder is 7-9%, preferably 8%, the mass percentage of silicon powder is 0.5-3.5%, preferably 0.7-1.2%, and the balance is iron-based metal powder.

3. The method for preparing Al2O3 metal-ceramic composite coating by ultra-high-speed laser cladding according to claim 1, characterized in that: The content of each element and mass percentage of the iron-based metal powder is: Cr: 16-20%, Ni: 9-13%, Mo: 1-2%, B: 0.5-2%, Si: 0-1%, and the balance is Fe; The purity of the Al2O3 ceramic powder and Si powder is greater than 99.99%.

4. The method for preparing Al2O3 metal-ceramic composite coating by ultra-high-speed laser cladding according to claim 1, characterized in that: The sphericity of iron-based metal powder is ≥90%, and the particle size distribution range is 70~100μm; The sphericity of Al2O3 powder is ≥90%, and the particle size distribution range is 50~70μm; The Si powder is irregular in shape and has a particle size distribution range of 1~5μm.

5. The method for preparing Al2O3 metal-ceramic composite coating by ultra-high-speed laser cladding according to claim 1, characterized in that: Alumina powder, iron-based metal powder and silicon powder are mixed in proportion and loaded into a powder tank. When the mass ratio of the ball material is 1-2:1, preferably 1:1, the powder is placed in a horizontal mixer and uniformly mixed at a speed of 120 rpm for 4-10 hours, preferably 7-9 hours. The obtained powder is dried in a drying oven before use at a drying temperature of 60-85°C for 30-150 minutes.

6. The method for preparing Al2O3 metal-ceramic composite coating by ultra-high-speed laser cladding according to claim 1, characterized in that: When the substrate is a rod, before ultra-high-speed laser cladding, the pre-treated rod-shaped substrate is fixed in the coordinate system of the equipment with a fixture and wiped with alcohol to ensure that no impurities remain on the surface.

7. The method for preparing Al2O3 metal-ceramic composite coating by ultra-high-speed laser cladding according to claim 1, characterized in that: When performing ultra-high-speed laser cladding, coaxial powder feeding is used for powder feeding.

8. The method for preparing Al2O3 metal-ceramic composite coating by ultra-high-speed laser cladding according to claim 1, characterized in that: The obtained coated rod is directly used or cut; after cutting, it is grinded with sandpaper of 400, 800, 1200 and 2000 meshes in sequence, and then polished.

9. The method for preparing Al2O3 metal-ceramic composite coating by ultra-high-speed laser cladding according to claim 1, characterized in that: In step 2, during printing, the laser power is controlled to 2100 W, the scanning speed is 12 m / min, the defocus is +1 mm, the powder feeding amount is 26 g / min, the overlap rate is 60%, the powder feeding gas and the protective gas are both argon, and the base rod is one of 40Cr steel and 45 steel.

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