High-hardness nickel-based composite powder for laser cladding and laser cladding method thereof

Abstract

The invention discloses high-hardness nickel-based composite powder for laser cladding and a laser cladding method thereof.The composite powder is composed of 1-4 wt% of nearly-spherical pure aluminum powder and the balance nickel-based high-temperature alloy powder, the average particle size of the nearly-spherical pure aluminum powder is 100-150 microns, the average particle size of the nickel-based high-temperature alloy powder is 75-150 microns, and the nickel-based high-temperature alloy powder is composed of 15-17 wt% of Cr, 2-4 wt% of Fe, 3-4 wt% of B, 1-2 wt% of Si, 0.5-1 wt% of C and the balance Fe. And the balance of Ni. According to the method, the two kinds of powder are evenly mixed through the acoustic resonance mixing technology, molten pool flowing and solidification in laser cladding are changed by regulating and controlling the content of aluminum powder, the crack sensitivity is reduced, and therefore a large-area crack-free cladding layer is obtained, meanwhile, the Cr element in the nickel-based high-temperature alloy powder can react with the B element and the C element so that hard ceramic phase chromium boride and chromium carbide can be separated out, and therefore the large-area crack-free cladding layer can be obtained. And the hardness of the cladding layer is greatly improved.

Description

Technical Field

[0001] This invention relates to the field of laser cladding and surface modification technology, specifically to a high-hardness nickel-based composite powder for laser cladding and its laser cladding method. Background Technology

[0002] Laser cladding is an advanced surface modification technology that uses a high-energy laser beam to simultaneously melt alloy powder and a thin layer on the substrate surface, forming a reinforced coating that is metallurgically bonded to the substrate after rapid solidification. Nickel-based alloys are often chosen as laser cladding materials due to their high hardness, excellent wear resistance, and good high-temperature oxidation resistance, and are widely used in industrial fields to improve the surface properties of substrate materials such as steel.

[0003] However, due to the significant differences in physical and chemical properties between nickel-based alloy powders and iron-based materials, the cladding layer generates substantial thermal stress during rapid laser heating and cooling, leading to crack initiation and propagation. Furthermore, to obtain a reinforced layer with higher hardness, a high chromium content is typically added to the nickel-based powder. During solidification of the molten pool, chromium tends to form coarse, hard chromium compounds. While these brittle phases increase hardness, they severely impair the ductility and toughness of the cladding layer, further exacerbating crack susceptibility and making it difficult to obtain a high-quality cladding layer.

[0004] Existing technologies have attempted to improve wettability by adding elements such as Al and Ti, or to control thermal stress through processes such as preheating and post-heating. However, it remains difficult to achieve large-area crack-free cladding while maintaining high hardness. For example, invention patent CN109355652B discloses a nickel-based alloy powder for laser cladding. By adding trace elements such as Al, Ti, and Cu to enhance the wettability of the cladding layer, a large-area crack-free cladding layer was obtained. However, due to the reduced proportion of B and C elements, the highest hardness of the resulting coating is only 54 HRC, equivalent to 500-600 HV. Invention patent CN102465294B discloses a method for large-area laser cladding of high-hardness nickel-based alloy materials. A defect-free coating was obtained by using preheating before the experiment, heating during the experiment, and holding the temperature after the experiment. However, under prolonged holding temperature, the coating structure became coarse, and the hardness decreased.

[0005] Therefore, there is an urgent need in this field for a new type of nickel-based alloy powder and a matching optimized process that can balance the toughness and hardness of the cladding layer, and realize large-area, crack-free, high-hardness, thick-coating nickel-based alloy additive manufacturing. Summary of the Invention

[0006] To address the existing technical problems, this invention provides a high-hardness nickel-based composite powder for laser cladding and a laser cladding method thereof. The method involves introducing pure aluminum powder of a specific form and content into a nickel-based alloy through mechanical mixing, and combining optimized mixing process and cladding parameters to achieve a synergistic improvement in coating hardness and toughness.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a high-hardness nickel-based composite powder for laser cladding, comprising 1-4 wt% near-spherical pure aluminum powder, with the balance being nickel-based high-temperature alloy powder; The average particle size of the pure aluminum powder is 100-150 μm, the purity is greater than 99.90%, and the roundness is greater than 0.9. The nickel-based superalloy powder is a near-spherical gas-atomized powder with an elemental content of 15-17wt%Cr, 2-4wt%Fe, 3-4wt%B, 1-2wt%Si, 0.5-1wt%C, and the balance being Ni; its particle size distribution is controlled at 75-150μm.

[0008] The near-spherical pure aluminum powder has an average particle size of 100-150 μm, a purity greater than 99.90%, and a sphericity greater than 0.9. Higher sphericity improves powder flowability and ensures uniform powder output during feeding. The amount of aluminum powder added should be strictly controlled between 1-4 wt%. Multiple tests have verified that excessive addition leads to a sharp decrease in the toughness of the cladding layer, while insufficient addition has little effect on molten pool control.

[0009] The high-hardness nickel-based composite powder designed in this invention achieves the purpose of strengthening the cladding layer by inhibiting the formation of intermetallic compounds and enhancing the formation of chromium-rich hard phases through optimized alloy composition, while also possessing breakthrough performance in terms of high ductility, toughness, and high hardness. The composition design principle is as follows: Cr is partially dissolved in the nickel matrix phase, and most of it precipitates between dendrites to form hard phases such as chromium carbide and chromium boride, which greatly improves the hardness of the cladding layer. Fe adjusts the coefficient of thermal expansion, reduces thermal stress, and improves the bonding quality between the cladding layer and the iron-based substrate; B lowers the melting point of the molten pool, forms a low-melting-point eutectic with nickel, improves the fluidity of the molten pool, and forms hard borides with Cr. Si helps to lower the melting point of the molten pool and improve wettability, while also deoxidizing the cladding layer and reducing porosity; C, forms hard carbide phases with chromium (such as Cr7C3, Cr23C7), which enhances the hardness of the coating; Ni, as the most basic toughness matrix phase of the cladding layer, provides basic hardness and toughness. Al is used to enhance the fluidity of the molten pool and refine the microstructure of the cladding layer. However, in order to avoid generating too many Ni-Al intermetallic compounds and significantly reducing the toughness of the cladding layer, mechanical powder mixing is used instead of conventional powder metallurgy mixing.

[0010] This invention employs acoustic resonance mixing technology to physically and uniformly mix pure aluminum powder and nickel-based superalloy powder. By controlling the aluminum powder content, the flow and solidification of the molten pool during laser cladding are altered. An appropriate amount of aluminum powder can reduce cracks caused by cooling, but excessive content can lead to the formation of intermetallic compounds between Al and Ni elements, thereby impairing the toughness of the cladding layer. The Cr element in the nickel-based superalloy powder reacts with B and C elements to precipitate as hard ceramic phases of chromium boride and chromium carbide, significantly increasing the hardness of the cladding layer, with an average hardness exceeding 800 HV and some areas exceeding 1000 HV.

[0011] Furthermore, in an argon atmosphere, pure aluminum powder and nickel-based high-temperature alloy powder are uniformly mixed through an acoustic resonance process to obtain high-hardness nickel-based composite powder.

[0012] Specifically, pure aluminum powder and nickel-based superalloy powder are placed in a stainless steel container in a certain proportion and filled with inert gas (argon) to prevent oxidation of the powder during violent shaking. The parameters for the automatic resonance process are then set as follows: first stage resonance acceleration of 20-40g for 5-10 min; second stage resonance acceleration of 70-80g for 20-30 min; and third stage resonance acceleration of 40-60g for 10-20 min. Due to the significant difference in mass and density between aluminum powder and nickel-based powder, a three-stage accelerated resonance is used. In the first stage, low acceleration is used to fluidize both powders, providing a uniform foundation for high acceleration and avoiding localized overload. In the second stage, higher acceleration energy is applied, generating strong nonlinear motion. The two powders collide violently in this stage, achieving thorough mixing. This stage is the most time-consuming and critical. In the third stage, after high acceleration, the energy is reduced to a moderate level, allowing the powder to become more uniform while maintaining good flowability, preventing secondary agglomeration, and reducing unnecessary energy input and heat accumulation.

[0013] Furthermore, the purity of the nickel-based superalloy powder is 99.9%, and the oxygen content is less than 140 ppm to prevent porosity during the cladding process. The flowability of the composite powder is evaluated using a Hall effect flowmeter, following the national standard method (GB / T 1482-2022), with the flow rate strictly maintained within the range of 20-25 s / 50 g.

[0014] This invention also provides a method for forming a high-hardness nickel-based coating on the surface of 42CrMo steel by laser cladding, using high-hardness nickel-based composite powder as the cladding material, and including the following steps: S1. Vacuum drying treatment is performed on high-hardness nickel-based composite powder; S2. Perform laser cleaning and ultrasonic cleaning on the surface of the 42CrMo substrate. S3. Preheat the cleaned substrate. S4. A rectangular spot laser cladding system is used for coaxial powder feeding and cladding.

[0015] Furthermore, in step S4, in order to obtain a large-area, crack-free, high-hardness laser cladding nickel-based coating, the laser spot shape is 19mm×6mm, and the angle between the cladding head and the substrate is 90°.

[0016] Furthermore, in step S4, the laser cladding head moving speed is 2-6 mm / s, the laser power is 4000-7000W, the overlap distance is 13-15 mm, and the powder feeding rate is 20-40 g / min.

[0017] Compared to conventional small circular laser spots, rectangular laser spots offer more uniform energy distribution, preventing localized overheating and thermal cracking. The larger spot shape also increases production efficiency, achieving a cladding rate 8-10 times faster than commercially available 4mm circular spots. This reduces the number of overlaps when forming large-area cladding layers, thus minimizing defects at these points. High-purity argon is used for powder feeding to prevent oxygen in the air from reacting with carbon and other oxygen-loving elements in the powder, thus avoiding defects such as pores and inclusions. In optimizing the cladding process parameters, a laser power of 4000-7000W is selected. Too low a laser power will not completely melt the powder, resulting in numerous unmelted particles on the surface and reduced forming quality. Too high a laser power will burn the cladding layer, causing coarse microstructure and dissolving hard precipitates such as chromium carbide and chromium boride, significantly reducing the hardness of the cladding layer. A lower cladding head movement speed is selected compared to conventional experiments to achieve a smaller temperature gradient and reduce cold cracking. The powder feeding rate, carrier gas pressure, and moving speed are matched. To ensure good forming quality of the top surface of the cladding layer, an appropriate overlap rate is selected based on the slope of the cladding edge.

[0018] Furthermore, in step S3, since the coefficients of thermal expansion of nickel-based materials and iron-based materials differ significantly, the substrate needs to be preheated before the experiment at a temperature of 200-600℃.

[0019] In step S1, the drying temperature is 120℃, the heating rate is 10K / min, and the vacuum condition is 1×10⁻⁶. -2 Pa, heat treatment time is 4h, to remove moisture adhering to the powder mixture and the water of crystallization of the powder itself.

[0020] In step S2, a pulsed laser is used to remove the oxide film and rust from the substrate surface. The laser power is 100W, the pulse width is 10ns, and the pulse frequency is 50kHz. After laser cleaning, an ultrasonic cleaner is used to remove residue and clean oil stains, and then a dryer is used to dry the surface moisture.

[0021] The present invention also provides a laser cladding coating, which is prepared by the above method.

[0022] Compared with the prior art, the present invention has the following beneficial effects: 1. Chromium in nickel-based superalloy powder forms ceramic precipitates with carbon and boron, significantly enhancing the hardness of the cladding layer. By adding and precisely controlling Al powder, the surface tension of the molten alloy is reduced, enhancing the wettability and fluidity of the molten pool and reducing cracks formed during cladding.

[0023] 2. In order to avoid the formation of excessive Ni-Al intermetallic compounds and significantly reduce the toughness of the cladding layer, the present invention uses mechanical mixing of Al powder and nickel-based high-temperature alloy powder instead of conventional powder metallurgy method.

[0024] 3. In order to reduce cracks formed by cladding, the substrate is preheated by a heating table, which effectively reduces tensile stress caused by the difference in thermal expansion coefficients between nickel-based powder and steel substrate, and significantly reduces defects and cracks formed inside the cladding layer and along the bonding area between the cladding layer and the substrate.

[0025] 4. This invention uses laser cladding of nickel-based alloy powder, with a large-area cladding layer size of 60×60×30mm, and no macroscopic cracks are generated. Under preferred process parameters, the highest hardness of the cladding layer exceeds 1000HV, and the hardness of the cladding layer can reach 4 times that of the substrate. Attached Figure Description

[0026] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0027] Figure 1 The images show the macroscopic morphology and flaw detection results of the cladding layer in Example 1. Figure 2 The microstructure of the cladding layer in Example 1; Figure 3 The EDS results for the cladding layer in Example 1 are shown. Figure 4 The EDS spot scan location of the cladding layer in Example 1; Figure 5 The XRD results are for the cladding layer in Example 1; Figure 6 The microhardness of the cladding layer in Example 1; Figure 7The images show the macroscopic morphology and flaw detection results of the cladding layer in Example 2. Figure 8 The microstructure of the cladding layer in Example 2; Figure 9 The EDS spot scan location of the cladding layer in Example 2; Figure 10 The XRD results are for the cladding layer in Example 2; Figure 11 The microhardness of the cladding layer in Example 2; Figure 12 The EDS spot scan location of the cladding layer in Example 3; Figure 13 The microhardness of the cladding layer in Example 3; Figure 14 The EDS spot scan location of the cladding layer in Example 4; Figure 15 The image shows the macroscopic morphology and flaw detection results of the cladding layer in Comparative Example 1. Figure 16 The macroscopic morphology and flaw detection results of the cladding layer in Comparative Example 2 are shown in the figure. Figure 17 The image shows the macroscopic morphology and flaw detection results of the cladding layer in Comparative Example 3. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Example 1 This embodiment provides a high-hardness nickel-based composite powder for laser cladding. The base powder is a nickel-based high-temperature alloy powder with a particle size range of 75-150μm and an element content ratio of 16%Cr, 3.5wt%Fe, 3wt%B, 2wt%Si, 0.8wt%C, with the balance being Ni. The added powder is a near-spherical pure aluminum powder with an average particle size of 100-150μm, a roundness of 0.92, a purity of 99.90%, and an addition ratio of 2%.

[0030] The composite powder was mixed evenly using an acoustic resonance apparatus. The apparatus was set with the following parameters: first stage resonance acceleration of 30g for 5 minutes; second stage resonance acceleration of 70g for 25 minutes; and third stage resonance acceleration of 50g for 15 minutes.

[0031] Before the cladding experiment, the composite powder was dried at 120℃ with a heating rate of 10K / min and a vacuum condition of 1×10⁻⁶. -2 Pa, constant temperature for 4 hours, and flowability test of the treated composite powder was performed using a Hall effect flow meter, with a flow rate of 22.4 s / 50g.

[0032] The 42CrMo substrate was pretreated by removing the surface oxide film and oil using a pulsed laser, followed by ultrasonic cleaning. The laser power was 100 W, the pulse width was 10 ns, and the pulse frequency was 50 kHz.

[0033] Before the cladding experiment, the substrate was preheated using a heating table at a temperature of 300°C.

[0034] A wide-spot laser cladding system was used to perform coaxial powder feeding cladding on a heated substrate. The spot size was 19mm × 6mm, the angle between the cladding head and the aluminum alloy substrate was 90°, the moving speed was 3mm / s, the carrier gas pressure was 0.5MPa, the powder feeding rate was 24.6g / min, the laser power was 5000W, the overlap distance was 13mm, and 3 layers were stacked. The resulting cladding layer thickness was approximately 3.5mm.

[0035] Crack detection was performed on the cladding layer formed on the substrate surface using a flaw detection agent. The cladding morphology and flaw detection results are as follows: Figure 1 As shown, there are no obvious cracks on the surface, and the cladding quality is good. Further observation of the cladding microstructure yielded the following results: Figure 2 As shown, the laser cladding coating is mainly composed of chromium-rich compounds, nickel-aluminum compounds, and γ(Ni) toughening phase. Figure 3 This image shows the elemental scanning results of a laser-clad nickel-based coating. The substrate phase of the cladding layer mainly consists of nickel, iron (due to matrix dilution), and small amounts of silicon and aluminum. The gray-black precipitates are primarily chromium-rich compounds. To further determine the elemental distribution within the microstructure, spot scanning was used to analyze the precipitates. The scanning locations are shown below. Figure 4 As shown in Table 1, points 1 and 3 (grayish-black precipitates) are mainly CrB2; point 2 (base phase) is mainly a toughening phase formed by Ni, Fe, Al, and Si; and points 4 and 5 (white precipitates) are mainly some eutectic structures formed by Ni and Fe, as well as chromium-rich hard phases. Figure 5 The XRD results show that the grayish-white chromium-rich hard phase mainly consists of CrB, Cr7C3, and Cr. 23 Composed of C7.

[0036] Table 1 element 1 (At%) 2 (At%) 3 (At%) 4 (At%) 5 (At%) B 52.78 4.18 54.85 35.08 12.57 C 7.59 15.25 8.13 10.56 15.05 Al 0.02 6.29 0.04 0.04 3.51 Si 0.09 6.75 0.06 0.13 0.79 Cr 35.41 1.93 33.65 10.47 3.02 Fe 3.61 16.23 2.81 30.16 20.09 Ni 0.51 49.38 0.46 13.55 44.97 Total 100.00 100.00 100.00 100.00 100.00 Microhardness tests were performed on the cladding layer, and the results are as follows: Figure 6As shown, the average hardness of the cladding layer exceeds 800 HV, and the highest hardness exceeds 1000 HV, which is 4 times the hardness of the substrate.

[0037] Example 2 This embodiment is the same as Embodiment 1, except that in Embodiment 2, when the heating table is used for preheating, the set temperature is 600℃. The resulting cladding layer has a good surface morphology and a thickness of approximately 3mm. After flaw detection, no obvious cracks are found, and only a small number of micropores (such as...) appear at the overlap. Figure 7 (As shown). Observation of the cladding structure yielded the following results. Figure 8 As shown, compared to Example 1, the increased preheating temperature caused the precipitates to redissolve in the matrix, and the chromium boride content began to decrease. EDS point scan locations are shown below. Figure 9 As shown in Table 2, the results are as follows: Points 1 and 2 (grayish-black precipitates) are mainly CrB2; Points 3 and 4 (white strip-shaped precipitates) are mainly eutectic structures formed by Ni, Fe, Si, and C, as well as carbides; Points 5 and 6 (base phase) are mainly toughening phases composed of Ni, Fe, and Al. Figure 10 The results are shown in the XRD test results. Microhardness testing was performed on the cladding layer, and the results are as follows: Figure 11 As shown, the average hardness of the cladding layer exceeds 600 HV, and the highest hardness exceeds 700 HV, which is 3 times the hardness of the substrate.

[0038] Table 2 element 1 (At%) 2 (At%) 3 (At%) 4 (At%) 5 (At%) 6 (At%) B 52.82 53.50 0.00 0.00 0.00 0.00 C 6.89 8.39 24.06 18.83 15.24 16.22 Al 0.01 0.07 0.61 0.55 10.48 10.34 Si 0.07 0.06 15.94 17.68 7.05 7.01 Cr 32.15 35.58 1.18 0.82 2.00 1.62 Fe 6.75 1.60 9.76 8.31 8.19 7.97 Ni 1.30 0.80 48.45 53.81 57.05 56.83 Total 100.00 100.00 100.00 100.00 100.00 100.00 Example 3 This embodiment is the same as Example 1, except that the amount of near-spherical pure aluminum powder added to the composite powder in Comparative Example 2 is 4 wt%. The resulting cladding layer has a good surface morphology and a thickness of approximately 2.8 mm, and no obvious cracks were found after flaw detection. The cladding structure was observed, and the EDS point scanning positions are as follows... Figure 12 As shown in Table 3, the white blocky precipitates in the cladding layer and the aluminum content in the substrate phase increased significantly compared to Example 1. Microhardness testing of the cladding layer yielded the following results: Figure 13 As shown, the average hardness of the cladding layer exceeds 600 HV, which is three times the hardness of the substrate. The increase in aluminum content slightly reduced the hardness of the cladding layer.

[0039] Table 3 element 1 (At%) 2 (At%) 3 (At%) 4 (At%) 5 (At%) 6 (At%) B 53.36 53.4 18.81 14.72 0.00 0.00 C 8.82 8.57 15.46 16.37 14.82 14.97 Al 0.08 0.04 3.76 4.22 12.41 10.56 Si 0.09 0.08 0.77 0.93 7.21 8.26 Cr 36.02 36.23 2.32 2.32 2.41 2.02 Fe 0.62 0.59 5.76 5.9 2.56 2.59 Ni 1.01 1.1 53.12 55.54 60.59 61.6 Total 100.00 100.00 100.00 100.00 100.00 100.00 Example 4 This embodiment is the same as Embodiment 1, except that the amount of near-spherical pure aluminum powder added to the composite powder in Comparative Example 2 is 1 wt%, and the scanning speed is 6 mm / s. The resulting cladding layer has a good surface morphology and a thickness of approximately 2 mm, and no obvious cracks were found after flaw detection. The cladding structure was observed, and the EDS point scanning positions are as follows... Figure 14As shown in Table 3, the reduced aluminum content led to a decrease in its impact on the solidification of the molten pool, resulting in a significant reduction in precipitates in the cladding layer structure, with the gray-black precipitates (chromium boride) almost disappearing. Microhardness testing of the cladding layer revealed an average hardness of 550 HV.

[0040] Table 4 element 1 (At%) 2 (At%) 3 (At%) 4 (At%) B 0.00 5.48 0.00 1.36 ·C 32.15 29.33 12.83 15.29 Al 0.01 0.05 6.80 6.73 Si 0.12 0.01 5.28 6.59 Cr 45.51 44.99 3.49 1.85 Fe 17.70 16.23 21.87 17.76 Ni 4.50 3.90 49.73 50.42 Total 100.00 100.00 100.00 100.00 Comparative Example 1 This comparative example is a comparative test example of Example 1. The difference between the two is that only the basic powder - nickel-based high-temperature alloy powder - was used in Comparative Example 1, and no near-spherical pure aluminum powder was added.

[0041] Due to compositional segregation during the later solidification stage of laser cladding, and the presence of hard and brittle phases in the generated chromium boride and chromium carbide, the toughness of the cladding layer is significantly reduced. Crack detection was performed on the cladding layer on the substrate surface using a flaw detector. The cladding morphology and flaw detection results are as follows: Figure 15 As shown, numerous pores exist at the tail end of the cladding layer surface. In the overlapping area, the microstructure of the subsequent cladding layer grows on the basis of the previous cladding layer, and their lattice trends are similar. This causes cracks formed in the previous cladding layer to continue to propagate to the next cladding layer, eventually forming large cracks across the entire sample surface. After testing, the hardness was 760 HV, and the cladding layer thickness was approximately 3.7 mm. Due to the tendency of boron, carbon, and silicon elements in the nickel-based powder to undergo deoxidation and slagging reactions during the cladding process, coupled with the prolonged molten pool time, pores appear on the cladding layer surface, making it unsuitable for practical application.

[0042] Comparative Example 2 This comparative example is a comparative test example of Example 1. The difference between the two is that the amount of near-spherical pure aluminum powder added in the composite powder of Comparative Example 2 is 0.5 wt%.

[0043] Compared to Example 1, less aluminum was added. A flaw detector was used to inspect the cladding layer on the substrate surface for cracks. The cladding morphology and flaw detection results are as follows: Figure 16 As shown, cracks exist in the cladding layer. The relatively low aluminum content does not significantly improve the flow of the molten pool. During the solidification and shrinkage stage after cladding, the thermal mismatch between the substrate and the cladding layer leads to tensile stress, causing cracks to still initiate. After testing, the hardness is 750 HV, and the cladding layer thickness is approximately 3.8 mm. Increasing the aluminum content can absorb oxygen and reduce surface tension, allowing pores to escape quickly. However, insufficient aluminum content results in insufficient molten pool flow when pores converge, leading to new cracks and making it difficult to apply in practice.

[0044] Comparative Example 3 This comparative example is a comparative test example of Example 1. The difference between the two is that the amount of near-spherical pure aluminum powder added in the composite powder of Comparative Example 3 is 5 wt%.

[0045] Compared to Example 1, with the addition of excessive aluminum, a flaw detector was used to inspect the cladding layer on the substrate surface for cracks. The cladding morphology and flaw detection results are as follows: Figure 17 As shown, aluminum reacts with nickel to form intermetallic compounds such as AlNi, and AlNi, being a hard catalytic phase, reduces the toughness of the cladding layer, leading to the re-emergence of numerous cracks. Testing revealed a hardness of 640 HV and a cladding layer thickness of approximately 3.3 mm. The nickel-aluminum alloy phase, being a brittle phase, has a hardness of only 300-400 HV. Furthermore, excessive addition of aluminum, a highly reflective material, reduces light absorption, severely impacting cladding efficiency.

[0046] Comparative Example 4 This comparative example is a comparative test example of Example 1. The difference between the two is that the preheating temperature in Comparative Example 4 is 0°C.

[0047] Due to the rapid heating and cooling effect of laser cladding, significant thermal stress is generated when the powder melts under laser radiation. During the solidification stage, the powder is constrained by the substrate during cooling and shrinkage, resulting in residual tensile stress. Compared to Example 1, the lack of substrate preheating leads to a larger temperature gradient, generating numerous cracks and poor cladding quality. Testing revealed a hardness of 880 HV and a cladding layer thickness of approximately 2.9 mm. While the hardness is improved compared to Example 1, the sacrifice in cladding layer toughness results in cracks that are difficult to apply in practice, and the cladding efficiency is also reduced.

[0048] Comparative Example 5 This comparative example is a comparative test example of Example 1. The difference between the two is that in Comparative Example 5, the laser power is 3000W, the cladding head moving speed is 4mm / s, and the matching powder feeding rate is 32.5g / min.

[0049] Due to the low laser power, a large amount of composite powder failed to completely melt and form a coating in this comparative example, resulting in micro-cracks on the surface and poor cladding quality. After testing, the hardness was 580HV and the cladding layer thickness was approximately 1mm.

[0050] Comparative Example 6 This comparative example is a comparative test example of Example 1. The difference between the two is that in Comparative Example 6, the laser power is 8000W, the cladding head moving speed is 2mm / s, and the matching powder feeding rate is 12.6g / min.

[0051] Due to the high laser parameters, this comparative example provided excessive line energy for powder melting during the cladding process. Although the powder was fully melted, the excessive heat input resulted in a prolonged growth time and significantly enlarged grains. After testing, the hardness was 440 HV and the cladding layer thickness was approximately 3.9 mm.

[0052] Comparative Example 7 This comparative example is a comparative test example of Example 1. The difference between the two is that in Comparative Example 7, the laser power is 8000W, the cladding head moving speed is 8mm / s, and the matching powder feeding rate is 49.2g / min.

[0053] Due to the high moving speed, the powder was fully melted in this comparative example. However, due to the rapid cooling rate of the molten pool and the large temperature gradient difference, the cladding layer rapidly contracted during solidification, forming a large number of cracks. After testing, the hardness was 630 HV and the thickness of the cladding layer was approximately 2.3 mm.

[0054] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A high-hardness nickel-based composite powder for laser cladding, characterized in that, It consists of 1-4 wt% pure aluminum powder, with the balance being nickel-based high-temperature alloy powder; The average particle size of the pure aluminum powder is 100-150 μm, the purity is greater than 99.90%, and the roundness is greater than 0.

9. The average particle size of nickel-based superalloy powder is 75-150 μm; Nickel-based superalloy powder consists of 15-17 wt% Cr, 2-4 wt% Fe, 3-4 wt% B, 1-2 wt% Si, 0.5-1 wt% C, and the balance Ni.

2. The high-hardness nickel-based composite powder according to claim 1, characterized in that, In an argon atmosphere, pure aluminum powder and nickel-based high-temperature alloy powder are uniformly mixed through an acoustic resonance process to obtain high-hardness nickel-based composite powder.

3. The high-hardness nickel-based composite powder according to claim 2, characterized in that, The acoustic resonance process includes three stages of resonant acceleration; The first resonance acceleration is 20-40g, and the first resonance time is 5-10min; The second resonance acceleration is then 70-80g, and the second resonance time is 20-30min; The final third-stage resonance acceleration is 40-60g, and the third-stage resonance time is 10-20min.

4. The high-hardness nickel-based composite powder according to claim 1, characterized in that, The purity of the nickel-based superalloy powder is 99.9%, and the oxygen content is less than 140 ppm.

5. A method for forming a high-hardness nickel-based coating on the surface of 42CrMo steel by laser cladding, characterized in that, Using the high-hardness nickel-based composite powder as described in any one of claims 1-4 as the cladding material, the method includes the following steps: S1. Vacuum drying treatment is performed on high-hardness nickel-based composite powder; S2. Perform laser cleaning and ultrasonic cleaning on the surface of the 42CrMo substrate. S3. Preheat the cleaned substrate; S4. A rectangular spot laser cladding system is used for coaxial powder feeding and cladding.

6. The method according to claim 5, characterized in that, In step S4, the laser spot shape is 19mm×6mm, and the angle between the cladding head and the substrate is 90°.

7. The method according to claim 6, characterized in that, In step S4, the laser cladding head moves at a speed of 2-6 mm / s, the laser power is 4000-7000 W, the overlap distance is 13-15 mm, and the powder feeding rate is 20-40 g / min.

8. The method according to claim 5, characterized in that, The preheating temperature in step S3 is 200-600℃.

9. A laser cladding coating, characterized in that, It is prepared by the method of claim 5.

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