The present invention relates to an ultra-high-speed laser cladding fully amorphous crack-free iron-based amorphous coating and a preparation method. The workpiece to be clad is preheated, the preheated workpiece to be clad is clamped with a chuck, and placed flat on a rotating carrier; the powder feeding speed, carrier gas flow rate, and shielding gas flow rate of the cladding device are adjusted; the distance between the cladding head and the workpiece to be clad, the laser focus, and the powder flow focus are adjusted, and the cladding head movement speed is set; the rotating carrier drives the workpiece to be clad to rotate, and laser cladding is started from the outside to the inside, and an ultra-high-speed laser cladding fully amorphous crack-free iron-based amorphous coating is formed on the surface of the workpiece to be clad. The present invention adjusts the ultra-high-speed laser cladding process parameters to select parameters suitable for processing amorphous coatings, and realizes rapid cooling and defect-free preparation of the coating while ensuring that the coating is completely amorphous. The coating has high corrosion resistance and excellent mechanical properties.

1. A method for preparing a fully amorphous, crack-free, iron-based amorphous coating by ultra-high-speed laser cladding, characterized in that it comprises the following steps:
S1, surface treatment of a disc-shaped workpiece to be clad;
S2, preheating the workpiece to be clad, clamping the preheated workpiece to be clad with a chuck, and placing it flat on a rotating carrier
;
S3, adding alloy powder to the cladding device, adjusting the powder feeding speed, carrier gas flow rate, and shielding gas flow rate of the cladding device;
S4, adjusting the distance between the cladding head and the workpiece to be clad, the laser focus, and the powder flow focus to ensure that the laser focus and the powder focus coincide, and the defocus range during the ultra-high-speed laser cladding process is always 0-10 mm above the surface of the workpiece to be clad;
S5, setting the moving speed of the cladding head;
S6, the rotating carrier drives the workpiece to be clad to rotate, and laser cladding is started from the outside to the inside, forming an ultra-high-speed laser cladding fully amorphous, crack-free, iron-based amorphous coating on the surface of the workpiece to be clad.

2. A method for preparing a fully amorphous, crack-free, iron-based amorphous coating by ultra-high-speed laser cladding according to claim 1, characterized in that, in step S1, the base material of the workpiece to be clad is 316L, 304SS, Inconel625;
In step S1, surface treatment of the workpiece to be clad includes: grinding and polishing the surface of the workpiece to be clad to remove oil stains, rust stains, and oxide films;
In step S1, the thickness of the workpiece to be clad is not less than 5mm.

3. A method for preparing a fully amorphous, crack-free, iron-based amorphous coating by ultra-high-speed laser cladding according to claim 1, characterized in that, in step S2, the temperature of preheating the workpiece to be clad is 200-400℃.

4. A method for preparing a fully amorphous, crack-free iron-based amorphous coating by ultra-high-speed laser cladding according to claim 1, characterized in that, in step S3, the alloy powder is a sieved and dried powder, the alloy powder particle size range is 35-75μm, the sphericity is ≥90%, and the oxygen content is ≤150ppm.

5. A method for preparing a fully amorphous, crack-free iron-based amorphous coating by ultra-high-speed laser cladding according to claim 1, characterized in that, in step S3, the powder feeding speed is 15-25g/min, the carrier gas flow rate is 20-30L/min, and the shielding gas flow rate is 10-15L/min.

6. A method for preparing a fully amorphous, crack-free iron-based amorphous coating by ultra-high-speed laser cladding according to claim 1, characterized in that, in step S4, the defocus is 1-10mm, the powder flow focus is 0-1mm above the laser focus, and the spot diameter is 1.5-2.5mm.

7. A method for preparing a fully amorphous, crack-free iron-based amorphous coating by ultra-high-speed laser cladding according to claim 1, characterized in that, in step S5, the cladding head movement speed is set to 1-3 mm/s.

8. A method for preparing a fully amorphous, crack-free iron-based amorphous coating by ultra-high-speed laser cladding according to claim 1, characterized in that, in step S6, the laser power used in the cladding process is 2-4 kW, the rotation speed of the rotating carrier is 0-350 rpm, and the corresponding scanning speed is 0-200 m/min, wherein the rotation speed of the rotating carrier and the scanning speed are not 0.

9. According to the method for preparing a fully amorphous, crack-free, iron-based amorphous coating by ultra-high-speed laser cladding as described in claim 1, it is characterized in that, during the laser cladding process, the laser cladding parameters are optimized by the following method: fix the disc-shaped workpiece to be clad for the test on the chuck on the rotating carrier;
According to the method for preparing a fully amorphous, crack-free, iron-based amorphous coating by ultra-high-speed laser cladding, cladding is performed, and the obtained coating is sampled and analyzed, and a sample is taken out at intervals of 1 cm, and the cladding parameters are judged to be appropriate based on the surface quality, coating thickness, and coating cross-sectional quality; according to the relationship between the coating thickness and the parameters, a graph is drawn to obtain the most suitable process parameters for the alloy powder;
The parameters are readjusted to determine the position where the coating quality is best, and the radius R test and the rotation speed N test at this time are recorded. Without changing other parameters such as the cladding head feed speed, the rotation speed N of the rotating carrier is changed with time; the gradient change formula is as follows, assuming that the radius of the target cladding disc-shaped workpiece to be clad is R, the cladding head moving speed is v, and the time is t: N=Rtest*Ntest/(R-vt).
Reset the rotation speed of the rotating carrier, start cladding, and prepare a uniform thickness coating of the amorphous material on the target substrate.
10. A fully amorphous, crack-free iron-based amorphous coating obtained by ultra-high-speed laser cladding according to the method described in any one of claims 1-9, characterized in that the thickness of the iron-based amorphous coating is 50-100μm, the porosity is less than 1%, and there are no surface pores and crack defects, and the width of the heat-affected zone is less than 5μm.

The present invention relates to the technical field of surface coating preparation, and in particular to an ultra-high-speed laser cladding all-amorphous crack-free iron-based amorphous coating and a preparation method thereof.

Iron-based amorphous alloys have the characteristics of long-range disorder, short-range order, and no crystal defects, which give them many excellent properties such as high corrosion resistance, high wear resistance, and high hardness.

At present, amorphous alloy coatings prepared by surface coating technology have been widely used in practice. Ultra-high-speed laser cladding, as an emerging surface technology, uses high-energy laser as a heat source to melt alloy powder and deposit it on the surface of a substrate to form a coating. Since the energy of the high-energy laser is mainly absorbed by the powder, the thermal effect on the workpiece substrate is small. At the same time, the high cooling rate brought by the high scanning speed is conducive to the generation of metastable amorphous phase. Compared with traditional surface treatment technologies (thermal spraying, magnetron sputtering, conventional laser cladding, etc.), ultra-high-speed laser cladding greatly shortens the cladding time and improves the powder utilization rate. It can achieve the preparation of high-efficiency and high-quality amorphous alloy coatings.

Chinese patent CN109023351A discloses a method for preparing crack-free amorphous coating by laser cladding. By pre-melting the substrate, laser cladding forms a cladding layer, and remelting the cladding layer, a completely crack-free laser cladding amorphous alloy coating is prepared, with an average microscopic Vickers hardness of 807.4HV0.1, but the amorphous content in the laser cladding amorphous coating is relatively small, only 40%. Pre-melting the substrate will not only eliminate coating defects, but also dilute the amorphous components of the coating. This scheme changes the substrate preheating conditions, while eliminating residual stress and minimizing the impact of the preheating process on the coating preparation process.

Chinese patent CN113584477A discloses a method for ultra-high-speed laser cladding amorphous alloy coating, with a laser power range of 1.0-2.5kW and a scanning speed range of 100-250mm/s. By adjusting the cladding parameters, a defect-free surface protective iron-based amorphous alloy coating of 100 microns is prepared, avoiding the limitations of brittleness and size effect of amorphous alloys. The patent increases the self-corrosion potential of ultra-high-speed laser cladding iron-based amorphous coating to ‑0.437V, which is 41% higher than that of the substrate. The surface wear rate of the amorphous coating after protection is 2.99×10’‑5mm’3N’‑1m’‑1, which is 73% lower than that of the substrate. However, there are still serious crystallization areas inside the prepared iron-based amorphous alloy coating, and the excessively thick heat-affected zone causes the internal composition of the coating to be non-uniform.

At present, the main problems of using ultra-high-speed laser cladding to prepare amorphous coatings are as follows: (1) The coating and the substrate are poorly or excessively bonded, and defects such as cracks and holes are prone to appear on the surface or inside the amorphous alloy coating; (2) The heat accumulation caused by the excessive thickness of the coating and the dilution of the substrate composition caused by the high-energy laser during cladding cause the composition of the amorphous alloy coating to change; (3) The high scanning rate during the high-speed cladding process leads to obvious overlap marks. When using ultra-high-speed laser cladding to prepare amorphous coatings, high energy input will cause the coating composition to change, and various defects and precipitated phases on the surface and inside of the amorphous coating will provide potential paths for corrosion. Therefore, how to improve the corrosion resistance and mechanical properties of the coating by increasing the amorphous content and surface quality of the amorphous coating is a problem to be solved in this field.

Aiming at the problems of low amorphous phase ratio and internal crystallization of the amorphous coating prepared by the current high-speed laser cladding technology, the present invention provides a fully amorphous and crack-free iron-based amorphous coating and a preparation method by ultra-high-speed laser cladding.

The present invention uses ultra-high-speed laser technology to melt amorphous powder, increases the amorphous phase content in the coating by adjusting process parameters, and directly melts the powder material by utilizing the technical characteristics of high laser energy density, fast laser path scanning speed, and laser acting on the workpiece during high-speed cladding, and then adheres to the surface of the substrate and condenses into a solid state, forming a metallurgical bond with the substrate to obtain a fully amorphous and crack-free iron-based amorphous coating.

Aiming at the problems existing in the existing laser cladding, the present invention starts from the preparation process, studies the relationship between coating thickness and parameters through pretreatment and adjustment of process parameters, and obtains a fully amorphous and crack-free iron-based amorphous coating through parameter screening and process optimization. The solution provided in this application can solve the problems of amorphous brittleness and size effect, low amorphous phase content in the coating, and easy cracking.
The purpose of the present invention can be achieved by the following technical solutions:
The present invention provides a method for preparing a fully amorphous and crack-free iron-based amorphous coating by ultra-high-speed laser cladding, comprising the following steps:
S1. Surface treatment of a disc-shaped workpiece to be clad;
S2. Preheating the workpiece to be clad, clamping the preheated workpiece to be clad with a chuck, and placing it flat on a rotating carrier;
S3. Adding alloy powder to the cladding device, adjusting the powder feeding speed, carrier gas flow rate, and shielding gas flow rate of the cladding device;
S4. Adjusting the distance between the cladding head and the workpiece to be clad, the laser focus, and the powder flow focus to ensure that the laser focus coincides with the powder focus, and the defocus range during the ultra-high-speed laser cladding process is always 0-10 mm above the surface of the workpiece to be clad;
S5. Setting the moving speed of the cladding head;
S6. The rotating carrier drives the workpiece to be clad to rotate, and laser cladding is started from the outside to the inside, forming an ultra-high-speed laser cladding fully amorphous and crack-free iron-based amorphous coating on the surface of the workpiece to be clad.
In one embodiment of the present invention, in step S1, the base material of the workpiece to be clad is 316L, 304SS, Inconel 625.
In one embodiment of the present invention, in step S1, the surface treatment of the workpiece to be clad includes: grinding and polishing the surface of the workpiece to be clad, removing oil stains, rust stains, oxide film, etc., to ensure good laser absorption and adhesion of the cladding layer.
In one embodiment of the present invention, in step S1, the area of ​​the workpiece to be clad is selected according to actual needs, and the thickness of the workpiece to be clad is not less than 5mm.
In one embodiment of the present invention, in step S2, the temperature for preheating the workpiece to be clad is 200-400℃, preferably 200-300℃.
In one embodiment of the present invention, in step S3, the alloy powder is a sieved and dried powder, the alloy powder particle size range is 35-75μm, the sphericity is ≥90%, and the oxygen content is ≤150ppm.
In one embodiment of the present invention, in step S3, the alloy powder is an iron-based amorphous alloy powder with a particle size of 45 μm to 60 μm, a sphericity of ≥90%, and an oxygen content of ≤150 ppm.
In one embodiment of the present invention, in step S3, the powder feeding speed is 15-25 g/min, the carrier gas flow rate is 20-30 L/min, and the shielding gas flow rate is 10-15 L/min.
In one embodiment of the present invention, in step S4, the defocusing amount is 1-10 mm, the powder flow focus is 0-1 mm above the laser focus, and the spot diameter is 1.5-2.5 mm.
In one embodiment of the present invention, in step S5, the cladding head movement speed is set to 1-3 mm/s.
In one embodiment of the present invention, in step S6, the laser power used in the cladding process is 2-4 kW, the rotation speed of the rotating carrier is 0-350 rpm, and the corresponding scanning speed is 0-200 m/min, wherein the rotation speed of the rotating carrier and the scanning speed are not 0. Preferably, the laser power during the cladding process is 3.5-4.5kW, and the carrier speed is 100-1000rpm.
The equipment used in the cladding process of the present invention includes a laser, a laser cladding head, a control terminal, a chuck and a rotating carrier. The workpiece to be clad is clamped by the chuck and placed on the rotating carrier. The laser cladding head is located at the lower end of the laser. The laser is also connected to the control terminal. The control terminal can control the feed of the laser and the parameters related to cladding, and can adjust the rotation speed of the rotating carrier in real time.
During the laser cladding process, the laser cladding parameters were optimized using the following method:
Fix the disc-shaped workpiece to be clad for the test on the chuck on the rotating carrier;
According to the preparation method of the fully amorphous crack-free iron-based amorphous coating by ultra-high-speed laser cladding, the cladding was performed, and the obtained coating was sampled and analyzed. A sample was taken out every 1 cm, and the surface quality, coating thickness, and coating cross-sectional quality were used to determine whether the cladding parameters were selected appropriately; a graph was drawn based on the relationship between the coating thickness and the parameters to obtain the most suitable process parameters for the alloy powder;
Re-adjust the parameters to determine the position with the best coating quality, and record the radius R test and the rotation speed N test at this time. Without changing other parameters such as the cladding head feed speed, the rotation speed N of the rotating carrier is changed gradually over time; the gradient change formula is as follows (taking the disc-shaped workpiece to be clad as an example, assuming that the radius of the target cladding disc-shaped workpiece is R, the cladding head moving speed is v, and the time is t): N=Rtest*Ntest/(R-vt)
Reset the rotation speed of the rotating carrier, start cladding, and prepare a uniform thickness coating of the amorphous material on the target substrate.
The present invention further provides a fully amorphous crack-free iron-based amorphous coating obtained by ultra-high-speed laser cladding based on the above method, wherein the thickness of the iron-based amorphous coating is controlled to be 50-100μm, the porosity is controlled to be less than 1% and there are no surface pores, cracks and other defects, and the width of the heat-affected zone is less than 5μm.
The present invention provides a method for preparing an ultra-high-speed laser cladding iron-based completely amorphous coating. Through pre-treatment, parameter optimization and post-treatment, the dilution rate of the obtained iron-based amorphous coating is extremely low, the metallurgical bonding area between the coating and the substrate is only 2μm, and no overlap marks and nanocrystalline structures are found inside the coating. This completely amorphous continuous coating with a size of hundreds of microns and no obvious defects can not only avoid the limitation of the amorphous size effect, but also prevent the service instability caused by component segregation and overlap, greatly improve the application upper limit of the amorphous coating, and broaden its application field.
Compared with the prior art, the beneficial effects of the present invention are reflected in the following aspects:
1. The laser energy mainly acts on the amorphous alloy powder. The higher laser energy allows the powder to be combined with the substrate material in the form of droplets rather than particles. By reasonably setting the position of the laser focus and the powder flow focus and related parameters, the amorphous content of the cladding layer is greatly increased.
2. The combination of high rotation speed (cladding speed can reach 200m/min) and appropriate laser power not only greatly improves the cladding speed, but also obtains higher bonding strength and surface roughness.
3. By optimizing the coordination between powder feeding rate, scanning speed and overlap rate, the optimization law of rotation speed is obtained, the thickness and molding quality of the iron-based amorphous coating are improved to the best, and the dilution rate of the substrate to the iron-based amorphous coating is reduced to the minimum while ensuring good metallurgical bonding between the substrate and the coating. At the same time, through a specific relationship (reasonable control of laser power, scanning speed, and powder feeding speed), the iron-based amorphous alloy is prepared into a defect-free and completely amorphous coating with uniform thickness.

In order to more clearly illustrate the technical solution in the embodiment of the present invention, the following is a brief introduction to the drawings required for the description of the embodiment.

Figure 1 is a schematic diagram of the ultra-high-speed laser cladding process in Example 1 of the present invention;

Figure 2 (a) (b) (c) are cross-sectional SEM images of the coating obtained in Example 1 of the present invention at different magnifications, and Figure 2 (d) is a process optimization diagram obtained during the parameter adjustment process;

Figure 3 is an XRD comparison diagram of the coating and the substrate in Example 1 of the present invention;

Figure 4 is a TEM image of the middle part of the coating in Example 1 of the present invention;

Figure 5 is a corrosion polarization curve of the coating in Example 1 of the present invention in 3.5% NaCl solution;

Figure 6 is a hardness curve of an iron-based completely amorphous coating with a scanning speed of 100.56 m/min.

The numbers in the figure are as follows:

1. Laser; 2. Laser cladding head; 3. Workpiece to be clad; 4. Control terminal; 5. Chuck; 6. Rotating carrier.

Specific implementation methods
In the description of the present invention, it should be understood that the terms “lateral”, “thickness”, “outer”, “inner” and other orientation indication terms are based on the orientation shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention.

In one embodiment of the present invention, the amorphous powder is prepared by gas atomization, the powder particle size range is 30μm to 75μm, the sphericity is ≥90%, and the oxygen content is ≤150ppm; the material is an iron-based amorphous alloy material.

In one embodiment of the present invention, the coating thickness is set according to demand, which is about 54μm.
Combined with Figures 1 to 5, the preparation method of the ultra-high-speed laser cladding full amorphous crack-free iron-based amorphous coating of the embodiment of the present invention is described in detail.
Referring to Figures 1-5, the present invention provides a method for preparing a fully amorphous, crack-free, iron-based amorphous coating by ultra-high-speed laser cladding, comprising the following steps:
S1. Surface treatment is performed on a disc-shaped workpiece to be clad;
S2. Preheating is performed on the workpiece to be clad, the preheated workpiece to be clad is clamped with a chuck, and is placed flat on a rotating carrier;
S3. The alloy powder is added to the cladding device, and the powder feeding speed, carrier gas flow rate, and shielding gas flow rate of the cladding device are adjusted;
S4. The distance between the cladding head and the workpiece to be clad, the laser focus, and the powder flow focus are adjusted to ensure that the laser focus and the powder focus coincide, and the defocus range during the ultra-high-speed laser cladding process is always 0-10 mm above the surface of the workpiece to be clad;
S5. The cladding head movement speed is set;
S6. The rotating carrier drives the workpiece to be clad to rotate, and laser cladding is started from the outside to the inside, and an ultra-high-speed laser cladding fully amorphous, crack-free, iron-based amorphous coating is formed on the surface of the workpiece to be clad.
In step S1, the base material of the workpiece to be clad is a disc of 304SS steel, 5mm thick and 200mm in diameter. The surface treatment of the workpiece to be clad includes: grinding and polishing the surface of the workpiece to be clad, removing oil stains, rust stains, oxide film, etc., to ensure good laser absorption and adhesion of the cladding layer.

In step S1, the area of ​​the workpiece to be clad is selected according to actual needs, and the thickness of the workpiece to be clad is not less than 5mm.
In step S2, the temperature for preheating the workpiece to be clad is 200-400℃, preferably 200-300℃.
In step S3, the alloy powder is a sieved and dried powder, the alloy powder particle size range is 35-75μm, the sphericity is ≥90%, and the oxygen content is ≤150ppm.
After optimizing the parameters, the laser power in the ultra-high-speed laser cladding process is 1.5kW and the scanning speed is 200mm/s.
During the pretreatment process, the disc-shaped workpiece 3 needs to be polished with sandpaper, cleaned with anhydrous ethanol, and dried at room temperature. Preheating temperature before cladding is 300℃
During the cladding process, the laser power of the ultra-high-speed laser cladding process is 3.5kW, the workpiece rotation speed is 200rpm, the spot diameter is 2.5mm, and the powder feeding speed is 15/20/25g/min. Scanning speed 20-200m/min (the diameter of the disc-shaped substrate used is 200mm); cladding head feed speed is 1mm/s; protective gas flow rate is 30L/min; carrier gas flow rate is 10L/min.
The laser focus position coincides with the powder flow focus position, and the defocus amount is 1mm. The defocus amount is controlled by the control terminal so that the distance between the cladding head and the substrate is always maintained at 10mm.
After the cladding is completed, the formed workpiece needs to be moved to an argon protection box and cooled at room temperature.
Preferably, in the ultra-high-speed laser cladding process described in the present invention, the optimal laser power is 3.5kW, the scanning speed is 100.56m/min, and the powder feeding speed is 25g/min.
The equipment used in the cladding process of the present invention includes a laser 1, a laser cladding head 2, a control terminal 4, a chuck 5 and a rotating carrier 6. The workpiece 3 to be clad is clamped by the chuck 5 and placed on the rotating carrier 6. The laser cladding head 2 is located at the lower end of the laser 1. The laser 1 is also connected to the control terminal 4. The control terminal can control the feeding of the laser and the parameters related to cladding, and can adjust the rotation speed of the rotating carrier 6 in real time. During the laser cladding process, the laser cladding parameters are optimized by the following method: The disc-shaped workpiece to be clad for the test is fixed on the chuck on the rotating carrier; The cladding is performed according to the preparation method of the fully amorphous crack-free iron-based amorphous coating by ultra-high-speed laser cladding, and the obtained coating is sampled and analyzed. A sample block is taken out at every 1 cm interval, and the cladding parameters are judged from the surface quality, coating thickness, and coating cross-sectional quality. The relationship between the coating thickness and the parameters is plotted to obtain the most suitable process parameters for the alloy powder; The parameters are readjusted to determine the position of the best coating quality, and the radius R test and the rotation speed N test at this time are recorded. Without changing other parameters such as the cladding head feed speed, the rotation speed N of the rotating carrier changes with time; the gradient change formula is as follows (taking the disc-shaped workpiece to be clad as an example, assuming that the radius of the target disc-shaped workpiece to be clad is R, the cladding head moving speed is v, and the time is t): N=Rtest*Ntest/(R-vt)
Reset the rotation speed of the rotating carrier, start cladding, and prepare a uniform thickness coating of the amorphous material on the target substrate.
In order to better highlight the significant advantages of the ultra-high-speed laser cladding complete amorphous coating prepared by the present invention, the iron-based complete amorphous coating under the optimal process of the present invention is further described below in conjunction with the accompanying drawings:

Example 1
A method for preparing a completely amorphous, crack-free iron-based amorphous coating by ultra-high-speed laser cladding, comprising the following steps:
S1, surface treatment of the disc-shaped workpiece to be clad;
S2, preheating the workpiece to be clad, clamping the preheated workpiece to be clad with a chuck, and placing it flat on the rotating
carrier;
S3, adding alloy powder to the cladding device Set the center, adjust the powder feeding speed, carrier gas flow rate, and shielding gas flow rate of the cladding device;
S4, adjust the distance between the cladding head and the workpiece to be clad, the laser focus, and the powder flow focus to ensure that the laser focus coincides with the powder focus, and the defocus range during the ultra-high-speed laser cladding process is always 0-10mm above the surface of the workpiece to be clad;
S5, set the cladding head moving speed;
S6, the rotating carrier drives the workpiece to be clad to rotate, and laser cladding starts from the outside to the inside, forming an ultra-high-speed laser-clad fully amorphous, crack-free, iron-based amorphous coating on the surface of the workpiece to be clad.
In step S1, the base material of the workpiece to be clad is 304S steel, a disc with a thickness of 5mm and a diameter of 200mm. Surface treatment of the workpiece to be clad includes: grinding and polishing the surface of the workpiece to be clad, removing oil stains, rust stains, oxide films, etc., to ensure good laser absorption and adhesion of the cladding layer.
After optimizing the parameters, the laser power of the ultra-high-speed laser cladding process is 1.5kW and the scanning speed is 200mm/s.
During the pre-treatment process, the disc-shaped workpiece to be clad needs to be polished with sandpaper, cleaned with anhydrous ethanol, and dried at room temperature. The preheating temperature before cladding is 300℃
During the cladding process, the laser power of the ultra-high-speed laser cladding process is 3.5kW, the workpiece rotation speed is 200rpm, the spot diameter is 2.5mm, and the powder feeding speed is 15/20/25g/min. The scanning speed is 100.56m/min (the diameter of the disc-shaped substrate used is 200mm); the cladding head feed speed is 1mm/s; the protective gas flow rate is 30L/min; the carrier gas flow rate is 10L/min.
The laser focus position coincides with the powder flow focus position, and the defocus amount is 1mm. The defocus amount is controlled by the control terminal so that the distance between the cladding head and the substrate is always maintained at 10mm.
After the cladding is completed, the formed workpiece needs to be moved to an argon protection box and cooled at room temperature.
Before obtaining Example 1, the corresponding preliminary test was carried out. The test parameters are shown in the following table. After the relationship between the coating thickness, quality and process parameters (Figure 2d) was statistically analyzed, according to the relationship diagram and the experience in the test, it was found that the coating thickness was most affected by the powder feeding speed at the same scanning speed. The surface defects and heat accumulation of the over-thick coating were difficult to eliminate, so the coating thickness needed to be controlled below 150μm as much as possible. At the same time, generally speaking, when the laser power is greater than 3kW, powders with a particle size of less than 100μm will be melted, so minimizing the laser power and appropriately increasing the powder feeding speed are the first considerations in the test.
The 10×5×5mm metallographic sample processed by the coating wire cutting of the embodiment of the present invention was ultrasonically cleaned of surface oil, washed with anhydrous ethanol, dried, mounted, ground the sample section perpendicular to the cladding direction (polished with 400/1500/3000/4000/5000 mesh sandpaper in turn), polished to a mirror finish, dried, etc.
The cross-sectional morphology of the amorphous coating was observed using a scanning electron microscope. According to the cross-sectional morphology of the iron-based amorphous coating shown in Figure 2, Figure 2(a) is the cross-sectional morphology of the coating under low-magnification SEM. It can be seen that there are no obvious macroscopic defects inside the coating, and the coating thickness is relatively uniform, and the internal structure is dense. This is due to the high scanning speed and the parameter optimization in the present invention. It fully proves that a coating with uniform thickness can be formed on a disc-shaped workpiece through reasonable parameter settings. Figure 2
(b) and Figure 2(c) correspond to regions A and B respectively. It can be seen from Figure 2(b) that no obvious crystallization phase and overlap marks are observed inside the coating except for the bonding area with the substrate. This shows that under this process parameter, the coating can achieve good bonding with the substrate, and the molten pool can also perfectly overlap with the previous track. Figure 2(c) shows the interface state between the coating and the substrate under the optimal process. Under this process, since the cooling rate at the bottom of the molten pool is lower than that in other areas, the metallurgical bonding area with the substrate is a cellular crystal, and its growth state is perpendicular to the interface. This is because the temperature gradient perpendicular to the cladding coating/interface (metallurgical bonding area) is the largest, which is conducive to crystallization and growth. Appropriate heat input is conducive to the formation of a more stable metallurgical bond. The advantage of the present invention is that the average bonding area width of 2.43μm is much smaller than the ultra-high-speed laser cladding coating prepared in recent studies, and there is no obvious crystallization area inside the coating, maintaining the composition stability of the amorphous coating.
The prepared coating was analyzed by X-ray diffraction technology. Figure 3 shows the XRD spectrum comparison of the completely amorphous coating in Example 1 and the amorphous powder sample of the material. It can be seen that the amorphous coating generally still has a wide diffuse scattering peak, although the position of the diffuse scattering peak becomes sharper relative to the powder sample, and a crystallization trend appears, which may be due to the local short-range structural changes caused by the overlap.
In order to observe the internal microstructure of the coating, a focused ion beam was used to sample the cross section of the sample (area B in Figure 2(b)) and perform transmission electron microscopy (TEM) analysis. Figure 4(a) is a high-resolution TEM spectrum of area B in Figure 2(b). It can be seen from the figure that the coating obtained by the present invention has a typical disordered structure. In addition, in the corresponding selected electron diffraction pattern (Figure 4(b)), the diffraction ring appears in a diffusely scattered halo state. This is because the amorphous alloy has a short-range ordered structure, which is almost a disordered state at the microscopic level.
The structure of the coating prepared by ultra-high-speed laser cladding is more refined and the composition is more uniform. In order to better describe the specific performance of the coating obtained in the embodiment of the present invention, an electrochemical corrosion test is used to characterize the corrosion resistance of the ultra-high-speed laser cladding coating.
An electrochemical corrosion sample with a size of 10×5×5mm was cut from the cladding coating. In order to avoid the influence of the uneven surface of the cladding coating and the oxide film, the test sample was ground, polished, cleaned with alcohol and dried for standby before testing.
The three-electrode system was used to perform electrochemical tests on the samples at room temperature, and the potential dynamic polarization method was used to test the corrosion resistance of the coating. The potential change rate was 1mV/s, and it was scanned from a low potential of 0.5V to a high potential of 1.2V.
The electrochemical polarization curve of the embodiment is shown in Figure 5. The corrosion potential and corrosion current density of the coating were calculated by fitting using the Tafel linear extrapolation method. The self-corrosion potential of the coating in the embodiment of the present invention was 0.266V, and the corrosion current density was 1.25×10-8A·cm’2. The corrosion current reflects the corrosion rate of the coating under the condition of no external current. The stronger the corrosion resistance of the coating, the slower the corrosion rate and the smaller the corrosion current; the corrosion potential mainly indicates the corrosion tendency of the coating. The higher the corrosion potential, the smaller the corrosion tendency of the coating. It can be seen that the coating has excellent corrosion resistance, which is mainly due to the uniformity of the coating composition and the high surface quality of the coating under the ultra-high-speed laser cladding optimization process.
The hardness curve of the iron-based completely amorphous coating with a scanning speed of 100.56m/min is shown in Figure 6. The microhardness of the ultra-high-speed laser cladding coating is much higher than that of the substrate, and it decreases rapidly in the metallurgical bonding area, reflecting the extremely narrow heat-affected zone during ultra-high-speed laser cladding. The average microhardness is about 1182.6HV0.2. The high scanning speed can reduce the fluctuation of the coating composition, thereby improving the mechanical properties of the coating.
The above description of the embodiments is to facilitate ordinary technicians in this technical field to understand and use the invention. It is obvious that those familiar with the technology in this field can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative labor. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.