A solid solution age treated erosion resistant nickel titanium alloy coating and method of manufacture

Abstract

This invention discloses a solution-treated and aging-treated anti-cavitation nickel-titanium alloy coating and its preparation method, belonging to the field of laser cladding coating technology. It includes a pure nickel transition layer and a nickel-titanium alloy coating formed by metallurgical bonding on the surface of a stainless steel substrate. The nickel-titanium alloy coating is formed by high-speed laser cladding of nickel-titanium powder onto the surface of the pure nickel transition layer, followed by solution treatment and aging treatment. Through solution treatment, Ni2Ti4O generated in the laser-clad NiTi coating... x Resolution treatment reduces component and microstructure segregation caused by unbalanced solidification during laser cladding, resulting in a homogenized coating microstructure with a single austenitic B2 phase. Then, aging treatment induces the redeposition of finely dispersed Ni2Ti4O3 within the coating. x Ni4Ti3 reduces the amount of O dissolved in the grains, improves its phase transformation behavior, and adjusts it to a suitable phase transformation range, thereby giving it a suitable critical stress for inducing phase transformation and a high resistance to dislocation movement, thus reducing cavitation damage and improving its resistance to cavitation.

Description

Technical Field

[0001] This invention relates to the field of laser cladding coating technology, and in particular to a solution-treated and aging-treated nickel-titanium alloy coating for cavitation resistance and its preparation method. Background Technology

[0002] Cavitation erosion is a common form of damage in liquid flow guides (flow-through components). When a liquid is disturbed, its pressure changes. When the pressure in a certain area of ​​the liquid is lower than its saturated vapor pressure, cavitation bubbles are generated due to cavitation. When these bubbles form and collapse on the surface of the flow-through component, they generate shock waves and microjets. Because the cavitation bubbles are small in size and have a small area and short duration of action upon collapse, they cause plastic deformation of the material surface, resulting in irreversible microscopic damage. As microscopic damage accumulates, it gradually develops into macroscopic damage, eventually leading to the failure of the flow-through component. Cavitation erosion significantly reduces the stability and safety of flow-through components. Currently, cavitation erosion has become one of the most pressing problems to be solved in the fields of hydropower, nuclear power, shipbuilding, and petrochemicals.

[0003] Currently, various methods for reducing cavitation erosion damage have been proposed both domestically and internationally, with energy-absorbing phase change materials being a research hotspot. NiTi alloys, due to their martensitic transformation characteristics, are excellent materials for absorbing cavitation erosion energy. However, on the one hand, compared to commonly used stainless steel flow components, NiTi alloys have higher production costs; on the other hand, due to the presence of martensitic phase transformation, NiTi alloys have poor machinability, making production difficult for flow components with complex shapes. The development of surface modification technology has provided a powerful means for applying NiTi alloys in the field of cavitation erosion resistance. Among these methods, laser cladding for NiTi coatings is a promising direction and has attracted widespread attention. However, currently, due to the easy oxidation of NiTi powder during cladding, the easy cracking of the coating, the large dilution rate of the coating by Fe elements in the matrix, and the significantly lower cavitation erosion resistance of laser-clad NiTi coatings compared to NiTi alloy bulk materials, laser cladding-prepared NiTi coatings cannot be applied to the cavitation erosion resistance of flow components. Summary of the Invention

[0004] This invention provides a solution-treated and aged anti-cavitation erosion nickel-titanium alloy coating and its preparation method, aiming to solve the problem that the anti-cavitation erosion performance of laser-clad NiTi coatings on stainless steel substrates is significantly lower than that of superelastic NiTi alloys. Through process optimization, a defect-free, low-oxidation, and low-dilution NiTi coating is prepared. By using a Ni transition layer process in conjunction with a high-speed laser cladding process, the dilution rate of the NiTi coating is greatly reduced, the melting of the substrate is reduced, and the penetration of Fe elements from stainless steel into the NiTi coating is isolated, reducing the generation of brittle and hard phases, thus achieving the preparation of a defect-free nickel-titanium alloy coating without cracks or pores.

[0005] The specific technical solution provided by this invention is as follows:

[0006] In a first aspect, the present invention provides a solution-treated and aging-treated anti-cavitation nickel-titanium alloy coating comprising a pure nickel transition layer metallurgically bonded to the surface of a stainless steel substrate and a nickel-titanium alloy coating metallurgically bonded to the surface of the pure nickel transition layer. The nickel-titanium alloy coating is formed by high-speed laser cladding of nickel-titanium powder onto the surface of the pure nickel transition layer and then by solution treatment and aging treatment. The thickness of the nickel-titanium alloy coating is 4 to 6 times the thickness of the pure nickel transition layer.

[0007] Optionally, the particle size of the nickel-titanium powder is 50-100 μm; the particle size of the nickel powder used in the pure nickel transition layer is 15-30 μm.

[0008] Optionally, the thickness of the nickel-titanium alloy coating is 600μm to 1000μm, and the thickness of the pure nickel transition layer is 100μm to 180μm.

[0009] Secondly, embodiments of the present invention provide a method for preparing the above-mentioned solution-treated and aging-treated cavitation-resistant nickel-titanium alloy coating, the method comprising:

[0010] Use an angle grinder or laser cleaner to remove the oxide film on the surface of the stainless steel substrate, and then use acetone to clean the oil stains on the surface of the stainless steel substrate.

[0011] Pure nickel powder was classified using a powder sieve, and pure nickel powder with a particle size of 15–30 μm was used as cladding powder.

[0012] Turn on the high-speed laser cladding system, add 15-30μm pure nickel powder to the powder feeder, introduce argon gas, set the argon gas flow rate to 8L / min, adjust the laser defocusing amount to 53mm, and the powder distance to 13mm.

[0013] Set the cladding path, laser power to 1.2-1.8KW, high-speed cladding scanning speed to 150-200mm / s, single-pass offset to 0.5mm, powder feeding speed to 15g / min, and then start cladding to form a pure nickel transition layer;

[0014] After the pure nickel transition layer is prepared, the oxide film on the surface of the pure nickel transition layer is cleaned using a laser cleaner;

[0015] Nickel-titanium powder was classified using a powder sieve, and 50-100 μm nickel-titanium powder was used as the cladding powder for nickel-titanium alloy coating.

[0016] Add 50-100μm nickel-titanium powder to the powder feeder, introduce argon gas, and set the argon gas flow rate to 8L / min; adjust the laser defocusing amount to 53mm and the powder distance to 13mm.

[0017] Set the cladding path, laser power to 720-900W, scanning speed to 15-30mm / s, single-pass offset to 1.1-1.3mm, and powder feeding speed to 10-15g / min. Then begin cladding a nickel-titanium alloy coating on the surface of the pure nickel transition layer.

[0018] The nickel-titanium alloy coating was first heated to 950-1000℃ at a heating rate of 10℃ / min and held for 60min, followed by quenching.

[0019] The quenched nickel-titanium alloy coating was then heated to 450–500°C at a heating rate of 5–10°C / min and held for 30–90 min. After furnace cooling, a solution-treated and cavitation-resistant nickel-titanium alloy coating was obtained.

[0020] The beneficial effects of this invention are as follows:

[0021] This invention provides a solution-treated and aging-treated anti-cavitation erosion nickel-titanium alloy coating comprising a pure nickel transition layer metallurgically bonded to the surface of a stainless steel substrate and a nickel-titanium alloy coating metallurgically bonded to the surface of the pure nickel transition layer. The nickel-titanium alloy coating is formed by high-speed laser cladding of nickel-titanium powder onto the surface of the pure nickel transition layer, followed by solution treatment and aging treatment. The thickness of the nickel-titanium alloy coating is 4 to 6 times the thickness of the pure nickel transition layer. The use of a Ni transition layer process combined with a high-speed laser cladding process significantly reduces the dilution rate of the NiTi coating, reduces the melting of the substrate, and effectively isolates the penetration of Fe elements from the stainless steel into the NiTi coating, reducing the generation of brittle and hard phases. This results in the preparation of a crack-free, pore-free, defect-free nickel-titanium alloy coating. Furthermore, the superelasticity of the nickel-titanium alloy coating formed on the surface of the stainless steel substrate absorbs cavitation erosion energy during repeated reversible phase transformations. This effect greatly dissipates the cavitation erosion energy, thereby significantly delaying fatigue failure caused by cavitation erosion. Through solution treatment, Ni2Ti4O generated in the laser-clad NiTi coating is... x Resolution treatment reduces component and microstructure segregation caused by unbalanced solidification during laser cladding, resulting in a homogenized coating microstructure with a single austenitic B2 phase. This process also eliminates residual stress generated during laser cladding, preparing the coating for aging treatment. Finally, aging treatment induces the redeposition of finely dispersed Ni2Ti4O3 within the coating. x Ni4Ti3 reduces the amount of O dissolved in the grains, improves its phase transformation behavior, and adjusts it to a suitable phase transformation range, thereby giving it a suitable critical stress for inducing phase transformation and a high resistance to dislocation movement, thus reducing cavitation damage and improving its resistance to cavitation. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic diagram of the cross-sectional morphology of a pure nickel transition layer according to an embodiment of the present invention;

[0024] Figure 2 This is a schematic diagram of the middle EDS line scan of a pure nickel transition layer according to an embodiment of the present invention;

[0025] Figure 3 This is a schematic diagram of the cross-sectional morphology of a solution-treated and aging-treated anti-cavitation nickel-titanium alloy coating before solution aging treatment, according to an embodiment of the present invention.

[0026] Figure 4 This is a schematic diagram of the cross-sectional morphology of a solution-treated and aging-treated anti-cavitation nickel-titanium alloy coating according to an embodiment of the present invention.

[0027] Figure 5 This is a schematic diagram of the cross-sectional morphology of a solution-aged and aging-treated anti-cavitation nickel-titanium alloy coating according to an embodiment of the present invention.

[0028] Figure 6 This is a schematic diagram of the heat treatment XRD pattern of a solution-treated and aging-treated anti-cavitation nickel-titanium alloy coating according to an embodiment of the present invention.

[0029] Figure 7 This is a hardness curve of a solution-treated and aging-treated cavitation-resistant nickel-titanium alloy coating according to an embodiment of the present invention.

[0030] Figure 8 This is a schematic diagram of the cavitation volume loss curve of a solution-treated and aging-treated anti-cavitation nickel-titanium alloy coating according to an embodiment of the present invention. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0032] The terms “comprising” and “having”, and any variations thereof, in the specification and claims of this invention are intended to cover non-exclusive inclusion, for example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such process, method, product, or device.

[0033] The following will combine Figures 1 to 8 This invention provides a detailed description of a solution-treated and aging-treated nickel-titanium alloy coating for cavitation resistance and its preparation method.

[0034] After observing the cavitation phenomenon on the surface of a stainless steel substrate, the inventors of this invention attempted to prepare a nickel-titanium alloy coating on the surface of the stainless steel substrate. However, due to the infiltration of Fe elements in the substrate, brittle and hard phases such as FeTi and Ni3Ti often appeared in the prepared nickel-titanium alloy coating, which led to cracking of the coating and made it unusable. Based on this, the technical solution claimed in this application uses a Ni transition layer process combined with a high-speed laser cladding process to add a pure nickel transition layer between the stainless steel substrate and the nickel-titanium alloy coating. The Ni transition layer prepared by the optimized high-speed laser cladding process has a relatively low dilution rate, effectively blocks the Fe elements in the substrate, and reduces the brittle and hard phases such as FeTi and Ni3Ti in the nickel-titanium alloy coating, thereby effectively solving the problem of cracking of the laser-clad nickel-titanium alloy coating. At the same time, the oxidation and dilution rate of the coating are also relatively low. By utilizing the superelasticity of NiTi alloy, the energy of cavitation erosion is absorbed during repeated reversible phase transformation. The cavitation energy is greatly consumed by this effect, thereby significantly delaying the fatigue failure caused by cavitation erosion. After 80 hours of cavitation erosion, its volume loss is only half that of 304 stainless steel.

[0035] Example 1

[0036] refer to Figures 1 to 8 As shown in Embodiment 1 of the present invention, a solution-treated and aging-treated anti-cavitation nickel-titanium alloy coating comprises a pure nickel transition layer metallurgically bonded to the surface of a stainless steel substrate and a nickel-titanium alloy coating metallurgically bonded to the surface of the pure nickel transition layer. The nickel-titanium alloy coating is formed by high-speed laser cladding of nickel-titanium powder onto the surface of the pure nickel transition layer, followed by solution treatment and aging treatment. The thickness of the nickel-titanium alloy coating is 4 to 6 times the thickness of the pure nickel transition layer. The particle size of the nickel-titanium powder used in the laser cladding process is 50 to 100 μm; the particle size of the nickel powder used in the pure nickel transition layer is 15 to 30 μm. Preferably, the thickness of the nickel-titanium alloy coating is 600 μm to 1000 μm, and the thickness of the pure nickel transition layer is 100 μm to 180 μm.

[0037] The solution-treated and aging-treated anti-cavitation nickel-titanium alloy coating provided in Embodiment 1 of this invention is prepared by the following method:

[0038] Use an angle grinder or laser cleaner to remove the oxide film on the surface of the stainless steel substrate, and then use acetone to clean the oil stains on the surface of the stainless steel substrate.

[0039] Pure nickel powder was classified using a powder sieve, and pure nickel powder with a particle size of 15–30 μm was used as cladding powder.

[0040] Turn on the high-speed laser cladding system, add 15-30μm pure nickel powder to the powder feeder, introduce argon gas, set the argon gas flow rate to 8L / min, adjust the laser defocusing amount to 53mm, and the powder distance to 13mm.

[0041] Set the cladding path, laser power to 1.2-1.8KW, high-speed cladding scanning speed to 150-200mm / s, single-pass offset to 0.5mm, powder feeding speed to 15g / min, and then start cladding to form a pure nickel transition layer;

[0042] After the pure nickel transition layer is prepared, the oxide film on the surface of the pure nickel transition layer is cleaned using a laser cleaner;

[0043] Nickel-titanium powder was classified using a powder sieve, and 50-100 μm nickel-titanium powder was used as the cladding powder for nickel-titanium alloy coating.

[0044] Add 50-100μm nickel-titanium powder to the powder feeder, introduce argon gas, and set the argon gas flow rate to 8L / min; adjust the laser defocusing amount to 53mm and the powder distance to 13mm.

[0045] Set the cladding path, laser power to 720-900W, scanning speed to 15-30mm / s, single-pass offset to 1.1-1.3mm, and powder feeding speed to 10-15g / min. Then, begin cladding a nickel-titanium alloy coating on the surface of the pure nickel transition layer. The thickness of the nickel-titanium alloy coating is 800μm, and the thickness of the pure nickel transition layer is 150μm.

[0046] The nickel-titanium alloy coating was first heated to 950-1000℃ at a heating rate of 10℃ / min and held for 60min, followed by quenching.

[0047] The quenched nickel-titanium alloy coating was then heated to 450–500°C at a heating rate of 5–10°C / min and held for 30–90 min. After furnace cooling, a solution-treated and cavitation-resistant nickel-titanium alloy coating was obtained.

[0048] During the preparation process, the high energy density of laser cladding is utilized to efficiently leverage laser energy. A smaller powder feeding diameter and speed ensure better inert gas protection during cladding, reducing the oxidation of nickel-titanium powder and thus minimizing oxides in the coating, ensuring no significant difference between the actual and nominal composition. Furthermore, concentrating the nickel-titanium powder in the center of higher laser energy density allows for more efficient use of laser energy, enabling powder melting with lower laser power and further reducing oxidation. Secondly, process optimization achieves the preparation of defect-free, low-oxidation, and low-dilution NiTi coatings. The use of a Ni transition layer process combined with high-speed laser cladding significantly reduces the dilution rate of the nickel-titanium alloy coating, minimizing substrate melting, isolating Fe from the stainless steel, reducing the formation of brittle and hard phases, and achieving a defect-free coating without cracks or pores. Optimal process parameter combinations are adjusted during the cladding of the nickel-titanium alloy coating to achieve the preparation of low-oxidation, low-dilution, and defect-free nickel-titanium alloy coatings. The above measures can solve the technical problems of easy oxidation of laser clad nickel-titanium alloy powder, easy cracking of coating, large coating dilution rate, and the fact that the anti-cavitation performance of laser clad nickel-titanium alloy coating is significantly inferior to that of bulk nickel-titanium alloy, thereby improving the anti-cavitation performance and service life of flow components.

[0049] In this embodiment of the invention, Ni2Ti4O generated in the laser-clad NiTi coating is first subjected to a solution treatment. x Resolution treatment reduces component and microstructure segregation caused by unbalanced solidification during laser cladding, resulting in a homogenized coating microstructure with a single austenitic B2 phase. This process also eliminates residual stress generated during laser cladding, preparing the coating for aging treatment. Finally, aging treatment induces the redeposition of finely dispersed Ni2Ti4O3 within the coating. x Ni4Ti3 reduces the amount of O dissolved in the grains, improves its phase transformation behavior, and adjusts it to a suitable phase transformation range, thereby giving it a suitable critical stress for inducing phase transformation and a high resistance to dislocation movement, thus reducing cavitation damage and improving its resistance to cavitation.

[0050] Example 2

[0051] On the other hand, based on the same inventive concept, Embodiment 2 of the present invention provides a method for preparing the above-mentioned solution-treated and aging-treated anti-cavitation nickel-titanium alloy coating, comprising:

[0052] Use an angle grinder or laser cleaner to remove the oxide film on the surface of the stainless steel substrate, and then use acetone to clean the oil stains on the surface of the stainless steel substrate.

[0053] Pure nickel powder was graded using a powder sieve, and laser cladding powder with a thickness of 15–30 μm was selected as the pure nickel transition layer.

[0054] Turn on the high-speed laser cladding system, add 15-30μm pure nickel powder to the powder feeder, introduce argon gas, and set the argon gas flow rate to 8L / min; adjust the laser defocusing amount to 53mm and the powder distance to 13mm.

[0055] Set the cladding path, laser power of 1.8KW, scanning speed of 200mm / s, single-pass offset of 0.5mm, and powder feeding speed of 15g / min, and then start cladding the pure nickel transition layer;

[0056] The morphology and EDS composition analysis of the pure nickel transition layer are as follows: Figure 1 , Figure 2 As shown, according to Figure 1 and Figure 2 As shown, the pure nickel transition layer has a good morphology and proper overlap. EDS analysis was used to determine the elemental composition of the coating. Figure 1 The area marked by the red line indicates that the pure nickel transition layer contains only Ni, effectively preventing the penetration of Fe.

[0057] After the Ni transition layer is prepared, a laser cleaner can be used to remove the oxide film on its surface before proceeding to the next step of preparing the nickel-titanium alloy coating.

[0058] NiTi powder was classified using a powder sieve, and 50-100 μm nickel-titanium powder was used as the cladding powder for nickel-titanium alloy coating.

[0059] Add 50-100μm nickel-titanium powder to the powder feeder, introduce argon gas, and set the argon gas flow rate to 8L / min; adjust the laser defocusing amount to 53mm and the powder distance to 13mm.

[0060] Set the cladding path, laser power 720W, scanning speed 15mm / s, single-pass offset 1.3mm, powder feeding speed 15g / min, and then start cladding to form a nickel-titanium alloy coating.

[0061] The nickel-titanium alloy coating was first heated to 950-1000℃ at a heating rate of 10℃ / min and held for 60min, followed by quenching.

[0062] The quenched nickel-titanium alloy coating was then heated to 450–500°C at a heating rate of 5–10°C / min and held for 30–90 min. After furnace cooling, a solution-treated and cavitation-resistant nickel-titanium alloy coating was obtained.

[0063] Cross-sectional morphology and compositional analysis of the nickel-titanium alloy coating after laser cladding are as follows: Figure 3As shown, the cross-section of the nickel-titanium alloy coating is defect-free and well bonded to the pure nickel transition layer. EDS line scanning of the nickel-titanium alloy coating cross-section reveals a small variation range of Ni and Ti at the interface between the coating and the pure nickel transition layer, indicating a low dilution rate. EDS scanning shows that the Ni:Ti ratio in the nickel-titanium alloy coating is 49.1:50.9 (atomic ratio). This process yields a low-dilution nickel-titanium alloy coating, ensuring that the composition of the clad nickel-titanium alloy coating does not significantly deviate from the nominal composition.

[0064] The solution-treated and cavitation-resistant nickel-titanium alloy coating prepared according to this invention was cut into samples using wire cutting. Metallographic images of the cross-sections of the solution-treated and cavitation-resistant nickel-titanium alloy coating were prepared. The hardness of the coating was tested every 100 micrometers using a microhardness tester. The results are as follows: Figure 7 As shown, the interface coating has uniform hardness.

[0065] The cavitation erosion resistance of the solution-treated and aged nickel-titanium alloy coating samples from this embodiment of the invention was tested according to the GB / T 6383-2009 standard for cavitation erosion testing. The solution-treated and aged nickel-titanium alloy coating and the 304 substrate were respectively processed into samples with a diameter of 20 mm and a thickness of 3 mm. The surface of the solution-treated and aged nickel-titanium alloy coating was polished with sandpaper. Before testing, the samples were ultrasonically cleaned for 10 minutes, dried at 50°C for 30 minutes, and then weighed using an electronic balance with an accuracy of 0.1 mg. Samples were taken every 4 hours for ultrasonic cleaning, drying, and weighing, and the cumulative volume loss of the samples was recorded for a total of 80 hours. Images were plotted. The results are as follows: Figure 8 As shown, compared to the 304 substrate, the solution-treated and aged anti-cavitation nickel-titanium alloy coating of this embodiment of the invention greatly improves the anti-cavitation performance. The anti-cavitation performance is greatly improved by adjusting the coating preparation process. In addition, the addition of heat treatment makes the anti-cavitation performance of the coating significantly improved, and the anti-cavitation performance is almost the same as that of the bulk nickel-titanium alloy.

[0066] This invention provides a solution-treated and aging-treated anti-cavitation erosion nickel-titanium alloy coating comprising a pure nickel transition layer metallurgically bonded to the surface of a stainless steel substrate and a nickel-titanium alloy coating metallurgically bonded to the surface of the pure nickel transition layer. The nickel-titanium alloy coating is formed on the surface of the pure nickel transition layer by high-speed laser cladding of nickel-titanium powder. The thickness of the nickel-titanium alloy coating is 2 to 4 times the thickness of the pure nickel transition layer. By using a Ni transition layer process in conjunction with a high-speed laser cladding process, the dilution rate of the NiTi coating is greatly reduced, the melting of the substrate is reduced, and the penetration of Fe elements from the stainless steel into the NiTi coating is isolated, reducing the generation of brittle and hard phases. This achieves the preparation of a defect-free nickel-titanium alloy coating without cracks or pores. Furthermore, by utilizing the shape memory effect of the nickel-titanium alloy coating formed on the surface of the stainless steel substrate, the energy of cavitation erosion is absorbed during repeated reversible phase transformations. The cavitation erosion energy is greatly consumed by this effect, thereby significantly delaying fatigue failure caused by cavitation erosion.

[0067] Example 3

[0068] Furthermore, based on the same inventive concept, Embodiment 3 of the present invention provides a method for preparing the above-mentioned solution-treated and aging-treated cavitation-resistant nickel-titanium alloy coating, comprising:

[0069] Use an angle grinder or laser cleaner to remove the oxide film on the surface of the stainless steel substrate, and then use acetone to clean the oil stains on the surface of the stainless steel substrate.

[0070] Pure nickel powder was graded using a powder sieve, and 25μm powder was selected as the laser cladding powder for the pure nickel transition layer.

[0071] Turn on the high-speed laser cladding system, add 25μm pure nickel powder to the powder feeder, introduce argon gas, and set the argon gas flow rate to 8L / min; adjust the laser defocusing amount to 53mm and the powder distance to 13mm;

[0072] Set the cladding path, laser power of 1.8KW, scanning speed of 200mm / s, single-pass offset of 0.5mm, and powder feeding speed of 15g / min, and then start cladding the pure nickel transition layer;

[0073] The morphology and EDS composition analysis of the pure nickel transition layer are as follows: Figure 1 , Figure 2 As shown, according to Figure 1 and Figure 2 As shown, the pure nickel transition layer has a good morphology and proper overlap. EDS analysis was used to determine the elemental composition of the coating. Figure 1 The area marked by the red line indicates that the pure nickel transition layer contains only Ni, effectively preventing the penetration of Fe.

[0074] After the Ni transition layer is prepared, a laser cleaner can be used to remove the oxide film on its surface before proceeding to the next step of preparing the nickel-titanium alloy coating.

[0075] NiTi powder was classified using a powder sieve, and 75μm nickel-titanium powder was used as the cladding powder for nickel-titanium alloy coating.

[0076] Add 75μm nickel-titanium powder to the powder feeder, introduce argon gas, and set the argon gas flow rate to 8L / min; adjust the laser defocusing amount to 53mm and the powder distance to 13mm.

[0077] Set the cladding path, laser power 720W, scanning speed 15mm / s, single-pass offset 1.3mm, powder feeding speed 15g / min, and then start cladding to form a nickel-titanium alloy coating.

[0078] The morphology of the original cladding-formed nickel-titanium alloy coating is as follows: Figure 3 As shown, the prepared nickel-titanium alloy coating was then placed in a heat treatment furnace. The heat treatment process was as follows: first, the temperature was raised to 1000℃ at a heating rate of 10℃ / min and held for 60 min, followed by quenching; then, the quenched sample was heated to 500℃ at a heating rate of 5℃ / min and held for 60 min, followed by furnace cooling to obtain a solution-treated and aging-resistant cavitation-resistant nickel-titanium alloy coating. The microstructure of the solution-treated nickel-titanium alloy coating is shown below. Figure 4 As shown, no second phase was found in the coating, and the XRD pattern is as follows. Figure 6 As shown, only a single B2 austenitic phase is present. Residual stress in the coating was eliminated through heat treatment. The aged coating is as follows... Figure 5 As shown, dot-like Ni2Ti4O was precipitated. x Second phase. XRD showed the presence of Ni₂Ti₄O. x And Ni4Ti3 and R transformation phase.

[0079] The solution-treated and cavitation-resistant nickel-titanium alloy coating prepared according to this invention was cut into samples using wire cutting. Metallographic images of the cross-sections of the solution-treated and cavitation-resistant nickel-titanium alloy coating were prepared. The hardness of the coating was tested every 100 micrometers using a microhardness tester. The results are as follows: Figure 7 As shown, the interface coating has uniform hardness.

[0080] The cavitation erosion resistance of the solution-treated and aged nickel-titanium alloy coating samples from this embodiment of the invention was tested according to the GB / T 6383-2009 standard for cavitation erosion testing. The solution-treated and aged nickel-titanium alloy coating and the 304 substrate were respectively processed into samples with a diameter of 20 mm and a thickness of 3 mm. The surface of the solution-treated and aged nickel-titanium alloy coating was polished with sandpaper. Before testing, the samples were ultrasonically cleaned for 10 minutes, dried at 50°C for 30 minutes, and then weighed using an electronic balance with an accuracy of 0.1 mg. Samples were taken every 4 hours for ultrasonic cleaning, drying, and weighing, and the cumulative volume loss of the samples was recorded for a total of 80 hours. Images were plotted. The results are as follows: Figure 8 As shown, compared to the 304 substrate, the solution-treated and aged anti-cavitation nickel-titanium alloy coating of this embodiment of the invention greatly improves the anti-cavitation performance. The anti-cavitation performance is greatly improved by adjusting the coating preparation process. In addition, the addition of heat treatment makes the anti-cavitation performance of the coating significantly improved, and the anti-cavitation performance is almost the same as that of the bulk nickel-titanium alloy.

[0081] Obviously, those skilled in the art can make various modifications and variations to the embodiments of the present invention without departing from the spirit and scope of the embodiments of the present invention. Thus, if these modifications and variations to the embodiments of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention also intends to include these modifications and variations.

Claims

1. A solution-treated and aging-treated nickel-titanium alloy coating for cavitation erosion resistance, characterized in that, The solution-treated and aging-treated anti-cavitation nickel-titanium alloy coating comprises a pure nickel transition layer metallurgically bonded to the surface of a stainless steel substrate and a nickel-titanium alloy coating metallurgically bonded to the surface of the pure nickel transition layer. The nickel-titanium alloy coating is formed by high-speed laser cladding of nickel-titanium powder onto the surface of the pure nickel transition layer, followed by solution treatment and aging treatment. The thickness of the nickel-titanium alloy coating is 4 to 6 times the thickness of the pure nickel transition layer. The particle size of the nickel-titanium powder is 50 to 100 μm, and the scanning speed is set to 15 to 30 mm / s. The nickel powder used in the pure nickel transition layer has a particle size of 15 to 30 μm, and the high-speed cladding scanning speed is 150 to 200 mm / s. The thickness of the nickel-titanium alloy coating is 600 μm to 1000 μm, and the thickness of the pure nickel transition layer is 100 μm to 180 μm. The solution treatment involves heating the nickel-titanium alloy coating to 950-1000℃ at a heating rate of 10℃ / min and holding it for 60min, followed by quenching. The aging treatment involves heating the quenched nickel-titanium alloy coating to 450-500℃ at a heating rate of 5-10℃ / min and holding it for 30-90min, followed by furnace cooling. The solution treatment causes the Ni2Ti4Ox generated in the laser-clad NiTi coating to re-dissolve, reducing compositional and microstructure segregation caused by unbalanced solidification during laser cladding, and homogenizing the coating microstructure to a single austenitic B2 phase. The aging treatment causes the redeposition of finely dispersed Ni2Ti4Ox and Ni4Ti3 in the coating, reducing the O dissolved in the grains, improving its phase transformation behavior, and adjusting the phase transformation range.

2. A method for preparing a solution-treated and aging-treated cavitation-resistant nickel-titanium alloy coating as described in claim 1, characterized in that, The method includes: Use an angle grinder or laser cleaner to remove the oxide film on the surface of the stainless steel substrate, and then use acetone to clean the oil stains on the surface of the stainless steel substrate. Pure nickel powder was classified using a powder sieve, and pure nickel powder with a particle size of 15~30μm was used as cladding powder. Turn on the high-speed laser cladding system, add 15~30μm pure nickel powder to the powder feeder, introduce argon gas, set the argon gas flow rate to 8L / min, adjust the laser defocusing amount to 53mm, and the powder distance to 13mm; Set the cladding path, laser power to 1.2~1.8KW, high-speed cladding scanning speed to 150~200mm / s, single-pass offset to 0.5mm, powder feeding speed to 15g / min, and then start cladding to form a pure nickel transition layer; After the pure nickel transition layer is prepared, the oxide film on the surface of the pure nickel transition layer is cleaned using a laser cleaner; Nickel-titanium powder was classified using a powder sieve, and 50-100μm nickel-titanium powder was used as the cladding powder for nickel-titanium alloy coating. Add 50~100μm nickel-titanium powder to the powder feeder, introduce argon gas, and set the argon gas flow rate to 8L / min; adjust the laser defocusing amount to 53mm and the powder distance to 13mm. Set the cladding path, laser power to 720~900W, scanning speed to 15~30mm / s, single-pass offset to 1.1~1.3mm, powder feeding speed to 10~15g / min, and then begin to clad the pure nickel transition layer to form a nickel-titanium alloy coating. The nickel-titanium alloy coating is first heated to 950~1000℃ at a heating rate of 10℃ / min and held for 60min, followed by quenching. The quenched nickel-titanium alloy coating was then heated to 450-500℃ at a heating rate of 5-10℃ / min and held for 30-90min. After furnace cooling, a solution-treated and cavitation-resistant nickel-titanium alloy coating was obtained.

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