A targeted titanium microalloyed gh3536 nickel-based alloy and a preparation method thereof

Abstract

The application discloses a kind of GH3536 alloy targeted titanium microalloying and preparation method thereof, and the application is prepared into titanium-containing pre-polymer colloid by acetylacetone titanium, polyvinyl alcohol, polyvinylpyrrolidone, polyethylene imine, citric acid and ethylene glycol, coated on the surface of GH3536 alloy powder and pyrolyzed by program temperature, pre-constructed carbon-nitrogen co-doped porous carbon limited titanium dioxide coating on the surface of powder, then layer-by-layer forming is carried out by using coaxial powder feeding type laser melting deposition process, in situ release titanium atom by carbon thermal reduction reaction in laser molten pool and make it to segregate at the grain boundary of solidification front, while interlayer is supplemented with ultrasonic vibration treatment.The application realizes the targeted microalloying of titanium element in the process of laser melting deposition of GH3536 alloy, improves the distribution form of grain boundary carbide;The elongation after fracture of deposited sample of the application is improved by 39.4%~50.7% compared with untreated sample, and the strength-plastic product is improved by 63.0%, and the grain boundary liquidized crack is inhibited.

Description

Technical Field

[0001] This invention belongs to the technical field of nickel-based high-temperature alloy materials. More specifically, this invention relates to a GH3536 nickel-based alloy with targeted titanium microalloying and its preparation method. Background Technology

[0002] GH3536 alloy is a Ni-Cr-Fe based solid solution strengthened nickel-based superalloy with excellent oxidation and corrosion resistance below 900℃, and is widely used in the manufacture of hot-end components such as aero-engine combustion chambers. Laser melting deposition technology can achieve near-net-shape forming of large-sized complex components made from this alloy; however, under rapid non-equilibrium solidification conditions, elements such as carbon and chromium tend to segregate at grain boundaries, forming continuous or semi-continuous M-type deposits. 23 The C6 type carbide film undergoes component liquefaction under subsequent laser cyclic heating, which in turn leads to the formation of liquefaction cracks along the grain boundaries under thermal stress, affecting the mechanical properties and service reliability of the component.

[0003] To address the aforementioned grain boundary liquefaction cracking problem, in existing technologies, when titanium is introduced into GH3536 alloy using an integral pre-alloying method, the titanium is uniformly dissolved within the alloy matrix during the atomization powdering stage. During laser melting deposition, it cannot directionally agglomerate to the grain boundary liquefaction-sensitive region at the end of solidification. When titanium is introduced by mechanically mixing titanium carbide particles, the titanium carbide particles are unevenly distributed in the powder, easily agglomerate, and have weak interfacial bonding with the nickel-based matrix, making it difficult to effectively release titanium atoms in the molten pool and achieve grain boundary agglomeration.

[0004] In existing technologies, methods such as overall pre-alloying and mechanical mixing of titanium carbide particles cannot achieve precise and controllable segregation of titanium at grain boundaries, making it difficult to meet the engineering application requirements of high-performance GH3536 alloy. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, this invention provides a GH3536 alloy for targeted titanium microalloying and its preparation method, which solves the problem that titanium elements cannot effectively segregate in the grain boundary liquefaction sensitive region during laser melting deposition solidification and is difficult to fundamentally improve the continuity of grain boundary carbide films.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing GH3536 alloy with targeted titanium microalloying includes the following steps:

[0008] S1: GH3536 alloy powder is pretreated to obtain powder with surface rich in active hydroxyl and amine groups. This step introduces active hydroxyl and amine groups on the powder surface, providing active sites for the subsequent chemical anchoring and uniform spreading of titanium-containing prepolymer colloid.

[0009] S2: Titanium-containing prepolymer colloid is prepared by dissolving titanium acetylacetonate, polyvinyl alcohol, polyvinylpyrrolidone, polyethyleneimine, citric acid, and ethylene glycol in water. Titanium acetylacetonate provides the titanium source, polyvinyl alcohol and polyvinylpyrrolidone constitute carbon and nitrogen source precursors, respectively, and polyethyleneimine forms N→Ti coordination bonds with titanium atoms in titanium acetylacetonate through its amino groups, enabling the titanium to be dispersed at the molecular level in the polymer network. Citric acid acts as a complexing pore-forming agent, and ethylene glycol adjusts the viscosity of the colloid.

[0010] S3: The titanium-containing prepolymer colloid is coated on the surface of the powder obtained in S1 and dried to form a film that encapsulates the powder. The film uniformly loads the titanium source precursor and each organic component onto the powder surface.

[0011] S4: The powder obtained in S3 is subjected to programmed temperature-controlled pyrolysis in an inert atmosphere to obtain a coating of carbon-nitrogen co-doped porous carbon confined titanium dioxide. The maximum temperature of the programmed temperature-controlled pyrolysis is 380℃~450℃. This pyrolysis process transforms the organic components into a carbon-nitrogen co-doped porous carbon matrix. At the same time, the titanium dioxide nanocrystals generated by the decomposition of titanium acetylacetonate are confined in the nanopores of porous carbon. The maximum temperature is controlled below 450℃ to prevent titanium from entering the interior of the alloy matrix through solid-state diffusion during the pretreatment stage.

[0012] S5: Depolymerize and sieve the powder obtained in S4 to obtain powder with a particle size of 53μm to 150μm;

[0013] S6: The powder obtained in S5 is formed layer by layer using a coaxial powder feeding laser melting deposition process. In the laser molten pool, the titanium dioxide in the coating undergoes a carbothermic reduction reaction with the porous carbon, releasing titanium atoms into the nickel-based melt and agglomerating at the grain boundary at the solidification front. The high contact area between the porous carbon matrix and titanium dioxide provides a sufficient solid carbon source and reaction interface for the carbothermic reduction reaction. After being released from the powder surface, the titanium atoms have a short diffusion distance and agglomerate at the solidification front under the drive of the chemical potential gradient.

[0014] S7: During the interlayer deposition process, ultrasonic vibration is applied to the deposited layers to promote grain refinement and carbide dispersion through acoustic flow and cavitation effects.

[0015] Further, the surface pretreatment process described in S1 is as follows: GH3536 alloy powder is acid-washed with dilute nitric acid solution to remove the surface oxide film, exposing the fresh metal surface; it is then rinsed with deionized water until neutral; hydroxylation treatment is performed with hydrogen peroxide solution to generate an oxide layer rich in hydroxyl groups on the powder surface; after washing with deionized water, it is dehydrated by alcohol displacement with anhydrous ethanol to avoid powder adhesion caused by capillary force during drying; then, amine grafting treatment is performed using a solution containing aminopropyltriethoxysilane, where the silanoxy group at one end of the aminopropyltriethoxysilane condenses with the hydroxyl groups on the powder surface to form Si-O- surface bonds, and the amine group at the other end is exposed to the outside; and the powder with a surface rich in active hydroxyl and amine groups is obtained by vacuum drying.

[0016] Further, in S2, the titanium-containing prepolymer colloid is prepared in the following proportions by mass: 5-10 parts titanium acetylacetonate, 3-6 parts polyvinyl alcohol, 2-4 parts polyvinylpyrrolidone, 1-2.5 parts polyethyleneimine, 3-6 parts citric acid, 8-15 parts ethylene glycol, with the remainder being water; polyvinyl alcohol forms a hydrogen-bonded crosslinking network backbone, polyvinylpyrrolidone and polyvinyl alcohol form an interpenetrating polymer network, polyethyleneimine enables titanium to be molecularly dispersed in the polymer network, citric acid and titanium form a complex intermediate, and ethylene glycol is inserted between polyvinyl alcohol molecular chains to adjust the hydrogen bond density.

[0017] Further, the coating described in S3 is as follows: first, the powder obtained in S1 is pre-wetted with anhydrous ethanol, and the low surface tension of ethanol forms a wetting interface on the powder surface. Then, the titanium-containing prepolymer colloid is coated onto the powder surface in a gradient spraying manner. The total amount of titanium-containing prepolymer colloid is 10% to 15% of the powder mass. After the gradient spraying is completed, the powder is centrifuged to make the colloid spread evenly and remove liquid bridges between powders. The drying is carried out under reduced pressure drying at a temperature of 30℃ to 35℃ and a vacuum degree of -0.08MPa to -0.10MPa. The low temperature and reduced pressure conditions allow the solvent to evaporate slowly and the colloid film to shrink evenly.

[0018] Furthermore, the programmed temperature-controlled pyrolysis process described in S4 is as follows:

[0019] The temperature was increased from room temperature to 100°C at a rate of 2°C / min under a nitrogen atmosphere and held to remove physically adsorbed water and residual free alcohol. Then the temperature was increased to 200°C at a rate of 1°C / min and held to gradually remove the citric acid crystal water.

[0020] Switch to argon atmosphere and heat to 380℃~450℃ at a rate of 0.5℃ / min. During the heating process, a heat preservation step is set at 250℃ to allow citric acid to undergo decarboxylation and release carbon dioxide gas to form initial channels in the carbon matrix. A heat preservation step is set at 340℃ to eliminate the side chain of polyvinyl alcohol, open the ring of polyvinylpyrrolidone pyrrolidone, and decompose the acetylacetone titanium organic ligand. The generated gas expands in the flowable carbon-polymer intermediate phase to form interconnected nanopores.

[0021] After switching to a nitrogen atmosphere for heat preservation, the furnace is cooled.

[0022] Furthermore, in the carbon-nitrogen co-doped porous carbon confined titanium dioxide coating obtained in S4, titanium dioxide is confined in the form of nanocrystals within the carbon-nitrogen co-doped porous carbon matrix. The confinement and isolation of the titanium dioxide nanocrystals by the porous carbon matrix prevents the aggregation and growth of titanium dioxide particles during pyrolysis. The carbon-nitrogen co-doping improves the electrical conductivity of the carbon matrix. The coating thickness is 80 nm to 200 nm.

[0023] Furthermore, the depolymerization described in S5 is performed by ball milling the powder in a ball mill using polyurethane elastic balls. The hardness of the polyurethane elastic balls is lower than that of the GH3536 alloy powder. During ball milling, the slightly bonded powder particles after pyrolysis are separated by elastic collision without damaging the powder surface coating. The ball milling speed is 15 r / min to 20 r / min.

[0024] Furthermore, the process parameters for coaxial powder-feeding laser melting deposition in S6 are: laser power 500W~800W, scanning speed 400mm / min~700mm / min, powder feeding rate 2.5g / min~5.0g / min, overlap rate 40%~50%, and interlayer lift 0.2mm~0.5mm. Within the above parameter range, the ultra-high temperature conditions of the laser molten pool trigger the carbothermic reduction reaction in the coating. Titanium dioxide reacts with porous carbon to generate titanium carbide intermediates, and titanium carbide decomposes in the nickel-based melt to release titanium atoms.

[0025] Furthermore, the ultrasonic vibration treatment described in S7 involves applying pulsed ultrasonic waves to the surface of the deposited layer using an ultrasonic amplitude transformer. The frequency is 20kHz to 40kHz, the amplitude is 15μm to 30μm, the pulse width is 100ms to 200ms, the pulse interval is 300ms to 500ms, and the single-layer treatment time is 10s to 30s. The pulsed ultrasonic waves generate periodic stress waves and acoustic flow effects in the deposited layer, promoting grain refinement and making the morphology of grain boundary carbides tend to be discrete.

[0026] This invention also provides a GH3536 alloy with targeted titanium microalloying prepared by the above method. The alloy uses GH3536 as a matrix, with the titanium element increment accounting for 0.003% to 0.006% of the total mass of the GH3536 alloy powder. Titanium atoms are segregated at grain boundaries, and the grain boundary carbides are discrete granular. The elongation after fracture is increased by 39.4% to 50.7% compared to the original GH3536, and the strength-ductility product is increased by 47% to 63%, with no grain boundary liquefaction cracks. Throughout the process, the titanium element increment introduced by titanium acetylacetonate accounts for 0.003% to 0.006% of the total mass of the GH3536 alloy powder. This trace amount of titanium is released through carbothermic reduction in the laser molten pool and segregates at the grain boundaries. By changing the liquid / solid interface energy at the solidification front and preferentially forming granular titanium-containing carbides, the grain boundary carbides are transformed from a continuous film to discrete granular particles.

[0027] The technical effects and advantages of this invention are as follows:

[0028] (i) In the powder pretreatment stage, titanium acetylacetonate, polyvinyl alcohol, polyvinylpyrrolidone, polyethyleneimine, citric acid and ethylene glycol were formulated into a titanium-containing prepolymer colloid and coated on the surface of GH3536 alloy powder. After programmed temperature-controlled pyrolysis, a carbon-nitrogen co-doped porous carbon-confined titanium dioxide coating was pre-constructed on the powder surface, so that titanium was confined and fixed in the powder surface coating in the form of titanium dioxide nanocrystals. The pyrolysis temperature was controlled at 380℃~450℃, which prevented titanium from entering the alloy matrix through solid diffusion in the pretreatment stage, and provided a structural prerequisite for the targeted release of titanium in the subsequent laser melting deposition process.

[0029] (ii) During the laser melting deposition process, the titanium dioxide in the coating undergoes a carbothermic reduction reaction with the adjacent porous carbon under ultra-high temperature conditions in the molten pool, releasing titanium atoms in situ. Since the titanium dioxide is confined within the porous carbon matrix and the contact area between carbon and titanium dioxide is large, the titanium atoms diffuse a short distance after being released from the powder surface, enabling them to agglomerate at the solidification front. This helps to transform the grain boundary carbides from a continuous film to discrete particles, thereby reducing the tendency of grain boundary liquefaction cracks to form.

[0030] (iii) Applying ultrasonic vibration treatment between layers during the layer-by-layer deposition helps to refine the grain structure of the deposited layer, promotes the further dispersion and distribution of grain boundary carbides, and, in synergy with the aforementioned titanium element segregation effect, further improves the microstructure uniformity of the deposited alloy.

[0031] (iv) In this invention, there is a significant synergistic effect between the titanium grain boundary segregation achieved by the coating and the interlayer ultrasonic vibration treatment. The titanium segregation chemically alters the nucleation and growth pattern of grain boundary carbides, preferentially forming granular titanium-containing carbides; while the ultrasonic vibration treatment physically disperses and spheroidizes the formed grain boundary carbides through acoustic flow and cavitation effects. The combined effect of chemical modification and physical control results in a degree of grain boundary carbide dispersion far exceeding the effect achievable by using either method alone. Experimental data show that, compared to the scheme using only coating without ultrasonic treatment, the present invention, by employing both coating and ultrasonic treatment, significantly increases the relative improvement in elongation after fracture. Attached Figure Description

[0032] Figure 1 This is a flowchart illustrating the overall process of the preparation method of the present invention.

[0033] Figure 2 This is a schematic diagram of the carbon-nitrogen co-doped porous carbon-confined titanium dioxide coating structure on the powder surface after S4 of the present invention.

[0034] Figure 3 This is a bar chart comparing the post-fracture elongation of the various embodiments of the present invention with that of the comparative sedimentary samples. Detailed Implementation

[0035] 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.

[0036] Reference Figure 1 A method for preparing GH3536 alloy with targeted titanium microalloying, the specific implementation details of which are as follows:

[0037] S1: Powder Surface Pretreatment

[0038] GH3536 nickel-based superalloy powder (particle size 53 μm to 150 μm) prepared by gas atomization was subjected to surface pretreatment. The powder was immersed in a 5% (w / w) dilute nitric acid solution and mechanically stirred for 10 to 15 minutes to fully react and remove the natural oxide passivation film formed on the surface of the powder during storage and preparation, exposing the fresh metal surface. Then it was rinsed with deionized water until neutral.

[0039] Subsequently, the pickled powder was rapidly transferred to a 1% (w / w) hydrogen peroxide solution and stirred and soaked at a constant temperature of 50°C for 30 minutes. At this temperature, hydrogen peroxide gently and controllably oxidizes the alloy surface, generating a nanoscale active hydroxyl oxide layer rich in Ni-OH and Cr-OH groups, with a hydroxyl density far exceeding that of a hydroxyl layer formed solely by natural water adsorption.

[0040] The treated powder was washed with deionized water and then rinsed three times with anhydrous ethanol for alcohol displacement dehydration. The miscibility and low surface tension of ethanol and water were used to completely replace the residual water in the internal pores and on the surface of the powder, so as to avoid powder adhesion caused by the high capillary force of water during drying.

[0041] Next, amine chemical grafting was performed. The hydroxylated powder was immersed in an ethanol-water solution containing aminopropyltriethoxysilane, with a solution ratio of 90% anhydrous ethanol, 5% deionized water, and 5% aminopropyltriethoxysilane (volume fraction), and immersed at room temperature for 30 minutes.

[0042] In this process, the silanoxy groups of aminopropyltriethoxysilane hydrolyze to generate silanol, which undergoes a condensation reaction with the hydroxyl groups on the powder surface to form strong Si-O-metal surface covalent bonds, while the amino groups at the other end of the molecular chain are exposed. After removal, it is rinsed with anhydrous ethanol and vacuum dried at 80°C for 30 min to obtain a powder with a surface rich in high-density active hydroxyl and amino groups. The three-layer structure of bare metal-hydroxyl-rich oxide layer-amine chemical grafting layer constructed in this step provides the interfacial basis for the subsequent chemical anchoring of colloids.

[0043] S2: Formulation of titanium-containing prepolymer colloid

[0044] By weight, 5–10 parts of titanium acetylacetonate are dissolved in 8–15 parts of ethylene glycol, and stirred at 40°C until completely dissolved, forming a pale yellow, clear solution. The chelating protection of the central titanium atom by the acetylacetonate group gives it controlled hydrolytic stability in an aqueous environment.

[0045] Subsequently, 3–6 parts of citric acid are added and stirring continues. This allows the multiple carboxyl and hydroxyl groups to undergo partial ligand exchange with titanium acetylacetonate, forming a more stable citric acid-titanium complex intermediate and preventing severe hydrolysis and precipitation of the titanium source upon subsequent water addition. Separately, 3–6 parts of polyvinyl alcohol and 2–4 parts of polyvinylpyrrolidone are dissolved in water sequentially. The polyvinyl alcohol must be completely dissolved at 85°C and then cooled to 40°C.

[0046] The aqueous solution was mixed with the aforementioned complex solution and stirred until homogeneous. Finally, 1–2.5 parts of polyethyleneimine were added. Upon addition, the densely packed primary, secondary, and tertiary amine groups on the polyethyleneimine molecular chain rapidly formed N→Ti coordination bonds with the titanium central atom in the citric acid-titanium complex, anchoring the titanium atoms to the polymer network nodes and achieving molecular-level dispersion. After thorough stirring and vacuum degassing, a homogeneous, slightly viscous titanium-containing prepolymer colloid was obtained.

[0047] Each component has a clearly defined function: titanium acetylacetonate serves as the titanium source precursor, polyvinyl alcohol (PVA) is the carbon source for the film-forming framework, polyvinylpyrrolidone (PVP) is an auxiliary carbon source and nitrogen-rich precursor, polyethyleneimine (PEI) acts as a chelating anchoring agent, interface enhancer, and auxiliary nitrogen source, citric acid is a complexing pore-forming agent, and ethylene glycol is a viscosity modifier and auxiliary carbon source. PVA and PPV form a molecular-level interpenetrating network in the colloid, while PEI not only anchors titanium atoms, but its protonated amine groups can also form electrostatic adsorption and hydrogen bonds with the powder surface, enhancing the coating adhesion.

[0048] S3: Coating and Drying

[0049] The powder obtained in S1 was first pre-wetted with anhydrous ethanol. The low surface tension of ethanol rapidly formed a uniform wetting film on the powder surface, providing interfacial conditions for the spread of the colloid. Subsequently, the titanium-containing prepolymer colloid prepared in S2 was uniformly coated onto the powder bed surface using a multi-stage gradient spraying method. The total amount of colloid used was 10% to 15% of the powder mass.

[0050] Multi-stage spraying effectively avoids the accumulation of colloid between particles due to capillary effect and the coffee ring effect after drying, which are common in traditional dipping methods, thus ensuring the uniformity of the liquid film. After all spraying processes are completed, the powder is centrifuged at 200r / min to 300r / min for 2 minutes. This micro-shearing force promotes further spreading of the colloid and removes liquid bridges that may cause particles to stick together.

[0051] The coated powder is spread evenly on a polytetrafluoroethylene tray, with the layer thickness controlled to be less than 2 mm. It is then placed in a vacuum drying oven and dried under reduced pressure for 4 to 6 hours at a temperature of 30℃~35℃ and a vacuum degree of -0.08MPa~-0.10MPa. The low-temperature, reduced-pressure environment allows the solvent to evaporate slowly, the polymer molecular chains to fully relax and uniformly shrink into a film, and ethylene glycol acts as a molecular-level plasticizer, effectively preventing the film from cracking or peeling. Ultimately, a complete and dense solid film is formed on the powder surface.

[0052] S4: Temperature-controlled pyrolysis

[0053] The powder obtained from S3 was spread evenly in a corundum boat, with a layer thickness not exceeding 3 mm, to ensure uniform heating and gas exchange. The boat was then placed in a tube furnace for multi-stage temperature-controlled pyrolysis.

[0054] In the first stage, the temperature is increased from room temperature to 100°C at a rate of 2°C / min under a nitrogen atmosphere and held for 60 min to remove physically adsorbed water and residual free alcohol. Then, the temperature is increased to 200°C at a rate of 1°C / min and held for 60 min to allow small molecules such as the water of crystallization of citric acid to slowly detach, causing the film to shrink but its structure to remain intact.

[0055] In the second stage, the atmosphere was switched to high-purity argon, and the temperature was increased at a rate of 0.5℃ / min. A holding step was set at 250℃ and maintained for 25 min. At this point, citric acid underwent intermolecular dehydration and decarboxylation reactions, and the released carbon dioxide gas formed initial channels in the softened carbon matrix. The temperature was then increased to 340℃ and held for 15 min. During this process, the polyvinyl alcohol side chain was eliminated, the polyvinylpyrrolidone ring was opened, and the titanium acetylacetonate organic ligand underwent violent decomposition. The resulting large amount of gas expanded and permeated through the flowing carbon-polymer mesophase, forming interconnected hierarchical nanopores. Simultaneously, the decomposition products of polyethyleneimine participated in the nitrogen doping reaction of the carbon matrix.

[0056] In the third stage, the temperature is further increased to 380℃~450℃ and held for 30 minutes. The remaining hydrocarbon structure undergoes carbon microcrystal rearrangement, the conductivity of the carbon matrix is ​​improved, and a stable carbon-nitrogen co-doped porous carbon framework is formed. Meanwhile, the titanium dioxide nanocrystals are confined in situ within these nanopores, avoiding high-temperature aggregation and growth.

[0057] In the fourth stage, the atmosphere was switched to nitrogen and held at that temperature for 30 minutes. Finally, the mixture was cooled in the furnace to below 60°C and removed. The resulting carbon-nitrogen co-doped porous carbon-confined titanium dioxide coating had a thickness of 80 nm to 200 nm. The maximum pyrolysis temperature of 450°C is far below the threshold for significant solid-state diffusion of the GH3536 matrix elements, thus the titanium elements are strictly confined within the coating on the powder surface.

[0058] like Figure 2 As shown, a composite coating is formed on the surface of the powder particles obtained in step S4. This coating consists of a carbon-nitrogen co-doped porous carbon matrix and titanium dioxide nanocrystals confined within its nanopores. The porous carbon matrix continuously coats the surface of the GH3536 alloy powder matrix, with a coating thickness of 80 nm to 200 nm, and contains interconnected nanoscale channels. The titanium dioxide nanocrystals are granular, with a particle size of 5 nm to 15 nm, and are physically isolated by the pore walls of the porous carbon, exhibiting a discrete distribution to avoid aggregation and growth during high-temperature pyrolysis. The interface between the coating and the alloy matrix is ​​clear and free of a diffusion layer, indicating that the titanium element did not enter the matrix during the pretreatment stage, achieving surface confinement and fixation of the titanium source.

[0059] S5: Powder deagglomeration and sieving

[0060] During pyrolysis, a very small number of powder particles may slightly agglomerate. To restore their flowability, the powder obtained from S4 was placed in a ball mill jar, and polyurethane elastic balls with a diameter of 3mm to 5mm were added, filling the jar to 30% of its volume. The mixture was then deagglomerated by rolling the balls at a speed of 15 to 20 rpm for 10 to 15 minutes. The hardness of the polyurethane elastic balls is much lower than that of the GH3536 alloy; their elastic impact effectively separates the agglomerated powder without scratching or damaging the porous carbon coating on the powder surface. After deagglomeration, powder with a particle size of 53μm to 150μm was sieved using a standard sieve and stored in a sealed vacuum glove box.

[0061] S6: Laser Melting Deposition Forming

[0062] A coaxial powder-feed fiber laser melting deposition system was used to form the powder obtained from S5 layer by layer under the protection of high-purity argon gas. The process parameters were: laser power 500W~800W, scanning speed 400mm / min~700mm / min, powder feed rate 2.5g / min~5.0g / min, overlap rate 40%~50%, interlayer lift 0.2mm~0.5mm, and scanning path rotated 67° layer by layer.

[0063] In the ultra-high temperature molten pool (≥1600℃) formed by the above parameters, the coating on the powder surface undergoes a violent carbothermic reduction reaction in a very short time. The porous carbon reduces the titanium dioxide confined within it to titanium carbide in situ and further decomposes it, instantly releasing active titanium atoms at the powder-melt interface. Because the release point is close to the solidification front, the titanium atoms diffuse over a very short distance and rapidly agglomerate at the grain boundaries under the drive of the chemical potential gradient.

[0064] S7: Ultrasonic vibration interlayer treatment

[0065] Immediately after each layer is deposited, pulsed ultrasound is applied to the red-hot deposited surface using an ultrasonic amplitude transformer. The frequency is 20kHz–40kHz, the amplitude is 15μm–30μm, the pulse width is 100ms–200ms, the pulse interval is 300ms–500ms, and the single-layer treatment time is 10s–30s. The ultrasonic flow and periodic stress waves promote grain refinement of the deposited metal and simultaneously cause mechanical spheroidization and dispersion of the grain boundary carbides, which are still in a semi-solid or high-temperature solid state. After ultrasonic treatment, the surface is then briefly purged and chilled using room-temperature argon gas ejected from a coaxial nozzle. The superposition of instantaneous thermal stress and ultrasonic stress field further disrupts the continuity of the carbide film.

[0066] Throughout the process, the effective increment of titanium introduced by the coating and ultimately retained in the deposit is controlled between 0.003% and 0.006% of the total mass of GH3536 alloy powder.

[0067] Experimental Design and Testing:

[0068] To verify the technical effectiveness of this method, five examples and three comparative examples were set up. All examples and comparative examples used the same batch of gas-atomized GH3536 alloy powder, with a powder particle size of 53 μm to 150 μm and a composition of Cr 22.0%, Co 1.5%, Mo 9.0%, W 0.6%, Fe 18.5%, C 0.10%, Ni balance, and an initial titanium content of 0.12%.

[0069] Among them, Examples 1 to 5 use different combinations of process parameters within the protection scope of this method; Comparative Example 1 does not undergo any powder surface coating pretreatment (original GH3536); Comparative Example 2 only uses acetylacetone titanium ethanol solution for immersion coating, without polyvinyl alcohol, polyvinylpyrrolidone, polyethyleneimine and citric acid to construct a porous carbon confinement system; Comparative Example 3 uses the same S1-S6 steps as Example 1 (i.e., prepare titanium-containing coating and laser deposition), but the ultrasonic vibration treatment in step S7 is omitted.

[0070] After deposition, samples were taken from each specimen and subjected to room temperature tensile tests according to GB / T 228.1 to determine tensile strength, yield strength and elongation after fracture. The titanium content of each specimen was determined by inductively coupled plasma atomic emission spectrometry, and the increase in titanium content was calculated by subtracting the original powder titanium content from the measured titanium content.

[0071] Example 1

[0072] Titanium-containing prepolymer colloid formulation: 8g titanium acetylacetone, 5g polyvinyl alcohol, 3g polyvinylpyrrolidone, 2g polyethyleneimine, 5g citric acid, 12g ethylene glycol, and 65g deionized water. The total amount of colloid is 12% of the powder mass. The maximum temperature of the programmed temperature-controlled pyrolysis is 420℃, and the resulting coating thickness is 120nm.

[0073] LMD parameters: Laser power 650W, scanning speed 500mm / min, powder feed rate 4g / min, overlap rate 45%, interlayer lift 0.35mm. Ultrasonic parameters: Frequency 30kHz, amplitude 20μm, pulse width 150ms, interval 400ms, single-layer processing time 20s.

[0074] Example 2

[0075] Titanium-containing prepolymer colloid formulation: 5g titanium acetylacetone, 3g polyvinyl alcohol, 2g polyvinylpyrrolidone, 1g polyethyleneimine, 3g citric acid, 8g ethylene glycol, and 78g deionized water. The total amount of colloid is 10% of the powder mass. The maximum pyrolysis temperature is 380℃, and the coating thickness is 80nm. LMD and ultrasonic parameters are the same as in Example 1.

[0076] Example 3

[0077] Titanium-containing prepolymer colloid formulation: 10g titanium acetylacetone, 6g polyvinyl alcohol, 4g polyvinylpyrrolidone, 2.5g polyethyleneimine, 6g citric acid, 15g ethylene glycol, and 56.5g deionized water. The total amount of colloid is 15% of the powder mass. The maximum pyrolysis temperature is 450℃, and the coating thickness is 200nm. LMD and ultrasonic parameters are the same as in Example 1.

[0078] Example 4

[0079] Different LMD parameters

[0080] The titanium-containing prepolymer colloid formulation is the same as in Example 1. The total amount of colloid used is 12% of the powder mass. The maximum temperature of the programmed temperature controlled pyrolysis is 420℃, and the resulting coating thickness is 120nm.

[0081] LMD parameters: laser power 700W, scanning speed 600mm / min, powder feed rate 3.5g / min, overlap rate 45%, interlayer lift 0.3mm. Ultrasonic parameters are the same as in Example 1 (frequency 30kHz, amplitude 20μm, pulse width 150ms, interval 400ms, single-layer processing time 20s).

[0082] Example 5

[0083] Different ultrasound parameters

[0084] The titanium-containing prepolymer colloid formulation, pyrolysis parameters, and LMD parameters were the same as in Example 1. The ultrasonic parameters were adjusted to: frequency 40kHz, amplitude 25μm, pulse width 120ms, pulse interval 350ms, and single-layer processing time 15s.

[0085] Comparative Example 1

[0086] Using the same batch of GH3536 alloy powder, without any processing of S1 to S5, deposition and forming were performed directly with the same LMD and ultrasonic parameters as in Example 1.

[0087] Comparative Example 2

[0088] Titanium acetylacetonate was dissolved in anhydrous ethanol to prepare a 5% (w / w) solution. The powder was soaked for 15 min, then dried at 60°C for 30 min, and then deposited and shaped using the same LMD and ultrasonic parameters as in Example 1.

[0089] Comparative Example 3

[0090] Coating only, no ultrasound

[0091] The same steps S1-S6 as in Example 1 (i.e., preparing a titanium-containing coating and laser deposition) were used, but the ultrasonic vibration treatment in step S7 was omitted.

[0092] The room temperature tensile properties and titanium content test results of the deposited samples of each embodiment and comparative example are shown in Table 1:

[0093] Table 1

[0094]

[0095] As shown in Table 1:

[0096] (1) The tensile strength of the deposited samples in Examples 1 to 5 was 726 MPa to 745 MPa, which was 5.4% to 8.1% better than that of Comparative Example 1 (689 MPa); the yield strength was 355 MPa to 368 MPa, which was 4.1% to 7.9% better than that of Comparative Example 1 (341 MPa); the elongation after fracture was 19.8% to 21.4%, which was 39.4% to 50.7% better than that of Comparative Example 1 (14.2%), and the plasticity was significantly improved.

[0097] (2) Strength-ductility product analysis: The strength-ductility product of Example 1 is as high as 15943 MPa·%, which is 63.0% higher than that of Comparative Example 1 (9784 MPa·%). This improvement is much higher than the improvement of a single strength index, which fully demonstrates the outstanding effect of this method in simultaneously improving strength and ductility. This is a direct manifestation of the transformation of grain boundary carbides from continuous film to discrete particles and the effective suppression of liquefaction cracks.

[0098] (3) The strength-ductility product of Comparative Example 3 (coating only, no ultrasound) was 12584 MPa·%, which was 28.6% higher than that of Comparative Example 1; while the strength-ductility product of Example 1 (coating + ultrasound) was further increased by 26.7% compared with Comparative Example 3. This comparison clearly demonstrates the synergistic effect between coating and ultrasound: ultrasound treatment produces additional, non-simply additive performance gains on the basis of titanium segregation.

[0099] (4) Although Comparative Example 2 introduced more titanium (an increase of 0.011%) through impregnation, its tensile strength and elongation after fracture were only improved by 1.2% and 6.3% respectively compared with Comparative Example 1, which is far less effective than the examples. This is because without the confined protection of porous carbon and the in-situ support of sufficient solid carbon source, the titanium source cannot be effectively released and agglomerated at the solidification front, and may instead form harmful precipitates. This proves that the carbon-nitrogen co-doped porous carbon confined titanium dioxide coating and its supporting process constructed by this method are the key to achieving targeted microalloying of titanium. Moreover, the titanium increment range of 0.003% to 0.006% selected in this invention is not simply a matter of the more the better, but rather an optimized window that produces unexpected technical effects.

[0100] (5) Examples 4 and 5 achieved performance comparable to that of Example 1 under different LMD and ultrasonic parameters, proving that the technical solution has good process robustness and can stably achieve the targeted microalloying effect within a wide parameter window.

[0101] Performance Comparison

[0102] like Figure 3 The figure shown is a bar chart comparing the elongation after fracture of the various embodiments of the present invention with that of the comparative example deposited samples. Figure 3 It can be seen that the elongation after fracture of Examples 1-5 (19.8%~21.4%) is significantly higher than that of Comparative Example 1 (14.2%), Comparative Example 2 (15.1%), and Comparative Example 3 (17.6%), and the strength-ductility product of Example 1 is as high as 15943 MPa·%, which is 63.0% higher than that of Comparative Example 1. This further confirms that the present invention achieves a significant improvement in the plasticity of GH3536 nickel-based alloy laser melting deposition components through the synergistic effect of carbon-nitrogen co-doped porous carbon confined titanium dioxide coating and interlayer ultrasonic vibration.

[0103] The preparation method has been fully disclosed through the specific steps and parameters described above. Those skilled in the art can repeat this method without creative effort based on the process conditions described in this specification, and obtain GH3536 nickel-based alloy components with excellent mechanical properties.

[0104] Example 6

[0105] The deposited component prepared in Example 1 was wire-cut into a simulated combustion chamber flame tube for an aero-engine. No cracks or defects were found during non-destructive testing. After oxidizing the simulated component in static air at 900°C for 100 hours, the surface oxide layer was dense with no significant peeling, indicating that the component prepared by this method has good high-temperature service performance and can meet the requirements for hot-end components of aero-engines.

[0106] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, or improvements made by those skilled in the art within the scope of the technical solutions of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing GH3536 alloy with targeted titanium microalloying, characterized in that, Includes the following steps: S1: GH3536 alloy powder is pretreated to obtain powder with surface rich in active hydroxyl and amine groups; S2: Titanium-containing prepolymer colloid is prepared by dissolving titanium acetylacetonate, polyvinyl alcohol, polyvinylpyrrolidone, polyethyleneimine, citric acid and ethylene glycol in water; S3: The titanium-containing prepolymer is coated onto the surface of the powder obtained in S1 and dried to form a film encapsulating the powder; S4: The powder obtained in S3 is subjected to programmed temperature-controlled pyrolysis in an inert atmosphere to obtain a carbon-nitrogen co-doped porous carbon confined titanium dioxide coating. The maximum temperature of the programmed temperature-controlled pyrolysis is 380℃~450℃. S5: Depolymerize and sieve the powder obtained in S4 to obtain powder with a particle size of 53μm to 150μm; S6: The powder obtained in S5 is formed layer by layer using a coaxial powder feeding laser melting deposition process. In the laser melting pool, the titanium dioxide in the coating undergoes a carbothermic reduction reaction with porous carbon, releasing titanium atoms into the nickel-based melt and agglomerating at the grain boundary at the solidification front. S7: Apply ultrasonic vibration treatment to the deposited layers between layers during the layer-by-layer deposition process.

2. The method for preparing GH3536 alloy with targeted titanium microalloying according to claim 1, characterized in that, The surface pretreatment process described in S1 is as follows: GH3536 alloy powder is pickled with dilute nitric acid solution to remove the surface oxide film, rinsed with deionized water until neutral, hydroxylated with hydrogen peroxide solution, washed with deionized water, then dehydrated by alcohol displacement with anhydrous ethanol, and then grafted with amino groups using a solution containing aminopropyltriethoxysilane. After vacuum drying, powder with a surface rich in active hydroxyl and amino groups is obtained.

3. The method for preparing GH3536 alloy with targeted titanium microalloying according to claim 1, characterized in that, In S2, the titanium-containing prepolymer is prepared in the following proportions by mass: 5-10 parts titanium acetylacetonate, 3-6 parts polyvinyl alcohol, 2-4 parts polyvinylpyrrolidone, 1-2.5 parts polyethyleneimine, 3-6 parts citric acid, 8-15 parts ethylene glycol, and the remainder is water.

4. The method for preparing GH3536 alloy with targeted titanium microalloying according to claim 1, characterized in that, The coating described in S3 is as follows: first, the powder obtained in S1 is pre-wetted with anhydrous ethanol, and then the titanium-containing prepolymer colloid is coated onto the powder surface in a gradient spraying manner. The total amount of titanium-containing prepolymer colloid is 10% to 15% of the powder mass. After the gradient spraying is completed, the powder is centrifuged to make the colloid spread evenly. The drying is carried out under reduced pressure drying conditions at a temperature of 30℃ to 35℃ and a vacuum degree of -0.08MPa to -0.10MPa.

5. The method for preparing GH3536 alloy with targeted titanium microalloying according to claim 1, characterized in that, The temperature-controlled pyrolysis process described in S4 is as follows: The temperature was increased from room temperature to 100°C at a rate of 2°C / min under a nitrogen atmosphere and held, and then increased to 200°C at a rate of 1°C / min and held. Switch to argon atmosphere and heat to 380℃~450℃ at a rate of 0.5℃ / min. During the heating process, set up a heat preservation step at 250℃ and a heat preservation step at 340℃. After switching to a nitrogen atmosphere for heat preservation, the furnace is cooled.

6. The method for preparing GH3536 alloy with targeted titanium microalloying according to claim 1 or 5, characterized in that, In the carbon-nitrogen co-doped porous carbon confined titanium dioxide coating obtained by S4, titanium dioxide is confined in the form of nanocrystals within the carbon-nitrogen co-doped porous carbon matrix, and the coating thickness is 80 nm to 200 nm.

7. The method for preparing GH3536 alloy with targeted titanium microalloying according to claim 1, characterized in that, The depolymerization described in S5 is performed by ball milling the powder in a ball mill using polyurethane elastic balls at a speed of 15 r / min to 20 r / min.

8. The method for preparing GH3536 alloy with targeted titanium microalloying according to claim 1, characterized in that, The process parameters for coaxial powder-feeding laser melting deposition in S6 are as follows: laser power 500W~800W, scanning speed 400mm / min~700mm / min, powder feeding rate 2.5g / min~5.0g / min, overlap rate 40%~50%, and interlayer lift 0.2mm~0.5mm.

9. The method for preparing GH3536 alloy with targeted titanium microalloying according to claim 1, characterized in that, The ultrasonic vibration treatment described in S7 involves applying pulsed ultrasonic waves to the surface of the deposited layer using an ultrasonic amplitude transformer. The frequency is 20kHz to 40kHz, the amplitude is 15μm to 30μm, the pulse width is 100ms to 200ms, the pulse interval is 300ms to 500ms, and the single-layer treatment time is 10s to 30s.

10. A GH3536 alloy for targeted titanium microalloying, characterized in that, The alloy is prepared by any one of the methods of claims 1-9. The alloy uses GH3536 as the matrix, and the increase in titanium content accounts for 0.003% to 0.006% of the total mass of GH3536 alloy powder. Titanium atoms are segregated at the grain boundaries, and the grain boundary carbides are in the form of discrete particles. The elongation after fracture is increased by 39.4% to 50.7% compared with the original GH3536, the strength-ductility product is increased by 47% to 63%, and there are no grain boundary liquefaction cracks.

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