Nickel-based superalloy and stainless steel gradient combination method based on laser near-net forming

Abstract

The invention belongs to the technical field of metal material bonding, and discloses a nickel-based high-temperature alloy and stainless steel gradient bonding method based on laser near-net forming, which comprises the following steps: combining GH3230 high-temperature alloy powder and 316L austenitic stainless steel alloy powder into a GH3230-316L alloy by adopting a laser near-net forming process; in the laser near-net forming process, the mixing proportion of GH3230 high-temperature alloy powder and 316L austenitic stainless steel alloy powder is regulated and controlled by adopting synchronous powder feeding and regulating the powder feeding speed layer by layer in a gradient manner; wherein the powder feeding speed of the GH3230 high-temperature alloy powder is adjusted in a layer-by-layer gradient decreasing mode according to the initial powder feeding speed, and the 316L austenitic stainless steel alloy powder is adjusted in a layer-by-layer gradient increasing mode according to the initial powder feeding speed. The gradient connection of the nickel-based superalloy and the stainless steel ladder is realized through the laser near-net forming technology, the thermal stress distribution is optimized, the size and distribution of a precipitated phase are accurately controlled, and the interface bonding strength is enhanced.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal material bonding, and particularly relates to a method for gradient bonding of nickel-based superalloy and stainless steel based on laser near-net shaping. Background Art

[0002] As a special energy conversion device, during the operation of a reactor, the internal environment is extremely harsh and complex. The material is under the combined action of multiple extreme conditions such as high temperature, high pressure, strong radiation, and corrosive media, which poses unprecedentedly severe challenges to various properties of the material. Deeply understanding and accurately grasping these requirements are crucial for ensuring the safe, stable, and efficient operation of the reactor.

[0003] Nickel-based superalloy (GH3230) is a high-performance alloy material that has been carefully designed and optimized. It is prepared through specific alloy element ratios and fine metallurgical processes. Its unique composition and microstructure exhibit significant advantages in high-temperature strength and radiation resistance, making it a research and application hotspot in fields with extremely demanding material property requirements such as aerospace and nuclear energy.

[0004] 316L stainless steel is a super-low-carbon austenitic stainless steel, and its chemical composition mainly includes elements such as chromium (Cr), nickel (Ni), molybdenum (Mo), manganese (Mn), carbon (C), silicon (Si), phosphorus (P), and sulfur (S). Among them, the chromium element content is usually between 16% - 18.5%, which is the key element for forming the stainless steel passivation film and can form a dense and stable chromium oxide film on the material surface to effectively prevent the erosion of the substrate by external corrosive media; the nickel element content is about 10% - 14%, and its main function is to stabilize the austenite phase region, making the stainless steel have a single austenite structure at room temperature, thereby endowing the material with good toughness and weldability; the molybdenum element content is generally about 2% - 3%, which can further enhance the corrosion resistance of the stainless steel in reducing media, especially in an environment containing chloride ions; the carbon element content is strictly controlled at an extremely low level (usually less than 0.03%) to reduce the sensitivity of the material to intergranular corrosion caused by the precipitation of carbides at grain boundaries.

[0005] Combining GH3230 alloy and 316L stainless steel can give full play to their respective advantages and meet the performance requirements of different parts in the reactor structure. However, there are differences in the thermal expansion coefficient, metallurgical compatibility, etc. between GH3230 alloy and 316L stainless steel. Direct bonding is likely to cause problems such as thermal stress, cracks, and brittle phases, resulting in a decline in the performance of the joint. Traditional welding methods are difficult to achieve high-quality connection and are prone to defects such as pores and inclusions. When joining dissimilar materials, the precipitated phases are unevenly distributed in the connection area, which may lead to a decline in local performance. At the same time, the size of the precipitated phases is difficult to control, affecting the mechanical properties of the material. Summary of the Invention

[0006] The object of the present invention is to provide a gradient bonding method for nickel-based superalloy and stainless steel based on laser near-net shaping, which realizes the gradient connection of nickel-based superalloy and stainless steel ladder through laser near-net shaping technology, optimizes the thermal stress distribution, precisely controls the size and distribution of precipitation phases, and enhances the interfacial bonding strength.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A gradient bonding method for nickel-based superalloy and stainless steel based on laser near-net shaping, comprising: depositing GH3230 superalloy powder and 316L austenitic stainless steel alloy powder by laser near-net shaping process to form GH3230-316L alloy;

[0009] In the laser near-net shaping process, the mixing ratio of GH3230 superalloy powder and 316L austenitic stainless steel alloy powder is regulated by synchronous powder feeding and layer-by-layer gradient adjustment of the powder feeding speed; wherein, the powder feeding speed of GH3230 superalloy powder is adjusted in a way of decreasing layer by layer with the initial powder feeding speed, and the powder feeding speed of 316L austenitic stainless steel alloy powder starts from the initial powder feeding speed and is adjusted in a way of increasing layer by layer.

[0010] In the laser near-net shaping process, the parameter settings are: the laser power is 800W, the scanning speed is 8mm / s, and the cooling rate of the molten pool is >10 3 ℃ / s.

[0011] The GH3230 superalloy powder refers to: the purity >99.9%, the particle size is 53-105μm, and the mass percentage of alloy components is Fe≤3.00%, Co≤5.00%, Cr-20.00-24.00%, W-13.00-15.00%, Mo-1.00-3.00%, Ni-remainder.

[0012] The 316L austenitic stainless steel alloy powder refers to: the purity >99.9%, the particle size is 53-105μm, and the mass percentage of alloy components is Mn-20.00-24.00%, S≤5.00%, C-0.05-0.15%, Cr-1.00-3.00%, Si-13.0-15.00%, Mo≤0.10%, Fe-remainder.

[0013] The initial powder feeding speed of the GH3230 superalloy powder is 1.6-2r / min, and its decreasing step size is 0.2-0.4r / min. The initial powder feeding speed of the 316L austenitic stainless steel alloy powder is 0r / min, and its increasing step size is 0.2-0.4r / min.

[0014] The decreasing step size of the GH3230 superalloy powder includes 2, and the powder feeding speed is adjusted alternately; the increasing step size of the 316L austenitic stainless steel alloy powder includes 2, and the powder feeding speed is adjusted alternately.

[0015] The present invention adopts the laser near-net shaping (LENS) technology to achieve the efficient connection of GH3230 nickel-based superalloy and 316L austenitic stainless steel through layer-by-layer gradient deposition; by precisely controlling the laser energy input (power 800W, scanning speed 8mm / s) and the powder feeding speed (GH3230 decreases layer by layer by 0.2 - 0.4r / min, 316L increases layer by layer by 0.2 - 0.4r / min), it is ensured that the molten pool cools rapidly (>10 3 ℃ / s), completely inhibiting the formation of brittle precipitation phases such as σ phase and carbides. Through synchronous powder feeding and dynamic parameter matching, the continuous and smooth transition of key elements such as Ni, Cr, and Fe is achieved (EDS verification shows that the Cr content fluctuation <5%), eliminating the sudden change of interface composition and the concentration of thermal stress (EBSD shows that the residual stress <200MPa). The finally obtained gradient joint has a tensile strength of 550MPa (equivalent to the 316L matrix), an elongation after fracture of 26%, and no post-treatment processes such as annealing are required, and complex structures (such as nuclear reactor pipes and aeroengine load-bearing components) can be directly formed.

[0016] The present invention shows better interfacial bonding strength, fatigue resistance and long-term service stability under extreme environments such as high irradiation, high temperature and high pressure, and corrosive media, providing an efficient and reliable solution for the connection of dissimilar materials. Brief Description of the Drawings

[0017] Figure 1 It is the Fe-Ni phase diagram of samples a - f.

[0018] Figure 2 It is the EDS element analysis diagram of samples d and e.

[0019] Figure 3 It is the XRD diagram of sample e.

[0020] Figure 4 It is the mechanical property diagram of sample e.

[0021] Figure 5 It is the EBSD diagram of the interfacial bonding situation between layers of sample e.

[0022] Figure 6 It is the diagram of the stress situation between layers of sample e. Detailed Description of the Invention

[0023] A method for gradient bonding of nickel-based superalloy and stainless steel based on laser near-net shaping provided in this embodiment includes the following steps:

[0024] (1) Powder selection:

[0025] GH3230 superalloy powder (purity > 99.9%, particle size 53 - 105 μm, mass percentage of alloying elements: Fe ≤ 3.00%, Co ≤ 5.00%, Cr - 20.00 - 24.00%, W - 13.00 - 15.00%, Mo - 1.00 - 3.00%, Ni - balance);

[0026] 316L austenitic stainless steel alloy powder (purity > 99.9%, particle size 53 - 105 μm, mass percentage of alloying elements: Mn - 20.00 - 24.00%, S ≤ 5.00%, C - 0.05 - 0.15%, Cr - 1.00 - 3.00%, Si - 13.0 - 15.00%, Mo ≤ 0.10%, Fe - balance).

[0027] (2) Parameter settings in the laser near - net - shape forming process: Laser power is 800 W, scanning speed is 8 mm / s, and the cooling rate of the molten pool is > 10 3 ℃ / s.

[0028] (3) Powder feeding speed setting: GH3230 superalloy powder and 316L austenitic stainless steel alloy powder cannot form intermetallic compounds; since the main element of austenitic stainless steel is Fe and the main element of superalloy is Ni, according to the Fe - Ni binary phase diagram, within the ranges of Ni content of 20 - 30 wt.% and 40 - 55 wt.%, they will form Fe3Ni and FeNi intermetallic compounds respectively. Therefore, when designing the gradient composition, the above mass fraction ranges should be avoided. For this purpose, 6 schemes shown in Table 1 are designed.

[0029] Table 1 Powder feeding speed design for Schemes 1 - 6

[0030]

[0031]

[0032] Samples a - f are deposited through Schemes 1 - 6, and metallographic analysis is performed on the 6 samples, as Figure 1As shown, it can be seen from the figure that cracks and pores are visible in the interface area of sample a of Scheme 1, and there are unfused defects locally; due to the sudden change in powder feeding speed, the energy input to the molten pool is insufficient, and the cooling rate fluctuates, resulting in stress concentration. The grain size of sample b of Scheme 2 is uneven (some coarse grains), and σ-phase precipitates; because the Ni content briefly enters the Fe3Ni formation area (20 - 30wt.%) in the transition layer, brittle phases are induced; the greater composition mutation at the interface leads to greater residual stress. For sample c of Scheme 3, the powder feeding speeds of GH3230 and 316L are set to be adjusted synchronously, but the Fe3Ni formation area (20 - 30wt.%) is not avoided, and precipitation phases are formed. For sample d of Scheme 4, a small amount of carbides precipitate, and the composition mutation at the interface causes microcracks to propagate along the interface, and the residual stress is relatively high in the local area; there is a deviation in the matching between the laser energy input and the powder feeding rate, and the cooling rate of the molten pool is insufficient. The interface of sample e of Scheme 5 is tightly bonded (no cracks and pores), there are no precipitation phases (the grains are fine and uniform), and the elements are continuously transitional; the powder feeding rate and the laser parameters are precisely matched. Although sample f of Scheme 6 has the same number of layers as sample e of Scheme 5, the Fe3Ni formation area (20 - 30wt.%) is not avoided, and precipitation phases are formed.

[0033] Analyze the elements of samples d and e, as Figure 2 shown, key elements such as nickel (Ni), chromium (Cr), and iron (Fe) show continuous and smooth concentration changes in the gradient transition zone, eliminating the element mutation interface (such as a sudden drop in Cr content > 15%) commonly found in traditional dissimilar metal joints, significantly reducing the compositional stress concentration at the interface, and providing compositional stability guarantee for the long-term service of materials in high-temperature and corrosive environments.

[0034] From the metallographic analysis of sample e of Scheme 5, it can be seen that it is the optimal product. Conduct XRD pattern analysis, mechanical property testing, and EBSD characterization of the bonding situation between its layers and the stress situation map from sample e.

[0035] As Figure 3 shown, XRD analysis shows that no diffraction peaks of brittle precipitation phases such as σ-phase and carbides are detected in the connection area, indicating that through precise control of laser energy input and rapid cooling of the molten pool (cooling rate > 10 3 ℃ / s) during the laser near-net shaping process, the generation of harmful phases is effectively inhibited, ensuring the purity of the interface area.

[0036] As Figure 4As shown, at room temperature, the tensile strength of the specimen reaches 550 MPa (equivalent to that of the 316L matrix), and the elongation after fracture is 26%; at high temperatures, the tensile strength of the specimen is equivalent to that of 316L (316L will significantly soften at 600 - 800 °C, and the fracture strength may drop to 100 - 200 MPa; above 900 °C, the material enters the stage dominated by recrystallization and creep, and the fracture strength further decreases, possibly below 50 MPa). Generally speaking, the bonding performance of the gradient material has reached the level of pure 316L, the bonding between surface layers is stable, and it meets the requirements of extreme environments.

[0037] As Figure 5 shown, EBSD analysis further reveals the microstructural characteristics between gradient layers; there is a wide distribution of small grains at the joints between each transition layer, and the orientation distribution is randomized (texture strength < 3.0), indicating that no strong texture is formed due to the accumulation of thermal stress during the gradient connection process; at the same time, as Figure 6 shown, through the KAM (Kernel Average Misorientation) residual stress mapping, it can be seen that the residual stress values in the gradient region are generally low, confirming the optimization effect of the gradient design and the thermal-mechanical co-regulation strategy on thermal stress.

[0038] Generally speaking, through the synergistic effect of no precipitation phase, continuous element transition, and low residual stress, the tensile strength of the connection joint of this sample reaches 550 MPa (reaching 550 MPa of the 316L matrix), and the elongation after fracture reaches 26%, fully meeting the stringent requirements for connection reliability, fatigue resistance, and environmental adaptability of nuclear reactor pipes, special-shaped load-bearing structures of aero-engines, etc.

[0039] The above are only the preferred embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any modification and replacement based on the technical solutions and inventive concepts provided by the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for gradient bonding of nickel-based high-temperature alloy and stainless steel based on laser near-net forming, characterized in that: include: GH3230 high temperature alloy powder and 316L austenitic stainless steel alloy powder are combined into GH3230-316L alloy by laser near net forming process; In the laser near-net forming process, synchronous powder feeding and layer-by-layer gradient adjustment of powder feeding speed are used to control the mixing ratio of GH3230 high-temperature alloy powder and 316L austenitic stainless steel alloy powder. The powder feeding speed of the GH3230 high temperature alloy powder is adjusted in a layer-by-layer gradient decreasing manner with the initial powder feeding speed, and the 316L austenitic stainless steel alloy powder is adjusted in a layer-by-layer gradient increasing manner starting from the initial powder feeding speed.

2. The method for gradient bonding of nickel-based high-temperature alloy and stainless steel based on laser near-net forming according to claim 1, characterized in that: The GH3230 high temperature alloy powder refers to: purity>99.9%, particle size of 53-105μm, and the mass percentage of alloy components is Fe≤3.00%, Co≤5.00%, Cr-20.00-24.00%, W-13.00-15.00%, Mo-1.00-3.00%, Ni-balance.

3. The method for gradient bonding of nickel-based high-temperature alloy and stainless steel based on laser near-net forming according to claim 1, characterized in that: The 316L austenitic stainless steel alloy powder refers to: purity>99.9%, particle size of 53-105μm, alloy components by mass percentage of Mn-20.00-24.00%, S≤5.00%, C-0.05-0.15%, Cr-1.00-3.00%, Si-13.0-15.00%, Mo≤0.10%, Fe-balance.

4. The method for gradient bonding of nickel-based high-temperature alloy and stainless steel based on laser near-net forming according to claim 1, characterized in that: The initial powder feeding speed of the GH3230 high temperature alloy powder is 1.6-2.0 r / min, and the initial powder feeding speed of the 316L austenitic stainless steel alloy powder is 0 r / min.

5. The method for gradient bonding of nickel-based high-temperature alloy and stainless steel based on laser near-net forming according to claim 4, characterized in that: The decreasing step length of the powder feeding speed of GH3230 high temperature alloy powder is 0.2 to 0.4 r / min; the increasing step length of 316L austenitic stainless steel alloy powder is 0.2 to 0.4 r / min.

6. The method for gradient bonding of nickel-based high-temperature alloy and stainless steel based on laser near-net forming according to claim 5, characterized in that: The decreasing step length of the GH3230 high temperature alloy powder is realized by alternating two step lengths; the increasing step length of the 316L austenitic stainless steel alloy powder is realized by alternating two step lengths.

7. The method for gradient bonding of nickel-based high-temperature alloy and stainless steel based on laser near-net forming according to claim 6, characterized in that: The initial powder feeding speed of the GH3230 high temperature alloy powder is 2 r / min, and its decreasing step is 0.2 r / min and 0.3 r / min alternately. The initial powder feeding speed of the 316L austenitic stainless steel alloy powder is 0 r / min, and its increasing step is 0.2 r / min.

8. The method for gradient bonding of nickel-based high-temperature alloy and stainless steel based on laser near-net forming according to any one of claims 1 to 7, characterized in that: The parameters of the laser near-net forming process are as follows: laser power is 800 W, scanning speed is 8 mm / s, and cooling rate of the molten pool is >10 3 ℃ / s.

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