A method of making a gadolinium-containing nickel-based alloy component

Abstract

The application discloses a preparation method of a gadolinium-containing nickel-based alloy component. The gadolinium-containing nickel-based alloy pre-alloy powder is prepared into the gadolinium-containing nickel-based alloy component by using a hot isostatic pressing process with a temperature of 1080-1160 DEG C and a pressure of 120-200 MPPa, so that a Ni5Gd rare earth phase is refined to micron / submicron dispersion distribution, a matrix is an equiaxed crystal organization of complete recrystallization, original particle boundaries are completely eliminated, and grain sizes are uniformly distributed at about 5.3 mu m, thereby obtaining a near-net-shape product of the gadolinium-containing nickel-based alloy component. The application further discloses a gadolinium-containing nickel-based alloy component. Compared with the prior art, the application realizes the synergistic optimization of a rare earth phase and a matrix organization in the same process: the Ni5Gd rare earth phase is inhibited from coarsening, meanwhile, the matrix is completely recrystallized and the original particle boundaries are eliminated, and a near-net-shape gadolinium-containing nickel-based high-temperature alloy component with highly uniform organization and excellent strength-plasticity matching is obtained at one time.

Description

Technical Field

[0001] This invention relates to a method for preparing nickel-based alloy components, and more particularly to a method for preparing gadolinium (Gd)-containing nickel-based alloy components. Background Technology

[0002] As one of the fourth-generation advanced nuclear reactors, molten salt reactors have attracted widespread international attention due to their inherent advantages such as high safety, high fuel utilization, and suitability for thorium-based fuel cycles. Molten salt reactor components operate for extended periods in a high-temperature (650–800°C) molten fluoride salt environment, placing stringent requirements on structural materials: they need both good high-temperature strength and long-term structural stability, as well as excellent resistance to molten salt corrosion.

[0003] Nickel-based superalloys are the preferred system for molten salt reactor structural materials due to their excellent high-temperature strength and corrosion resistance. However, the application of molten salt reactors imposes multiple constraints on the alloying element design of nickel-based alloys: (1) Cr is a key element for the high-temperature oxidation resistance of conventional nickel-based alloys, but Cr is easily selectively dissolved in molten fluoride salts. Therefore, the Cr content of alloys used in molten salt reactors needs to be controlled at a low level (usually ≤8 wt%), which is much lower than that of conventional nickel-based superalloys such as Inconel 625 and Inconel 718 (20-22 wt% Cr). (2) Mo is an important solid solution strengthening element and is beneficial to the resistance to molten salt corrosion. However, excessively high Mo content will promote the formation of topologically close-packed phases (TCP phases, such as μ phase and P phase), which will damage the long-term structural stability and hot working performance of the alloy. Therefore, the Mo content of alloys used in molten salt reactors needs to be strictly controlled in the range of 15-18 wt%.

[0004] The aforementioned multiple constraints result in a significantly lower degree of alloying for typical nickel-based alloys used in molten salt reactors (such as Hastelloy N in the United States and GH3535 in China) compared to similar nickel-based high-temperature alloys. Consequently, their high-temperature mechanical properties are also limited, with room-temperature yield strength of only about 300–350 MPa and tensile strength of about 800 MPa, making it difficult to meet the higher load-bearing capacity requirements of advanced molten salt reactors for structural materials.

[0005] To overcome the strength bottleneck of nickel-based alloys used in molten salt reactors, researchers have turned their attention to the introduction of rare earth elements for strengthening. Rare earth elements have been widely and successfully used as strengthening elements in lightweight alloys such as magnesium and aluminum alloys. Due to its large atomic radius and unique electronic structure, rare earth element Gd can both act as a microalloying agent to remove harmful impurities at grain boundaries and is expected to form rare earth intermetallic compound phases that contribute to precipitation strengthening effects. However, the solid solubility of rare earth elements in nickel-based alloys is extremely low. During conventional solidification, most Gd is segregated and expelled into the interdendritic region, forming a coarse divorced eutectic structure (Ni-Gd eutectic compound, mainly Ni5Gd). The size of this coarse rare earth phase often reaches tens of micrometers or even larger, making it difficult to achieve effective solid solution strengthening and precipitation strengthening; instead, it becomes a crack initiation source, significantly impairing the alloy's ductility and toughness. Therefore, the mechanical properties of Gd-containing nickel-based alloy components prepared using conventional casting, forging, and rolling processes are only slightly improved, and their ductility is severely reduced.

[0006] To refine the rare earth phase, recent studies have attempted to use additive manufacturing technologies (such as selective laser melting (SLM) and laser direct energy deposition (LDED)) to prepare Gd-containing nickel-based alloys, relying on extremely high cooling rates (10⁻⁶ m / s). 4 ~10 6 K / s) suppresses rare earth phase coarsening to obtain submicron-sized fine Ni5Gd particles. However, additive manufacturing of nickel-based alloys generally suffers from process defects (cracks, incomplete fusion defects, residual porosity, etc.) and is accompanied by high residual stress, resulting in extremely poor alloy plasticity (room temperature elongation of less than 5%). Although subsequent high-temperature annealing or hot isostatic pressing can partially improve plasticity, the process is complex and costly; more importantly, the rare earth phase will coarsen again during post-processing, and the deformation during post-processing will adversely affect the dimensional accuracy of near-net-shape products.

[0007] In summary, existing technologies cannot simultaneously achieve rare earth phase refinement, matrix microstructure optimization, and near-net-shape manufacturing in the same process, nor can they simultaneously achieve a synergistic improvement in strength and plasticity. There is an urgent need to develop new preparation technologies to meet the industrial application requirements of high-performance rare earth nickel-based alloys for advanced molten salt reactors. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of existing Gd nickel-based alloy component preparation technology and provide a method for preparing gadolinium nickel-based alloy components. This method achieves synergistic optimization of rare earth phase and matrix structure in the same process: suppressing the coarsening of Ni5Gd rare earth phase, while enabling the matrix to undergo complete recrystallization and eliminate the original particle boundaries, thereby obtaining a near-net-shape Gd nickel-based high-temperature alloy component with highly uniform structure and excellent strength-plasticity matching in one step.

[0009] The present invention specifically adopts the following technical solutions to solve the above-mentioned technical problems: A method for preparing gadolinium-nickel-based alloy components involves using a hot isostatic pressing process at a temperature of 1080–1160°C and a pressure of 120–200 MPa to prepare gadolinium-nickel-based alloy pre-alloyed powder into the gadolinium-nickel-based alloy components. This yields a near-net-shape product of gadolinium-nickel-based alloy components with Ni5Gd rare earth phases refined to micron / submicron level dispersion, a fully recrystallized equiaxed crystal structure in the matrix, complete elimination of original particle boundaries, and uniform distribution of grain size at approximately 5.3 μm.

[0010] Preferably, the gadolinium-nickel-based alloy pre-alloy powder is prepared using a vacuum induction melting-gas atomization or plasma rotating electrode method.

[0011] Preferably, the hot isostatic pressing process uses a 304L or 316L stainless steel sheath.

[0012] Preferably, in the hot isostatic pressing process, the pre-alloyed gadolinium-nickel based alloy powder encapsulated in the casing is first subjected to a compaction treatment to increase the powder density to more than 60% of the theoretical density; then, at 300–500°C and a vacuum degree ≤1×10⁻⁶, the powder is further compacted. -2 The degassing process under Pa conditions lasted for no less than 12 hours; subsequently, the evacuation tube was sealed under high temperature and vacuum conditions.

[0013] Preferably, the temperature of the hot isostatic pressing process is 1100–1130°C, and the pressure is 140–180 MPa.

[0014] In one embodiment, the chemical composition of the gadolinium-nickel-based alloy, by mass percentage, is: Cr 6.0–8.0%, Mo 15.0–18.0%, Fe ≤5.0%, Si ≤1.0%, Mn ≤1.0%, C 0.02–0.12%, Gd 1.5–2.5%, with the balance being Ni and unavoidable impurities.

[0015] Preferably, the cooling rate in the hot isostatic pressing process is ≤10℃ / min.

[0016] A gadolinium-nickel based alloy component is prepared using the method described in any of the above technical solutions.

[0017] Compared with the prior art, the present invention has the following beneficial effects: (1) The rare earth phase is significantly refined and the matrix structure is uniform: Compared with the nickel-based alloy containing Gd prepared by conventional casting and forging processes (Ni5Gd eutectic compounds often reach tens of micrometers), the Ni5Gd rare earth phase of the gadolinium nickel-based alloy parts obtained by this invention is refined to micrometer / submicrometer level dispersion distribution; the matrix is ​​a fully recrystallized equiaxed crystal structure, the original particle boundaries are completely eliminated, and the grain size is uniform (~ 5.3 μm).

[0018] (2) Synergistic improvement in strength and plasticity: Compared with conventionally cast and forged gadolinium-nickel alloy parts, the gadolinium-nickel alloy parts prepared by this invention have a tensile strength increased by about 20% and a yield strength increased by about 80%, while maintaining good plasticity; compared with the reference alloy GH3535 without Gd, the yield strength is increased by more than 125%.

[0019] (3) One-step near-net-shape product without additional heat treatment: The hot isostatic pressing process simultaneously completes three functions: powder densification, rare earth phase size control, and matrix recrystallization, directly obtaining near-net-shape high-performance products. This significantly simplifies the process, reduces manufacturing costs, and avoids the adverse effects of post-processing deformation on the dimensional accuracy of near-net-shape products.

[0020] (4) It has good process repeatability and high uniformity of structure, making it suitable for mass industrial manufacturing of large and complex molten salt reactor components. Attached Figure Description

[0021] Figure 1 These are electron backscatter diffraction (EBSD) inverse pole figure (IPF) microstructure comparison diagrams and nickel matrix grain size diagrams of the nickel-based alloy components prepared in Examples 1, 2, and Comparative Examples 1-5 of this invention; wherein, (a) is Example 1 (hot isostatic pressing 1100℃ / 140 MPa / 4 h); (b) is Example 2 (hot isostatic pressing 1130℃ / 180 MPa / 2 h); (c) is Comparative Example 1 (hot isostatic pressing 1230℃ / 140 MPa / 4 h, excessive temperature caused Ni5Gd coarsening); (d) is Comparative Example 2 (hot isostatic pressing 1070℃ / 140 MPa / 4 h, excessively low temperature caused PPB not to be eliminated); (e) is Comparative Example 3 (standard Gd-free nickel-based alloy hot isostatic pressing 1100℃ / 140 MPa / 4 h). (h); (f) is Comparative Example 4 (conventional casting, forging and rolling process for Gd-containing nickel-based alloys); (g) is Comparative Example 5 (conventional casting, forging and rolling process for standard nickel-based alloys without Gd); (h) is a comparison diagram of nickel matrix grain size; Figure 2The IPF and phase diagrams of the nickel-based alloy components prepared in Examples 1, 2, and Comparative Examples 1-5 of this invention are shown below. (a) is Example 1 (hot isostatic pressing 1100℃ / 140 MPa / 4 h); (b) is Example 2 (hot isostatic pressing 1130℃ / 180 MPa / 2 h); (c) is Comparative Example 1 (hot isostatic pressing 1230℃ / 140 MPa / 4 h, excessively high temperature leads to Ni5Gd coarsening); (d) is Comparative Example 2 (hot isostatic pressing 1070℃ / 140 MPa / 4 h, excessively low temperature results in PPB not being eliminated); (e) is Comparative Example 3 (standard Gd-free nickel-based alloy hot isostatic pressing 1100℃ / 140 MPa / 4 h); (f) is Comparative Example 4 (conventional casting, forging, and rolling process for Gd-containing nickel-based alloy); and (g) is Comparative Example 5 (conventional casting, forging, and rolling process for Gd-free standard nickel-based alloy). Figure 3 This is a bar chart comparing the room temperature tensile mechanical properties (tensile strength, yield strength, elongation) of the alloy components prepared in Examples 1-2 and Comparative Examples 1-5 of the present invention. Detailed Implementation

[0022] To address the technical problems of low strength of nickel-based alloys used in molten salt reactors, coarse rare earth phases in Gd-containing nickel-based alloys under conventional casting, forging, and rolling processes, and poor plasticity and high cost of alloys under additive manufacturing routes, this invention is based on in-depth research on the unique evolution law of Ni5Gd rare earth phase in Gd-containing nickel-based alloys during hot isostatic pressing (HIP). By employing HIP and finely controlling the HIP process parameter window, the invention achieves synergistic optimization of the rare earth phase and matrix structure in the same process: suppressing the coarsening of Ni5Gd rare earth phase while enabling complete recrystallization of the matrix and eliminating the original particle boundaries, thus obtaining near-net-shape Gd-containing nickel-based high-temperature alloy parts with highly uniform microstructure and excellent strength-plasticity matching in one step.

[0023] Hot isostatic pressing (HIP) is a process in which a product is placed in a sealed container and subjected to isotropic pressure while being kept at high temperature. Under the influence of high temperature and high pressure, the product is sintered and densified. HIP can be used for direct powder molding, where the powder is placed in a casing (similar to a mold). The casing can be made of metal or ceramic (low-carbon steel, Ni, Mo, glass, etc.), and nitrogen or argon is used as the pressurizing medium to directly heat and pressurize the powder into shape – a powder metallurgy process. Alternatively, it can be used to heat-densify castings, including those with shrinkage cavities such as aluminum alloys, titanium alloys, and high-temperature alloys. After HIP, the castings can achieve 100% densification, improving their overall mechanical properties.

[0024] Through in-depth research on the evolution of the Ni5Gd rare earth phase in Gd-containing nickel-based alloys during hot isostatic pressing, the inventors discovered the following special laws: (1) Unlike the conventional evolution law of strengthening phases such as γ′ / γ″ in conventional nickel-based superalloys, which is that the higher the temperature, the more fully the solid solution is dissolved, the Ni5Gd rare earth phase in Gd nickel-based alloys also exhibits the characteristic of "the higher the temperature, the coarser it becomes" during hot isostatic pressing. That is, as the hot isostatic pressing temperature increases, Ni5Gd particles coarsen significantly through the Ostwald ripening mechanism.

[0025] (2) If the hot isostatic pressing temperature is too high (e.g. ≥1200℃), the size of the Ni5Gd rare earth phase can coarsen from the submicron level in the original powder within a few hours, and even local coarse particles of tens of micrometers may appear, becoming crack initiation sources, resulting in a significant decrease in the yield strength of the alloy.

[0026] (3) If the hot isostatic pressing temperature is too low (e.g. ≤1080℃), although the Ni5Gd rare earth phase remains fine, only sintering necks are formed between the powder particles in the matrix, and sufficient static / dynamic recrystallization does not occur. At this time, the original particle boundary (PPB) is not eliminated, and the structure retains the cellular / dendritic solidification substructure formed during the powder atomization process and the oxide / carbide segregation film on the PPB. The matrix structure is not uniform, and the mechanical properties, especially the plasticity, are severely damaged.

[0027] Based on the above-mentioned patterns and combined with a large number of experiments, the inventors discovered that there is a narrow hot isostatic pressing process window (temperature 1080~1160℃) in the Gd-containing nickel-based alloy system. Within this window, the matrix is ​​just completed and fully recrystallized, forming a uniform equiaxed recrystallized structure. The original particle boundaries are completely eliminated, and at the same time, the Ni5Gd rare earth phase has not undergone significant coarsening, thereby achieving synergistic optimization of the rare earth phase and the matrix structure.

[0028] The specific technical solution proposed in this invention is as follows: A method for preparing gadolinium-nickel-based alloy components involves using a hot isostatic pressing process at a temperature of 1080–1160°C and a pressure of 120–200 MPa to prepare gadolinium-nickel-based alloy pre-alloyed powder into the gadolinium-nickel-based alloy components. This yields a near-net-shape product of gadolinium-nickel-based alloy components with Ni5Gd rare earth phases refined to micron / submicron level dispersion, a fully recrystallized equiaxed crystal structure in the matrix, complete elimination of original particle boundaries, and uniform distribution of grain size at approximately 5.3 μm.

[0029] The preparation method specifically includes the following steps: S1. Preparation of pre-alloyed powder: Gadolinium-nickel-based alloy pre-alloyed powders were prepared according to the chemical composition of gadolinium-nickel-based alloys. This invention preferably employs vacuum induction melting-gas atomization (VIGA) or plasma rotating electrode (PREP) methods to prepare the gadolinium-nickel-based alloy pre-alloyed powders. The prepared powders have a particle size range of 15–150 μm; oxygen content ≤300 ppm, nitrogen content ≤50 ppm; and exhibit good flowability and suitable bulk density.

[0030] S2. Packaging and vacuum degassing: This invention preferably uses a 304L or 316L stainless steel sheath. The gadolinium-nickel-based alloy pre-alloyed powder prepared in S1 is loaded into the sheath, and the powder density is first increased to more than 60% of the theoretical density through vibration compaction; then, at 300–500℃ and a vacuum degree ≤1×10⁻⁶, the powder is further processed. -2 The degassing process under Pa conditions lasted for no less than 12 hours; subsequently, the evacuation tube was sealed under high temperature and vacuum conditions.

[0031] S3, Hot Isostatic Pressing Densification: The sealed sheath is placed in a hot isostatic pressing furnace for hot isostatic pressing treatment. The hot isostatic pressing process parameters of this invention are: temperature 1080~1160℃, pressure 120~200 MPa; preferably, the temperature is 1100~1130℃, and the pressure is 140~180 MPa; the processing time can be adjusted according to the size of the component.

[0032] S4. Cooling and unpacking: After hot isostatic pressing, the component is preferably cooled to room temperature in the furnace at a rate of ≤10℃ / min. After cooling, the cladding is removed by machining, yielding a near-net-shape product of the Gd-containing nickel-based alloy component. This product does not require additional heat treatment such as solution treatment and aging to meet service performance requirements.

[0033] To facilitate public understanding, the technical solution and effects of the present invention will be further described in detail below through a set of specific embodiments, comparative examples, and in conjunction with the accompanying drawings: In the following examples and comparative examples, all pre-alloyed powders were prepared by vacuum induction melting-gas atomization (VIGA) method. The nominal chemical composition of the powder, by mass percentage, was: Cr 7.39%, Mo 16.79%, Fe 3.99%, Mn 0.65%, Si 0.50%, C 0.05%, Gd 1.68%, P 0.060%, S 0.0024%, with the balance being Ni. The powder particle sizes were D10 = 20.31 μm, D50 = 58.07 μm, and D90 = 125.2 μm; the oxygen content was 158 ppm, the nitrogen content was 6 ppm, and the bulk density was 4.98 g / cm³. 3 Tap density 5.84 g / cm³ 3The fluidity was 12.42 s / 50 g. Comparative Examples 3 and 5 contained no Gd, while the contents of other elements remained the same. Comparative Examples 4 and 5 were prepared into bars using a conventional vacuum induction melting + electroslag remelting + forging + hot rolling + annealing process.

[0034] The room temperature tensile properties of the alloys obtained in each example and comparative example were tested according to GB / T 228.1-2021. The tensile specimens were taken from the central part of the alloy in the HIP state or deformed annealed state. The microstructure was characterized by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD).

[0035] Example 1 (1): The Gd-containing nickel-based alloy pre-alloyed powder prepared by the above VIGA method was packed into a 304L stainless steel sleeve and mechanically compacted until the relative density of the powder was about 65%; (2): Place the powder package in a vacuum degassing system and heat it to 400℃, with a vacuum degree ≤5×10 -3 Degassing was performed for 16 hours under Pa conditions. After degassing was completed, the extraction pipe was sealed under high temperature and vacuum conditions. (3): The sealed sleeve is placed in a hot isostatic pressing furnace for hot isostatic pressing treatment. The process parameters are: temperature 1100℃, pressure 140 MPa, and holding time 4 hours. (4): After hot isostatic pressing, the furnace is cooled to room temperature at a rate of 5℃ / min, and the cladding is removed by machining to obtain Gd nickel-based alloy bars.

[0036] Characterization of the obtained alloy rods: EBSD observation showed that the matrix was a uniform equiaxed recrystallized structure with an average grain size of approximately 5.26 ± 1.81 μm, and the original grain boundaries were completely eliminated (see [link to relevant documentation]). Figure 1 (a and h in the text); the Ni5Gd rare earth phase is uniformly dispersed within the matrix grains and at grain boundaries, with an average size of approximately 0.60 ± 0.18 μm (see a and h in the text). Figure 2 (a) of the sample, with a maximum dimension not exceeding 2 μm. Room temperature tensile properties (see [reference]). Figure 3 ): Tensile strength 963.8 ± 6.5 MPa, yield strength 732.1 ± 5.8 MPa, elongation 14.8 ± 0.0%.

[0037] Example 2 (1): The Gd-containing nickel-based alloy pre-alloyed powder prepared by the above VIGA method was packed into a 304L stainless steel sleeve and mechanically compacted until the relative density of the powder was about 65%; (2): Place the powder package in a vacuum degassing system and heat it to 400℃, with a vacuum degree ≤5×10 -3 Degassing was performed for 16 hours under Pa conditions. After degassing was completed, the extraction pipe was sealed under high temperature and vacuum conditions. (3): The sealed sleeve is placed in a hot isostatic pressing furnace for hot isostatic pressing treatment. The process parameters are: temperature 1130℃, pressure 180 MPa, and holding time 2 hours. (4): After hot isostatic pressing, the furnace is cooled to room temperature at a rate of 5℃ / min, and the cladding is removed by machining to obtain Gd nickel-based alloy bars.

[0038] Characterization of the obtained alloy rods: EBSD observation showed that the matrix also exhibited a uniform equiaxed recrystallized structure with an average grain size of approximately 5.31 ± 1.91 μm (slightly larger than in Example 1), and the original grain boundaries were completely eliminated (see [reference]). Figure 1 (b and h in the text); the average size of the Ni5Gd rare earth phase is approximately 0.60 ± 0.21 μm (see [reference]). Figure 2 (b)). Room temperature tensile properties (see Figure 3 ): Tensile strength 946.5±32.1 MPa, yield strength 727.2±2.1 MPa, elongation 13.0±3.8%.

[0039] Comparative Example 1 (Hot Isostatic Pressing Temperature Too High) (1): The Gd-containing nickel-based alloy pre-alloyed powder prepared by the above VIGA method was packed into a 304L stainless steel sleeve and mechanically compacted until the relative density of the powder was about 65%; (2): Place the powder package in a vacuum degassing system and heat it to 400℃, with a vacuum degree ≤5×10 -3 Degassing was performed for 16 hours under Pa conditions. After degassing was completed, the extraction pipe was sealed under high temperature and vacuum conditions. (3): The sealed sleeve is placed in a hot isostatic pressing furnace for hot isostatic pressing treatment. The process parameters are: temperature 1230℃, pressure 140 MPa, and holding time 4 hours. (4): After hot isostatic pressing, the furnace is cooled to room temperature at a rate of 5℃ / min, and the cladding is removed by machining to obtain Gd nickel-based alloy bars.

[0040] The obtained alloy rods were characterized: the matrix was a fully recrystallized structure, but the grains were significantly coarsened, with an average grain size of approximately 6.74 ± 3.32 μm (see [reference]). Figure 1 (c and h in the text); the Ni5Gd rare earth phase undergoes significant Ostwald ripening, with the average size coarsening to approximately 0.74 ± 0.32 μm (see c and h in the text). Figure 2 (c)). Room temperature tensile properties (see (c)). Figure 3The tensile strength was 924.6 ± 6.1 MPa, the yield strength was only 548.6 + 4.5 MPa, and the elongation was 17.9 ± 1.5%. The yield strength decreased by about 25% compared with Example 1, indicating that when the hot isostatic pressing temperature is too high, the coarse Ni5Gd rare earth phase cannot play a strengthening role and instead becomes a source of stress concentration.

[0041] Comparative Example 2 (Hot Isostatic Pressing Temperature Too Low) (1): The Gd-containing nickel-based alloy pre-alloyed powder prepared by the above VIGA method was packed into a 304L stainless steel sleeve and mechanically compacted until the relative density of the powder was about 65%; (2): Place the powder package in a vacuum degassing system and heat it to 400℃, with a vacuum degree ≤5×10 -3 Degassing was performed for 16 hours under Pa conditions. After degassing was completed, the extraction pipe was sealed under high temperature and vacuum conditions. (3): The sealed sleeve is placed in a hot isostatic pressing furnace for hot isostatic pressing treatment. The process parameters are: temperature 1070℃, pressure 140 MPa, and holding time 4 hours. (4): After hot isostatic pressing, the furnace is cooled to room temperature at a rate of 5℃ / min, and the cladding is removed by machining to obtain Gd nickel-based alloy bars.

[0042] Characterization of the obtained alloy rods: Although the density reached over 99% of the theoretical density, EBSD observation showed that the original powder particle outlines (i.e., obvious original particle boundaries PPB) could be clearly identified within the matrix. The matrix did not undergo complete recrystallization, with an average grain size of 5.26 ± 1.98 μm. The particles retained the cellular / dendritic solidification substructure formed during powder atomization (see...). Figure 1 (d and h in the text); the Ni5Gd rare earth phase maintains a submicron-scale fine size (0.60±0.23 μm) (see...) Figure 2 (d) in the middle). Room temperature tensile properties (see (d)). Figure 3 The tensile strength is 939.9±13.9 MPa, and the yield strength is 746.3±7.2 MPa (the yield strength is slightly higher due to the combined effect of PPB interface strengthening and fine Ni5Gd), but the elongation is only 9.1+0.7%. The cracks propagate along the original particle boundaries that have not been eliminated, resulting in a severe loss of plasticity.

[0043] Comparative Example 3 (Standard Gd-free alloy hot isostatic pressing) The raw material powder is a standard GH3535 alloy powder without Gd (the content of other elements is the same as in Example 1). It is prepared according to the same steps (1) to (4) as in Example 1. The hot isostatic pressing process parameters are: temperature 1100℃, pressure 140 MPa, and holding time 4 hours.

[0044] The obtained alloy rods were characterized: the matrix was a fully recrystallized equiaxed grain structure with a grain size of approximately 7.49 ± 4.27 μm (see [reference]). Figure 1 (e and h in the text). Room temperature tensile properties (see...) Figure 3 The tensile strength was 913.9 ± 20.9 MPa, the yield strength was 454.5 ± 2.1 MPa, and the elongation was 35.3 ± 4.4%. This comparative example shows that under the same HIP process, adding 1.68 wt% Gd can increase the yield strength from 454 MPa to 732 MPa (Example 1), an increase of up to 61%, verifying the significant strengthening effect of the Gd rare earth phase.

[0045] Comparative Example 4 (Conventional casting, forging, and rolling process for Gd alloy) Gd-containing nickel-based alloy ingots with the same nominal composition as in Example 1 were prepared by vacuum induction melting and electroslag remelting. Then, bars were prepared by homogenization treatment (1180℃ / 24 h), hot forging, hot rolling (initial forging temperature 1150℃, final forging temperature ≥900℃), and solution treatment (1160℃ / 1 h water cooling).

[0046] The obtained alloy rods were characterized: the matrix grains were coarse and uneven (average grain size was 15.4 ± 13.57 μm) (see [reference]). Figure 1 In (f) of the figure, the Ni5Gd rare earth phase precipitates in the form of a divorced eutectic during the casting solidification process, exhibiting a coarse interdendritic network distribution with an average grain size of 2.13±1.19 μm (see [f]). Figure 1 (h)); During hot rolling deformation, some coarse eutectic phases break down, but still exist in chain / granular bands. Room temperature tensile properties (see...) Figure 3 The tensile strength is 807.1 ± 16.4 MPa, the yield strength is 399.9 ± 6.0 MPa, and the elongation is 28.1 ± 1.5%. Compared with Example 1, the alloy obtained by conventional casting and forging processes has a reduced tensile strength of approximately 17% and a reduced yield strength of approximately 47%.

[0047] Comparative Example 5 (Standard Gd-free alloy conventional casting, forging, and rolling process) Standard GH3535 alloy bars without Gd were prepared using the same conventional casting, forging, and rolling process as Comparative Example 4. Room temperature tensile properties (see...) Figure 3 The tensile strength is 783.2 ± 14.0 MPa, the yield strength is 302.3 ± 8.3 MPa, and the elongation is 52.0 ± 2.9%. This comparative example reflects the typical mechanical properties of currently commercially available nickel-based alloys (GH3535) for molten salt reactors and serves as a benchmark for performance improvement in this invention.

[0048] Table 1 summarizes the hot isostatic pressing process parameters (except for Comparative Examples 4 and 5) and room temperature tensile mechanical property data of the various embodiments and comparative examples of the present invention: Table 1 Summary of process parameters and mechanical properties of the examples and comparative examples

[0049] Combined Table 1 and Figure 1 , Figure 2 The data shows that: (1) Compared with Comparative Example 4 (conventional casting, forging and rolling of Gd alloy), the tensile strength of Examples 1 and 2 of the present invention increased from 807 MPa to 946-964 MPa (an increase of 17%-19%), and the yield strength increased significantly from 400 MPa to 727-732 MPa (an increase of 82%-83%). This proves that the hot isostatic pressing preparation method provided by the present invention can effectively refine the Ni5Gd rare earth phase and significantly exert its strengthening effect.

[0050] (2) Compared with Comparative Example 3 (standard Gd-free alloy with the same process HIP), Example 1 of the present invention: the yield strength increased from 454 MPa to 732 MPa (an increase of 61%), and the tensile strength increased from 914 MPa to 964 MPa, proving that the Ni5Gd rare earth phase brought by the addition of Gd is the main source of strengthening; at the same time, the elongation decreased from 35% to 15%, but still maintained a practical level (>12%).

[0051] (3) Compared with Comparative Example 1 (HIP temperature too high 1230℃), the yield strength of the embodiment of the present invention increased from 549 MPa to 727-732 MPa (an increase of about 33%), which proves that the hot isostatic pressing temperature must be strictly controlled below 1150℃ to prevent Ostwald coarsening of the Ni5Gd rare earth phase (the average particle size of Ni5Gd in Comparative Example 1 was coarsened to about 12 μm). This is one of the fundamental differences between the present invention and the conventional nickel-based high-temperature alloy HIP process.

[0052] (4) Compared with Comparative Example 2 (HIP temperature too low 1070℃), the yield strength of the embodiments of the present invention is not much different (732 MPa in Example 1 and 746 MPa in Comparative Example 2), but the elongation is greatly increased from 9% to 15%. This is because the matrix completes complete recrystallization and the original particle boundaries are completely eliminated within the HIP window of 1100~1130℃, eliminating the plastic failure path along PPB fracture and achieving a synergistic match of strong plasticity.

[0053] (5) In summary, the embodiments of the present invention surpass all the comprehensive performance indicators of comparative examples 1 to 5. They achieve a synergistic improvement in strength and plasticity with the simplest single-process HIP process, and do not require subsequent heat treatment such as solution treatment and aging. The process is significantly simplified and has good prospects for industrial application.

[0054] This invention is applicable to the near-net-shape manufacturing of various complex-shaped structural components for molten salt reactors. Through encapsulation shape design, components such as pipes, flanges, valves, and heat exchanger shells can be directly formed, avoiding problems such as low material utilization and large processing deformation in conventional forging and rolling processes. Furthermore, when implementing this invention, the hot isostatic pressing (HIP) holding time can be adjusted according to the component size and thickness: for thick-walled large components, a longer holding time (e.g., 3-5 hours) can be used to ensure adequate central densification; for thin-walled or small components, the holding time can be appropriately shortened (e.g., 1-2 hours) to improve efficiency. Good densification can be achieved within a pressure range of 120-200 MPa, with 140-180 MPa being the optimal pressure range. Those skilled in the art can make appropriate adjustments within the process window described in this invention based on powder characteristics and equipment conditions without departing from the spirit and scope of this invention.

Claims

1. A method of making a gadolinium-containing nickel-based alloy component, characterized by, The gadolinium-nickel-based alloy pre-alloyed powder is prepared into the gadolinium-nickel-based alloy component using a hot isostatic pressing process at a temperature of 1080–1160℃ and a pressure of 120–200 MPa. This process yields a near-net-shape product of the gadolinium-nickel-based alloy component, in which the Ni5Gd rare earth phase is refined to a micron / submicron level dispersion, the matrix is ​​a fully recrystallized equiaxed crystal structure, the original particle boundaries are completely eliminated, and the grain size is uniformly distributed at around 5.3 μm.

2. The method for preparing gadolinium-nickel based alloy components as described in claim 1, characterized in that, The gadolinium-nickel-based alloy pre-alloyed powder was prepared using a vacuum induction melting-gas atomization or plasma rotating electrode method.

3. The method for preparing gadolinium-nickel based alloy components as described in claim 1, characterized in that, The hot isostatic pressing process uses a 304L or 316L stainless steel sheath.

4. The method for preparing gadolinium-nickel based alloy components as described in claim 1, characterized in that, In the hot isostatic pressing process, the gadolinium-containing nickel-based alloy pre-alloy powder in the canning is first treated by jolting to improve the powder loading density to more than 60% of the theoretical density; then, the powder is degassed at 300-500°C under a vacuum degree of ≤1×10 -2 Pa for not less than 12 hours. The evacuation tube was then sealed under high temperature and vacuum conditions.

5. The method for preparing gadolinium-nickel based alloy components as described in claim 1, characterized in that, The hot isostatic pressing process is carried out at a temperature of 1100–1130°C and a pressure of 140–180 MPa.

6. The method for preparing the gadolinium-nickel based alloy component as described in claim 1, characterized in that, The chemical composition of the gadolinium-nickel-based alloy, by mass percentage, is: Cr 6.0–8.0%, Mo 15.0–18.0%, Fe ≤5.0%, Si ≤1.0%, Mn ≤1.0%, C 0.02–0.12%, Gd 1.5–2.5%, with the balance being Ni and unavoidable impurities.

7. The method for preparing gadolinium-nickel based alloy components as described in claim 1, characterized in that, The cooling rate in the hot isostatic pressing process is ≤10℃ / min.

8. A component containing a gadolinium-nickel based alloy, characterized in that, Prepared using the method described in any one of claims 1 to 7.

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