A dense GdH2 bulk material bonded by a low-melting-point alloy and its preparation method

Abstract

This invention discloses a dense GdH2 bulk material bonded with a low-melting-point alloy and its preparation method. By introducing a low-melting-point alloy into the raw material powder and utilizing liquid-phase wetting and particle rearrangement mechanisms, efficient densification sintering of GdH2 powder is achieved at low temperatures, ensuring that the GdH2 bulk material maintains a high H / Gd atomic ratio. The high hydrogen content of this bulk material ensures excellent fast neutron moderation capability. Combined with the fact that Gd has the highest thermal neutron absorption cross section, the dense structure also blocks the neutron "penetration effect" caused by micropores, thus achieving efficient neutron protection. The dense GdH2 bulk material itself has a high density, which, combined with the high atomic number of Gd, effectively weakens high-energy gamma rays through the photoelectric effect and Compton scattering. This solution solves the technical challenge of achieving both high density and a high H / Gd ratio in GdH2 shielding materials, providing key shielding material support for the radiation shielding system of fusion reactor superconducting magnets.

Description

Technical Field

[0001] This invention relates to the preparation of rare earth hydrides, and more particularly to a dense GdH2 bulk material bonded by a low-melting-point alloy and its preparation method. Background Technology

[0002] Gadolinium hydride (GdH2), a rare-earth hydride possessing both excellent neutron absorption and gamma-ray shielding properties, has irreplaceable application value in cutting-edge fields such as nuclear reactor safety shielding. In the field of magnetic confinement fusion, GdH2 bulk material serves as the core material of the radiation shielding system for fusion reactor superconducting magnets. Its extremely high hydrogen content can rapidly slow down fast neutrons penetrating the blanket, and the high thermal neutron absorption cross-section of gdolinium enables in-situ neutron capture. Simultaneously, GdH2 bulk material boasts a relatively high density (7.12 g / cm³). 3 It can also effectively reduce Co 60 This material effectively reduces irradiation damage to superconducting coils from high-energy particles, ensuring the superconducting stability and service life of the magnet system. Furthermore, based on its excellent shielding efficiency and relatively high thermal stability, it also shows great potential in the lightweight shielding design of space nuclear propulsion systems, capable of simultaneously attenuating high-energy neutrons and gamma-ray streams, significantly reducing the load pressure on spacecraft. Currently, the preparation of dense hydride bulk materials mainly employs direct hydrogenation and powder metallurgy solid-state sintering methods, but achieving high density while maintaining structural integrity still faces significant challenges. Existing processes mainly suffer from the following inherent defects:

[0003] First, the direct hydrogenation method suffers from severe phase transformation stress damage. During the transformation of Gd metal to GdH2, there is a huge lattice volume expansion (up to 10%~15%), which easily induces severe non-uniform thermal stress and structural stress inside the material, leading to spontaneous pulverization of the bulk or the formation of through-macro cracks. In addition, due to the limited diffusion depth of hydrogen atoms in the solid phase, this method is difficult to achieve high-density preparation of large-size and complex geometric parts.

[0004] Secondly, the slow diffusion kinetics of powder metallurgy solid-state sintering present a bottleneck. Due to the low atomic diffusion rate between GdH2 particles and insufficient sintering driving force, a large number of closed pores are generally left in the sintered block, resulting in low relative density. More importantly, GdH2 is prone to thermal decomposition and dehydrogenation during high-temperature sintering, leading to a significant reduction in the hydrogen content of the material and a deterioration in phase stability. The superposition of residual pores and structural defects caused by dehydrogenation not only exacerbates the penetration and scattering loss of neutron flux and reduces shielding effectiveness, but also significantly deteriorates the compressive strength and seismic performance of the material, making it difficult to meet the high requirements for the structural integrity of shielding modules in the harsh service environments of fusion reactor superconducting magnets.

[0005] Therefore, how to avoid the risk of stress cracking in the direct hydrogenation process, resolve the technical contradiction between densification and high hydrogen content in solid-state sintering, and develop a new preparation route that takes into account high density, high hydrogen content and high structural strength has become a key challenge for the promotion and application of gadolinium hydride materials. Summary of the Invention

[0006] The purpose of this invention is to provide a dense GdH2 bulk material bonded with a low-melting-point alloy and its preparation method, which can improve the technical defects of GdH2 bulk material sintering preparation process, which makes it difficult to achieve both densification and high hydrogen content.

[0007] In a first aspect, this application provides a dense GdH2 bulk material bonded by a low-melting-point alloy, the bulk material being prepared by sintering raw material powder comprising GdH2 and a low-melting-point binder alloy; wherein the low-melting-point binder alloy is selected from at least one of Al, Al-Gd alloy or Mg-Gd alloy, and the content of the low-melting-point binder alloy is 10-30% by volume percentage of the raw material powder.

[0008] Optionally, the Al-Gd alloy includes at least one of AlGd10 or AlGd30, and the Mg-Gd alloy includes at least one of MgGd10 or MgGd20.

[0009] Optionally, when the low-melting-point binder alloy is selected from at least one of Al or Al-Gd alloy, the phase structure of the bulk material includes GdH2 phase, Al2Gd phase and Al3Gd phase; the content of Al2Gd phase is 6%~12% by volume percentage of the total of each phase, the content of Al3Gd phase is 13%~21%, and the balance is GdH2 phase;

[0010] When the low-melting-point binder alloy is selected from Mg-Gd alloy, the phase structure of the bulk material includes GdH2 phase and Mg phase, or includes GdH2 phase, Mg phase and MgH2 phase; the content of Mg phase is 18%~21% by volume percentage of the total of each phase, the content of MgH2 phase is 0%~6%, and the balance is GdH2 phase.

[0011] Optionally, the content of the Al2Gd phase is 10%~12%, the content of the Al3Gd phase is 19%~21%, and the balance is the GdH2 phase; or,

[0012] The content of the Mg phase is 18%~21%, and the balance is GdH2 phase.

[0013] Optionally, the density of the bulk material is 95% or higher; and / or,

[0014] The H / Gd atomic ratio of the bulk material is 1.9 or higher; and / or,

[0015] When the low-melting-point binder phase alloy is selected from at least one of Al or Al-Gd alloy, the Vickers hardness of the bulk material is 280~310HV and the compressive strength is 179~195MPa.

[0016] When the low-melting-point binder alloy is selected from Mg-Gd alloy, the Vickers hardness of the bulk material is 185~200HV and the compressive strength is 300~370MPa.

[0017] Secondly, the present invention provides a method for preparing a dense GdH2 bulk material bonded by a low-melting-point alloy, comprising the following preparation steps:

[0018] S1. Raw material powder weighing: Weigh GdH2 powder and low melting point binder phase alloy powder according to the ratio;

[0019] S2. Raw material powder mixing: The GdH2 powder and the low-melting-point binder phase alloy powder are mixed evenly;

[0020] S3. Raw material powder sintering: The mixed raw material powder is hot-pressed and sintered at a temperature between the melting point of the low melting point binder alloy and the peak value of the main dehydrogenation temperature of GdH2, and at a sintering pressure of 200 MPa or higher.

[0021] Optionally, in step S1, the particle size ratio of the GdH2 powder and the low-melting-point binder phase alloy powder is 20~150μm:0.5~300μm.

[0022] Optionally, in step S2, the raw material powder is mixed by ball milling with a ball-to-material ratio of 3~20:1, a ball milling speed of 50~1000 rpm, and a ball milling time of 1~30 h.

[0023] Optionally, in step S3, the sintering temperature is 600~780℃, the sintering pressure is 200~650MPa, the sintering time is 1~15min, and the hot pressing sintering is carried out in an inert protective atmosphere.

[0024] Optionally, in step S3, before the hot pressing sintering begins, the raw material powder is pre-pressed at a pressure of 300MPa to 650MPa.

[0025] In summary, the present invention has at least one of the following beneficial technical effects:

[0026] 1. This invention provides a dense GdH2 bulk material bonded by a low-melting-point alloy and its preparation method. By introducing a low-melting-point binder alloy, a synergistic mechanism of "low-temperature liquid phase flow filling + high-pressure assisted densification" is constructed for the first time. Within the temperature range of the melting point of the low-melting-point binder alloy and the peak temperature of the main dehydrogenation temperature of GdH2 (815℃), the capillary force generated by the liquid phase formed by the melting of the alloy is used to fill the pores of GdH2 powder. Combined with external high pressure to promote densification, while effectively avoiding the risk of stress cracking in the direct hydrogenation method, the high density (above 95%) and high hydrogen content retention rate (H / Gd above 1.9) of the GdH2 bulk material are simultaneously achieved.

[0027] 2. This invention provides a dense GdH2 bulk material bonded with a low-melting-point alloy and its preparation method. The method effectively suppresses GdH2 dehydrogenation by utilizing the pressure during hot-pressing densification: high pressure drives (200MPa~650MPa) to plastically deform the particles and eliminate interconnected pores, physically blocking the H2 escape path and transforming hydrogen migration from low-energy-barrier gas diffusion to high-energy-barrier solid-phase diffusion. Secondly, the confined trace hydrogen atoms form a localized high hydrogen pressure at the particle interface, which, according to Le Chatelier's principle, can significantly reduce hydrogen dehydrogenation from a thermodynamic equilibrium perspective. The decomposition reaction of GdH2 is suppressed. Simultaneously, the high pressure significantly compresses the internal free volume, prompting the dehydrogenated metallic Gd to come into close contact with the local hydrogen pressure environment, thereby inducing its dynamic re-hydrogen absorption behavior. This mechanism essentially reconciles the contradiction between the sintering densification kinetics and the dehydrogenation thermodynamics, ensuring a high hydrogen content retention rate while achieving densification. Furthermore, the use of rapid, short-time sintering allows the low-melting-point alloy to promote sintering, significantly shortening the bulk material preparation time, thereby further suppressing GdH2 dehydrogenation and preventing the outflow of low-melting-point alloy liquid. Moreover, the low-melting-point alloy binder phase can also act as a hydrogen molecule trap. Even after GdH2 dehydrogenation at high temperatures, the formed hydrogen molecules can be captured by the binder phase alloy distributed around the GdH2 powder, forming low-melting-point alloy hydrides, effectively reducing H desorption and maintaining a high H / Gd ratio after hot pressing.

[0028] 3. This invention provides a dense GdH2 bulk material bonded with a low-melting-point alloy and its preparation method. The excellent wettability of the alloy bond to the GdH2 particles creates a continuous and tough microstructure within the material. The Al-based alloy significantly improves the local rigidity and Vickers hardness of the bulk through interfacial strengthening, making it suitable for high-rigidity applications. The Mg-based alloy, through the plastic buffering effect of the continuous skeleton, significantly increases the compressive strength of the bulk, enhancing the fracture toughness and impact resistance of the material. This process avoids phase transformation stress cracking and ensures structural integrity while significantly reducing the preparation temperature (below 800℃) and equipment dependence, achieving efficient and low-cost preparation of high-performance radiation shielding materials. Combined with mold design and molding pressure control, it can realize the preparation of large-size and even complex-shaped GdH2 materials. Attached Figure Description

[0029] Figure 1 This is the refined XRD Rietveld image of the bulk material in Example 1.

[0030] Figure 2 This is the refined XRD Rietveld image of the bulk material in Example 2.

[0031] Figure 3 This is the refined XRD Rietveld image of the bulk material in Example 3.

[0032] Figure 4 This is the refined XRD Rietveld image of the bulk material in Example 4.

[0033] Figure 5 This is the refined XRD Rietveld image of the bulk material in Example 5.

[0034] Figure 6 This is the XRD pattern of the bulk material in Comparative Example 1.

[0035] Figure 7 This is the XRD pattern of the bulk material in Comparative Example 2.

[0036] Figure 8 This is the XRD pattern of the bulk material in Comparative Example 3.

[0037] Figure 9 This is the XRD pattern of the bulk material in Comparative Example 4.

[0038] Figure 10 This is the XRD pattern of the bulk material in Comparative Example 5.

[0039] Figure 11 These are metallographic micrographs of the bulk materials in Examples 1-5 and Comparative Example 1.

[0040] Figure 12These are SEM images of the bulk materials in Examples 1-5 and Comparative Example 1.

[0041] Figure 13 These are metallographic micrographs of the bulk materials in Comparative Examples 2 to 5. Detailed Implementation

[0042] This invention provides a dense GdH2 bulk material bonded with a low-melting-point alloy and its preparation method. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention.

[0043] To prepare GdH2 bulk materials with high density and high hydrogen content retention, current research often employs high-temperature solid-state sintering, sintering GdH2 powder at temperatures above 900°C. While this can improve the bulk density to some extent, this temperature far exceeds the thermal dehydrogenation threshold of GdH2, leading to severe dehydrogenation and a significant decrease in the H / Gd ratio. Conversely, lowering the sintering temperature below the thermal dehydrogenation threshold makes it difficult for the GdH2 powder itself to achieve effective densification, resulting in high porosity and poor structural stability. Addressing the contradiction between "high-temperature dehydrogenation" and "insufficient low-temperature density" in related technologies, this invention provides a preparation scheme using a low-melting-point alloy binder combined with high-pressure hot pressing. The technical principle lies in introducing a low-melting-point alloy binder phase in a specific ratio into the GdH2 powder matrix. This binder phase melts first in the temperature range (600~780°C) below the severe dehydrogenation threshold of GdH2 (815°C). Driven by capillary forces, the molten alloy liquid phase rapidly penetrates and fills the micron-sized pores between GdH2 particles, effectively cutting off the pathways for hydrogen escape. Through extensive research, the inventors discovered that low-melting-point alloys (such as Al, Al-Gd, and Mg-Gd) possess good plasticity, suitable coefficients of thermal expansion, and excellent interfacial compatibility and wettability with gadolinium hydride. Their melting temperatures are lower than the peak temperature range of severe dehydrogenation in gadolinium hydride. Introducing such alloys not only significantly improves material density through liquid-phase sintering technology but also avoids the substantial decrease in hydrogen content caused by the high-temperature decomposition of GdH2. Furthermore, the strengthening and toughening effect of the resulting alloy binder phase helps improve the intrinsic brittleness of the gadolinium hydride bulk.

[0044] In particular, when an Al-based alloy binder phase is used, a controlled interfacial metallurgical reaction occurs between the liquid aluminum and the surface of GdH2 particles, generating intermediate phases such as Al2Gd and Al3Gd in situ. The chemical bonding force significantly enhances the interfacial bonding strength. When a Mg-based alloy binder phase is used, the liquid magnesium physically fills the micropores with excellent fluidity, constructing a continuous and dense network. More importantly, the Mg matrix distributed around GdH2 can act as a hydrogen molecule trap, capturing hydrogen atoms released at high temperatures and generating phases such as MgH2. This effectively inhibits the macroscopic desorption of hydrogen. The Mg-based binder phase exerts a dual hydrogen-locking effect of "physical blocking" and "in-situ capture". Building upon this foundation, and through the synergistic effect of high-pressure short-time sintering, residual closed pores are kinetically eliminated, resulting in an extremely compact particle interface. Furthermore, the localized high hydrogen pressure caused by physical blockade generates a strong reverse inhibitory force on GdH2 decomposition, significantly raising the hydrogen atom evolution barrier and promoting the reabsorption of hydrogen by the powder after dehydrogenation. Thus, while completely avoiding the risk of thermal dehydrogenation of GdH2, rapid densification and structural strengthening of the GdH2 bulk material are achieved. The resulting GdH2 bulk material maintains an extremely high hydrogen atom density, meeting the stringent requirements of special service scenarios demanding exceptional shielding effectiveness. This invention is based on this research.

[0045] In some embodiments of the present invention, a dense GdH2 bulk material with a low-melting-point alloy bond is provided. The bulk material is prepared by sintering raw material powder comprising GdH2 and a low-melting-point binder alloy. The low-melting-point binder alloy is selected from at least one of Al, Al-Gd alloy, or Mg-Gd alloy, and its content, based on the volume percentage of the raw material powder, is 10-30%. Preferably, the content of the low-melting-point binder alloy is 15-25%, more preferably 18-22%.

[0046] In some embodiments of the present invention, the Al-Gd alloy comprises at least one of AlGd10 or AlGd30, and the Mg-Gd alloy comprises at least one of MgGd10 or MgGd20. Preferably, the Al-Gd alloy is selected from AlGd10; and the Mg-Gd alloy is selected from MgGd10.

[0047] In some embodiments of the present invention, when the low-melting-point binder alloy is selected from at least one of Al or Al-Gd alloys, the phase structure of the bulk material includes GdH2 phase, Al2Gd phase and Al3Gd phase; the content of Al2Gd phase is 6%~12% by volume percentage of the total of each phase, the content of Al3Gd phase is 13%~21%, and the balance is GdH2 phase; preferably, the content of Al2Gd phase is 10%~12%, the content of Al3Gd phase is 19%~21%, and the balance is GdH2 phase;

[0048] When the low-melting-point binder alloy is selected from Mg-Gd alloy, the phase structure of the bulk material includes GdH2 phase and Mg phase, or includes GdH2 phase, Mg phase and MgH2 phase; the content of Mg phase is 18%~21% by volume percentage of the total of each phase, the content of Mg phase is 0%~6%, and the balance is GdH2 phase; preferably, the content of Mg phase is 18%~21%, and the balance is GdH2 phase.

[0049] In some embodiments of the present invention, the density of the bulk material is 95% or higher; preferably, the density of the bulk material is 96.9% to 98.5%; more preferably, the density of the bulk material is 97.0% to 98.2%; and / or,

[0050] The H / Gd atomic ratio of the bulk material is 1.9 or higher; preferably, the H / Gd atomic ratio of the bulk material is 2.0 or higher, more preferably 2.02 to 2.18; and / or,

[0051] In some embodiments of the present invention, when the low-melting-point binder alloy is selected from at least one of Al or Al-Gd alloys, the Vickers hardness of the bulk material is 280~310 HV, the compressive strength is 179~195 MPa, and the H / Gd atomic ratio is 2.0~2.1; preferably, the Vickers hardness of the bulk material is 290~310 HV, the compressive strength is 180~195 MPa, and the H / Gd atomic ratio is 2.03~2.1.

[0052] When the low-melting-point binder alloy is selected from Mg-Gd alloy, the Vickers hardness of the bulk material is 185~200HV, the compressive strength is 300~370MPa, and the atomic ratio of H / Gd is 2.1~2.2; preferably, the compressive strength of the bulk material is 350~370MPa.

[0053] In some embodiments of the present invention, a method for preparing a dense GdH2 bulk material bonded by a low-melting-point alloy is provided, comprising the following preparation steps:

[0054] S1. Raw material powder weighing: Weigh GdH2 powder and low melting point binder phase alloy powder according to the ratio;

[0055] S2. Raw material powder mixing: The GdH2 powder and the low-melting-point binder phase alloy powder are mixed evenly;

[0056] S3. Raw material powder sintering: The mixed raw material powder is hot-pressed and sintered at a temperature between the melting point of the low melting point binder alloy and the peak value of the main dehydrogenation temperature of GdH2, and at a sintering pressure of 200 MPa or higher.

[0057] In some embodiments of the present invention, in step S1, the particle size ratio of the GdH2 powder to the low-melting-point binder alloy powder is 20~150 μm:0.5~300 μm; preferably, the particle size ratio of the GdH2 powder to the low-melting-point binder alloy powder is 20~100 μm:0.5~100 μm; more preferably, the particle size ratio of the GdH2 powder to the low-melting-point binder alloy powder is 30~100 μm:3~100 μm; even more preferably, the particle size ratio of the GdH2 powder to the low-melting-point binder alloy powder is 30~80 μm:3~80 μm. The H / Gd ratio of the GdH2 powder in the raw material powder is 2.4 or higher.

[0058] In some embodiments of the present invention, in step S2, the raw material powder is mixed by ball milling with a ball-to-material ratio of 3~20:1, a ball milling speed of 50~1000 rpm, and a ball milling time of 1~30 h; preferably, the ball-to-material ratio is 5~15:1, the ball milling speed is 200~800 rpm, and the ball milling time is 1~8 h.

[0059] In some embodiments of the present invention, in step S3, the sintering temperature is between 600 and 780°C, the sintering pressure is between 200 and 650 MPa, the sintering time is between 1 and 15 min, and the sintering is carried out in an inert protective atmosphere. Preferably, the sintering temperature is between 650 and 750°C, more preferably between 680 and 720°C; the sintering pressure is preferably between 200 and 650 MPa, more preferably between 280 and 500 MPa; preferably, the sintering time is between 2 and 10 min; preferably, the sintering is carried out in an argon or nitrogen protective atmosphere, and the pressure of the atmosphere is between 0.01 and 0.1 MPa, preferably between 0.01 and 0.06 MPa.

[0060] In some embodiments of the present invention, in step S3, before the hot pressing sintering begins, the raw material powder is pre-pressed. The pre-pressing pressure is 300MPa~650MPa, preferably 300MPa~450MPa. Pre-pressing is preferably cold pressing, and the cold pressing time is 1~10min, preferably 2~5min.

[0061] The present invention will be further described in detail below with reference to specific embodiments. In the embodiments of the present invention, unless otherwise specified, the raw materials are all commercially available. It should be noted that the particle size of the raw material powder is measured using scanning electron microscopy (SEM) images combined with ImageJ software statistical methods; the true density is measured using the argon gas displacement method; the powder melting point is measured using differential scanning calorimetry (DSC); the hydrogen / gadolinium atomic ratio (H / Gd) is calculated using the pulse melting-thermal conductivity method after determining the hydrogen content, according to the formula nH / nGd=(ωH / MH) / [(ωGdH2-ωH) / MGd, where n...H n Gd These represent the amounts of substance of hydrogen and gadolinium atoms, respectively, with ωH representing the mass fraction of hydrogen. GdH2 express GdH2 Mass fraction; M H M Gd The molar masses of hydrogen and gadolinium were used to determine the hydrogen / gadolinium atomic ratio (H / Gd) of the GdH2 powder in the raw material powder, which was found to be 2.46. The peak dehydrogenation temperature of the GdH2 powder in the raw material powder was determined to be 815℃ by TG-DSC.

[0062] Example 1

[0063] This embodiment provides a method for preparing a low-melting-point alloy-bonded, densified GdH2 bulk material, including the following steps:

[0064] S1. Weighing of raw material powder: Weigh 20 vol.% Al powder (Hunan Fuqia Technology, purity 99.9%, particle size 4.38±1.58μm) and 80 vol.% GdH2 powder (Jiangxi Zhongxi Metal Materials, powder purity 99.9%, true density 7.1168 g / cm³) according to the volume percentage of the raw material powder. 3 The particle size was 50.43±17.8μm, and the hydrogen / gadolinium atomic ratio (H / Gd) was 2.46.

[0065] S2. Raw material powder mixing: The raw material powder is mixed by ball milling. The ball milling is carried out using a stainless steel ball milling jar and stainless steel grinding balls. The mass ratio of balls to material is 8:1. Anhydrous ethanol is used as a solvent for wet milling. The volume ratio of material + grinding balls to anhydrous ethanol is 1:1.2. The ball milling speed is 400 rpm and the ball milling time is 4 hours. After the mixture is uniform, the material is taken out and vacuum dried to obtain uniformly mixed raw material powder.

[0066] S3. Raw material powder sintering: The uniformly mixed raw material powder is placed into a mold of predetermined size, and then placed in a hot press sintering furnace, and vacuumed to 1×10⁻⁶. -1 After Pa, 0.04 MPa Ar gas was introduced for atmosphere protection. At room temperature (25℃), 500 MPa pressure was applied to the mold and held for 3 minutes. The pressure was then released to 350 MPa. The temperature was then increased to 700℃ at a rate of 120℃ / min and held for 3 minutes. The sintering process was carried out under pressure of 350 MPa throughout. After sintering, the mold was cooled with the furnace to obtain Al / GdH2 bulk material with a diameter of 15 mm.

[0067] Example 2

[0068] The difference between Example 2 and Example 1 is that in step S1 of Example 2, 20 vol.% AlGd10 powder is used instead of 20 vol.% Al powder in Example 1. The remaining preparation steps are the same as in Example 1, resulting in AlGd10 / GdH2 bulk material. The AlGd10 powder is prepared by melting and smelting the alloy according to the target alloy composition (90 wt% Al and 10 wt% Gd by mass percentage), followed by gas atomization powdering. The particle size of the prepared AlGd10 powder is measured to be 24.74 ± 8.62 μm, and the true density is 2.9757 g / cm³. 3 Its melting point is 667℃.

[0069] Example 3

[0070] The difference between Example 3 and Example 1 is that in step S1 of Example 3, 15 vol.% AlGd30 powder + 85 vol.% GdH2 powder is used instead of 20 vol.% Al powder + 80 vol.% GdH2 powder in Example 1. The remaining preparation steps are the same as in Example 1, and AlGd30 / GdH2 bulk material is prepared. The AlGd30 powder is prepared by melting and preparing an alloy liquid according to the target alloy composition (70 wt% Al and 30 wt% Gd by mass percentage), and then obtaining the powder through gas atomization. The particle size of the prepared AlGd30 powder is measured to be 19.94 ± 9.14 μm, and the true density is 3.3696 g / cm³. 3 Its melting point is 650℃.

[0071] Example 4

[0072] The difference between Example 4 and Example 1 is that in step S1 of Example 4, 20 vol.% MgGd10 powder is used instead of 20 vol.% Al powder in Example 1. The remaining preparation steps are the same as in Example 1, and MgGd10 / GdH2 bulk material is prepared. The MgGd10 powder is prepared by melting the alloy liquid according to the target alloy composition (Mg mass fraction of 90 wt% and Gd mass fraction of 10 wt%), followed by gas atomization powdering. The particle size of the prepared MgGd10 powder is measured to be 21.91 ± 8.65 μm, and the true density is 1.9222 g / cm³. 3 Its melting point is 648.4℃.

[0073] Example 5

[0074] The difference between Example 5 and Example 1 is that in step S1 of Example 5, 20 vol.% MgGd20 powder is used instead of 20 vol.% Al powder in Example 1. The remaining preparation steps are the same as in Example 1, and MgGd20 / GdH2 bulk material is prepared. The MgGd20 powder is prepared by melting the alloy liquid according to the target alloy composition (Mg mass fraction of 80 wt% and Gd mass fraction of 20 wt%), followed by gas atomization powdering. The particle size of the prepared MgGd20 powder is measured to be 34.54 ± 5.83 μm, and the true density is 2.1374 g / cm³. 3 Its melting point is 642.7℃.

[0075] Comparative Example 1

[0076] The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 did not add a low-melting-point binder alloy to prepare GdH2 bulk material. Specifically, it included the following steps: placing the raw material powder GdH2 into a mold of a predetermined size, then placing it in a hot-pressing sintering furnace and evacuating it to a vacuum of 1×10⁻⁶. -1 After Pa, 0.04 MPa Ar gas was introduced for atmosphere protection. At room temperature (25℃), 500 MPa pressure was applied to the mold and held for 3 minutes before being depressurized to 350 MPa. Then, the temperature was increased to 700℃ at a heating rate of 120℃ / min and held for 3 minutes. The sintering process was carried out under pressure of 350 MPa throughout. After sintering, the mold was cooled with the furnace to obtain GdH2 block material with a diameter of 15 mm.

[0077] Comparative Example 2

[0078] The difference between Comparative Example 2 and Example 3 is that in Comparative Example 2, step S1. uses 20 vol.% AlGd30 powder + 80 vol.% GdH2 powder instead of 15 vol.% AlGd30 powder + 85 vol.% GdH2 powder in Example 3, and Comparative Example 2 uses step S3' of low-pressure sintering instead of step S3 in Example 3. The remaining preparation steps are the same as in Example 3. Step S3' includes: placing the above-mentioned uniformly mixed raw material powder into a mold of a predetermined size, then placing it in a hot-pressing sintering furnace, and evacuating it to 1×10⁻⁶. - 1 After Pa, 0.04 MPa Ar gas was introduced for atmosphere protection. At room temperature (25℃), 50 MPa pressure was applied to the mold, and then the temperature was increased to 700℃ at a heating rate of 120℃ / min and held for 3 min. During the sintering process, the pressure was maintained at 50 MPa throughout the process. After sintering, the mold was cooled with the furnace to obtain AlGd30 / GdH2 block material with a diameter of 15 mm.

[0079] Comparative Example 3

[0080] The difference between Comparative Example 3 and Example 3 is that in step S1. of Comparative Example 3, 5 vol% AlGd30 powder + 95 vol.% GdH2 powder is used instead of 15 vol.% AlGd30 powder + 85 vol.% GdH2 powder in Example 3. The remaining preparation steps are the same as in Example 3, and AlGd30 / GdH2 bulk material is prepared.

[0081] Comparative Example 4

[0082] The difference between Comparative Example 4 and Example 3 is that in step S1. of Comparative Example 4, 50 vol% AlGd30 powder + 50 vol.% GdH2 powder is used to replace 15 vol.% AlGd30 powder + 85 vol.% GdH2 powder in Example 3. The remaining preparation steps are the same as in Example 3, and AlGd30 / GdH2 bulk material is prepared.

[0083] Comparative Example 5

[0084] The difference between Comparative Example 5 and Example 4 is that in step S1. of Comparative Example 5, 5 vol% MgGd10 powder + 95 vol.% GdH2 powder is used instead of 20 vol% MgGd10 powder + 80 vol.% GdH2 powder in Example 4. The remaining preparation steps are the same as in Example 4, and MgGd10 / GdH2 bulk material is prepared.

[0085] The phase composition of the bulk materials prepared in Examples 1-5 and Comparative Examples 1-5 was characterized by X-ray diffraction (XRD) (test method: step measurement, scanning angle: 20-80°; tube voltage: 40KV; tube current: 30mA).

[0086] XRD test results are as follows Figures 1-10 As shown, from Figures 1-3 As can be seen from the data, in addition to GdH2 powder, Al powder or Al-Gd alloy powder was added to the raw material powders in Examples 1-3. The bulk materials prepared by sintering contained not only the main phase GdH2, but also intermetallic compound phases of Al2Gd and Al3Gd. This confirms that an in-situ interfacial reaction occurred between Al or Al-Gd alloy and the surface of GdH2 particles during hot pressing, forming intermetallic compounds. No other phases were observed to form. Figure 4 , 5 As can be seen from the examples, in Examples 4 and 5, in addition to GdH2 powder, Mg-Gd alloy powder was added to the raw material powder. The bulk materials prepared by sintering contained not only the main phase GdH2, but also Mg phase or Mg phase and a small amount of MgH2 phase, and no other phases were observed to form, confirming that the sintering process achieved good phase stability and in-situ strengthening. Figure 6 As can be seen from the data, in Comparative Example 1, no low-melting-point alloys were added to the raw material powder except for GdH2 powder, and only the GdH2 phase was detected in the prepared bulk material. Figure 7 As can be seen from the data, in Comparative Example 2, Al-Gd alloy powder was added to the raw material powder in addition to GdH2 powder. The bulk material prepared by low-pressure sintering showed the presence of both GdH2 and Al2Gd phases, but no Al3Gd phase was detected. This is likely because the reaction between the Al-Gd alloy and GdH2 is weakened under low pressure. Figure 8 As can be seen, adding a small amount of Al-Gd alloy powder to the raw material powder of Comparative Example 3 resulted in the preparation of a bulk material in which, in addition to the GdH2 phase, the Al2Gd phase was also detected, but the Al3Gd phase was not detected. Figure 9 As can be seen, adding a large amount of Al-Gd alloy powder to the raw material powder in Comparative Example 4 resulted in bulk material containing not only the GdH2 phase, but also Al2Gd, Al3Gd, and Gd phases. During hot pressing, a large amount of Al-Gd alloy reacted violently with the surface of the GdH2 particles, generating Al2Gd and Al3Gd phases. Additionally, some hydrogen atoms from the GdH2 phase escaped as hydrogen gas from the material's interior, forming the Gd phase. Figure 10 It can be seen that when a small amount of Mg-Gd alloy powder is added to the raw material powder of Comparative Example 5, the bulk material prepared contains not only the GdH2 phase but also a small amount of Mg phase.

[0087] The actual density of the bulk materials obtained in Examples 1-5 and Comparative Examples 1-5 after sintering was determined by Archimedes' displacement method. In Comparative Example 1, the sintered bulk material was pure phase GdH2. The bulk density of GdH2 in Comparative Example 1 was calculated to be 90.00% using the formula η = actual density / theoretical density × 100% = 6.405 / 7.1168 × 100%.

[0088] XRD tests on the bulk materials of Examples 1-5 and Comparative Examples 2-5 showed significant changes in phase content. The density of the bulk materials was calculated using the formula η = actual density / refined density × 100%. Refined density = volume fraction of each phase after refinement × density of each phase (refined density) plus the sum of these. For example, the refined density of the bulk material in Example 1 = volume fraction of GdH2 after refinement × density of GdH2 + volume fraction of Al2Gd after refinement × density of Al2Gd + volume fraction of Al3Gd after refinement × density of Al3Gd. The volume fraction of each phase is calculated using the formula... In the formula: To obtain the mass fraction of the i-th phase after refinement, To obtain the refined density of the corresponding phases, i.e., the volume fraction of each phase, the Rietveld full-spectrum refinement calculation was performed: first, the mass fraction of each phase was refined, and then, combined with the refined density of the corresponding phase, the volume fraction of each phase was normalized according to the mass fraction to density ratio to obtain the volume fraction of each phase. The XRD refinement analysis results, actual density, and compaction density of the bulk materials of Examples 1-5 and Comparative Examples 2-5 are shown in Table 1.

[0089] Table 1. XRD refinement analysis results of bulk materials in Examples 1-5 and Comparative Examples 2-5

[0090] The microstructure of the bulk materials in Examples 1-5 and Comparative Examples 1-5 was tested using metallurgical microscopy and scanning electron microscopy (SEM), respectively. The test results are as follows: Figure 11 , 12 As shown in Figure 13. From Figure 11 It can be seen that the microstructure of the sintered bulk material without the addition of low-melting-point alloy in Comparative Example 1 has obvious porosity and is not dense; in the sintered bulk materials with Al, Al-Gd or Mg-Gd alloys added in Examples 1-5, the bright white Al-based, Al-Gd or Mg-Gd alloy binder phase in the metallographic images is uniformly filled in the gaps between the dark GdH2 particles, forming a continuous and complete matrix skeleton, which greatly eliminates the micron-sized pores that are easy to occur during the sintering of pure GdH2, resulting in a dense structure; at the same time Figure 12 The SEM images shown further confirm the good bonding state at the interface between the low-melting-point binder alloy and the GdH2 phase, indicating that the Al or Al-Gd or Mg-Gd alloy binder phase is optimized through in-situ reaction with GdH2 via liquid-phase coating, eliminating porosity and forming a dense microstructure. As shown in Table 1, compared to the 90% density of the bulk material in Comparative Example 1 without the addition of the low-melting-point alloy, the bulk density of Examples 1-5 is significantly increased to over 95%, reaching 96.98-98.14%. Figure 13It can be seen that in Comparative Example 2, low-pressure sintering was used. Although the binder phase could still react with the matrix to a certain extent to generate an Al2Gd reinforcing phase, due to the lack of sufficient external driving force, the Al-Gd liquid phase alloy could not effectively overcome capillary resistance to penetrate into the deep micropores. This resulted in a large number of interconnected and coarse micropores and unfilled areas in the metallographic structure, with a final density of only 80.21%, far lower than that of the high-pressure sintered bulk material. In Comparative Examples 3 and 5, a small amount of Al-Gd and Mg-Gd alloys were added to the raw material powders, respectively. The small amount of alloy liquid phase flow could not completely fill the interparticle gaps, and some residual pores still existed in the microstructure of the bulk material, with a density not reaching 93%. In Comparative Example 4, an excessive amount of Al-Gd alloy was added to the raw material powder. The alloy liquid phase flow completely filled the interparticle gaps, and the density of the bulk material reached 99.37%. However, a large amount of Al-Gd alloy reacted violently with GdH2 during hot pressing, and some hydrogen atoms escaped, significantly reducing the amount of hydrogen retained, which was not conducive to the shielding performance of the bulk material.

[0091] The hydrogen content ω of the bulk materials in each embodiment and comparative example was determined using the pulse melting-thermal conductivity method. H And according to formula n H / n Gd =(ω H / M H ) / [(ω GdH2 -ω H) / M Gd Calculate the H / Gd atomic ratio of the bulk material, where n H n Gd ω and ωH represent the amounts of hydrogen and gadolinium atoms in the bulk material, respectively; ωH is the mass fraction of hydrogen in the bulk material measured by the pulse melting-thermal conductivity method; ω GdH2 In the block GdH2 Phase mass fraction; M H M Gd The molar masses of hydrogen and gadolinium are given in Table 2. The calculation results are shown in Table 2.

[0092] The Vickers hardness of the bulk materials in each embodiment and comparative example was tested using a micro Vickers hardness tester according to GB / T 4340.1 standard. The test load was 5 kgf, and the loading time was 10 s. The compressive strength of the bulk materials in each embodiment and comparative example was tested using a universal testing machine according to GB / T 7314 standard. The displacement loading rate was 0.5 mm / min. The test results of Vickers hardness and compressive strength are shown in Table 2.

[0093] Table 2. H / Gd atomic ratio and mechanical properties of bulk materials from Examples 1-5 and Comparative Examples 1-5

[0094]

[0095] As shown in Table 2, compared to the bulk material prepared without the addition of low-melting-point alloys to the raw material powder in Comparative Example 1, the bulk materials prepared by adding Al or Al-Gd low-melting-point alloys in Examples 1-3 have higher hardness and strength. The main reason for this is that the Al-based alloy liquid has excellent fluidity and wettability, which can fill pores and increase the density of the sintered bulk material. Simultaneously, the Al-based binder phase undergoes an in-situ interfacial metallurgical reaction with the matrix particles, generating Al2Gd (phase content of 6-12 vol.%) and Al3Gd (phase content of 6-12 vol.%). High-hardness intermetallic compounds (containing 13-21 vol.%) are used in situ to reinforce the interface through atomic-level bonding, constructing a high-strength interfacial bonding layer. This significantly improves the bulk Vickers hardness and compressive strength while maintaining a high H / Gd atomic ratio (>1.9), resulting in excellent neutron shielding performance. The 20% addition in Examples 1 and 2, specifically Al2Gd (10-12 vol.%) and Al3Gd (19-21 vol.%), demonstrates particularly good performance. In Comparative Examples 3 and 5, the addition of small amounts of Al-Gd or Mg-Gd low-melting-point alloys did not significantly improve the bulk material density or performance. In Comparative Example 4, the addition of excessive Al-Gd low-melting-point alloys significantly reduced the H / Gd atomic ratio to 1.61, making it difficult to guarantee the neutron shielding performance of the bulk material. In Comparative Example 2, low-pressure sintering was used, which significantly reduced the effective load-bearing area of ​​the material due to its volumetric porosity and formed severe stress concentration sources inside, causing its Vickers hardness to collapse to 125 HV. In addition, this non-dense microstructure provides a fast channel with low energy barriers for the escape of hydrogen molecules. In the absence of high-pressure physical blockade, the H / Gd atomic ratio dropped to 1.87. This comparative analysis fully confirms the irreplaceable key role of high-pressure sintering process in eliminating microstructural defects, improving mechanical rigidity, and maintaining thermodynamic hydrogen content stability.

[0096] As shown in Table 2, compared to the bulk material prepared without the addition of low-melting-point alloy in the raw material powder of Comparative Example 1, the bulk materials prepared by adding Mg-Gd low-melting-point alloy in Examples 4 and 5 exhibit excellent liquid-phase fluidity at the sintering temperature. Following an efficient liquid-phase penetration and filling mechanism, it can quickly disperse and fill the micro-gap between particles, thereby achieving high density. Without violent interfacial reactions, the tough Mg-based alloy (Mg phase content of 18~21 vol.%) effectively eliminates stress concentration sources and plays a plastic buffering role, resulting in a significant increase in the bulk compressive strength (up to 365.4 MPa), nearly double that of the pure phase. At the same time, the Mg-based binder phase acts as an efficient "hydrogen molecule trap," intercepting hydrogen desorption by forming stable phases such as MgH2 (MgH2 phase content of 0~6 vol.%) in situ, maintaining a high H / Gd atomic ratio, and ensuring the material's excellent neutron shielding performance.

[0097] In summary, Mg-based binder phases, with their comprehensive advantages in compressive strength, densification efficiency, and hydrogen content retention, are the preferred solution for improving the service reliability of radiation shielding materials. Al-based binder phases, relying on their unique in-situ metallurgical interface strengthening mechanism, possess irreplaceable technical advantages in high-hardness and high-rigidity construction. The performance gradient formed by these two phases provides solid experimental and theoretical support for the customized development of high-performance radiation shielding materials for different practical operating conditions.

[0098] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A dense GdH2 bulk material bonded by a low-melting-point alloy, characterized in that, The bulk material is prepared by sintering raw material powder comprising GdH2 and a low-melting-point binder alloy; wherein the low-melting-point binder alloy is selected from at least one of Al, Al-Gd alloy or Mg-Gd alloy, and the content of the low-melting-point binder alloy is 10~30% by volume percentage of the raw material powder.

2. The dense GdH2 bulk material bonded with a low-melting-point alloy according to claim 1, characterized in that, The Al-Gd alloy includes at least one of AlGd10 or AlGd30, and the Mg-Gd alloy includes at least one of MgGd10 or MgGd20.

3. The low-melting-point alloy-bonded dense GdH2 bulk material according to claim 1 or 2, characterized in that, When the low-melting-point binder alloy is selected from at least one of Al or Al-Gd alloy, the phase structure of the bulk material includes GdH2 phase, Al2Gd phase and Al3Gd phase; the content of Al2Gd phase is 6%~12% by volume percentage of the total of each phase, the content of Al3Gd phase is 13%~21%, and the balance is GdH2 phase; When the low-melting-point binder alloy is selected from Mg-Gd alloy, the phase structure of the bulk material includes GdH2 phase and Mg phase, or includes GdH2 phase, Mg phase and MgH2 phase; the content of Mg phase is 18%~21% by volume percentage of the total of each phase, the content of MgH2 phase is 0%~6%, and the balance is GdH2 phase.

4. The dense GdH2 bulk material bonded by a low-melting-point alloy according to claim 3, characterized in that, The content of the Al2Gd phase is 10%~12%, the content of the Al3Gd phase is 19%~21%, and the balance is GdH2 phase; or, The content of the Mg phase is 18%~21%, and the balance is GdH2 phase.

5. The dense GdH2 bulk material bonded with a low-melting-point alloy according to claim 1 or 2, characterized in that, The density of the bulk material is above 95%; and / or, The H / Gd atomic ratio of the bulk material is 1.9 or higher; and / or, When the low-melting-point binder phase alloy is selected from at least one of Al or Al-Gd alloy, the Vickers hardness of the bulk material is 280~310HV and the compressive strength is 179~195MPa. When the low-melting-point binder alloy is selected from Mg-Gd alloy, the Vickers hardness of the bulk material is 185~200HV and the compressive strength is 300~370MPa.

6. A method for preparing a dense GdH2 bulk material bonded with a low-melting-point alloy as described in any one of claims 1 to 5, characterized in that, The preparation steps include the following: S1. Raw material powder weighing: Weigh GdH2 powder and low melting point binder phase alloy powder according to the ratio; S2. Raw material powder mixing: The GdH2 powder and the low-melting-point binder phase alloy powder are mixed evenly; S3. Raw material powder sintering: The mixed raw material powder is hot-pressed and sintered at a temperature between the melting point of the low melting point binder alloy and the peak value of the main dehydrogenation temperature of GdH2, and at a sintering pressure of 200 MPa or higher.

7. The method for preparing a dense GdH2 bulk material with low melting point alloy bonding according to claim 6, characterized in that, In step S1, the particle size ratio of the GdH2 powder and the low-melting-point binder phase alloy powder is 20~150μm:0.5~300μm.

8. The method for preparing a dense GdH2 bulk material bonded with a low melting point alloy according to claim 6, characterized in that, In step S2, the raw material powder is mixed by ball milling with a ball-to-material ratio of 3~20:1, a ball milling speed of 50~1000 rpm, and a ball milling time of 1~30 h.

9. The method for preparing a dense GdH2 bulk material bonded with a low melting point alloy according to claim 6, characterized in that, In step S3, the sintering temperature is 600~780℃, the sintering pressure is 200~650MPa, the sintering time is 1~15min, and the hot pressing sintering is carried out in an inert protective atmosphere.

10. The method for preparing a dense GdH2 bulk material bonded with a low melting point alloy according to claim 6, characterized in that, In step S3, before the hot pressing sintering begins, the raw material powder is pre-pressed at a pressure of 300 MPa to 650 MPa.

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