Pure Tungsten Research Articles

Effect of contact materials on the transient characteristics of vacuum arc plasma and anode erosion

In this study, the mechanisms of the anode phenomena and anode erosion with various contact materials were investigated. Arc parameters were calculated, and the anode temperature was predicted with a transient self-consistent model. The simulation results predicted a constricted arc column and obvious anode phenomena in Cu–Cr alloy contacts than in W–Cu alloy contacts. This observation could be the reason for the concentrated anode erosion in Cu–Cr alloys. For the contacts made by pure tungsten (W) and W–Cu alloy, the anode temperature increased rapidly because of the low specific heat of W. However, the maximum energy flux from the arc column to the anode surface was lower than in other cases. The simulation results were compared with experimental results.

Large-Size and Ultrahigh Purity Tungsten with Enhanced Physical Properties via Chemical Vapor Deposition.

Conventional powder metallurgy techniques fail to meet the demands for ultrahigh purity tungsten (UHPW) and scalable component sizes required by the semiconductor industry. In this study, ultrahigh purity (99.999998 wt %) large-size tungsten parts, with an adjustable thickness and a diameter of 350 mm, were prepared via a chemical vapor deposition (CVD) method using ultrahigh purity (99.9999 wt %) tungsten hexafluoride (WF6) as the precursor. The microstructure and physical properties of the resulting CVD-UHPW were evaluated and compared with those of powder metallurgy tungsten (PM-W). The results indicate that CVD-UHPW displays a columnar grain microstructure with a lower dislocation density and internal strain, whereas PM-W shows an equiaxed grain microstructure. CVD-UHPW has a density of 19.17 g/cm3, closely matching the theoretical density of tungsten (19.35 g/cm3) and significantly higher than PM-W's density of 18.79 g/cm3. The specific heat capacities of CVD-UHPW, measured from 298 to 1473 K, range from 0.113 to 0.146 J/g·K, similar to PM-W's range of 0.120 to 0.151 J/g·K. CVD-UHPW shows improved electrical and thermal conductivities compared to PM-W, with values ranging from 1.68 × 106 to 1.78 × 107 S/m and 105.7 to 196.4 W/(m·K) from 298 to 1473 K. This study highlights the potential of the CVD method for the large-scale production of ultrahigh purity tungsten parts, emphasizing its significant applicability across various industries.

Quantitative analysis of transmutation nuclides in pure tungsten irradiated with high-energy protons and spallation neutrons at 6.4 and 28 dpa

Tungsten is a key material for applications of spallation targets and fusion reactors. Irradiation-induced transmutation products can significantly affect the mechanical and thermal properties of tungsten. However, detailed quantitative analysis of transmutation elements of irradiated tungsten has not been reported and is therefore in high demand, especially in the cases of spallation targets where a large amounts of transmutation elements are produced. In this work, we analyzed the transmutation products in pure tungsten samples irradiated in a target of Swiss Spallation Neutron Source (SINQ) at doses of 6.4 and 28 dpa, the latter being the highest dose ever achieved in spallation targets. Quantitative measurements of 40 nuclides ranging from 144Sm to 188Os were performed using the atom probe tomography (APT) technique. The measured concentrations of transmutation elements are in good agreement with those of neutronic calculations. The APT analysis also revealed clusters of transmutation elements. Due to low irradiation temperature (<500 °C) and low concentration of transmutation elements, the clusters are 1–2 nm in diameter.

Excellent radiation resistance via enforced local non-directional He diffusion in a WTaCrV multicomponent alloy containing coherent ordered nanoprecipitates

We design and investigate a W15Ta15Cr35V35 (at.%) multicomponent alloy (MCA) with exceptional radiation resistance. The sintered WTaCrV alloy exhibits a body-centered cubic (BCC) matrix with dispersed coherent ordered nanoprecipitates. After ∼3-hour irradiation under 400 keV He+ at room temperature (RT) and 450°C with a fluence of 2 × 1017 ions/cm2, the irradiation hardening values of the MCA are about a quarter of those of pure tungsten counterparts irradiated at identical conditions. Besides, helium bubbles generated in the irradiated matrix of the MCA are much smaller, compared with those in the pure tungsten and other tungsten-rich alloys previously reported. The exceptional radiation resistance of the present WTaCrV alloy can be mainly attributed to two synergistic mechanisms. First, the high lattice distortion of the solid solution matrix promotes the local non-directional diffusion of irradiation defects, effectively suppressing the aggregation of irradiation defects and helium atoms along specific orientations. This facilitates more uniform nucleation of helium bubbles in the alloy matrix. Second, carbon was introduced during fast hot pressing sintering as interstitial solute to form carbon-rich coherent ordered nanoprecipitates. The carbon-vacancy complexes generated in the nanoprecipitates inhibit the nucleation and aggregation of helium atoms at the vacancies during He+ irradiation. The above two mechanisms synergistically enhance the resistance against He+ irradiation. This work thus demonstrates a design strategy for high radiation resistance alloys by introducing well-tuned ordered coherent nanoprecipitates in multicomponent alloy systems.

Dynamic failures at the metal-glass interface under impact loading

To investigate dynamic fracture behavior in the metal, three metal spheres (e.g., steel sphere, high purity tungsten sphere, and high purity lead sphere) are accelerated by the gas gun devices to impact glass spheres under the critical speed range (i.e., from 70 m/s to 210 m/s). The velocity interferometer system for any reflector (VISAR) devices are employed to measure the particle velocities at the back surface of glass sphere, and high-speed photographs are utilized to capture the failure process at the metal-glass interface. Due to the asynchronous evolutions of stress fields and strain fields in the violent failure process, the results illustrate quite different failure mechanisms from those by the Split Hopkinson Pressure Bar (SHPB) impacting. Fragmentations of the glass sphere are caused mainly by the radial cracks and the lateral cracks around the metal-glass interface and the edges of the sphere with increasing impact velocity. Dynamic failures in the three metal impactors exhibit different modes, e.g., tensile fracture in the steel impactor, shear fracture in the tungsten impactor, and compressed yielding in the lead impactor. The transferring of strain energy releasing is introduced to describe the failure behavior at the metal-glass interface, and a relaxation-diffusion equation of strain energy releasing is then established based on the experimental results and the numeric results by the discrete element method (DEM). The evolutions of failures at the metal-glass interface are discussed. Further investigation is conducted to describe the dynamic fractures in tungsten impactors and steel impactors based on the dimensional analyses, and the quantitative expressions of these strain rate dependent fracture strains and crack width in the metal impactors are obtained. The results are helpful for the profound understanding of the dynamic fracture in the metal structures and the dynamic fragmentations in the brittle material when subjected to impact loading.

Multi-objective, multi-constraint high-throughput design, synthesis, and characterization of tungsten-containing refractory multi-principal element alloys

Refractory multi-principal element alloys (RMPEAs) have gained interest recently due to their superior properties at elevated temperatures, including outstanding yield and ultimate strengths, high thermal conductivity, and resistance to creep. RMPEAs can be designed to exhibit a wide range of properties by tailoring their composition. However, the vast chemical design space makes brute-force experimental screening inefficient and costly. In this work, we follow a closed-loop, iterative computational/experimental screening approach that combines computational alloy design methodologies with high-throughput synthesis and characterization tools to explore the vast RMPEAs space and design new RMPEAs that satisfy multiple objectives and constraints. In particular, we targeted compositions with yield strengths higher than 50 MPa at 2000 °C, W content of more than 30 at.% for high-temperature strength and operability up to 2000 °C, narrow solidification range for additive manufacturability, competitive ductility metrics, among other property constraints. We evaluated the mechanical properties and microstructure of 58 alloys designed in 5 batches, in both as-cast and homogenized conditions, synthesized using vacuum arc melting, utilizing scanning electron microscopy, X-ray diffraction, Vickers microhardness, nanoindentation, and high-temperature compression testing. Based on the microhardness screening experiments in each batch, the best-performing alloys were selected for scale-up. High-temperature compression at 1800 °C was performed in these alloys, demonstrating that the designed alloys exhibit up to five times higher yield strength than a pure tungsten benchmark. We conclude that W-containing RMPEAs designed in this study merit further consideration for next-generation structural materials for ultra-high temperature applications.

An investigation of the microstructure and properties of rolled W-Al2O3 alloy

Pure tungsten and tungsten alloys have been widely used in metallurgy, energy, chemical industry, aerospace, national defense, electronics and other fields. However, there are inevitably some problems in the use of the process, such as high deformation resistance in the forming process prone to crack and fracture, coarse grain and low bending strength problems. Al2O3 particles were added to improve the comprehensive properties of tungsten alloys. In this paper, the W-0.2 wt%Al2O3 tungsten alloy sheets with different thicknesses of 3 mm, 2 mm, and 1 mm were prepared by induction sintering combined with hot rolling. For comparison, the pure tungsten sheet with a thickness of 3 mm was fabricated by the same preparation process. Comparative assessments were made on the microstructure, hardness, and three-point bending properties across types of three thicknesses of W-Al2O3 sheets and pure tungsten sheet with a thickness of 3 mm. The outcomes demonstrate that the microstructure and properties of the tungsten alloy vary considerably depending on the applied rolling degree, which exerts a profound impact on the grain size, morphology, and distribution within the tungsten alloy matrix. Furthermore, the tungsten alloy consistently exhibits significant enhancements over pure tungsten. Characterization of the rolled tungsten alloy revealed that the incorporation of alumina contributes to a reduction in shear band formation and an improvement in texture strength, thereby substantiating its positive impact on the overall mechanical properties of the alloy.

Integrated experimental and computational study on the effect of hydrogen in mechanical responses of pure tungsten

Hydrogen irradiation profoundly changes the microstructure and morphological characteristics of tungsten, ultimately resulting in the modifications to its mechanical properties. Unfortunately, the specific mechanisms through which hydrogen irradiation influences the mechanical behavior of tungsten have not been clearly elucidated. Therefore, this study aims to further improve the understanding of the impact of hydrogen irradiation on the mechanical responses and its microstructure dependence in tungsten by employing two advanced techniques: nano-indentation experiments and Molecular dynamics (MD) simulations. The experimental findings revealed that deuterium (D) exposure decreased the maximum shear stress required for the incipient plasticity and led to the occurrence of multiple pop-ins. Particularly noteworthy was the most remarkable change in mechanical behaviors observed prominently in the recrystallized tungsten after D exposure. The microstructure dependence of irradiation-induced change in mechanical responses was investigated by two series of MD simulation, indentation and dislocation glide simulation, focusing on the independent effects of each irradiation-induced defect type (interstitial, substitutional, vacancy, vacancy-hydrogen (Vac-H) cluster, void-hydrogen (Vo-H) cluster) on dislocation activities. Based on the MD simulations, it was eventually revealed that Vo-H clusters were the most influential agent affecting dislocation activities. They not only lowered the pop-in stress by heterogeneous dislocation nucleation but also caused strain serration by a continuous pinning/unpinning process during dislocation glide. Consequently, we concluded that the dominant presence of d-induced Vo-H clusters facilitated the onset of plastic yielding and led to multiple pop-in phenomena in recrystallized tungsten, whereas inserted hydrogen caused minimal change in mechanical responses by interacting with pre-existing dislocation in cold-rolled tungsten.

Simulation and Experimental Investigation on Additive Manufacturing of Highly Dense Pure Tungsten by Laser Powder Bed Fusion.

Tungsten and its alloys have a high atomic number, high melting temperature, and high thermal conductivity, which make them fairly appropriate for use in nuclear applications in an extremely harsh radioactive environment. In recent years, there has been growing research interest in using additive manufacturing techniques to produce tungsten components with complex structures. However, the critical bottleneck for tungsten engineering manufacturing is the high melting temperature and high ductile-to-brittle transition temperature. In this study, laser powder bed fusion has been studied to produce bulk pure tungsten. And finite element analysis was used to simulate the temperature and stress field during laser irradiation. The as-printed surface as well as transverse sections were observed by optical microscopy and scanning electron microscopy to quantitatively study processing defects. The simulated temperature field suggests small-sized powder is beneficial for homogenous melting and provides guidelines for the selection of laser energy density. The experimental results show that ultra-dense tungsten bulk has been successfully obtained within a volumetric energy density of 200-391 J/mm3. The obtained relative density can be as high as 99.98%. By quantitative analysis of the pores and surface cracks, the relationships of cracks and pores with laser volumetric energy density have been phenomenologically established. The results are beneficial for controlling defects and surface quality in future engineering applications of tungsten components by additive manufacturing.

Conceptional Pure-Tungsten Metasurfaces Based on Femtosecond Laser Nanomanufacturing

A laser-induced periodic surface structure (LIPSS), which can be easily produced by femtosecond laser ablation, is a unique nanostructure with a visible refractive color that can be controlled by altering its orientation and uniformity, making it suitable for use in colorful marking, camouflage, and anti-counterfeiting measures. However, single-mode information camouflage can no longer meet increasingly higher-level security requirements. Therefore, metasurfaces offer revolutionary solutions. In this study, conceptual metasurfaces of pure tungsten are theoretically proposed and verified using hierarchical LIPSS/nanoparticle (NP) nanostructures as meta-atoms. The anisotropy of the LIPSS nanostructure enables polarization-sensitive optical modulation, whereas the spatial configuration, particle size, and period of LIPSS in the LIPSS/NP meta-atoms provide flexibility for tailoring broadband optical responses. In x-polarization, the LIPSS/NP meta-atom system provides more visible colors and divergent infrared absorbance (emission) than in y-polarized and unpolarized modes, paving the way for vividly colorful polarization-sensitive displays and information camouflage in infrared bands. A simplified rendition of the world-famous painting “The Starry Night” by Van Gogh is used as a proof-of-concept. Preliminary experimental results are presented, based on which the feasibility and challenges for laser nanomanufacturing of the proposed conceptual metasurfaces are discussed, aiming to provide inspiration for the development of novel metasurfaces through interdisciplinary studies.

Experimental study of micro-prismatic electrode array wear during EDM and application to the preparation of microcylindrical electrode array

The focus of this study is to compare the wear characteristics of different types of micro-prismatic electrode array during EDM, and to propose a method for preparing microcylindrical electrode array based on micro-prismatic electrode array. Firstly, the characteristic of the micro-prismatic electrode that the front cross-section becomes circular after wear during EDM is clarified, and the wear form of the micro-prismatic electrode is analyzed. Then, the laws of the influence of electrode shape (triangle, square, hexagon), electrode material (pure copper, copper-tungsten alloy, pure tungsten), electrode size (200 μm, 300 μm, 400 μm) on the wear characteristics of the micro-prismatic electrode array, including the length of the wear of each part of the electrodes, the length of the area of the front cross-section that becomes rounded, the consistency of the wear of the electrode array, the machining efficiency, and electrode wear rate are summarized. After that, the process of changing the electrode array from square columns to cylinders using the new method is given, which confirms the feasibility of the method. Finally, the effects of peak current and pulse width on the size, machining efficiency, surface roughness, and surface micro-morphology of micro-cylindrical electrode array prepared by the new method are summarized. This study is of great significance for achieving mass production of microcylindrical electrode array.

Research on Microstructure, Mechanical Properties, and High-Temperature Stability of Hot-Rolled Tungsten Hafnium Alloy.

W-(0, 0.1, 0.3, 0.5) wt.% Hf (mass fraction, wt.%) materials were fabricated by the powder metallurgy method and hot rolling. The microstructure, mechanical properties, and high-temperature stability of alloys with varying compositions were systematically studied. The active element Hf can react with the impurity O segregated at the grain boundary to form fine dispersed HfO2 particles, refining the grains and purifies and strengthening the grain boundary. The average size of the sub-grains in the W-0.3 wt.% Hf alloy is 4.32 μm, and the number density of the in situ-formed second phase is 6.4 × 1017 m-3. The W-0.3 wt.% Hf alloy has excellent mechanical properties in all compositions of alloys. The ultimate tensile strength (UTS) is 1048 ± 17.02 MPa at 100 °C, the ductile fracture occurs at 150 °C, and the total elongation (TE) is 5.91 ± 0.41%. The UTS of the tensile test at 500 °C is 614 ± 7.55 MPa, and the elongation is as high as 43.77 ± 1.54%. However, more Hf addition will increase the size of the second-phase particles and reduce the number density of the second-phase particles, resulting in a decrease in the mechanical properties of the tungsten alloy. The isochronal annealing test shows that the recrystallization temperature of W-Hf alloy is 1400 °C, which is 200 °C higher than rolling pure tungsten.

Indium-doped tungsten oxide architectures anchored on 2D rGO Matrix with enhanced visible-light-response and efficient charge separation for photocatalytic degradation of organic pollutants

Visible-light-responsive photocatalysis has been recognized as a sustainable strategy to address environmental pollution, but semiconductor-based photocatalysts often suffer from many shortcomings, including low visible light absorption and rapid recombination of photo-generated charge carriers. In this regard, rationally designed composite materials have gained substantial prominence, as achieving an ideal photocatalyst's characteristics in a single component material is frequently difficult. In the present study, we have synthesized pure (WO3) and indium-doped tungsten oxide (In-WO3) by the facile solvothermal route. The doped material was anchored on a 2D rGO matrix to fabricate the In-WO3/rGO composite. The structural, morphological, electrical, and optical properties of the as-synthesized materials were investigated as a function of doping and composite fabrication by various physical and electrochemical techniques. The comparative photocatalytic performance was evaluated by degrading Congo Red (CR) dye and paracetamol (PCM) drug. The composite material shows degradation efficiencies of ∼96 % (K=0.0174 min−1) and ∼91 % (K=0.0144 min−1) for CR dye and PCM drug, respectively. The boosted catalytic performance corresponds to the declined band gap (2.53 eV) and increased conductivity (0.1270 Sm−1), which enhances its visible light absorption and a surge in the charge carrier's population. The kinetics, relative contribution of different active species generated, and the potential mechanism of photodegradation reaction are discussed in detail. The significant increase in photocatalytic performance of the fabricated In-WO3/rGO composite discloses its promising catalytic potential for the degradation of recalcitrant organic pollutants.

Temperature dependence of the friction and wear behavior of pure tungsten

In this work, the friction and wear characteristics of rolled pure tungsten were investigated by using atomic force microscope (AFM) and field emission scanning electron microscope (SEM) with electron backscatter diffraction (EBSD) characterization techniques. A ductile to brittle transition (DBT) related frictional wear behaviors have been discovered. The results indicated that the coefficient of friction maintains an almost constant value of 0.45 at low temperatures (≤ 400 °C), whereas it consistently decreases at 600 °C due to the generation of a surface oxide. The wear rate varies with temperatures and reaches a maximum at 200 °C due to the transition of the tungsten matrix from brittleness to pseudoplasticity, which leads to severe adhesive wear and large mass loss. In addition, the evolution of sub-grains underneath the friction layer and Vickers microhardness were evaluated as well. This work provides insight into understanding the relationship between temperatures, microstructure and the frictional properties of tungsten materials, and thus provides guidance for improving frictional wear behaviors in tungsten materials.

Exploring the impact of pre-existing helium bubbles on nanoindentation in tungsten through molecular dynamics simulation

Gaining insight into the underlying mechanisms driving nanoindentation-induced behavior in tungsten is essential for comprehending its mechanical properties. Although the plasticity of conventional pure tungsten under nanocontact conditions is well understood, these theoretical constructs may become inadequate when applied to irradiated tungsten due to the interplay between helium bubbles and dislocations. Here, we employed an integrated approach, combining crystal defect theories, molecular dynamics simulations, and machine learning, to explore the initiation and progression of dislocations in tungsten containing helium bubbles during nanoindentation, focusing on elucidating the impact of helium bubbles. In contrast to the typical dislocation nucleation in pure tungsten, the presence of helium bubbles mitigates local shear strain, thereby hindering dislocation nucleation and propagation, leading to a reduction of indentation force. Additionally, we conducted a comparative analysis between samples with and without helium bubbles, examining factors such as atomic displacement, strain localization parameters, dislocation line length, and stress component distribution. More importantly, a significant outcome of our study is the establishment of a relationship between the consistent alteration in the shape of helium bubbles and their size during micro-scale nanoindentation, achieved through machine learning techniques. Our findings reveal that the area occupied by helium bubbles post-nanoindentation is inversely correlated with indentation depth and directly linked to helium bubble size. These discoveries represent a notable advancement in understanding the effects of irradiation to a certain degree.

Structure and properties of powders obtained by electrodispersion of pure tungsten metal waste in distilled water

Purpose. Investigation of the composition, structure and properties of powder materials obtained by electrodispersion of tungsten waste of the VA brand in an oxygen–containing medium - distilled water. Methods. To determine the composition, structure and properties of powder materials, samples of powders obtained from waste tungsten of the VA brand were studied. The powder material was obtained by electroerosive dispersion in distilled water. Microanalysis of powder particles was carried out using a scanning electron microscope, analysis of the size distribution of powder particles was obtained using a particle size analyzer, X-ray spectral microanalysis of powder particles was carried out using an energy dispersive X-ray analyzer integrated into a scanning electron microscope, analysis of the phase composition of powder particles was carried out using X-ray diffraction on a diffractometer. Results. During the study, it was revealed that the shape of the particles obtained from powdered tungsten materials is spherical and elliptical, and agglomerates of smaller particles are also marked on magnification. Oxygen and tungsten are present in the composition of powder materials, while there are no joint structural components. The phases of pure tungsten in α and β modifications are noted in the phase composition. It follows from the analysis of the granulometric histogram that the particle size spread varies in the range of 0.092–62.59 microns, while the average particle diameterwas 5.73 microns. Conclusion. The obtained research results can be used to develop a new heavy pseudo-alloy using metal waste of expensive raw materials by the method of electroerosive dispersion with subsequent improvement and optimization of the composition and structure of the alloy.

Preparation of high-density and excellent bending strength pure tungsten target by hot oscillatory pressing sintering and its magnetron sputtering coating

The high-strength, high-density pure tungsten (W) targets were fabricated using hot oscillatory pressing (HOP) sintering. This study examined the influence of sintering temperature, oscillation frequency, amplitude, and median pressure on the relative density, grain size, and bending strength of the tungsten targets. A tungsten target exhibiting a relative density of 99.51%, a grain size of 2.95 μm, a bending strength of 1200.1 MPa, and a purity of 99.95% was synthesized at a sintering temperature of 1600 °C, an oscillation pressure of 60 ± 15 MPa, and a frequency of 1 Hz. Grain rearrangement and plastic deformation (dislocation movement and grain boundary slip) were identified as the primary mechanisms for grain refinement and densification, respectively. The key strengthening mechanism was sub-grain boundary strengthening. The optimal tungsten target was utilized for magnetron sputtering on a reduced activation ferritic/martensitic (RAFM) steel substrate. The effects of sputtering time, power, deposition pressure, and substrate temperature on the crystallinity, roughness, thickness, and bonding force of the tungsten films were investigated. The optimal magnetron sputtering process was achieved by sputtering for 45 min at a power of 60 W, a deposition pressure of 15 Pa, and a substrate temperature of 100 °C. This resulted in dense W films with excellent comprehensive properties, including a roughness of Ra = 8.73 nm, Rq = 3.34 nm, a thickness of 999.05 nm, and a bonding force of 2.57 N.

Discovering tungsten-based composites as plasma facing materials for future high-duty cycle nuclear fusion reactors

Despite of excellent thermal properties and high sputtering resistance, pure tungsten cannot fully satisfy the requirements for plasma facing materials in future high-duty cycle nuclear fusion reactions due to the coupled extreme environments, including the high thermal loads, plasma exposure, and radiation damage. Here, we demonstrated that tungsten-based composite materials fabricated using spark-plasma sintering (SPS) present promising solutions to these challenges. Through the examination of two model systems, i.e., tungsten-zirconium composite for producing porous tungsten near the surface and dispersoid-strengthened tungsten, we discussed both the strengths and limitations of the SPS-fabricated materials. Our findings point towards the need for future studies aimed at optimizing the SPS process to achieve desired microstructures and effective control of oxygen impurities in the tungsten-based composite materials.

Effect of nanosecond laser irradiation on tungsten grain structure

The laser-induced grain structure of pure tungsten was evaluated using a nanosecond Q-switched Nd:YAG laser. The grain structure, crystal orientation, and grain boundary angular distribution were analyzed through electron backscatter diffraction analysis, both before and after laser processing. The mechanical properties of pure tungsten after laser processing were also measured. The results obtained indicate that laser processing-induced recrystallization can offer micro-nano surface treatment of materials without compromising the mechanical properties.

The Influence of Rhenium Content on Helium Desorption Behavior in Tungsten-Rhenium Alloy.

To investigate the influence of different rhenium contents on the helium desorption behavior in tungsten-rhenium alloys, pure tungsten and tungsten-rhenium alloys were irradiated with helium under the same conditions. All irradiated samples were characterized using TDS and DBS techniques. The results indicate that the addition of rhenium can reduce the total helium desorption quantity in tungsten-rhenium alloys and slightly accelerate the reduction in the concentration of vacancy-type defects accompanying helium dissociation. The desorption activation energy of helium is approximately 2 eV at the low-temperature peak (~785 K) and about 4 eV at the high-temperature peak (~1475 K). An increase in rhenium content causes the desorption peak to shift towards higher temperatures (>1473 K), which is attributed to the formation of the stable complex structures between rhenium and vacancies. Besides, the migration of He-vacancy complexes towards traps and dynamic annealing processes both lead to the recovery of vacancy-type defects, resulting in a decrease in the positron annihilation S parameters.