Examinando por Autor "Izaguirre, I."

Mostrando 1 - 5 de 5

Exploration and optimization of copper-based alloys incorporating amorphizing elements for heat transfer applications
(Elsevier, 2024-02) Izaguirre, I.; Prado, J. de; Rosero-Romo, J.J.; Sánchez, M.; Salazar, D.; Ureña, A.
Attaining an amorphous crystalline structure imparts unique properties to certain metallic alloys that are impossible to achieve with conventional crystalline alloys. This current study investigates the amorphization potential of small additions of Zr, Ni, or V in Cusingle bondTi alloys produced using the melt-spinning technique. The alloys are characterized using X-ray diffraction (XRD), differential thermal analysis (DTA), differential scanning calorimetry (DSC), and transmission electron microscopy (TEM) techniques. The need for filler materials with flexible and adaptable properties for joining the first wall and divertor components of future fusion reactors can be addressed by producing filler ribbons with amorphous structures. The results indicate that a combination of Zr (12 at. %) and Ni (8 at. %), when used as alloying elements with appropriate processing parameters such as a rectangular nozzle of 0.5 × 8.8 mm2 and a linear wheel speed of 30 m/s, can produce an amorphous structure. Only isolated nanocrystalline phases were detected by TEM analysis. As a result, ribbons fabricated under these conditions were several times longer and wider than those made using the Cusingle bondTi master alloy. More importantly, they exhibit enough flexibility to conform to and cover a simulated pipe of the reactor. Conversely, the addition of V led to the formation of brittle phases. Ribbons fabricated under the optimal conditions were tested as filler materials in W-CuCrZr joints at 960 °C and were microstructurally and mechanically characterized, demonstrating their suitability for the intended application
Exploring W-EUROFER brazed joints: S/TEM and nanoindentation analysis following post-brazing tempering treatment
(Elsevier, 2025-01) Izaguirre, I.; Roldán, M.; Prado, J. de; Bonache, V.; Sánchez, M.; Ureña, A.
Tempering treatments are essential for restoring the hardness and microstructure of EUROFER steel when W-EUROFER joints are formed at temperatures exceeding the steel's austenitization point (890 °C). This post-brazing heat treatment can, however, alter the microstructure and thereby affect the mechanical properties. This study explores the microstructural and nanomechanical effects in the brazed area of W-EUROFER joints following this heat treatment, utilizing copper as an intermediate filler material. Using Scanning Transmission Electron Microscopy (STEM) with Energy Dispersive Spectroscopy (EDS) on FIB lamellae and nanoindentation techniques we examined the stability and phase characteristics of the post-tempered microstructure in two lamellae that covers the whole phases of the braze microstructure. The tempering process enhances copper diffusion and the growth of copper precipitates without significantly altering the joint's overall microstructure. Despite the general stress-relief effects of tempering, which typically lower mechanical properties, the diffusion phases formed during brazing maintained high hardness and modulus, indicative of a complex, element-rich composition. A reduction in mechanical properties was observed in the iron-rich phase near the W-braze interface and the EUROFER base material, aligning with the purpose of the heat treatment. However, the copper braze and tungsten base material largely retained their stability and resilience to thermal treatments. This research provides vital insights into the behavior of these material systems under thermal processing, highlighting the necessity of optimizing heat treatment parameters to preserve joint integrity in high-performance applications such as nuclear fusion reactors. The findings contribute significantly to the development of durable and reliable materials for fusion energy, emphasizing the importance of controlled tempering processes to enhance material properties
Numerical and experimental development of cupronickel filler brazed joints for divertor and first wall components in DEMO fusion reactor
(Elsevier, 2023) Díaz-Mena, Víctor; de Prado, J.; Roldán, M.; Izaguirre, I.; Sánchez, M.; Rieth, M.; Ureña, A.
The brazeability of a cupronickel commercial alloy (Cu10Ni) was evaluated for its use as a filler alloy for high-temperature joining of tungsten to the reduced activation ferritic/martensitic steel EUROFER 97 (W-E) and between tungsten base materials (W-W) for its application at the first wall and divertor of future fusion reactors. In addition, given the importance of the residual stresses in these heterogenous joints, a study of the brazing conditions and the impact of the selected filler has been conducted using numerical software to understand its impact on the quality of the joint. Two thermal cycles were evaluated (1165 °C and 1190 °C) and selected based on the thermal characterization of the filler alloy. The microstructural examination revealed that, in W-E joints, nickel acts as an activator element, reacting and forming interfacial layers at the EUROFER 97 - Cu10Ni interface. In the case of the W-W joints, a lower level of diffusion phenomenon and metallurgical interaction between Cu10Ni and base materials were observed. The hardness profile indicated that the hardening process of EUROFER 97 was associated with the formation of untempered martensite. On the other hand, tungsten kept the received hardness. The mechanical characterization by shear test reported similar values between both types of joints carried out at 1190 °C but different when the temperature was increased (1165 °C), associated with the brittle character of tungsten and its lower metallurgical interaction. The numerical analysis of the brazing process carried out with ANSYS software shows that residual stresses are accumulated mainly at the interfaces. The information provided by the simulation shows, for a 50 µm filler thickness, the importance of mitigating the residual stress by selecting a filler with an intermediate Coefficient of Thermal Expansion (CTE) that alleviates mechanical stresses relative to the base materials.
Thermal fatigue response of W-EUROFER brazed joints by the application of High Heat Flux loads
(Elsevier, 2023) Izaguirre, I.; Loewenhoff, T.; Prado, J. de; Sánchez, M.; Wirtz, M.; Díaz-Mena, V.; Ureña, A.
The thermal fatigue effect on the microstructure and mechanical properties of the joints that form some components of the future fusion reactor is a concern within the scientific community. In this study, we analyze the metallurgical modifications caused by thermal fatigue and their impact on the mechanical properties of tungstenEUROFER brazed joints (blocks measuring 6 × 6 × 4 mm). We conduct the analysis using an actively cooled mock-up subjected to steady-state thermal loads, which provides valuable information about the operating conditions of the reactor. Three different surface conditions of tungsten were evaluated: 600 ºC (2 MW/m2 ), 700 ºC (2.5 MW/m2 ), and 800 ºC (3 MW/m2 ), with varying numbers of applied cycles ranging from 100 to 1000. Throughout the tests, infrared cameras and pyrometers were used to analyze the thermal behavior of the WEUROFER joint. At 600 ºC and 700 ºC target temperatures, no anomalies in the heating and cooling capacity of the W-EUROFER joint were observed. This represents an advancement compared to previous studies that employed Cu20Ti filler, as it demonstrates consistent and efficient cooling capabilities even at surface temperatures of up to 700 ºC, without any notable anomalies starting from the previous filler’s 500 ºC. However, in the case of 800 ºC, the test had to be prematurely stopped. Microstructural analysis revealed the formation of cracks in some cases due to the stresses generated by the mismatch in the coefficient of thermal expansion between the materials used. These cracks affected the mechanical integrity of the joint.
W-EUROFER97 brazed joints using Ag, Au, and Cu-based fillers for energy applications: A microstructural and mechanical study
(Elsevier, 2024-12) Díaz-Mena, V.; Prado, J. de; Izaguirre, I.; Carreras, J.; Sánchez, M.; Rieth, M.; Ureña, A.
The brazeability of four different alloys (Au, Cu, and two Ag-based alloys) was evaluated for their use as filler materials in joints between EUROFER 97 and tungsten for its application in future fusion reactors. The study aims to analyze the operational brazeability in terms of deep microstructural analysis and mechanical behavior. In general, high metallic continuity was observed for all filler compositions. In the case of the joints brazed with the Au-based filler alloy, a homogeneous microstructure based on an Au-Pd-Fe-Ni solid solution is obtained. The use of Ag-based filler alloys produced a solid solution phase at the EUROFER97-braze interface, and a Ag-based phase in contact with the tungsten base material. Finally, with the cupronickel filler alloy, a braze constituted by two different Cu-Ni-Fe solid solution phases is obtained. Regarding the mechanical characterization, the Cu-based filler shows a lower hardness value, while the higher values were obtained with one of the Ag-based filler alloy. In the case of the shear tests, a maximum 304 ± 57 MPa strength is obtained for Au-based filler alloy brazed at 1171 ºC due to the combination of a homogeneous and toughness microstructure and the lack of intermetallic compounds in the braze