Examinando por Autor "Wirtz, M."

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HHF response of an optimized W-EUROFER joint brazed with pure copper
(Elsevier, 2025-01) Izaguirre, I.; Dorow-Gerspach, D.; Prado, J. de; Sánchez, M.; Wirtz, M.; Ureña, A.
The optimization of joint microstructure plays a critical role in assessing joint performance under high heat flux (HHF) conditions, as it dictates the final properties of the joint. This study investigates tungsten-EUROFER joints brazed using a copper interlayer as filler material under optimized brazing cycle conditions (1110 °C, 3 min), and subjected to simulated high heat fluxes exposing the plasma facing material, tungsten in this case, to a heating source (accelerated electron bean), while the joint is refrigerated through the EUROFER side. This experiment aims to mimic the heat fluxes and cooling conditions experienced in a fusion reactor environment. An optimized microstructure of the braze joint, designed to mitigate the formation of intermetallic compounds and undesirable phases, was implemented to enhance joint responses under high heat flux loads. The joints were subjected to 100 and 1000 heating-cooling cycles of 10/12 s. The target during heating is to reach the thermal equilibrium. Three different tungsten surface temperature were evaluated (600 °C, 700 °C and 800 °C) in different sample batches while cooling on the EUROFER side, removing the heat source during the cooling stage. Some overheating events, associated with crack propagation through the EUROFER-braze interface identified during the subsequent postmortem analysis by SEM, were detected during the application of some conditions of the test. The microstructure examination also reported a modification of the failure mechanism of the joint comparing with the previous studies and literature. This modification is associated with the optimized microstructure resulting in improved response to high heat flux loads. Interestingly, the shear strength increased to an average of 95.0 MPa after HHF testing, compared to 40.2 MPa obtained in similar joints with different microstructures
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.