Additive Manufacturing For Thermal Management Applications: From Experimental Results To Numerical Modeling

Additive Manufacturing (AM) of copper and copper alloys has opened new frontiers in heat transfer applications, going beyond the capabilities of conventional technologies. Despite the great design freedom offered by AM, when dealing with metal powders, a few issues should be considered to exploit the great capabilities of this manufacturing technology. In fact, the surface roughness of the components is expected to affect the performance of the devices, which can be remarkably different from the ones simulated with software. This paper presents a critical analysis of the accuracy of the numerical tools to simulate the fluid flow behaviour inside cooling channels obtained via AM. The work shows the major limitations of the standard approaches to accurately predict the pressure drops in straight and complex channels. Three different copper channels of growing complexity were built via LPBF (Laser Powder Bed Fusion) and then they were experimentally tested at different water flow rates to evaluate the predictive abilities of the numerical model. The results revealed that the surface roughness deeply affects the fluid flow behaviour, thus the numerical models need to be calibrated to become a reliable design tool. The proposed procedure can be considered the first attempt in this direction and allows for a proper integration of the AM with the numerical simulation tools, to boost the design capabilities of LPBF technology

Correlation of Lack of Fusion Pores with Stress Corrosion Cracking Susceptibility of L-PBF 316L: Effect of Surface Residual Stresses

Stress corrosion cracking (SCC) of laser powder bed fusion-fabricated 316L was studied under the variation in energy input density to emulate the existence of distinctive types of defects. Various electrochemical polarization measurements were performed in as-received polished and ground states, to elucidate the effect of defect type on corrosion and SCC behaviour in marine solution. The results revealed severe localized corrosion attack and SCC initiation for specimens with a lack of fusion pores (LOF). Moreover, the morphology of SCC was different, highlighting a more dominant effect of selective dissolution of the subgrain matrix for gas porosities and a more pronounced effect of brittle fracture at laser track boundaries for the specimens with LOF pores

TUNGSTEN AND MOLYBDENUM FABRICATED BY LASER POWDER BED FUSION

Additive Manufacturing (AM) is the process that allows the production of complex geometry and lightweight components. According to refractory metals’ high density and their possible applications in the aerospace field, and for biomedical or future nuclear fusion devices, AM could be a good solution. However, selective laser melting of refractory metals as Ta, Mo, and W faces some challenges due to their main properties: high melting point, heat conductivity and susceptibility to cracks. The purpose of this study is to optimize the process parameters in order to produce high-density Tungsten and Molybdenum parts by SLM on an EOS M100 (maximum power of 170 W). Characterization is performed through physical properties measurements and microstructural analysis. Single Scan Tracks (SSTs) are produced on the top surfaces of Tungsten blocks to evaluate the process parameters that give regular-shape and continuous melt-pools. Both analytical and experimental optimization of process parameters were performed. Micro-hardness measurements were done for dense bulk specimens. Finally, a description of susceptibility to cracks of both additively manufactured Molybdenum and Tungsten was performed

Progress in European Thin Film Activities

International audienceThin-film cavities with higher Tc superconductors (SC) than Nb promise to move the operating temperature from 2 to 4.5 K with savings 3 orders of magnitude in cryogenic power consumption. Several European labs are coordinating their efforts to obtain a first 1.3 GHz cavity prototype through the I.FAST collaboration and other informal collaborations with CERN and DESY. R&D covers the entire production chain. In particular, new production techniques of seamless Copper and Niobium elliptical cavities via additive manufacturing are studied and evaluated. New acid-free polishing techniques to reduce surface roughness in a more sustainable way such as plasma electropolishing and metallographic polishing have been tested. Optimization of coating parameters of higher Tc SC than Nb (Nb₃Sn, V₃Si, NbTiN) via PVD and multilayer via ALD are on the way. Finally, rapid heat treatments such as Flash Lamp Annealing and Laser Annealing are used to avoid or reduce Cu diffusion in the SC film. The development and characterization of SC coatings is done on planar samples, 6 GHz cavities, choke cavities, QPR and 1.3 GHz cavities. This work presents the progress status of these coordinated efforts