There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

Additive manufacturing of metallic components – Process, structure and properties

Freedom of design, mass customisation, waste minimisation and the ability to manufacture complex structures, as well as fast prototyping, are the main benefits of additive manufacturing (AM) or 3D printing. A comprehensive review of the main 3D printing methods, materials and their development in trending applications was carried out. In particular, the revolutionary applications of AM in biomedical, aerospace, buildings and protective structures were discussed. The current state of materials development, including metal alloys, polymer composites, ceramics and concrete, was presented. In addition, this paper discussed the main processing challenges with void formation, anisotropic behaviour, the limitation of computer design and layer-by-layer appearance. Overall, this paper gives an overview of 3D printing, including a survey on its benefits and drawbacks as a benchmark for future research and development.

Additive manufacturing (3D printing): A review of materials, methods, applications and challenges

Additive manufacturing of metals

A microstructure has significant influence on the mechanical properties of parts. For isotropic properties, the formation of equiaxed microstructures by the nucleation of new grains during solidification is necessary. For conventional solidification processes, nucleation is well-understood. Regarding powder bed fusion, the repeated remelting of previous layers can cause nucleation under some conditions that are not explainable with classical theories. Here, we investigate this nucleation mechanism with an unprecedented level of detail. In the first step, we built samples with single crystalline microstructures from Ni-base superalloy IN718 by selective electron beam melting. In the second step, single lines with different parameters were molten on top of these samples. We observed a huge number of new grains by nucleation at the melt-pool border of these single lines. However, new grains can only prevail if the alignment of their crystallographic orientation with respect to the local temperature gradient is superior to that of the base material. The current hypothesis is that nucleation at the melt-pool border happens due to remelting microsegregations from former solidification processes leading to constitutional undercooling directly at the onset of solidification. This study offers the opportunity to understand and exploit this mechanism for different manufacturing processes.

New Grain Formation by Constitutional Undercooling Due to Remelting of Segregated Microstructures during Powder Bed Fusion.

https://iopscience.iop.org/article/10.1088/1361-651X/aaf0b8/pdf

MultOpt++: a fast regression-based model for the development of compositions with high robustness against scatter of element concentrations

Additively manufactured RANEY®-type copper catalyst for methanol synthesis

Selective electron beam melting (SEBM) is a powder bed–based additive manufacturing (AM) technology and allows the fabrication of complex metal components. However, the high building temperatures necessary for a stable process prohibit the fabrication of small internal features and intended cavities, e.g., for cooling purposes and heat exchangers. In this work, a novel scan strategy is used to seal prefabricated notches on the surface of Ti-6Al-4V substrates and to create microducts without applying additional materials. Influencing factors are identified and a process map for the SEBM sealing process is established. The impact of the determined strategy on the material properties regarding surface structure and composition is investigated. This sealing process can be followed by conventional SEBM-based additive manufacturing to build complex structures on the sealing layer due to its high flatness.

Carolin Körner

Papers

New Grain Formation by Constitutional Undercooling Due to Remelting of Segregated Microstructures during Powder Bed Fusion.

MultOpt++: a fast regression-based model for the development of compositions with high robustness against scatter of element concentrations

Additively manufactured RANEY®-type copper catalyst for methanol synthesis

Advanced process strategy to realize microducts free of powder using selective electron beam melting

In-Situ Aluminum Control for Titanium Aluminide Via Electron Beam Powder Bed Fusion to Realize a Dual Microstructure