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

• The crystallization behavior of a Zr-based bulk metallic glass - AMZ4 - during multiple laser beam melting is systematically investigated. • A better understanding of the changes in the microstructure, composition, and micromechanical properties of AMZ4 during laser beam processing. • The effect of oxygen content on the laser beam-induced crystallization behavior of AMZ4 is revealed. Selective laser melting (SLM), taking advantage of its inherent rapid cooling rates and near-net-shape forming ability, has been employed to fabricate bulk metallic glasses (BMGs). However, crystallization is frequently triggered during the SLM process, which results in the loss of advantageous properties of BMGs, such as extremely high hardness and near-theoretical yield strength. Although many studies have been conducted to investigate SLM of BMGs, there is still a lack of knowledge about the microstructural and compositional evolution during the laser beam processing, particularly the micromechanical property response upon crystallization. In the present work, a systematic investigation is performed to gain a much better understanding about the evolution of microstructure and composition as well as the corresponding micromechanical property change during multiple laser beam melting. The material used in this study is an industrial-grade Zr-based BMG Zr 59.3 Cu 28.8 Al 10.4 Nb 1.5 (AMZ4) with two different oxygen levels. AMZ4 demonstrates its good thermal stability by the fact that observable crystalline structure appears around the melt pool only after more than once laser beam treatment. The compositional stability of AMZ4 is manifested by the homogeneous elemental distribution on the melt pool area after even twenty-five laser beam remelting. The laser-metal interaction, melting and subsequent solidification are not effectively influenced by the emerging and expanding of crystallization zone (or heat affected zone, HAZ). Higher oxygen content results in not only a larger HAZ but also more quenched-in nuclei at the melt pool bottom. The HAZ does not exhibit a fully crystallized structure, but rather has a mixture of amorphous and crystalline phases. Crystallization of AMZ4 leads to an increase in hardness and Young’s modulus of the material. 

Evolution of an industrial-grade Zr-based bulk metallic glass during multiple laser beam melting

On stabilizing an α/α′/α″ microstructure in ferritic superalloys

Laser powder bed fusion (L-PBF) has been employed to fabricate bulk metallic glass (BMG) parts. However, traditional experimental trial-and-error methods to determine process parameters for specific materials and L-PBF machines are time-consuming and expensive. In this paper, a phenomenological crystallization model, namely the Nakamura model, is coupled with L-PBF process simulation. A convenient approach for the crystallization parameter determination and a two-step Euler method for the numerical implementation has been developed. Numerical simulations are performed using the material parameters of a Zr-based BMG Zr59.3Cu28.8Al10.4Nb1.5 (at.%, trade name: AMZ4). The numerical results are validated by comparing with experimental results from different perspectives. Based on the numerical findings, a comprehensive understanding of BMG crystallization behavior during L-PBF is gained. In the end, the crystallization model is implemented in our in-house developed software SAMPLE2D. SAMPLE2D simulation results are presented, whereby the L-PBF process window for fully amorphous AMZ4 parts is explored. Thereby, it is believed that the developed numerical software can be applied to aid process development for BMGs by taking the crystallization phenomenon into account. 

Predictive simulation of bulk metallic glass crystallization during laser powder bed fusion

Structural components with integrated piezoceramic sensors and actuators manufactured by high pressure die casting were studied using the thermal wave method. Thermal waves were created by irradiating the surface with an intensity modulated laser beam, and the pyroelectric current was monitored in dependence on modulation frequency. Laser modulation frequencies corresponding to specified penetration depths of the thermal wave were determined by a thermal finite element analysis. The current spectrum was fitted to complex relaxation models. The embedded piezoelectric transducer was described as a homogeneously poled, harmonically heated piezoelectric plate exhibiting heat losses to the environment. Nyquist plots were used for physical interpretation as an equivalent circuit.

Evaluation of polarisation state of light metal embedded piezoelectrics

In this feasibility study, a novel selective powder raking approach is used for Electron Beam Powder Bed Fusion (EB-PBF) to produce fully dense and compositionally graded composites. The adaption of the chemical composition along the thickness direction of the printed parts is based on the application of a powder blend composed of powders with different particle sizes combined with varying layer thicknesses during EB-PBF. The microstructure of EB-PBF-processed samples with a composition gradient is investigated. The distribution of different phases in the as-built samples is discussed. Based on the results derived in this work, this approach can be easily extended to other powder bed-based AM technologies as well as to other material systems to produce functionally graded materials. 

Carolin Körner

Papers

Evolution of an industrial-grade Zr-based bulk metallic glass during multiple laser beam melting

On stabilizing an α/α′/α″ microstructure in ferritic superalloys

Predictive simulation of bulk metallic glass crystallization during laser powder bed fusion

Evaluation of polarisation state of light metal embedded piezoelectrics

A novel approach for powder bed-based additive manufacturing of compositionally graded composites