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2020 Vol. 2, No. 3

Atomic and close-to-atomic scale manufacturing: perspectives and measures
Fengzhou Fang
2020, 2(3) doi: 10.1088/2631-7990/aba495

This article presents the three paradigms of manufacturing advancement: Manufacturing I, craft-based manufacturing by hand, as in the Stone, Bronze, and Iron Ages, in which manufacturing precision was at the millimeter scale; Manufacturing II, precision-controllable manufacturing using machinery whereby the scales of material removal, migration, and addition were reduced from millimeters to micrometers and even nanometers; and Manufacturing III, manufacturing objectives and processes are directly focused on atoms, spanning the macro through the micro- to the nanoscale, whereby manufacturing is based on removal, migration, and addition at the atomic scale, namely, atomic and close-to-atomic scale manufacturing (ACSM). A typical characteristic of ACSM is that energy directly impacts the atom to be removed, migrated, and added. ACSM, as the next generation of manufacturing technology, will be employed to build atomic-scale features for required functions and performance with the capacity of mass production. It will be the leading development trend in manufacturing technology and will play a significant role in the manufacture of high-end components and future products.

High-efficiency forming processes for complex thin-walled titanium alloys components: state-of-the-art and perspectives
Kehuan Wang, Liliang Wang, Kailun Zheng, Zhubin He, Denis J Politis, Gang Liu, Shijian Yuan
2020, 2(3) doi: 10.1088/2631-7990/ab949b

Complex thin-walled titanium alloy components play a key role in the aircraft, aerospace and marine industries, offering the advantages of reduced weight and increased thermal resistance. The geometrical complexity, dimensional accuracy and in-service properties are essential to fulfill the high-performance standards required in new transportation systems, which brings new challenges to titanium alloy forming technologies. Traditional forming processes, such as superplastic forming or hot pressing, cannot meet all demands of modern applications due to their limited properties, low productivity and high cost. This has encouraged industry and research groups to develop novel high-efficiency forming processes. Hot gas pressure forming and hot stamping-quenching technologies have been developed for the manufacture of tubular and panel components, and are believed to be the cut-edge processes guaranteeing dimensional accuracy, microstructure and mechanical properties. This article intends to provide a critical review of high-efficiency titanium alloy forming processes, concentrating on latest investigations of controlling dimensional accuracy, microstructure and properties. The advantages and limitations of individual forming process are comprehensively analyzed, through which, future research trends of high-efficiency forming are identified including trends in process integration, processing window design, full cycle and multi-objective optimization. This review aims to provide a guide for researchers and process designers on the manufacture of thin-walled titanium alloy components whilst achieving high dimensional accuracy and satisfying performance properties with high efficiency and low cost.

Bioinspired micro/nanostructured surfaces prepared by femtosecond laser direct writing for multi-functional applications
Yiyuan Zhang, Yunlong Jiao, Chuanzong Li, Chao Chen, Jiawen Li, Yanlei Hu, Dong Wu, Jiaru Chu
2020, 2(3) doi: 10.1088/2631-7990/ab95f6

Femtosecond laser direct writing (FLDW) has been widely employed in controllable manufacturing of biomimetic micro/nanostructures due to its specific advantages including high precision, simplicity, and compatibility for diverse materials in comparison with other methods (e.g. ion etching, sol-gel process, chemical vapor deposition, template method, and self-assembly). These biomimetic micro/nanostructured surfaces are of significant interest for academic and industrial research due to their wide range of potential applications, including self-cleaning surfaces, oil-water separation, and fog collection. This review presents the inherent relationship between natural organisms, fabrication methods, micro/nanostructures and their potential applications. Thereafter, we throw a list of current fabrication strategies so as to highlight the advantages of FLDW in manufacturing bioinspired microstructured surfaces. Subsequently, we summarize a variety of typical bioinspired designs (e.g. lotus leaf, pitcher plant, rice leaf, butterfly wings, etc) for diverse multifunctional micro/nanostructures through extreme femtosecond laser processing technology. Based on the principle of interfacial chemistry and geometrical optics, we discuss the potential applications of these functional micro/nanostructures and assess the underlying challenges and opportunities in the extreme fabrication of bioinspired micro/nanostructures by FLDW. This review concludes with a follow up and an outlook of femtosecond laser processing in biomimetic domains.

A review on microstructures and properties of high entropy alloys manufactured by selective laser melting
Chen Zhang, Junkai Zhu, Huai Zheng, Hui Li, Sheng Liu , Gary J Cheng
2020, 2(3) doi: 10.1088/2631-7990/ab9ead

High entropy alloys (HEAs) with multi-component solid solution microstructures have the potential for large-scale industrial applications due to their excellent mechanical and functional properties. However, the mechanical properties of HEAs limit the selection of processing technologies. Additive manufacturing technology possesses strong processing adaptability, making itthe best candidate method to overcome this issue. This comprehensive review examines the current state of selective laser melting (SLM) of HEAs. Introducing SLM to HEAs processing is motivated by its high quality for dimensional accuracy, geometric complexity, surface roughness, and microstructure. This review focuses on analyzing the current developments and challenges in SLM of HEAs, including defects, microstructures, and properties, as well as strengthing prediction models of fabricated HEAs. This review also offers directions for future studies to address existing challenges and promote technological advancement.

Thermal behavior of materials in laser-assisted extreme manufacturing: Raman-based novel characterization
Ridong Wang, Shen Xu, Yanan Yue, Xinwei Wang
2020, 2(3) doi: 10.1088/2631-7990/aba17c

Laser-assisted manufacturing (LAM) is a technique that performs machining of materials using a laser heating process. During the process, temperatures can rise above over 2000 °C. As a result, it is crucial to explore the thermal behavior of materials under such high temperatures to understand the physics behind LAM and provide feedback for manufacturing optimization. Raman spectroscopy, which is widely used for structure characterization, can provide a novel way to measure temperature during LAM. In this review, we discuss the mechanism of Raman-based temperature probing, its calibration, and sources of uncertainty/error, and how to control them. We critically review the Raman-based temperature measurement considering the spatial resolution under near-field optical heating and surface structure-induced asymmetries. As another critical aspect of Raman-based temperature measurement, temporal resolution is also reviewed to cover various ways of realizing ultrafast thermal probing. We conclude with a detailed outlook on Raman-based temperature probing in LAM and issues that need special attention.

Scanning probe lithography on calixarene towards single-digit nanometer fabrication
Marcus Kaestner, Ivo W Rangelow
2020, 2(3) doi: 10.1088/2631-7990/aba2d8

Cost effective patterning based on scanning probe nanolithography (SPL) has the potential for electronic and optical nano-device manufacturing and other nanotechnological applications. One of the fundamental advantages of SPL is its capability for patterning and imaging employing the same probe. This is achieved with self-sensing and self-actuating cantilevers, also known as 'active' cantilevers. Here we used active cantilevers to demonstrate a novel path towards single digit nanoscale patterning by employing a low energy (<100 eV) electron exposure to thin films of molecular resist. By tuning the electron energies to the lithographically relevant chemical resist transformations, the interaction volumes can be highly localized. This method allows for greater control over spatially confined lithography and enhances sensitivity. We found that at low electron energies, the exposure in ambient conditions required approximately 10 electrons per single calixarene molecule to induce a crosslinking event. The sensitivity was 80-times greater than a classical electron beam exposure at 30 keV. By operating the electro-exposure process in ambient conditions a novel lithographic reaction scheme based on a direct ablation of resist material (positive tone) is presented.

Directed self-assembly of block copolymers for sub-10 nm fabrication
Yu Chen, Shisheng Xiong
2020, 2(3) doi: 10.1088/2631-7990/aba3ae

Directed self-assembly (DSA) emerges as one of the most promising new patterning techniques for single digit miniaturization and next generation lithography. DSA achieves high-resolution patterning by molecular assembly that circumvents the diffraction limit of conventional photolithography. Recently, the International Roadmap for Devices and Systems listed DSA as one of the advanced lithography techniques for the fabrication of 3–5 nm technology node devices. DSA can be combined with other lithography techniques, such as extreme ultra violet (EUV) and 193 nm immersion (193i), to further enhance the patterning resolution and the device density. So far, DSA has demonstrated its superior ability for the fabrication of nanoscale devices, such as fin field effect transistor and bit pattern media, offering a variety of configurations for high-density integration and low-cost manufacturing. Over 1 T in−2 device density can be achieved either by direct templating or coupled with nanoimprinting to improve the throughput. The development of high χ block copolymer further enhances the patterning resolution of DSA. In addition to its superiority in high-resolution patterning, the implementation of DSA on a 300 mm pivot line fully demonstrates its potential for large-scale, high-throughput, and cost-effective manufacturing in industrial environment.

Cooling rate calibration and mapping of ultra-short pulsed laser modifications in fused silica by Raman and Brillouin spectroscopy
Michael Bergler, Kristian Cvecek, Ferdinand Werr, Martin Brehl, Dominique De Ligny, Michael Schmidt
2020, 2(3) doi: 10.1088/2631-7990/ab9583

This paper focuses on the preparation of a new extended set of calibrations of cooling rate (fictive temperature) in fused silica determined by inelastic light scattering and its subsequent use to characterize the local cooling rate distribution in ultra-short pulsed (USP) laser modification. In order to determine the thermal history (e.g. cooling rate and fictive temperature) of fused silica, high-resolution inelastic light-scattering experiments (Raman and Brillouin spectroscopy) were investigated. Calibrations were performed and compared to the existing literature to quantify structural changes due to a change of fictive temperature. Compared to existing calibrations, this paper provides an extension to lower and higher cooling rates. Using this new set of calibrations, we characterized a USP laser modification in fused silica and calculated the local fictive temperature distribution. An equation relating the fictive temperature (Tf ) to cooling rates is given. A maximum cooling rate of 3000 K min−1 in the glass transition region around 1200 °C was deduced from the Raman analysis. The Brillouin observations are sensitive to both the thermal history and the residual stress. By comparing the Raman and Brillouin observations, we extracted the local residual stress distribution with high spatial resolution. For the first time, combined Raman and Brillouin inelastic light scattering experiments show the local distribution of cooling rates and residual stresses (detailed behavior of the glass structure) in the interior and the surrounding of an USP laser modified zone.

Implications of using two low-power continuous-wave lasers for polishing
Wenxuan Zhang, Kiwan Wong, Miguel Morales, Carlos Molpeceres, Craig B Arnold
2020, 2(3) doi: 10.1088/2631-7990/ab94c6

Laser polishing is widely employed to reduce the surface roughness of products with complex geometries. Traditional laser polishing techniques use a single high-power Gaussian beam to melt and smooth a thin layer of surface material. However, the reliance on high power lasers can present practical challenges such as minimizing surface evaporation or reducing overall cost. In this work, we combined two identical low-power laser beams with a spatial offset in between them to construct an elliptical beam. By changing the spatial offset, combined beams with different lengths along the major axis can be created. We observe over 20% improvement in line roughness reduction using this approach compared to a single Gaussian laser beam with the same total power. Additionally, both experiment and simulation results suggest such improvement is because this dual-laser set-up can create a longer molten pool compared to a single laser.