Current Articles

2023, Volume 5,  Issue 3

Laser powder bed fusion additive manufacturing of NiTi shape memory alloys: a review
Shuaishuai Wei, Jinliang Zhang, Lei Zhang, Yuanjie Zhang, Bo Song, Xiaobo Wang, Junxiang Fan, Qi Liu, Yusheng Shi
2023, 5(3) doi: 10.1088/2631-7990/acc7d9

NiTi alloys have drawn significant attentions in biomedical and aerospace fields due to their unique shape memory effect (SME), superelasticity (SE), damping characteristics, high corrosion resistance, and good biocompatibility. Because of the unsatisfying processabilities and manufacturing requirements of complex NiTi components, additive manufacturing technology, especially laser powder bed fusion (LPBF), is appropriate for fabricating NiTi products. This paper comprehensively summarizes recent research on the NiTi alloys fabricated by LPBF, including printability, microstructural characteristics, phase transformation behaviors, lattice structures, and applications. Process parameters and microstructural features mainly influence the printability of LPBF-processed NiTi alloys. The phase transformation behaviors between austenite and martensite phases, phase transformation temperatures, and an overview of the influencing factors are summarized in this paper. This paper provides a comprehensive review of the mechanical properties with unique strain-stress responses, which comprise tensile mechanical properties, thermomechanical properties (e.g. critical stress to induce martensitic transformation, thermo-recoverable strain, and SE strain), damping properties and hardness. Moreover, several common structures (e.g. a negative Poisson’s ratio structure and a diamond-like structure) are considered, and the corresponding studies are summarized. It illustrates the various fields of application, including biological scaffolds, shock absorbers, and driving devices. In the end, the paper concludes with the main achievements from the recent studies and puts forward the limitations and development tendencies in the future.

Recent advances in the mechanics of 2D materials
Guorui Wang, Hongyu Hou, Yunfeng Yan, Ritesh Jagatramka, Amir Shirsalimian, Yafei Wang, Binzhao Li, Matthew Daly, Changhong Cao
2023, 5(3) doi: 10.1088/2631-7990/accda2

The exceptional physical properties and unique layered structure of two-dimensional (2D) materials have made this class of materials great candidates for applications in electronics, energy conversion/storage devices, nanocomposites, and multifunctional coatings, among others. At the center of this application space, mechanical properties play a vital role in materials design, manufacturing, integration and performance. The emergence of 2D materials has also sparked broad scientific inquiry, with new understanding of mechanical interactions between 2D structures and interfaces being of great interest to the community. Building on the dramatic expansion of recent research activities, here we review significant advances in the understanding of the elastic properties, in-plane failures, fatigue performance, interfacial shear/friction, and adhesion behavior of 2D materials. In this article, special emphasis is placed on some new 2D materials, novel characterization techniques and computational methods, as well as insights into deformation and failure mechanisms. A deep understanding of the intrinsic and extrinsic factors that govern 2D material mechanics is further provided, in the hopes that the community may draw design strategies for structural and interfacial engineering of 2D material systems. We end this review article with a discussion of our perspective on the state of the field and outlook on areas for future research directions.

Simultaneous multi-material embedded printing for 3D heterogeneous structures
Ziqi Gao, Jun Yin, Peng Liu, Qi Li, Runan Zhang, Huayong Yang, Hongzhao Zhou
2023, 5(3) doi: 10.1088/2631-7990/acd285

In order to mimic the natural heterogeneity of native tissue and provide a better microenvironment for cell culturing, multi-material bioprinting has become a common solution to construct tissue models in vitro. With the embedded printing method, complex 3D structure can be printed using soft biomaterials with reasonable shape fidelity. However, the current sequential multi-material embedded printing method faces a major challenge, which is the inevitable trade-off between the printed structural integrity and printing precision. Here, we propose a simultaneous multi-material embedded printing method. With this method, we can easily print firmly attached and high-precision multilayer structures. With multiple individually controlled nozzles, different biomaterials can be precisely deposited into a single crevasse, minimizing uncontrolled squeezing and guarantees no contamination of embedding medium within the structure. We analyse the dynamics of the extruded bioink in the embedding medium both analytically and experimentally, and quantitatively evaluate the effects of printing parameters including printing speed and rheology of embedding medium, on the 3D morphology of the printed filament. We demonstrate the printing of double-layer thin-walled structures, each layer less than 200 µm, as well as intestine and liver models with 5% gelatin methacryloyl that are crosslinked and extracted from the embedding medium without significant impairment or delamination. The peeling test further proves that the proposed method offers better structural integrity than conventional sequential printing methods. The proposed simultaneous multi-material embedded printing method can serve as a powerful tool to support the complex heterogeneous structure fabrication and open unique prospects for personalized medicine.

A systematic printability study of direct ink writing towards high-resolution rapid manufacturing
Qingyang Zheng, Bin Xie, Zhoulong Xu, Hao Wu
2023, 5(3) doi: 10.1088/2631-7990/acd090

Direct ink writing (DIW) holds enormous potential in fabricating multiscale and multi-functional architectures by virtue of its wide range of printable materials, simple operation, and ease of rapid prototyping. Although it is well known that ink rheology and processing parameters have a direct impact on the resolution and shape of the printed objects, the underlying mechanisms of these key factors on the printability and quality of DIW technique remain poorly understood. To tackle this issue, we systematically analyzed the printability and quality through extrusion mechanism modeling and experimental validating. Hybrid non-Newtonian fluid inks were first prepared, and their rheological properties were measured. Then, finite element analysis of the whole DIW process was conducted to reveal the flow dynamics of these inks. The obtained optimal process parameters (ink rheology, applied pressure, printing speed, etc) were also validated by experiments where high-resolution (<100 patterns="" were="" fabricated="" rapidly="">70 mm s-1). Finally, as a process research demonstration, we printed a series of microstructures and circuit systems with hybrid inks and silver inks, showing the suitability of the printable process parameters. This study provides a strong quantitative illustration of the use of DIW for the high-speed preparation of high-resolution, high-precision samples.

Fabrication of polyetheretherketone (PEEK)-based 3D electronics with fine resolution by a hydrophobic treatment assisted hybrid additive manufacturing method
Liexin Wu, Li Meng, Yueyue Wang, Ming Lv, Taoyuan Ouyang, Yilin Wang, Xiaoyan Zeng
2023, 5(3) doi: 10.1088/2631-7990/acd826

Additive manufacturing (AM) is a free-form technology that shows great potential in the integrated creation of three-dimensional (3D) electronics. However, the fabrication of 3D conformal circuits that fulfill the requirements of high service temperature, high conductivity and high resolution remains a challenge. In this paper, a hybrid AM method combining the fused deposition modeling (FDM) and hydrophobic treatment assisted laser activation metallization (LAM) was proposed for manufacturing the polyetheretherketone (PEEK)-based 3D electronics, by which the conformal copper patterns were deposited on the 3D-printed PEEK parts, and the adhesion between them reached the 5B high level. Moreover, the 3D components could support the thermal cycling test from -55 ℃ to 125 ℃ for more than 100 cycles. Particularly, the application of a hydrophobic coating on the FDM-printed PEEK before LAM can promote an ideal catalytic selectivity on its surface, not affected by the inevitable printing borders and pores in the FDM-printed parts, then making the resolution of the electroless plated copper lines improved significantly. In consequence, Cu lines with width and spacing of only 60 µm and 100 µm were obtained on both as-printed and after-polished PEEK substrates. Finally, the potential of this technique to fabricate 3D conformal electronics was demonstrated.

Development of a roll-to-roll high-speed laser micro processing machine for preparing through-holed anodes and cathodes of lithium-ion batteries
Mitsuru Yamada, Naohiko Soma, Masaya Tsuta, Susumu Nakamura, Nobuo Ando, Futoshi Matsumoto
2023, 5(3) doi: 10.1088/2631-7990/acd917

Aiming to improve the battery performance of lithium-ion batteries (LIBs), modification of the cathodes and anodes of LIBs using laser beams to prepare through-holes, non-through-holes or ditches arranged in grid and line patterns has been proposed by many researchers and engineers. In this study, a laser processing system attached to rollers, which realizes this modification without large changes in the present mass-production system, was developed. The laser system apparatus comprises roll-to-roll equipment and laser equipment. The roll-to-roll equipment mainly consists of a hollow cylinder with openings on its circumferential surface. Cathode and anode electrodes for LIBs are wound around the cylinder in the longitudinal direction of the electrodes. A pulsed beam reflected from the central axis of the cylinder can continuously open a large number of through-holes in the thin electrodes. Through-holes were formed at a rate of 100 000 holes per second on lithium iron phosphate cathodes and graphite anodes with this system. The through-holed cathodes and anodes prepared with this system exhibited higher C-rate performance than nontreated cathodes and anodes.

Electric-driven flexible-roller nanoimprint lithography on the stress-sensitive warped wafer
Yu Fan, Chunhui Wang, Jiaxing Sun, Xiaogang Peng, Hongmiao Tian, Xiangming Li, Xiaoliang Chen, Xiaoming Chen, Jinyou Shao
2023, 5(3) doi: 10.1088/2631-7990/acd827

Surface nanopatterning of semiconductor optoelectronic devices is a powerful way to improve their quality and performance. However, photoelectric devices’ inherent stress sensitivity and inevitable warpage pose a huge challenge on fabricating nanostructures large-scale. Electric-driven flexible-roller nanoimprint lithography for nanopatterning the optoelectronic wafer is proposed in this study. The flexible nanoimprint template twining around a roller is continuously released and recovered, controlled by the roller’s simple motion. The electric field applied to the template and substrate provides the driving force. The contact line of the template and the substrate gradually moves with the roller to enable scanning and adapting to the entire warped substrate, under the electric field. In addition, the driving force generated from electric field is applied to the surface of substrate, so that the substrate is free from external pressure. Furthermore, liquid resist completely fills in microcavities on the template by powerful electric field force, to ensure the fidelity of the nanostructures. The proposed nanoimprint technology is validated on the prototype. Finally, nano-grating structures are fabricated on a gallium nitride light-emitting diode chip adopting the solution, achieving polarization of the light source.

3D printing of high-precision and ferromagnetic functional devices
Zhiyuan Huang, Guangbin Shao, Dekai Zhou, Xinghong Deng, Jing Qiao, Longqiu Li
2023, 5(3) doi: 10.1088/2631-7990/acccbb

The development of projection-based stereolithography additive manufacturing techniques and magnetic photosensitive resins has provided a powerful approach to fabricate miniaturized magnetic functional devices with complex three-dimensional spatial structures. However, the present magnetic photosensitive resins face great challenges in the trade-off between high ferromagnetism and excellent printing quality. To address these challenges, we develop a novel NdFeB-Fe3O4 magnetic photosensitive resin comprising 20 wt.% solid loading of magnetic particles, which can be used to fabricate high-precision and ferromagnetic functional devices via micro-continuous liquid interface production process. This resin combining ferromagnetic NdFeB microparticles and strongly absorbing Fe3O4 nanoparticles is able to provide ferromagnetic capabilities and excellent printing quality simultaneously compared to both existing soft and hard magnetic photosensitive resins. The established penetration depth model reveals the effect of particle size, solid loading, and absorbance on the curing characteristics of magnetic photosensitive resin. A high-precision forming and ferromagnetic capability of the NdFeB-Fe3O4 magnetic photosensitive resin are comprehensively demonstrated. It is found that the photosensitive resin (NdFeB:Fe3O4 = 1:1) can print samples with sub-40 µm fine features, reduced by 87% compared to existing hard magnetic photosensitive resin, and exhibits significantly enhanced coercivity and remanence in comparison with existing soft magnetic photosensitive resins, showing by an increase of 24 times and 6 times, respectively. The reported NdFeB-Fe3O4 magnetic photosensitive resin is anticipated to provide a new functional material for the design and manufacture of next-generation micro-robotics, electromagnetic sensor, and magneto-thermal devices.