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Additive Manufacturing of a Strong and Ductile Oxygen-doped NbTiZr Medium-Entropy Alloy

Yaqiong An, Yijie Liu, Shujie Liu, Bozhao Zhang, Guanghui Yang, Cheng Zhang, Xipeng Tan, Jun Ding, En Ma

[摘要](37) [PDF 2539KB](33)

摘要:
Refractory multi-principal element alloys (RMPEAs) have garnered attention for their potential in high-temperature applications. Additive manufacturing provides opportunities to tailor RMPEAs' microstructures to enhance these properties. However, controlling defects and addressing the challenges posed by the complex thermal history during the additive manufacturing process are crucial for optimizing RMPEAs' performance. This study aims to fabricate a high-quality oxygen-doped NbTiZr alloys using laser powder bed fusion (L-PBF) and investigate their microstructure and mechanical properties. Our analysis reveals refined grain sizes and a periodic combination of fine near-equiaxed and columnar grain morphologies in the AM-fabricated alloy. Its substructure is characterized by the coexistence of loosely defined cellular dislocation networks and elemental segregation. Compared to its cast counterpart, the additively manufactured alloy exhibits a combination of high yield strength, excellent tensile ductility, and enhanced work hardening. These attributes make the AM-fabricated oxygen-doped NbTiZr alloy a promising candidate for applications required balanced mechanical properties. Understanding the specific effects of different crystal structures and deformation mechanisms is essential for optimizing AM processes to tailor the microstructure and achieve the desired mechanical performance in various engineering applications.

Interlayer excitons diffusion and transport in van der Waals heterostructures

Yingying Chen, Qiubao Lin, Haizhen Wang, Dehui Li

, doi: 10.1088/2752-5724/ad8cf2

[摘要](46) [PDF 5027KB](11)

摘要:
The assembly of monolayer transition metal dichalcogenides (TMDs) in van der Waals heterostructures yields the formation of spatially separated interlayer excitons (IXs) with large binding energies, long lifetimes, permanent dipole moments and valley-contrasting physics, providing a compelling platform for investigating and engineering spatiotemporal IX propagation with highly tunable dynamics. Further twisting the stacked TMD monolayers can create long-term periodic moiré patterns with spatially modified band structures and varying moiré potentials, featuring tailored traps that can induce strong correlations with densitydependent phase transitions to modulate the exciton transport. The rich exciton landscapes in TMD heterostructures, combined with advancements in valleytronics and twistronics, hold great promise for exploring exciton-integrated circuits base on manipulation of exciton diffusion and transport. In this Review, we provide a comprehensive overview of recent progress in understanding IXs and moiréexcitons, with a specific focus on emerging exciton diffusion and transport in TMD heterostructures. We put emphasis on spatial manipulation of exciton flux through various methods, encompassing exciton density, dielectric environment, electric field and structure engineering, for precise control. This ability to manipulate exciton diffusion opens up new possibilities for interconverting optical communication and signal processing, paving the way for exciting applications in high-performance optoelectronics, such as excitonic devices, valleytronic transistors and photodetectors. We finally conclude this Review by outlining perspectives and challenges in harnessing IX currents for nextgeneration optoelectronic applications.

Sub-millisecond keyhole pore detection in laser powder bed fusion using sound and light sensors and machine learning

Zhongshu Ren, Jiayun Shao, Haolin Liu, Samuel J. Clark, Lin Gao, Lilly Balderson, Kyle Mumm, Kamel Fezzaa, Anthony D. Rollett, Levent Burak Kara, Tao Sun

, doi: 10.1088/2752-5724/ad89e2

[摘要](132) [PDF 3216KB](53)

摘要:
Laser powder bed fusion is a mainstream additive manufacturing technology widely used to manufacture complex parts in prominent sectors, including aerospace, biomedical, and automotive industries. However, during the printing process, the presence of an unstable vapor depression can lead to a type of defect called keyhole porosity, which is detrimental to the part quality. In this study, we developed an effective approach to locally detect the generation of keyhole pores during the printing process by leveraging machine learning and a suite of optical and acoustic sensors. Simultaneous synchrotron x-ray imaging allows the direct visualization of pore generation events inside the sample, offering high-fidelity ground truth. A neural network model adopting SqueezeNet architecture using single-sensor data was developed to evaluate the fidelity of each sensor for capturing keyhole pore generation events. Our comparative study shows that the near infrared images gave the highest prediction accuracy, followed by 100kHz and 20kHz microphones, and the photodiode sensitive to processing laser wavelength had the lowest accuracy. Using a single sensor, over 90% prediction accuracy can be achieved with a temporal resolution as short as 0.1 ms. A data fusion scheme was also developed with features extracted using SqueezeNet neural network architecture and classification using different machine learning algorithms. Our work demonstrates the correlation between the characteristic optical and acoustic emissions and the keyhole oscillation behavior, and thereby provides strong physics support for the machine learning approach.

Dynamically customizable 4D printed shape memory polymer biomedical devices: a review

Xiaozhou Xin, Cheng Lin, Xiaofei Wang, Fukai Liu, Lili Dong, Liwu Liu, Yanju Liu, Jinsong Leng

, doi: 10.1088/2752-5724/ad8898

[摘要](58) [PDF 5730KB](12)

摘要:
There is an increased risk of complications and even surgical failures for various types of medical devices due to difficult to control configurations and performances, incomplete deployments, etc. Shape memory polymers (SMPs)-based 4D printing technology offers the opportunity to create dynamic, personalized, and accurately controllable biomedical devices with complex configurations. SMPs, typical representatives of intelligent materials, are capable of programmable deformation in response to stimuli and dynamic remodeling on demand. 4D printed SMP medical devices not only enable active control of configuration, performance and functionality, but also open the way for minimally invasive treatments and remote controllable deployment. Here, the shape memory mechanism, actuation methods, and printing strategies of active programmable SMPs are reviewed, and cutting-edge advances of 4D printed SMPs in the fields such as bone scaffolds, tracheal stents, cardiovascular stents, cell morphological regulation, and drug delivery are highlighted. In addition, promising and meaningful future research directions for 4D printed SMP biomedical devices are discussed. The development of 4D printed SMP medical devices is inseparable from the in-depth cooperation between doctors and engineers. The application of 4D printed SMP medical devices will facilitate the rapid realization of "smart medical care" and accelerate the process of "intelligentization" of medical devices.

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