Effect of Processing Route on Microstructure and Mechanical Properties of an Al-12Si Alloy.

Two different microstructures of an Al-12Si (wt. %) alloy were produced, respectively, via a powder laser bed fusion (P-LBF) additive manufacturing and casting. Compared to casting, additive manufacturing of Al-based alloy requires extra care to minimize oxidation tendency. The role of the microstructure on the mechanical properties of Al-12Si (wt. %) alloy was investigated by in situ compression of the micro-pillars. The microstructure of additively manufactured specimens exhibited a sub-cellular (~700 nm) nature in the presence of melt-pool arrangements and grain boundaries. On the other hand, the microstructure of the cast alloy contains typical needle-like eutectic structures. This striking difference in microstructure had obvious effects on the plastic flow of the materials under compression. The yield and ultimate compressive strength of the additively manufactured alloy were 23.69-27.94 MPa and 75.43-81.21 MPa, respectively. The cast alloy exhibited similar yield strength (31.46 MPa); however, its ultimate compressive strength (34.95 MPa) was only half that of the additively manufactured alloy. The deformation mechanism, as unrevealed by SEM investigation on the surface as well as on the cross-section of the distorted micro-pillars, confirms the presence of ductile and quasi-ductile facture of the matrix and the Si needle, respectively, in the case of the cast alloy. In contrast, the additively manufactured alloy exhibits predominantly ductile fractures.

Unlocking High-Performance, Ultra-Low Power van der Waals Photo-Transistors: Toward Back-End-of-Line in-Sensor Machine Vision Applications.

Recent reports on machine learning and machine vision (MV) devices have demonstrated the potential of two-dimensional (2D) materials and devices. Yet, scalable 2D devices are being challenged by contact resistance and Fermi level pinning (FLP), power consumption, and low-cost CMOS compatible lithography processes. To enable CMOS + 2D, it is essential to find a proper lithography strategy that can fulfill these requirements. Here, we explored a modified van der Waals (vdW) deposition lithography and demonstrated a relatively new class of van der Waals field effect transistors (vdW-FETs) based on 2D materials. This lithography strategy enabled us to unlock high-performance devices evident by high current on-off ratio (Ion/Ioff), high turn-on current density (Ion), and weak FLP. We utilized this approach to demonstrate a gate-tunable near-ideal diode using a MoS2/WSe2 heterojunction with an ideality factor of ∼1.65 and current rectification of 102. We finally demonstrated a highly sensitive, scalable, and ultralow power phototransistor using a MoS2/WSe2 vdW-FET for back-end-of-line integration. Our phototransistor exhibited the highest gate-tunable photoresponsivity achieved to date for white light detection with ultralow power dissipation, enabling ultrasensitive optoelectronic applications such as in-sensor MV. Our approach showed the great potential of modified vdW deposition lithography for back-end-of-line CMOS + 2D applications.

Non-Invasive Brain Sensing Technologies for Modulation of Neurological Disorders.

The non-invasive brain sensing modulation technology field is experiencing rapid development, with new techniques constantly emerging. This study delves into the field of non-invasive brain neuromodulation, a safer and potentially effective approach for treating a spectrum of neurological and psychiatric disorders. Unlike traditional deep brain stimulation (DBS) surgery, non-invasive techniques employ ultrasound, electrical currents, and electromagnetic field stimulation to stimulate the brain from outside the skull, thereby eliminating surgery risks and enhancing patient comfort. This study explores the mechanisms of various modalities, including transcranial direct current stimulation (tDCS) and transcranial magnetic stimulation (TMS), highlighting their potential to address chronic pain, anxiety, Parkinson's disease, and depression. We also probe into the concept of closed-loop neuromodulation, which personalizes stimulation based on real-time brain activity. While we acknowledge the limitations of current technologies, our study concludes by proposing future research avenues to advance this rapidly evolving field with its immense potential to revolutionize neurological and psychiatric care and lay the foundation for the continuing advancement of innovative non-invasive brain sensing technologies.

Micro-Scale Deformation Aspects of Additively Fabricated Stainless Steel 316L under Compression.

The deformation aspects associated with the micro-mechanical properties of the powder laser bed fusion (P-LBF) additively manufactured stainless steel 316L were investigated in the present work. Toward that, micro-pillars were fabricated on different planes of the stainless steel 316L specimen with respect to build direction, and an in situ compression was carried out inside the chamber of the scanning electron microscope (SEM). The results were compared against the compositionally similar stainless steel 316L, which was fabricated by a conventional method, that is, casting. The post-deformed micro-pillars on the both materials were examined by electron microscopy. The P-LBF processed steel exhibits equiaxed as well as elongated grains of different orientation with the characteristics of the melt-pool type arrangements. In contrast, the cast alloy shows typical circular-type grains in the presence of micro-twins. The yield stress and ultimate compressive stress of P-LBF fabricated steel were about 431.02 ± 15.51 - 474.44 ± 23.49 MPa and 547.78 ± 29.58 - 682.59 ± 21.59 MPa, respectively. Whereas for the cast alloy, it was about 322.38 ± 19.78 MPa and 477.11 ± 25.31 MPa, respectively. Thus, the outcome of this study signifies that the AM-processed samples possess higher mechanical properties than conventionally processed alloy of similar composition. Irrespective of the processing method, both specimens exhibit ductile-type deformation, which is typical for metallic alloys.

Microstructural and Nanoindentation Investigation on the Laser Powder Bed Fusion Stainless Steel 316L.

Additive manufacturing (AM) of stainless steel is more difficult than other metallic materials, as the major alloying elements of the stainless steel are prone to oxidation during the fabrication process. In the current work, specimens of the stainless steel 316L were made by the powder laser bed fusion (P-LBF) additive manufacturing process. These specimens were investigated by electron microscopy and micro-/nano-indentation techniques to investigate the microstructural aspects and the mechanical properties, respectively. Compositionally, a similar wrought stainless steel was subjected to identical investigation, and used as a benchmark material. The microstructure of the P-LBF-processed alloy shows both equiaxed and elongated grains, which are marginally smaller (3.2-3.4 µm) than that of the wrought counterpart (3.6 µm). Withstanding such marginal gain size refinement, the increase in shear stress and hardness of the L-PBF alloy was striking. The L-PBF-processed alloy possess about 1.92-2.12 GPa of hardness, which was about 1.5 times higher than that of wrought alloy (1.30 GPa), and about 1.15 times more resistant against plastic flow of material. Similarly, L-PBF-processed alloy possess higher maximum shear stress (274.5-294.4 MPa) than that of the wrought alloy (175.9 MPa).

Investigation into the Microstructure and Hardness of Additively Manufactured (3D-Printed) Inconel 718 Alloy.

Additive manufacturing (AM) of Ni-based super alloys is more challenging, compared to the production other metallic alloys. This is due to their high melting point and excellent high temperature resistance. In the present work, an Inconel 718 alloy was fabricated by a powder laser bed fusion (P-LBF) process and investigated to assess its microstructural evolution, together with mechanical properties. Additionally, the alloy was compared against the cast (and forged) alloy of similar composition. The microstructure of the P-LBF-processed alloy shows hierarchy microstructure that consists of cellular sub-structure (~100-600 nm), together with melt pool and grain boundaries, in contrast of the twin infested larger grain microstructure of the cast alloy. However, the effect of such unique microstructure on mechanical properties of the L-PBF alloy was overwritten, due to the absence of precipitates. The hardness of the L-PBF-processed alloy (330-349 MPa) was lower than that of cast alloy (408 MPa). The similar trend was also observed in other mechanical properties, such as Young's modulus, resistance to plasticity and shear stress.

Formation and Characterization of the Recast Layer Formed on Inconel 718 during Wire Electro Discharge Machining.

The present work investigates the formation and microstructural and micro-mechanical characterization of the recast layer that formed on Inconel 718 alloy in the course of the wire electro-discharge machining (WEDM). The as-machined surface contains globules, shallow cracks, and re-deposition of molten materials, together with the elements from the decomposition of wire electrode and electrolyte, which does not exceed beyond the surface of the recast layer. Under presently investigated machining parameters, the recast layer was about 6.2 ± 2.1 µm thick. There was no presence of a heat-affected zone (HAZ), as otherwise indicated for other hard-to-cut materials. The transmission electron microscopy (TEM) and electron back-scattered diffraction (EBSD) investigations show that the microstructure of the recast layer is similar to that of bulk alloy. Micro-mechanical characterizations of the recast layer were investigated via in-situ micro-pillar compression on the micro-pillars fabricated on the recast layer. The strength of the superficial layer (1151.6 ± 51.1 MPa) was about 2.2 times higher than that of the base material (523.2 ± 22.1 MPa), as revealed by the in-situ micro-pillar compression.

Lattice Transformation from 2D to Quasi 1D and Phonon Properties of Exfoliated ZrS2 and ZrSe2.

Recent reports on thermal and thermoelectric properties of emerging 2D materials have shown promising results. Among these materials are Zirconium-based chalcogenides such as zirconium disulfide (ZrS2 ), zirconium diselenide (ZrSe2 ), zirconium trisulfide (ZrS3 ), and zirconium triselenide (ZrSe3 ). Here, the thermal properties of these materials are investigated using confocal Raman spectroscopy. Two different and distinctive Raman signatures of exfoliated ZrX2 (where X = S or Se) are observed. For 2D-ZrX2 , Raman modes are in alignment with those reported in literature. However, for quasi 1D-ZrX2 , Raman modes are identical to exfoliated ZrX3 nanosheets, indicating a major lattice transformation from 2D to quasi-1D. Raman temperature dependence for ZrX2 are also measured. Most Raman modes exhibit a linear downshift dependence with increasing temperature. However, for 2D-ZrS2 , a blueshift for A1g mode is detected with increasing temperature. Finally, phonon dynamics under optical heating for ZrX2 are measured. Based on these measurements, the calculated thermal conductivity and the interfacial thermal conductance indicate lower interfacial thermal conductance for quasi 1D-ZrX2 compared to 2D-ZrX2 , which can be attributed to the phonon confinement in 1D. The results demonstrate exceptional thermal properties for Zirconium-based materials, making them ideal for thermoelectric device applications and future thermal management strategies.

Practice of Simulation and Life Cycle Assessment in Tribology-A Review.

To simulate today's complex tribo-contact scenarios, a methodological breakdown of a complex design problem into simpler sub-problems is essential to achieve acceptable simulation outcomes. This also helps to manage iterative, hierarchical systems within given computational power. In this paper, the authors reviewed recent trends of simulation practices in tribology to model tribo-contact scenario and life cycle assessment (LCA) with the help of simulation. With the advancement of modern computers and computing power, increasing effort has been given towards simulation, which not only saves time and resources but also provides meaningful results. Having said that, like every other technique, simulation has some inherent limitations which need to be considered during practice. Keeping this in mind, the pros and cons of both physical experiments and simulation approaches are reviewed together with their interdependency and how one approach can benefit the other. Various simulation techniques are outlined with a focus on machine learning which will dominate simulation approaches in the future. In addition, simulation of tribo-contacts across different length scales and lubrication conditions is discussed in detail. An extension of the simulation approach, together with experimental data, can lead towards LCA of components which will provide us with a better understanding of the efficient usage of limited resources and conservation of both energy and resources.