High-speed Scanning Research Articles

Comprehensive Analysis of Phosphorus-Doped Silicon Annealed by Continuous-Wave Laser Beam at High Scan Speed.

We report an in-depth analysis of phosphorus (P)-doped silicon (Si) with a continuous-wave laser source using a high scan speed to increase the performance of semiconductor devices. We systematically characterized the P-doped Si annealed at different laser powers using four-point probe resistance measurement, transmission electron microscopy (TEM), secondary-ion mass spectroscopy, X-ray diffractometry (XRD), and atomic force microscopy (AFM). Notably, a significant reduction in sheet resistance was observed after laser annealing, which indicated the improved electrical properties of Si. TEM images confirmed the epitaxial growth of Si in an upward direction without a polycrystalline structure. Furthermore, we observed the activation of P without diffusion, irrespective of the laser power in the secondary-ion mass-spectrometry characterization. We detected negligible changes in lattice spacing for the main (400) XRD peak, showing an insignificant effect of the laser annealing on the strain. AFM images of the annealed samples in comparison with those of the as-implanted sample showed that the laser annealing did not significantly change the surface roughness. This study provides an excellent heating method with high potential to achieve an extremely low sheet resistance without diffusion of the dopant under a very high scan speed for industrial applications.

Clinical Implications and Molecular Characterization of Drebrin-Positive, Tumor-Infiltrating Exhausted T Cells in Lung Cancer.

T cells express an actin-binding protein, drebrin, which is recruited to the contact site between the T cells and antigen-presenting cells during the formation of immunological synapses. However, little is known about the clinical implications of drebrin-expressing, tumor-infiltrating lymphocytes (TILs). To address this issue, we evaluated 34 surgical specimens of pathological stage I-IIIA squamous cell lung cancer. The immune context of primary tumors was investigated using fluorescent multiplex immunohistochemistry. The high-speed scanning of whole-slide images was performed, and the tissue localization of TILs in the tumor cell nest and surrounding stroma was automatically profiled and quantified. Drebrin-expressing T cells were characterized using drebrin+ T cells induced in vitro and publicly available single-cell RNA sequence (scRNA-seq) database. Survival analysis using the propensity scores revealed that a high infiltration of drebrin+ TILs within the tumor cell nest was independently associated with short relapse-free survival and overall survival. Drebrin+ T cells induced in vitro co-expressed multiple exhaustion-associated molecules. The scRNA-seq analyses confirmed that the exhausted tumor-infiltrating CD8+ T cells specifically expressed drebrin. Our study suggests that drebrin-expressing T cells present an exhausted phenotype and that tumor-infiltrating drebrin+ T cells affect clinical outcomes in patients with resectable squamous cell lung cancer.

Directed energy deposition additive manufacturing of CoCrFeMnNi high-entropy alloy towards densification, grain structure control and improved tensile properties

Additive manufacturing (AM) of high-entropy alloys (HEAs), such as CoCrFeMnNi, is of high interest owing to their potential applications for extreme conditions (e.g., cryogenic environment). However, a major drawback of additively manufactured (AMed) metallic components is their poor and anisotropic mechanical properties, which primarily originate from the presence of metallurgical defects and coarse columnar grains. This study herein aims to (i) manipulate directed energy deposition (DED) AM parameters towards densification and (ii) suppress the formation of coarse columnar grains in DED AMed CoCrFeMnNi HEA. First, the effects of laser powers and laser scan speeds on the formation of various metallurgical defects in the DED AMed CoCrFeMnNi samples were investigated. Contrary to the laser powder bed fusion (L-PBF) AMed CoCrFeMnNi HEAs which were reported to form lack-of-fusion defects in the regime of low laser powers and high laser scan speeds, the lack-of-fusion defects in DED AMed CoCrFeMnNi HEAs tend to form in the regime of high laser powers and low laser scan speeds. This abnormal observation was rationalized by recourse to the resultant large layer thickness and hence insufficient melting. Cracking was observed in the regime of high laser scan speeds, and these cracks were classified into solidification cracks based on the observation of the intruding cellular/dendritic features on the cracked surface. High angle grain boundaries were found to be more sensitive to solidification cracking and the inherent mechanisms were discussed. Through such a high throughput library of samples, a printability map and near-full density were achieved for DED AMed CoCrFeMnNi HEAs. Second, for the grain structure control, contrary to the previous works that tried to manipulate the solidification conditions or introduce the secondary heterogenous particles, the current paper employed ultrasonic-assisted DED AM processing of CoCrFeMnNi HEA. Despite the measured lowered cooling rate, the coarse columnar grains were replaced by finer equiaxed grains in the presence of ultrasound, i.e., the average grain size decreases from 140 to 44 μm. The formation of fine equiaxed grains were rationalized by the combined effects of the ultrasonic-facilitated dendrite fragmentation as heterogenous nucleation sites and the enhanced liquid supercooling in the columnar front. As a direct result, the tensile yield strength of the ultrasonic-assisted DED AMed CoCrFeMnNi HEA increases by ∼ 17%, with no obvious tensile ductility drop. The strength increase was well explained by the grain refinement effect based on the classic Hall-Petch relationship. These findings provide opportunities to additively manufacture high-performance and complex-geometry HEAs components for critical applications.

Bimorph sensor based in-line inspection method for corrosion defect detection in natural gas pipelines

Recently, bimorph sensors based on the in-line inspection (ILI) method have shown considerable promise for detecting surface defects (e.g., corrosions) in gas pipelines. However, the effect of physical parameters such as bimorph position and scanning speed on the performance of the bimorph sensor has not yet been investigated. As a result, the capability of the bimorph sensor for defect detection in pipelines is not clear. This study aims to optimize the physical parameters and investigate the influence of physical parameters on the performance of the bimorph sensor. For this purpose, first various corrosion defect sizes were considered and analyzed using piezoelectric theory. Next, an analytical relationship between the vibration response of the bimorph sensor and defect is derived using the Euler-Bernoulli beam theory. Finally, a real-time field test was conducted based on the installation of the proposed method on a developed smart PIG to demonstrate the detection efficiency of the bimorph sensor. The novel contributions of this study are as follows: (1) The proposed analytical method uses cantilever beam vibrational mode shapes together with the piezoelectric effect to detect and quantify the corrosion defects. (2) The current study proposed a bimorph sensor method capable of performing high scanning speed (0.5 m/s) in real-time pipeline inspection. (3) The performance of the proposed method on the various position of bimorph on the cantilever probe and scanning speed is studied analytically and experimentally. (4) Multiple corrosion defects and pipeline joints were detected and localized successfully in complex pipeline networks. • Proposed a bimorph sensor method to detect corrosion defects in gas pipelines. • Performance of the proposed method is investigated analytically and experimentally. • Bimorph sensor is designed and tested in a laboratory testbed. • Effectiveness of the proposed method on various physical parameters is presented. • Field test is conducted with the designed bimorph sensor array.

Random-access multi-focus manipulation through superpixel-encoding wavefront engineering

Random-access multi-focus manipulation of multiple light beams at high speed can accelerate various important processes, such as laser material processing and imaging, and benefit semiconductor manufacturing and biomedical research. In this letter, we propose random-access multi-focus manipulation through superpixel-encoding wavefront engineering (RMM-SWE). This method simultaneously manipulates 25 independent focal spots at a rate as high as 23 kHz, which considerably increased the efficiency of scanning over irregular, complicated paths. We applied RMM-SWE to direct laser writing and showed that RMM-SWE holds great potential for the applications requiring multi-focus manipulation with high scanning speed, flexibility, and spatial resolution.

True Atomic-Resolution Surface Imaging and Manipulation under Ambient Conditions via Conductive Atomic Force Microscopy.

A great number of chemical and mechanical phenomena, ranging from catalysis to friction, are dictated by the atomic-scale structure and properties of material surfaces. Yet, the principal tools utilized to characterize surfaces at the atomic level rely on strict environmental conditions such as ultrahigh vacuum and low temperature. Results obtained under such well-controlled, pristine conditions bear little relevance to the great majority of processes and applications that often occur under ambient conditions. Here, we report true atomic-resolution surface imaging via conductive atomic force microscopy (C-AFM) under ambient conditions, performed at high scanning speeds. Our approach delivers atomic-resolution maps on a variety of material surfaces that comprise defects including single atomic vacancies. We hypothesize that atomic resolution can be enabled by either a confined, electrically conductive pathway or an individual, atomically sharp asperity at the tip-sample contact. Using our method, we report the capability of in situ charge state manipulation of defects on MoS2 and the observation of an exotic electronic effect: room-temperature charge ordering in a thin transition metal carbide (TMC) crystal (i.e., an MXene), α-Mo2C. Our findings demonstrate that C-AFM can be utilized as a powerful tool for atomic-resolution imaging and manipulation of surface structure and electronics under ambient conditions, with wide-ranging applicability.

AlCo-rich AlCoNiFe and AlCoNiFeCr high entropy alloys: Synthesis and interaction pathway at high heating rates

Novel AlCo-rich AlCoNiFe and AlCoNiFeCr high entropy alloys (HEAs) were prepared from the non-activated and mechanically activated (MA) quaternary Al40Co40Ni10Fe10at% and quinary Al35Co35Ni10Fe10Cr10at% mixtures. The wide temperature range of the formation of a single high entropy alloy of BCC structure in quaternary system and the formation of pure quinary AlCoNiFeCr alloy above 740 °C was predicted by thermodynamic modelling. The underlying interaction mechanism was proposed, and the effective activation energy values were deduced at high heating rates up to 2600 °C·min−1 by thermal analysis method through high-speed temperature scanner. The presence of a single-stage exothermic interaction in the non-activated and mechanically activated quaternary and quinary mixtures was attributed to HEA formation via either solid + liquid or solid + solid mechanism depending on the heating rate and mechanoactivation (MA) duration. The influence of heating rate and MA duration on the self-heating profile and reaction onset temperature was also deduced. Microstructure evolution and phase formation sequence were monitored by the examination of products quenched at characteristic temperatures at synthesis and processing of AlCo-rich AlCoNiFe and AlCoNiFeCr HEAs. The crystallite size (CS), lattice strain (LS) and lattice parameter (LP) of CoFeNiAl and CoFeNiAlCr HEAs were estimated according to MA duration. The thermal stability in argon and air flow conditions at heating rate of 40 °C·min−1 for up to 1200 °C was studied by thermogravimetric analyser complemented with X-ray diffraction analysis.

Effects of Different Scan Speeds on Microstructural and Corrosion Properties of Additively Manufactured HSLA Steels in 3.5% NaCl Solution

In automotive applications, high-strength low alloy (HSLA) steels are providing enhanced material properties, due to the high yield strength, less fragility, and lower weight, which also promotes lower fuel consumption. HSLA steels contain a small amount of carbon (under 0.2%) and also contain small amounts of alloying elements such as copper, nickel, niobium, vanadium, chromium, molybdenum and zirconium. This eliminates the toughness reducing effect of a pearlitic volume fraction, yet maintains and increases the material's strength by refining the grain size. Therefore, HSLA steels are used for structures intended to handle large amounts of stress or that need a good strength-to-weight ratio. Traditional manufacturing methods for steel (e.g., blast furnace or electric arc furnace methods) fail to provide the necessary optimization for best output in terms of performance and application. The quality of molten steel is greatly affected by scrap steel. The smelting period is longer, and the power consumption is large. In addition, these processes allow more impurities into the molten steel, which compromises the quality of the final product. However, additive manufacturing (AM) can can be used to fabricate HSLA steel components without these drawbacks. In addition, AM can provide a relatively faster process with low manufacturing costs, in comparison with traditional processing methods. Although AM has several benefits, studies shows that AM processes can result in HSLA steels with microstructural defects, such as non-homogeneity, internal cavities, inclusions, and impurities. Consequently, these microstructural features have a significant affect on the corrosion properties of AM parts as corrosion tends to initiate in defective regions. The AM processing parameters directly impact the microstructure of the fabricated part. Hence, it is important to understand the relationship between the AM processing parameters on resulting microstructural features. The present work evaluated the electrochemical corrosion properties of HSLA steels fabricated by AM via selective laser melting (SLM) under different processing conditions. The goal of the work was to investigate the role of microstructure on electrochemical corrosion in high-strength low alloy steels due to SLM processing conditions.Two types of HSLA steels, Fe 367 and Fe 398, were fabricated by AM via (SLM). Fe 398 differs from Fe 367 as it contains molybdenum and nickel. Each type was fabricated at a laser power of 100W, and scan speed of 600, 800, 100 and 1200 mm/s. The samples were exposed to 3.5% NaCl for 15 days, individually. To acquire the electrochemical corrosion data and to perform analysis, a Gamry reference 600 potentiostat/galvanostat was used. The electrochemical data were obtained by collecting the impedance spectra, and measuring the polarization resistance every 5 days. On day 15, cyclic polarization data was collected for each sample. These measurements helped to identify the localized corrosion as well as provide detailed information about the corrosion properties, such as passive layer growth, initiation and secession of pitting, and corrosion rate. The topography of the materials was observed by SEM before and after the corrosion tests. Energy Dispersive Spectroscopy (EDS) was performed on the samples to identify the chemical elements. The surface roughness was observed through confocal microscope.The Confocal and SEM images showed the change in surface microstructure and topographical properties of the samples before and after the corrosion testing. The difference in laser power and scan speed affected the microstructure and corrosion properties of the materials. As the samples were manufactured at same laser power, the scan speed was responsible for different topographical and corrosion behavior. Samples manufactured at lower scan speed showed less flaws on the surface of the materials than the samples manufactured at higher scan speed. Therefore, both Fe 398 and Fe 367 showed better surface topography at 600 mm/s and 800 mm/s. They also demonstrated significantly lower corrosion rate than the other samples. EDS identified chemical oxides and chlorides which were formed during the corrosion test. Overall, this work demonstrated that Fe 398 shows better microstructural and corrosion properties than Fe 367 at lower scan speed.

Freehand scanning photoacoustic microscopy with simultaneous localization and mapping

Optical-resolution photoacoustic microscopy offers high-resolution, label-free hemodynamic and functional imaging to many biomedical applications. However, long-standing technical barriers, such as limited field of view, bulky scanning probes, and slow imaging speed, have limited the application of optical-resolution photoacoustic microscopy. Here, we present freehand scanning photoacoustic microscopy (FS-PAM) that can flexibly image various anatomical sites. We develop a compact handheld photoacoustic probe to acquire 3D images with high speed, and great flexibility. The high scanning speed not only enables video camera mode imaging but also allows for the first implementation of simultaneous localization and mapping (SLAM) in photoacoustic microscopy. We demonstrate fast in vivo imaging of some mouse organs, and human oral mucosa. The high imaging speed greatly reduces motion artifacts and distortions from tissue moving, breathing, and unintended handshaking. We demonstrate small-lesion localization in a large region of the brain. FS-PAM offers a flexible high-speed imaging tool with an extendable field of view, enabling more biomedical imaging applications.

Sub-wavelength patterned pulse laser lithography for efficient fabrication of large-area metasurfaces

Rigorously designed sub-micrometer structure arrays are widely used in metasurfaces for light modulation. One of the glaring restrictions is the unavailability of easily accessible fabrication methods to efficiently produce large-area and freely designed structure arrays with nanoscale resolution. We develop a patterned pulse laser lithography (PPLL) approach to create structure arrays with sub-wavelength feature resolution and periods from less than 1 μm to over 15 μm on large-area thin films with substrates under ambient conditions. Separated ultrafast laser pulses with patterned wavefront by quasi-binary phase masks rapidly create periodic ablated/modified structures by high-speed scanning. The gradient intensity boundary and circular polarization of the wavefront weaken diffraction and polarization-dependent asymmetricity effects during light propagation for high uniformity. Structural units of metasurfaces are obtained on metal and inorganic photoresist films, such as antennas, catenaries, and nanogratings. We demonstrate a large-area metasurface (10 × 10 mm2) revealing excellent infrared absorption (3–7 μm), which comprises 250,000 concentric rings and takes only 5 minutes to produce.

Multi-objective optimization of Nd:Yag laser machining’s conflicting responses while milling micro-channels

Laser processing of materials finds application in micro-nano devices mainly because of its accuracy, flexibility, and ability to machine almost any material. Although it offers numerous advantages, it is a complex process involving a large number of factors. The quality of machining often depends on the appropriate selection of parameters. Moreover, the output responses in machining processes have conflicting nature; some are to be minimized, and others have to be maximized. This work uses grey relationship analysis coupled with principal component analysis for multi-response optimization of conflicting responses during laser machining of micro-channels. Micro-channels with a cross-sectional size of 200 × 100 µm were created using Nd:YAG laser beam micro-milling in steel alloy (AISI 1045). The scan speed, layer thickness, and scan strategy were found to have a significant effect on the dimensional accuracy of the microchannel. At the same time, the material removal rate was mostly influenced by layer thickness. Multi-response optimization results suggest low pulse frequency, high scan speed, low layer thickness, and S3 scan strategy for accurately fabricating micro-channels.

Swept-source endoscopic optical coherence tomography real-time imaging system based on GPU acceleration for axial megahertz high-speed scanning.

In order to solve the problem of image real-time processing and correction for high-speed endoscopic swept-source optical coherence tomography (SS-OCT), we highly optimize a computer-unified device architecture-based platform and use a field-programmable gate array to summarize the application experience. We use the Half-Sync/Half-Asyn mode to optimize memory in order to build a high-throughput data thread pool for CPU. We use asynchronous streaming architecture to multiplex multiple threads at high speed to accelerate data processing. At the same time, we design a rotary scanning position information encoding feedback module to suppress image drift, which can realize 25ns logic-timing sequence synchronization control through FPGA 40MHz clock. The maximum complete attainable axial-scan-processing rate (including memory transfer and display of B-scan frames) is 3.52 MHz for a 16-bit pixel depth and A-scans/s of 1024 pixels. To our knowledge, this is the fastest processing rate reported to date with a single-chip graphical processing unit for SS-OCT. Finally, the established high-speed SS-OCT is used to image mouse esophagus and human fingers, and the output images are stable. When the image size is 1024 × 1024 pixels, the real-time imaging rate is 200 frames per second. This paper develops a real-time image processing and reconstruction technology suitable for high-throughput SS-OCT systems, which can have high-density operation and efficient parallelism, while suppressing high-speed image drift. It lays the foundation for the non-destructive, in vivo, non-staining, fast and convenient early tumor diagnosis of high-speed endoscopic SS-OCT.

Boosting Productivity of Laser Powder Bed Fusion for AlSi10Mg

The Laser Powder Bed Fusion (L-PBF) process is recognized for high-end industrial applications due to its ability to produce parts with high geometric complexity. If lightweighting is one of the main strengths of L-PBF, a weakness is still the trade-off between high mechanical properties and competitive productivity. This objective can be targeted through a fine tuning of the process parameters within the manufacturing window. The paper pursues the combined optimization of part quality and process productivity for AlSi10Mg by going beyond the commonly used approach based solely on volumetric energy density. The effects of hatch distance and scan speed on the two targets were analyzed in detail. The best results were achieved by the adoption of a high scan speed and a low hatch distance, with notably different outcomes for nearly the same energy density.

Influence of protocol scan on choroidal vascularity measurements: a spectralis optical coherence tomography study

ObjectivesTo compare choroidal vascularity index (CVI) measurements using the automated image binarization algorithm in healthy subjects with two Spectralis spectral-domain optical coherence tomography (SD-OCT) protocol scans.MethodsSixty-nine eyes of 69 healthy volunteers were included in this cross-sectional prospective study. Two subsequent horizontal 20°line scans passing through the fovea were acquired with enhanced-depth imaging mode with high speed (HS) and high resolution (HR) protocol scans. CVI and its subcomponents were measured with the previously validated automated algorithm. Differences between choroidal measurements obtained with HS and HR protocol scans were evaluated with t-test and Bland & Altman plots.ResultsA total of 33 male (47.8%) and 36 female (52.2%) subjects with a mean age of 35.1 ± 13.4 years were included. Overall, HS protocol scan was associated with significant lower values of total choroidal area (−0.047 mm2) and stromal choroidal area (−0.036 mm2), and a significant greater value of CVI (+0.010%) if compared to HR protocol. Luminal choroidal area was lower when calculated with the HS protocol, although it did not reach significance. To compare the two different protocols, the number of pixels should be multiplied for 3.87 ×5.73 when the CVI is measured on a HR OCT b scan and 3.87 ×11.46 for the HS OCT b scan.ConclusionsHS and HR acquisition modes significantly influence CVI and its subcomponents values measured with the automated software. However, adopting the scale factors can minimize the differences between the two protocol scans.

Deep learning alignment of bidirectional raster scanning in high speed photoacoustic microscopy

Simultaneous point-by-point raster scanning of optical and acoustic beams has been widely adapted to high-speed photoacoustic microscopy (PAM) using a water-immersible microelectromechanical system or galvanometer scanner. However, when using high-speed water-immersible scanners, the two consecutively acquired bidirectional PAM images are misaligned with each other because of unstable performance, which causes a non-uniform time interval between scanning points. Therefore, only one unidirectionally acquired image is typically used; consequently, the imaging speed is reduced by half. Here, we demonstrate a scanning framework based on a deep neural network (DNN) to correct misaligned PAM images acquired via bidirectional raster scanning. The proposed method doubles the imaging speed compared to that of conventional methods by aligning nonlinear mismatched cross-sectional B-scan photoacoustic images during bidirectional raster scanning. Our DNN-assisted raster scanning framework can further potentially be applied to other raster scanning-based biomedical imaging tools, such as optical coherence tomography, ultrasound microscopy, and confocal microscopy.

Fundamental Study on the Development of Pure Magnesium Parts by Additive Manufacturing: An Experimental and Computational Analysis

The low density and high biocompatibility of Mg-based materials make them suitable for lightweight structural and biomedical applications. In this study, we explored the use of selective laser melting (SLM)–an additive manufacturing process wherein metal powders are consolidated in a layer-by-layer manner, allowing the fabrication of complex components. SLM typically involves complex physicochemical phenomena and results in laser-processing defects, which makes it difficult to predict the densification mechanisms of the melt pool. Therefore, a full-scale model was developed to investigate the thermal behavior of the melt pool (e.g., temperature gradient distribution, melt pool dimensions, and cooling rate) and the resultant densification activity under various laser energy density (η) values. In parallel, experimental investigations of the densification behavior and microstructural evolution were undertaken with the same SLM processing parameters. The challenges associated with the SLM processability of Mg were comprehensively addressed. Both the peak temperature gradients within the molten pool and molten pool dimensions increased with increasing η, and an opposite trend was observed for the cooling rate. A low η (i.e., high scanning speed) results in a low operating temperature and short liquid lifetime, which in turn lead to poor wettability and many pore-chain and balling defects. However, high η values generated melt pool instability, which resulted in extensive evaporation, cracks, and porosity. The SLM-processed samples had fine twin-like microstructures as a result of rapid solidification. The experimental and simulation results agreed well, validating the thermal behavior of the molten pool and underlying physical mechanism.Graphic Abstract

Preparation Technology of Stretchable Electrode Based on Laser Cutting

Wearable electronics have showed their profound impact in military, sports, medical and other fields, but their large-scale applications are still limited due to high manufacturing costs. As an advanced micro-fabrication process, laser processing technology has the advantages of high speed, high flexibility, strong controllability, environmental protection and non-contact in preparing micro-nano structures of wearable electronics. In this paper, a 355 nm ultraviolet laser was used to pattern the copper foil pasted on the flexible substrate, and the interconnection electrodes and wires were constructed. A processing method of multi-parallel line laser cutting and high-speed laser scanning is proposed to separate and assist in peeling off excess copper foil. The process parameters are optimized. A stretchable 3 × 3 light-emitting diode (LED) array was prepared and its performance was tested. The results showed that the LED array can work normally under the conditions of folding, bending and stretching, and the stretch rate can reach more than 50%. A stretchable temperature measurement circuit that can be attached to a curved surface was further fabricated, which proves the feasibility of this process in the fabrication of small-scale flexible wearable electronic devices. Requiring no wet etching or masking process, the proposed process is an efficient, simple and low-cost method for the fabrication of stretchable circuits.

Research on the dynamic fracture toughness of reef limestone

The basic properties of reef limestone were measured to explore the dynamic fracture characteristics of reef limestone. The test results show that the physical and mechanical properties of blocky reef limestone are linearly related to the density. Hence, accurate mechanical parameters can be ascribed to standard mechanical specimens. Next, the fracture toughness of the reef limestone was measured using notched semi-circular bend (NSCB) specimens. Meanwhile, fracture energy and characteristics were studied with the help of a high-speed camera and scanning electron microscope. The findings show that the fracture toughness and energy of reef limestone are linearly related to the density with a rate effect. Moreover, the dynamic compressive strength is also linearly correrlated with the dynamic fracture toughness of reef limestone under the same loading rate; the fracture toughness of saturated reef limestone is larger than that of dry reef limestone. Besides, reef limestone has a rough fracture surface for its various crystal shapes and arrangements, with cracks propagating along the interface of varied crystals.

Manufacturing and toughening effects on the material properties of wind turbine blade adhesives

Hybrid adhesives can be developed using commercially available adhesive materials and customized to the required loading conditions. In this paper, SPABOND™ 820HTA (non-toughened) and SPABOND™ 840HTA (toughened) adhesives are hybridized by two strategies and fabricated by machine and manual mixing methods. The manufacturing and hybridization effects on the bulk adhesive properties are evaluated by dynamic mechanical analysis, quasi-static tensile, V-notch shear and single-edge-notch bending tests. X-ray micro-computed tomography, digital image correlation technique, high speed camera and scanning electron microscopic images are used for assessing the manufacturing quality, computing the full-field displacement and strain, and failure analysis. By considering the manufacturing methods, the measured properties are less influenced by the presence of voids but dependent on the glass fiber filler orientation. The adhesive toughening method improves the strain to failure and tensile toughness, decreases the strength and modulus and no significant effect on the glass transition temperature.

Additive Manufacturing of Tool Steels

The public funded project “AddSteel” aims to develop functionally adapted steel materials for additive manufacturing (AM). Based on the AM process laser powder bed fusion (LPBF), the holistic process chain, including alloy design, powder atomization, AM, and postheat treatment, is considered to achieve this objective. Tool steels are usually characterized by higher carbon content and limited weldability, leading to limited processability for LPBF. To extend these limitations, different approaches for tool steels are investigated: for high‐carbon tool steels, the effects of lower martensite start temperature are investigated using the alloy 1.2842 as an example. A low martensite start temperature seems to be advantageous for crack‐free processing with LPBF. In order to avoid a high hardness level after rapid cooling, the use of a hot work steel with a carbon content of 0.2 wt% is investigated. Due to the chemical composition of the material, a moderate preheating temperature <300 °C is required. In addition, very high scanning speeds are possible with an improved shielding gas flow. Finally, the experience along the process chain with the standard steels is used for a modification of the alloy 1.2344. The effects of this modification on AM and heat treatment are investigated.