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Cracks and keyhole pores are detrimental defects in alloys produced by laser directed energy deposition (LDED). Laser-material interaction sound may hold information about underlying complex physical events such as crack propagation and pores formation. However, due to the noisy environment and intricate signal content, acoustic-based monitoring in LDED has received little attention. This paper proposes a novel acoustic-based in-situ defect detection strategy in LDED. The key contribution of this study is to develop an in-situ acoustic signal denoising, feature extraction, and sound classification pipeline that incorporates convolutional neural networks (CNN) for online defect prediction. Microscope images are used to identify locations of the cracks and keyhole pores within a part. The defect locations are spatiotemporally registered with acoustic signal. Various acoustic features corresponding to defect-free regions, cracks, and keyhole pores are extracted and analysed in time-domain, frequency-domain, and time-frequency representations. The CNN model is trained to predict defect occurrences using the Mel-Frequency Cepstral Coefficients (MFCCs) of the lasermaterial interaction sound. The CNN model is compared to various classic machine learning models trained on the denoised acoustic dataset and raw acoustic dataset. The validation results shows that the CNN model trained on the denoised dataset outperforms others with the highest overall accuracy (89%), keyhole pore prediction accuracy (93%), and AUC-ROC score (98%). Furthermore, the trained CNN model can be deployed into an in-house developed software platform for online quality monitoring. The proposed strategy is the first study to use acoustic signals with deep learning for insitu defect detection in LDED process., 36 Pages, 16 Figures, accepted at journal Additive Manufacturing

With high strength and stiffness-to-weight ratios, Carbon-Fiber-Reinforced Polymer (CFRP) composite has been applied to the separation device of the rocket by shaped charge jet. But dynamic tensile and compressive properties of CFRP under high rate strain are still unclear. In the article, tensile testing along transverse direction are conducted. The quasi-static tests (10-3 s-1) use a universal testing machine and high dynamic loadings of 800 s-1 and 1600 s-1 tests adopt a high-speed tensile testing machine. Meanwhile, dynamic compressive tests of unidirectional and cross-ply laminated specimen under the thickness direction loading are implemented by a Split Hopkinson Pressure Bar (SHPB) from dynamic loading 500 s-1 to 2500 s-1. Test results show that compared with static tests data, both transverse tensile modulus and strength of CFRP composites materials at dynamic loadings are sensitive to tensile tests. The compressive peak stress and stiffness of specimens also have an increasing tendency with the increases of the strain rate. Furthermore, for failure mode of tensile specimens, the crack propagation of the specimen fracture is along the interface of the fiber/matrix under all loading conditions. The failure modes of compressive specimens are different as the strain rate changes. The higher the strain rate, the more severe the crushing.

Laser cladding coatings with excellent wear resistance behaviors are prepared on a titanium alloy substrate with a new precursor material system comprising nanoscale B4C and Ni60A self-fluxing alloy powder. Structural analysis reveals the existence of micron-size spherical or nearly spherical graphitic phases in the prepared coatings, which are composed of graphene-like microstructures closely associated with other reinforcement phases of high hardness such as TiC and CrB. The formation mechanism of these graphitic phases involves in situ superassembly of uncombined C atoms via repeated growth and reorientation of the graphene-like microstructures and is closely related to the laser processing parameters as well as the precursor compositions. The coexistence of these heterogeneous phases enable the obtained coatings with high wear resistance and low friction coefficient. It was found that the wear resistance of the coating has a remarkable 43.67 times enhancement than that of the titanium alloy while simultaneously showing a low friction coefficient (∼0.35). The understanding of the formation mechanism on the graphene-related novel microstructures with significantly improved mechanical properties is expected to lay the foundation for future developments and applications of graphene and its related carbon materials, such as large-scale production and further incorporation into composite materials with desired local structures., Surplus carbon atoms in the molten pool nucleate at the bubble/melt interface and grow into graphitic layers. The spherical graphic structure is formed by superassembly of these graphitic layers.

Hierarchical microchannels, which consist of the primary channel formation and superimposed secondary nanostructures, are attracting ever-increasing attention due to their unique capacity to enhance and modify the surface characteristics and functional performance. The mechanical machining methods for microchannel fabrication, such as micro-milling and diamond turning, can achieve high material removal rates without changing material properties. However, they have limited capacity to control the channel cross-section profiles and shapes due to the relative size between the channel dimension and tool geometry. This study proposes a new cutting-based approach for the fast and cost-effective fabrication of hierarchical microchannels with controllable profiles and orientations by utilizing modulated elliptical vibration texturing. The modulation motion is adopted to form the primary channel in an incremental approach, while the elliptical vibration texturing is utilized to create micro/nano-scale secondary textures. By controlling the tool modulation trajectory, hierarchical dimple arrays with controllable cross-section profiles are first demonstrated. Then, by programming the layout of dimples to adjust the overlapping ratio between each cut, channels can be formed with arbitrary cross-section profiles and orientations. The efficacy of the proposed process has been demonstrated through numerical simulation and experimental results. Hierarchical microchannels with straight and curving shapes, as well as different cross-section profiles (sinusoidal, triangular, trapezoidal), have been presented.

The delamination is a typical phenomenon when the carbon fiber reinforced composites (CFRC) undergoes blasting impact loading and the delamination will reduce both the strength and stiffness of the laminates, which can lead to catastrophic consequences while used as rocket skin. In this paper, the response of CFRC laminate is cut by flexible linear shaped charge (FLSC) and the delamination behavior of the CFRC is analyzed and discussed. The displacement interferometer system for any reflector (DISAR) is used to monitor the velocity of characteristic points of the laminate subjected to FLSC. Finite element analysis has been conducted to explain the mechanisms of delamination. Based on the numerical simulation, the influences of structural design parameters on the delamination effect of the CFRC after cutting are investigated. The results show that a large number of debris are produced at the center of the explosion and a small amount of large debris is produced at weakening groove on both sides. The delamination effect is greatly affected by the inter-laminar tensile strength and thickness of composite laminate, but it is not significantly affected by the linear density of the FLSC and stand-off.

Antimony selenide (Sb2Se3) films are widely used in phase change memory and solar cells due to their stable switching effect and excellent photovoltaic properties. These properties of the films are affected by the film thickness. A method combining the advantages of Levenberg–Marquardt method and spectral fitting method (LM–SFM) is presented to study the dependence of refractive index (RI), absorption coefficient, optical band gap, Wemple–DiDomenico parameters, dielectric constant and optical electronegativity of the Sb2Se3 films on their thickness. The results show that the RI and absorption coefficient of the Sb2Se3 films increase with the increase of film thickness, while the optical band gap decreases with the increase of film thickness. Finally, the reasons why the optical and electrical properties of the film change with its thickness are explained by x-ray diffractometer (XRD), energy dispersive x-ray spectrometer (EDS), Mott–Davis state density model and Raman microstructure analysis.

A two-step double-side friction stir welding (DS-FSW) technique was proposed to join 20 mm thick Mg–Y–Nd magnesium alloy plates. FSW was first carried out on one side of the butt joint, and then th...

Aromatic alcohols are essential components of many solvents, coatings, plasticizers, fine chemicals, and pharmaceuticals. Traditional manufacturing processes involving the oxidation of petroleum-de...

Thin 316L stainless steel rods were fabricated by continuous directed energy deposition in Z direction. The process parameters (laser power, scan velocity, and powder feeding rate) were carefully selected to obtain a stable deposition process and the effects of powder feeding rate and scan velocity were studied. A preliminary study on microstructure and tensile properties of the specimens was carried out. Results indicated that the specimen showed superior austenite/ferrite (γ/δ) dual phase microstructure, high strength (608.24 MPa), and good plastic deformation capacity (65.08% shrinkage rate) when setting the laser power at 45.2 W, powder feeding rate at 2.81 g/min, and scan velocity at 0.5 mm/s. The technique reported in this paper is expected to lay the foundation for the deposition of wire or frame structures more efficiently than traditional layer-by-layer directed energy deposition.

In traditional directed energy deposition (DED) processes, post-processing involving laser cutting or wire electrical discharge machining is necessary for removing printed parts from the substrate, which is time consuming and labor intensive. In this letter, a support interface method for DED is proposed for direct part removal without additional machining operations. A strut array is first printed as a sacrificial layer, upon which the actual part is then deposited. This letter demonstrates the method feasibility with a customized DED setup. It is expected that the proposed strategy will be beneficial in various DED processes to enhance process efficiency and automation.

It is well-known that grain refiners can tailor the microstructure and enhance the mechanical properties of titanium alloys fabricated by additive manufacturing (AM). However, the intrinsic mechanisms of Ni addition on AM-built Ti–6Al–4V alloy is not well established. This limits its industrial applications. This work systematically investigated the influence of Ni additive on Ti–6Al–4V alloy fabricated by laser aided additive manufacturing (LAAM). The results showed that Ni addition yields three key effects on the microstructural evolution of LAAM-built Ti–6Al–4V alloy. (a) Ni additive remarkably refines the prior-β grains, which is due to the widened solidification range. As the Ni addition increased from 0 to 2.5 wt. %, the major-axis length and aspect ratio of the prior-β grains reduced from over 1500 μm and 7 to 97.7 μm and 1.46, respectively. (b) Ni additive can discernibly induce the formation of globular α phase, which is attributed to the enhanced concentration gradient between the β and α phases. This is the driving force of globularization according to the termination mass transfer theory. The aspect ratio of the α laths decreased from 4.14 to 2.79 as the Ni addition increased from 0 to 2.5 wt. %. (c) Ni as a well-known β-stabilizer and it can remarkably increase the volume fraction of β phase. Room-temperature tensile results demonstrated an increase in mechanical strength and an almost linearly decreasing elongation with increasing Ni addition. A modified mathematical model was used to quantitatively analyze the strengthening mechanism. It was evident from the results that the α lath phase and the solid solutes contribute the most to the overall yield strength of the LAAM-built Ti–6Al–4V–xNi alloys in this work. Furthermore, the decrease in elongation with increasing Ni addition is due to the deterioration in deformability of the β phase caused by a large amount of solid-solution Ni atoms. These findings can accelerate the development of additively manufactured titanium alloys.

Additive manufacturing (AM) enables the processing of heterogeneous materials with customised architectures to improve strength-ductility synergy. Herein, layerwise-heterostructured high-strength steels were processed by AM of two steel powders following the designed architectures. The fabricated high-strength steels with hierarchical heterogeneous characteristics at the layer, melt-pool and grain scales, exhibit good strength-ductility combination, reaching a strength of 1.32 GPa together with an elongation of 7.5%. The increased strength attributes to hetero-deformation induced strengthening. In-situ deformation monitoring reveals many unique deformation bands in heterostructure materials, which delays necking and improves ductility. The findings demonstrate a novel potential approach to circumvent material property trade-offs. Additively manufactured heterogeneous materials with controllable architectures achieved a good strength-ductility combination; the underlying strengthening mechanism and unique deformation behaviour are revealed.

In this paper, a direct laser deposition (DLD) process was used to print ASTM A131 EH36 high strength low alloy steel samples in four different orientations, namely, horizontal 0° (XY_0°) & 45° (XY_45°) and vertical 90° (XZ_90°) & 45° (XZ_45°), with an EH36 steel powder. The microstructures, mechanical properties and fracture behavior of the printed materials, were evaluated in detail. Tensile, charpy impact and fatigue tests were conducted to measure the mechanical properties of the materials. The results showed that all the EH36 steel samples printed in the four orientations satisfied the ASTM standards for the tensile and charpy impact properties of EH36 steel. The microstructures of the EH36 steel samples and the thermal cycles encountered in the different build orientations could be tuned by controlling the printing process parameters and scanning method. The microstructure was closely correlated with the mechanical properties of the built samples. The fatigue fracture mechanism of the printed EH36 steel samples was also proposed. National Research Foundation (NRF) This work was supported by the Singapore Centre for 3D Printing, Nanyang Technological University, Singapore and funded by the National Research Foundation, Prime Minister's Office, Singapore under the Medium-Sized Centre funding scheme and the Research Collaboration Agreement between NTU and Keppel Marine & Deepwater Technology, Singapore.

Myotonic dystrophy (DM) is a genetic disorder featured by muscular dystrophy. It is caused by CUG expansion in the myotonic dystrophy protein kinase gene that leads to aberrant signaling and impaired myocyte differentiation. Many studies have shown that microRNAs are involved in the differentiation process of myoblasts. The purpose of this study was to investigate how the miR-322/miR-503 cluster regulates intracellular signaling to affect cell differentiation. The cell model of DM1 was employed by expressing GFP-CUG200 or CUGBP Elav-like family member 1 (Celf1) in myoblasts. Immunostaining of MF-20 was performed to examine myocyte differentiation. qRT-PCR and western blot were used to determine the levels of Celf1, MyoD, MyoG, Mef2c, miR-322/miR-503, and mitogen-activated protein kinase/extracellular signal-regulated kinase (MEK/ERK) signaling. Dual luciferase assay was performed to validate the interaction between miR-322/miR-503 and Celf1. CUG expansion in myoblasts impaired the cell differentiation, increased the Celf1 level, but it decreased the miR-322/miR-503 levels. miR-322/miR-503 mimics restored the impaired differentiation caused by CUG expansion, while miR-322/miR-503 inhibitors further suppressed. miR-322/miR-503 directly targeted Celf1 and negatively regulated its expression. Knockdown of Celf1 promoted myocyte differentiation. Further, miR-322/miR-503 mimics rescued the impaired differentiation of myocytes caused by CUG expansion or Celf1 overexpression through suppressing of MEK/ERK signaling. miR-322/miR-503 cluster recover the defective myocyte differentiation caused by RNA-toxic via targeting Celf1. Restoring miR-322/miR-503 levels could be an avenue for DM1 therapy.

Herein, we have shown that the [Ca–O–P] sites exposed on hydroxyapatite are clearly responsible for C–C formation in ethanol direct-coupling, and their high density accelerates the C–C coupling rate and boosts C6–12 alcohol production. Notably, nanowire-like hydroxyapatite exhibited 30.4% selectivity to n-butanol and 63.9% selectivity to C6–12OH at a conversion of 45.7% at 325 °C, and thereby close to 30% yield of C6–12OH, which is greatly higher than that using the state-of-the-art catalysts (6%).

The CoCrFeNiMn high entropy alloy (HEA) bulk alloy was successfully manufactured using laser aided additive manufacturing (LAAM). The microstructure and mechanical behaviors of the as-fabricated HEAs were investigated. The as-built HEAs exhibit directional solidification at regions close to the melt-pool boundaries, forming dendritic columnar grains and transiting to equiaxed grains further away from the boundaries. Compared with the conventionally cast HEAs, the CoCrFeNiMn fabricated using LAAM possesses significantly higher yield strength (518 MPa) and ultimate tensile strength (660 MPa). The strengthening effect is attributed to finer grains and could be explained quantitatively through grain boundary strengthening. The as-built HEA shows a simultaneous enhancement in yield strength and ductility with decreasing testing temperature. The improved low temperature tensile properties could be ascribed to the formation of deformation twins at low temperature, which results in a steady strain hardening behavior. This work demonstrates the potential of using LAAM technology to extend the application of HEAs with fabrication of larger and more complex parts with good mechanical properties.

Vacuum electron beam welding (EBW) was used to weld the thick TA1 titanium alloy sheets. Test results indicated that the coarse serrated-shape α and needle-shape α′ grains were observed in weld zone (WZ); the heat affected zone (HAZ) near the weld center consisted of α and α′ gains; the tensile strength of the TA1 joint was 344 MPa, which was significantly higher than that of the base metal (BM); the fracture of the tensile samples with different penetration depths all occurred on BM, the tensile property of the upper-bottom joint was better than that of the middle joint; moreover, lots of dimples can be observed on the fatigue fracture surface, exhibiting the characterization of the ductile fracture.

The electrochemical corrosion behavior of laser aided additive manufactured (LAAMed) CoCrNi medium entropy alloys (MEAs) with different oxide inclusion level was investigated in 3.5 wt.% NaCl solution. Different from the 316 L stainless steel, no pitting appeared on the LAAMed CoCrNi within the test regime used in this study. The LAAMed sample with a higher oxide inclusion level demonstrated lower corrosion current density and higher charge transfer resistance, implying a more compact passive film. After holding in the solution at 0.2 VSCE for 30 mins, the passive films formed on the LAAMed CoCrNi MEAs have similar thickness and dominant constituent (i.e. Cr2O3 and Cr(OH)3). More oxides in the LAAMed CoCrNi MEA could facilitate the formation of a compact passive film, which leads to superior corrosion resistance.

Micro- and nano-scale rare earth oxides (REOs) modified composites were fabricated by laser scanning the preplaced materials, similar to the process in selective laser melting (SLM). To conduct the comparative study on the effect of different REOs, single-layer composites were prepared on Ti-6Al-4V alloy with Ni60A+10 wt.% B4C mixture as the basic material and different REOs as the additives. Experiments with micro- and nano-scale REOs (Nd2O3, La2O3) demonstrated benefits in refining the microstructure, improving both the micro-hardness and wear property of the composites, amongst which the nano-scale REOs show better performance. Compared with the composite without REOs addition, the composite modified with 1 wt. % nano-La2O3 exhibited the finest microstructure. The mean micro-hardness increased by ~36.0% from 1058 HV0.2 to 1439 HV0.2, and the wear resistance was improved by 38.5% based on the wear volume loss. The better refining effect of the nano-scale REO was mainly attributed to the small particle size, which was more dispersive in the preplaced materials for increased nucleation. This study is not only useful for surface strengthening of titanium alloys, but also provides inspiration for fabricating bulk composite materials with suitable REO additives.

Current heterostructured materials demonstrate the high potential to circumvent strength-ductility tradeoff but face challenges with unconfigurable hetero-zone distribution and mechanical anisotropy. This study explored laser aided additive manufacturing (LAAM) of non-laminar spatially heterostructured materials (SHM) with configurable architectures to combine superior properties from the constitutive AISI 420 stainless steel and C300 maraging steel to enhance the overall properties. It is proven that the hatch spacing (h) has a significant effect on the microstructural evolutions and mechanical properties of the SHMs as it affects the layer thickness and inter-dilution regions. The mechanical properties of the SHMs were evaluated at multi-scales. The sample with h of 1.5 mm possesses a high tensile strength of about 1.6 GPa along with a reasonable break elongation of 8.1%, showing a good strength-ductility combination. Micropillar compression tests were conducted to measure localised mechanical properties, which is critical to understand the strengthening mechanism. Additionally, the SHM substantiates a much higher strength than many lamellar and linear functionally graded materials reported in the literature. This can be explained by the rule-of-mixture effect and hetero-deformation induced strengthening (HDIS). Furthermore, in-situ deformation observation reveals multiple deformation bands in SHM, which delays necking and contributed to ductility in tandem with the transformation induced plasticity (TRIP) effect. The findings highlight a novel approach for the development of SHM with a tunable performance by using LAAM of multiple materials following the configurable architectures.

Aerospace is a key market driver for the advancement of additive manufacturing (AM) due to the huge demands in high-mix low-volume production of high-value parts, integrated complex part geometries and simplified fabrication workflow. Rapid and significant progress has been made in the laser additive manufacturing (LAM) of aeroengine materials, including the advanced high-strength steels, nickel-based superalloys and titanium-based alloys. Despite the extensive investigation of these three families of materials by the research community, there is a lack of comprehensive review on LAM of high strength steels, and existing gaps in published reviews on Ti-based alloys and Ni-based superalloys. Furthermore, although emerging materials such as high/medium entropy alloys and heterostructured materials exhibit promising mechanical performance, rigorous characterization, testing, qualification, and certification are still required before actual application in engine parts. Thus, it is still important and relevant to have a deep understanding on the relationship between process parameters – microstructures – mechanical properties in these widely used aeroengine materials, to drive the development of superior high-value alloys. This review aims to provide a critical and in-depth evaluation of laser powder bed fusion (LPBF) and laser directed energy deposition (LDED) technologies of the mentioned aeroengine materials. The review will summarize the material properties, performance envelops and outlines the research gaps of these aeroengine materials. Furthermore, perspectives on research opportunities, materials development, and new R&D approaches of LAM for the aeroengine materials are also highlighted.

Ti 5 Si 3 /TiC reinforced Co-based composite coatings were fabricated on Ti-6Al-4V titanium alloy by laser cladding with Co42 and SiC mixture. Microstructure and wear property of the cladding coatings with different content of SiC were investigated. During the cladding process, the original SiC dissolved and reacted with Ti forming Ti 5 Si 3 and TiC. The complex in situ formed phases were found beneficial to the improvement of the coating property. Results indicated that the microhardness of the composite coatings was enhanced to over 3 times the substrate. The wear resistance of the coatings also showed distinct improvement (18.4–57.4 times). More SiC gave rise to better wear resistance within certain limits. However, too much SiC (20 wt%) was not good for the further improvement of the wear property.