Showing papers in "Optics and Laser Technology in 2019"
TL;DR: A noise removal and contrast enhancement algorithm for fundus image using Integration of filters and contrast limited adaptive histogram equalization (CLAHE) technique is applied for solving the issues of de-noising and enhancement of color fundus images.
Abstract: Now-a-days medical fundus images are widely used in clinical diagnosis for the detection of retinal disorders. Fundus images are generally degraded by noise and suffer from low contrast issues. These issues make it difficult for ophthalmologist to detect and interpret diseases in fundus images. This paper presents a noise removal and contrast enhancement algorithm for fundus image. Integration of filters and contrast limited adaptive histogram equalization (CLAHE) technique is applied for solving the issues of de-noising and enhancement of color fundus image. The efficacy of the proposed method is evaluated through different performance parameters like Peak Signal to Noise Ratio (PSNR), Structural Similarity Index (SSIM), Correlation coefficient (CoC) and Edge preservation index (EPI). The proposed method achieved 7.85% improvement in PSNR, 1.19% improvement in SSIM, 0.12% improvement in CoC and 1.28% improvement in EPI when compared to the state of the art method.
191 citations
TL;DR: Simulation results verify the effectiveness and reliability of the proposed image compression and encryption algorithm with considerable compression and security performance.
Abstract: For a linear image encryption system, it is vulnerable to the chosen-plaintext attack. To overcome the weakness and reduce the correlation among pixels of the encryption image, an effective image compression and encryption algorithm based on chaotic system and compressive sensing is proposed. The original image is first permuted by the Arnold transform to reduce the block effect in the compression process, and then the resulting image is compressed and re-encrypted by compressive sensing, simultaneously. Moreover, the bitwise XOR operation based on chaotic system is performed on the measurements to change the pixel values and a pixel scrambling method is employed to disturb the positions of pixels. Besides, the keys used in chaotic systems are related to the plaintext image. Simulation results verify the effectiveness and reliability of the proposed image compression and encryption algorithm with considerable compression and security performance.
164 citations
TL;DR: In this paper, a 3D heat transfer finite element model for laser powder-bed fusion (LPBF) was developed for accurately predicting melt pool dimensions and surface features, which can be used to reduce the process/material development costs.
Abstract: In this article, a 3-dimensional heat-transfer finite element model for Laser Powder-Bed Fusion (LPBF) was developed for accurately predicting melt pool dimensions and surface features. The sole deployment of trial-and-error experiments for arriving at optimal process parameters is very costly and time-consuming, thus the developed model can be used to reduce the process/material development costs. A literature review of heat source models was presented. Eight commonly used heat source models are evaluated and compared. All of their simulated depths are smaller than the experimental result, which may be due to the melt pool convection and inconstant laser absorptivity in the reality during the experiment. In order to enable the numerical model to predict melt pool dimensions for different combinations of process parameters, a novel model including expressions of varied anisotropically enhanced thermal conductivity and varied laser absorptivity is proposed and verified by both the melt pool dimensions and track surface morphology. It is found that the heat source expressions can be linear while causing the simulation results to be in better agreement with both experimental melt pool dimensions and track surface morphology.
159 citations
TL;DR: In this paper, three types of laser beam oscillating welding were applied on 5A06 aluminum alloy sheets and microstructure and mechanical properties of the welded joints were characterized.
Abstract: Three types of laser beam oscillating welding were applied on 5A06 aluminum alloy sheets. The microstructure and mechanical properties of the welded joints were characterized. The formation and elimination mechanisms of welding pores during laser beam oscillating welding was investigated. The results showed that laser beam oscillating welding using linear, circular and infinity paths allow to reduce the porosity of the welded joint when compared to the joint produced without beam without oscillation. Among the three oscillating paths, the infinity mode was the best in terms of decreasing the porosity in the weld and increasing the tensile strength. The decrease in porosity of the fusion zone was associated with the weld shape and the decrease of the depth-to-width ratio of the weld due to the oscillation of the heat source. Laser beam oscillating welding applied to aluminum alloys can be of significant interest to industry to decrease porosity problems typically encountered during laser welding of these materials.
142 citations
TL;DR: Experimental results demonstrate that the presented technique has a high-security, high embedding capacity and good visual quality, and the results prove that the constructed S-box has vital qualities for viable applications in security purposes.
Abstract: Substitution boxes play an essential role in designing secure cryptosystems. With the evolution of quantum technologies, current data security mechanisms may be broken due to their construction based on mathematical computation. Quantum walks, a universal quantum computational model, play an essential role in designing quantum algorithms. We utilize the benefits of quantum walks to present a novel technique for constructing substitution boxes (S-boxes) based on quantum walks (QWs). The performance of the presented QWs S-box technique is evaluated by S-box evaluation criteria, and our results prove that the constructed S-box has vital qualities for viable applications in security purposes. Furthermore, a new technique for image steganography is constructed. The proposed technique is an integrated mechanism between classical data hiding and quantum walks to achieve better security for the embedded data. The embedding and extraction procedures are controlled by QWs S-box. The inclusion of cryptographic QWs S-box ensures the security of both embedding and extraction phases. At the extraction phase, only the stego image and the secret values are needed for constructing the secret data. Experimental results demonstrate that the presented technique has a high-security, high embedding capacity and good visual quality.
124 citations
TL;DR: In this article, the authors proposed a HEA composite coating with the highest volume fraction of TiC particles phase (2.6%) exhibits the highest average microhardness (860.1 HV 0.3).
Abstract: AlCoCrFeNiTix (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) HEA coatings reinforced by in-situ TiC particles were successfully prepared on AISI1045 steel via laser cladding. The coatings are made up of two BCC phases identified as Fe-Cr and Al-Ni phases, and a few in-situ TiC phases with a shape of granular in micro-nano scale. Ti element prefers to dissolve into the Al-Ni phase and refines the equiaxed grains. The AlCoCrFeNiTi1.0 HEA composite coating with the highest volume fraction of TiC particles phase (2.6%) exhibits the highest average microhardness (860.1 HV0.3). It is found that the composite coating is strengthened by the effect of solid solution strengthening, dispersion strengthening, and fine-grain strengthening. The wear behaviour of the coatings was tested at 25 °C and 600 °C, respectively. The micromorphology and chemical composition analysis of the wear scars show that oxidation wear occurs in addition to adhesive wear during the wear process at 600 °C. The oxidation products are identified as Al2O3, CoO, Cr2O3, Fe2O3, Fe3O4, and NiO in terms of the calculation of flash temperature and Gibbs free energy. The calculation results of wear rates show that the AlCoCrFeNiTi1.0 composite coating exhibits the best wear resistance.
116 citations
TL;DR: This paper provides a comprehensive review of the research works related to optical image hiding and watermarking techniques conducted in the past decade with a summary of the state-of-the-art works.
Abstract: Information security is a critical issue in modern society and image watermarking can effectively prevent unauthorized information access. Optical image watermarking techniques generally have advantages of parallel high-speed processing and multi-dimensional capabilities compared to digital approaches. This paper provides a comprehensive review of the research works related to optical image hiding and watermarking techniques conducted in the past decade. The past research works have focused on two major aspects: various optical systems for image hiding, and the methods for embedding the optical system output into a host image. A summary of the state-of-the-art works is made from these two perspectives.
115 citations
TL;DR: In this article, the authors used directed energy deposition (DED) to repair damaged powder bed fusion (PBF) parts and observed their tensile properties, hardness, and metallurgical characteristics.
Abstract: Powder bed fusion (PBF), a 3D printing process, is widely used for manufacturing 316L stainless steel parts. When these PBF parts are damaged or worn severely during service, they can be repaired by conventional repair processes such as GTAW welding, metal spraying, brazing etc. However, these processes have several disadvantages such as creating a large heat affected zone and repair defects (pores and cracks). In contrast, directed energy deposition (DED) provides good metallurgical bonds, minimal dilution, and a small heat-affected zone. In this study, to verify the applicability of DED to repair of damaged PBF parts, we repaired sample parts and observed their tensile properties, hardness, and metallurgical characteristics. First, we designed hot-rolled and PBF specimens with trapezoidal grooves of varying depth. After filling the groove using DED, the specimens were tested for tensile properties. We found that in specimens with large groove depths (1 mm and 2 mm), cracks occurred around the repair due to thermal stresses and oxide inclusion. For this reason, strength and elongation were lower in these specimens. We also found that the micro-hardness of the deposition zone is greater than the original hot-rolled specimens and similar to the PBF specimens. The microstructure of the repaired area is mainly composed of complicated dendrite structures due to irregular nucleation. In addition, dimples were observed in the fracture surfaces, indicating that ductile fracture occurred. We conclude that the DED process can be employed to repair damaged 316L stainless steel parts, with the low severity of the damage to be repaired.
111 citations
TL;DR: This paper proposes an underwater image restoration method based on transferring an underwater style image into a recovered style using Multi-Scale Cycle Generative Adversarial Network (MCycle GAN) System and includes a Structural Similarity Index Measure loss (SSIM loss), which can provide more flexibility to model the detail structural to improve the image restoration performance.
Abstract: Underwater image restoration, which is the keystone to the underwater vision research, is still a challenging work. The key point of underwater image restoration work is how to remove the turbidity and the color distortion caused by the underwater environment. In this paper, we propose an underwater image restoration method based on transferring an underwater style image into a recovered style using Multi-Scale Cycle Generative Adversarial Network (MCycle GAN) System. We include a Structural Similarity Index Measure loss (SSIM loss), which can provide more flexibility to model the detail structural to improve the image restoration performance. We use dark channel prior (DCP) algorithm to get the transmission map of an image and design an adaptive SSIM loss to improve underwater image quality. We input this information into the network for multi-scale calculation on the images, which achieves the combination of DCP algorithm and Cycle-Consistent Adversarial Networks (CycleGAN). By compared the quantitative and qualitative with existing state-of-the-art approaches, our method shows a pleasing performance on the underwater image dataset.
99 citations
TL;DR: The proposed POF-based smart textile is a low-cost solution with good accuracy that can be readily applied in the remote monitoring of patients at home without disturbing their daily activities.
Abstract: In this paper, we present the development of a polymer optical fiber (POF) sensor for simultaneous measurement of breath (BR) and heart rates (HR). The sensor is embedded as a smart textile solution that can be used within the user’s clothes. In addition, a signal processing technique is proposed for obtaining the HR and BR without the influence of body movements and in different positions of the user’s chest. Sensor signal processing and analysis are made in the frequency domain and different filters are applied. Results show errors below 4 beats per minute and 2 breaths per minute for the HR and BR, respectively, even when the user is performing periodic body movements such as the ones induced by the gait. Thus, the proposed POF-based smart textile is a low-cost solution with good accuracy that can be readily applied in the remote monitoring of patients at home without disturbing their daily activities.
92 citations
TL;DR: In this paper, the processing parameters of a selective laser-melted (SLM) Ti6Al4V alloy were systematically optimized for optimal surface roughness and relative density, and the relationship between microstructure and mechanical properties were established in the optimal parameter range.
Abstract: The processing parameters of a selective laser-melted (SLM) Ti6Al4V alloy were systematically optimized for optimal surface roughness and relative density. The relationship between microstructure and mechanical properties were established in the optimal parameter range. The results showed that the optimal laser power and scan speed was 200–250 W and 850–1150 mm/s, respectively. The laser power and scan speed played contradicting roles in the resultant roughness and porosity. An appropriate increase in laser power and decrease in scan speed could reduce the surface roughness and simultaneously improve the density and dimensional accuracy. When the laser power was 200 W, the microstructure varied from equiaxed grains to mixed equiaxed-columnar grains, and then it varied to columnar grains as the scan speed changed from 250 mm/s to 850–1750 mm/s. The acicular structure inside the grains transformed from an α (α′) + β phase to an α′ (α) phase with gradual grain refinement. Some nano-β phase precipitated near the acicular phase. Micro-hardness measurements revealed different values at the top, middle and bottom of the samples with increasing laser power and showed a reduced hardness gap with increasing scan speed. However, the elongation continuously increased with increasing scan speed and reached a maximum value of 7.8% at a scanning speed of 1150 mm/s. Decrease in elongation was observed when the laser power increased to 275 W. These variations in the hardness and mechanical properties were attributed to the combined effects of nano-β phase and grain refinement of acicular α (α′) martensites.
TL;DR: In this article, the TEMPO-oxidized cellulose nanofibers (TOCN) was prepared from bagasse pulp, followed by embedding with CdO nanostructure via pulsed infrared laser ablation of cadmium sheets immersed in TOCN solution in just one step.
Abstract: The TEMPO-oxidized cellulose nanofibers (TOCN) was prepared from bagasse pulp, followed by embedding with cadmium oxide nanostructure via pulsed infrared laser ablation of cadmium sheets immersed in TOCN solution in just one step. The TOCN before and after embedding was studied via different characterization techniques as X-ray diffraction, Fourier transform infrared spectroscopy (FT-IR), UV–visible spectroscopy, Transmission electron microscope (TEM), and Energy dispersive X-ray (EDX). These techniques confirmed that TOCN were successfully prepared and the CdO nanostructure is well embedded with nanofiber structure of the prepared TOCN with dimension equaled about 59 nm. Then the prepared sample were studied their antibacterial activity against many pathogenic microorganisms. The minimal inhibition concentration (MIC) is emphasized that the prepared nanocomposite has broad spectrum antimicrobial activity with low MIC values which recorded 1.56 μg/ml for gram negative bacteria, less than 1.56 for gram positive bacterial and 0.19 μg/ml for Candida albican.
TL;DR: In this article, a simple synthesis method to produce multi walled carbon nanotubes (MWCNTs) decorated with metal oxide nanoparticles (e.g., cadmium oxide (CdO)) has been described by pulsed laser ablation of Cadmium sheets immersed in precursor solution from functionalized MWCNTs.
Abstract: A simple synthesis method to produce multi walled carbon nanotubes (MWCNTs) decorated with metal oxide nanoparticles (e.g., cadmium oxide (CdO)) has been described by pulsed laser ablation of Cadmium sheets immersed in precursor solution from functionalized MWCNTs. The as-prepared of decoration composites of MWCNTs with CdO nanoparticles were characterized by Fourier transform infrared spectroscopy, UV–Visible spectrophotometer, transmission electron microscopy, scanning electron microscopy, Energy dispersive X-ray spectroscopy, and X-ray diffraction, which revealed that these decorations of CdO nanoparticles were uniformly distributed on the surface of MWCNTs with diameter about 22 nm. Also, the optical properties of MWCNTs were successfully enhanced after decoration via metal oxide nanoparticles. This work could be used to decorate MWCNTs via different metals oxides via pulsed laser ablation in liquid media technique to produce interesting new properties of MWCNTs composite.
TL;DR: In this paper, the effect of laser energy density on the melt pool geometry and microstructure of Hastelloy X single tracks produced by fixed LED values at different laser powers and scanning velocities was investigated.
Abstract: An applied energy density approach defined as the ratio of laser power and scanning velocity is often used as a guideline for selecting appropriate process parameters in laser powder bed fusion (LPBF). In this study, amongst the many variables related to input energy, we investigate the effectiveness of laser energy density (LED) on the melt pool geometry and microstructure of Hastelloy X single tracks produced by fixed LED values at different laser powers and scanning velocities. The results reveal that for a fixed LED, the higher laser power has a higher effect on the melt pool depth. In addition, compared to the scanning velocity, laser power has a higher influence on the melt pool geometry. Moreover, it is proposed that the finer cell structure observed in the melt pool of high laser power is due to the higher cooling rates. Finally, the higher number of new grains observed in melt pools created with higher laser power and fixed LED are likely due to the grain detachment caused by the increase in the partially melted particles.
TL;DR: In this paper, a single polymer diaphragm-based fiber Bragg grating (FBG) sensor was developed for simultaneous measurement of pressure and temperature, where the frequency difference between temperature and pressure variations were used to decouple both variables.
Abstract: This paper presents the development of a single polymer diaphragm-based fiber Bragg grating (FBG) sensor for simultaneous measurement of pressure and temperature. The FBG response is analyzed through a transient model for heat conduction and the pressure is estimated with the diaphragm and FBG strain, where the frequency difference between temperature and pressure variations were used to decouple both variables. Results show root mean squared error (RMSE) of 1.86 °C for the temperature analysis with constant pressure and 0.92 kPa for the pressure analysis with constant temperature. Experiments with variation of both temperature and pressure were conducted and the errors were higher than the ones with only temperature or pressure variations due to a residual cross-sensitivity. Therefore, the variation of both pressure and sensitivity leads to a RMSE of 3.88 °C and 5.13 kPa for temperature and pressure, respectively, which represent low errors of about 5% for both pressure and temperature.
TL;DR: In this paper, the microstructure, microhardness and electrochemical properties of SiC-dispersed MMCs were investigated as a function of the SiC content.
Abstract: SiC dispersed (4, 8, 12 and 16 wt%) 316L stainless steel metal matrix composites (MMCs) have been prepared by laser melting deposition (LMD). The constituent phases, microstructure, microhardness and electrochemical properties of the MMCs were investigated as a function of SiC content. Experimental results showed that constituent phases of the MMCs evolved from single γ-(FeCrNi) phase with fcc structure for 4 wt% SiC dispersed MMC to γ-(FeCrNi) + α-(FeCrNi) + SiC phases for the 8, 12 and 16 wt% SiC dispersed MMCs. The presence of α-(FeCrNi) phase was due to the tensile stress resulting from the different coefficient of thermal expansion between SiC ceramic reinforcement and the γ-(FeCrNi) matrix in the MMCs. In addition, iron silicides (Fe3Si and FeSi) appeared in 16 wt% SiC dispersed MMC. The microstructure was dense, uniform and the addition of SiC obviously refined the solidification microstructure of the MMCs. In the 16 wt% SiC dispersed MMCs, a micro-crack can be clearly observed. The microhardness of MMCs increased obviously from 362 HV to 974 HV with the addition of SiC. Accompanying the increase in hardness, the corrosion current density increased and the charge transfer resistance decreased, and the corrosion resistance of 4 and 8 wt% SiC dispersed MMCs was superior compared to 12 and 16 wt% SiC dispersed MMCs in 3.5 wt% NaCl solution.
TL;DR: In this paper, a multiplexing technique for polymer optical fiber (POF) intensity variation-based sensors is presented, which relies on the side-coupling between the light source and the POF lateral section.
Abstract: This paper presents a multiplexing technique for polymer optical fiber (POF) intensity variation-based sensors. The technique relies on the side-coupling between the light source and the POF lateral section. Thus, each sensor has its own light source which has its activation as well as its signal acquisition (made with two photodetectors, one at each end of the POF) controlled by a microcontroller. With this technique, a matrix with the number of columns equal to the number of photodetectors multiplied by the number of light sources (or sensors) is obtained. This enables the decoupling of the response of each sensor. The presented analytical approach shows a tradeoff between the number of sensors and their sensitivities (considering the dynamic range of each sensor). In addition, experimental results show the feasibility of the technique to measure angles in a 3°-of-freedom (DOF) systems with errors as low as 3°. Furthermore, the proposed approach was also tested in multi-parameter applications, where temperature, angle and force were estimated with errors up to 5% with an array with 3 POF sensors. The results presented in this paper can pave the way for novel applications of quasi-distributed sensors with intensity variation-based sensors both in multi-DOF systems and in multi-parameter applications with the additional advantages of lower cost than fiber Bragg gratings-based systems and lower spatial resolution than distributed sensors.
TL;DR: In this paper, the authors present an extensive analysis, both from a practical and a theoretical perspective, of current biosensors, and analyze how subwavelength structures can be exploited to enhance their sensitivity.
Abstract: Silicon photonic biosensors hold the potential for highly accurate, yet low cost point-of-care devices. Maximizing the sensitivity of the sensing chips while reducing the complexity and cost of the read-out system is pivotal to realize this potential. Here we present an extensive analysis, both from a practical and a theoretical perspective, of current biosensors, and analyze how subwavelength structures can be exploited to enhance their sensitivity. This study is not restricted just to the near-infrared band as we also determine the sensing capabilities of the suspended silicon waveguides with subwavelength metamaterial cladding working in the mid-infrared range. These waveguides have been recently proposed to cover the full transparency window of silicon ( λ ∼ 8.5 μm), where the fingerprint spectral region of many molecules takes place and so a plethora of evanescent field absorption-based applications will be developed in the near future.
TL;DR: In this paper, experiments were conducted to investigate the effects of processing parameters including scanning speed, laser power and powder feeding rate on grain size of the solidified track during laser metal deposition.
Abstract: The processing parameters in laser additive manufacturing have a crucial impact on solidification microstructure especially grain size, thus influencing the properties of the final products. In this paper, experiments were conducted to investigate the effects of processing parameters including scanning speed, laser power and powder feeding rate on grain size of the solidified track during laser metal deposition. A three-dimensional model considering heat transfer, phase change and Marangoni convection flow had also been developed to simulate the solidification parameters especially cooling rate (G × R) to illustrate the underlying mechanisms. The experimental and simulated results indicated that cooling rate increased and grain size decreased from 8.7 μm to 4.7 μm with the increase of scanning speed from 2 mm/s to 10 mm/s. Contrarily, cooling rate decreased and grain size increased with the increase of laser power and powder feeding rate. The numerical and experimental results provide the additive manufacturing process with the potential of microstructure control and performance optimization.
TL;DR: In this article, a volumetric heat source is used in numerical modeling of selective laser melting (SLM) of Ti6Al4V powder, and the model is validated with the published experimental results for melt pool shape, size and temperature.
Abstract: A volumetric heat source is used in numerical modeling of selective laser melting (SLM) of Ti6Al4V powder. Single track and multi-track SLM simulations are performed by varying the two key process parameters-laser power and scan speed. The model is validated with the published experimental results for melt pool shape, size and temperature. The predictions are in good agreement with the experiments at low to medium energy density. The validated model is used for investigating the thermo-fluidic transport during SLM of Ti6Al4V and examining the dependence of the melt pool characteristics on the process parameters. As-solidified porosity is calculated numerically for the multi-track simulations and its formation is delineated with the transport phenomena. The predicted porosity compares reasonably well with the experimental values. Solidification parameters, such as temperature gradients and cooling rate are calculated at the instantaneous location of the solidification front and analyzed. This analysis suggests the formation of fully columnar grains of different sizes along the width and depth of the melt pool. Overall, the model provides a good description of thermo-fluidic transport in SLM of Ti6Al4V powder and the resulting temperature field, melt pool characteristics, as-solidified porosity and the expected grain structure. Based on the current analysis, an optimum processing window of 50–70 J mm−3 energy density is suggested for SLM of Ti6Al4V powder.
TL;DR: In this paper, metal matrix composites (MMCs) self-lubricating coatings were fabricated on 35CrMo steel by laser cladding using Co-based alloy and Ti3SiC2 mixture, aiming at improving the wear resistance of 35 CrMo steel.
Abstract: Metal matrix composites (MMCs) self-lubricating coatings were fabricated on 35CrMo steel by laser cladding using Co-based alloy and Ti3SiC2 mixture, aiming at improving the wear resistance of 35CrMo steel. Phase constituents, microstructure, microhardness and wear property of the MMCs coatings with different Ti3SiC2 content were investigated using XRD, SEM, microhardness tester, and friction-wear tester, respectively. Experimental results showed that with appropriate laser processing parameters, crack and porosity-free coatings with good metallurgical bonding to the substrate could be obtained. The coatings were mainly composed of γ-Co, Ti3SiC2, Cr7C3 and TiC. During the cladding process, Ti3SiC2 partially dissolved to form TiC. The microhardness of the coatings was significantly enhanced, which was at least 2.3 times that of substrate. The wear resistance of the coatings was 3.6–6.2 times that of substrate and the coating with 10 wt% Ti3SiC2 addition possessed the highest wear resistance.
TL;DR: In this paper, laser metal deposition was used to repair grooves on 20mm thickness 316L stainless steel plates using two different 316L commercial powders (Fe-0.15C-11.8Cr- 0.2Ni-1.2Mn- 11.2C-17.
Abstract: Laser metal deposition was used to repair grooves on 20 mm thickness 316L stainless steel plates using two different 316L stainless steel commercial powders – Fe-0.15C-11.8Cr-0.15Mn-0.2Ni-0.031P-0.56Si-0.05S (wt.%) powder and Fe-0.09C-17.05Cr-1.2Mn-11.28Ni-0.019P-0.46Si-0.09S (wt.%) powder. Good comprehensive performance of fine metallurgical bonding with were successfully achieved under optimized processing parameters. The microstructure and mechanical properties (micro-hardness, ultimate tensile strength, bending strength, low-temperature impact toughness) of the repaired specimens were investigated. Results indicated that chemical composition (different element contents) of the powders played an important role in determining the microstructure, phases and properties of the specimens. It was found that the microstructure of the specimens repaired with Fe-0.15C-11.8Cr-0.15Mn-0.2Ni-0.031P-0.56Si-0.05S (wt.%) powder was homogeneous and consisted of Cr-rich martensite while a number of cellular dendrite were presented in microstructure of specimens repaired with Fe-0.09C-17.05Cr-1.2Mn-11.28Ni-0.019P-0.46Si-0.09S (wt.%) powder and the repaired specimens consisted of ferrite and austenite. Due to solid solution strengthening, the average hardness of the specimens repaired with former powder was higher than that of the specimens with later powder. However, in the aspect of mechanical properties, LMD with Fe-0.09C-17.05Cr-1.2Mn-11.28Ni-0.019P-0.46Si-0.09S (wt.%) powder had better performance than the specimens repaired with another kind of powder. The relationship between the microstructure characteristics and mechanical performances of the repaired specimens was also discussed.
TL;DR: In this article, the effect of heat treatment on microstructure and mechanical behaviour of SLM-built 18Ni-300 maraging steels was investigated, and the experimental results showed that the densest parts with the smallest number of defects were fabricated at optimum laser energy density of 70 J/mm3 and laser power of 275 W.
Abstract: Selective laser melting (SLM) of 18Ni-300 maraging steel is an important research area in view of its numerous applications in the automotive domain. Heat treatment plays a significant role in the microstructure and mechanical behaviour of maraging steels and is a major area of interest. This paper investigated the effect of heat treatment on microstructure and mechanical behaviour of SLM-built 18Ni-300 maraging steel. The experimental results showed that the densest parts with the smallest number of defects were fabricated at optimum laser energy density of 70 J/mm3 and laser power of 275 W. When the laser power was fixed at 275 W, lower laser energy density resulted in the formation of balling and irregular pores, while higher laser energy density induced spherical pores and microcracks. The as-built samples consisted of cellular and columnar microstructures due to the fast cooling and solidification rates during SLM. However, solution treatment led to changes in the typical microstructure and massive lath martensite phase. The tensile strength and microhardness decreased slightly due to grain growth and residual stress relief upon solution treatment; an opposite effect was observed when the samples were subjected to solution treatment followed by aging at 490 °C for 2 h. With regard to the tensile anisotropy, yield strength and ultimate tensile strength of the horizontally-built samples slightly exceeded those vertically-built. These findings are significant as they allow an informed prediction about the effect of various heat treatments on the microstructure and mechanical behaviour of components manufactured from 18Ni-300 maraging steel using the SLM process.
TL;DR: In this paper, a three-parameter sensor for the simultaneous measurement of surrounding refractive index (SRI), temperature and strain is presented, based on a single Long Period Grating (LPG) written in a polarization-maintaining Panda fiber, by means of a simple technique based on Electric Arc Discharge.
Abstract: In this work, a three-parameter sensor for the simultaneous measurement of surrounding refractive index (SRI), temperature and strain is presented. It is based on a single Long Period Grating (LPG) written in a polarization-maintaining Panda fiber, by means of a simple technique based on Electric Arc Discharge. For the purpose, it is performed the monitoring of the wavelength shift of three different resonances, each one associated to a different cladding mode. Moreover, the set of resonances is acquired for two polarizations of the input light, i.e. aligned to the slow and fast axis of the fiber. The three-parameter sensing is promoted by the fact that the resonance dips show different sensitivities to SRI, temperature and strain, which change their magnitudes and signs when the polarization is switched. It was demonstrated that the sensor can be applied to simultaneously measure SRI in range 1.33–1.40, temperatures comprised in 20–60 °C, and strain of hundreds of μe. This device could find application in the fields of materials science and structural health monitoring.
TL;DR: In this article, the effect of WS2 contents on the microstructure, microhardness and tribological properties of the TiN reinforced Ni matrix composite coating was investigated by X-ray diffractometer (XRD), scanning electron microscope (SEM) with energy dispersive spectrometer (EDS) as well as a multi-functional Tribometer.
Abstract: TiN reinforced Ni matrix composite coating with in-situ synthesized TiS lubricant phase were fabricated on Ti-6Al-4V alloy by laser cladding with NiCrBSi, TiN and WS2 powder mixtures. The phase compositions, microstructure, microhardness and tribological behaviors are investigated by X-ray diffractometer (XRD), scanning electron microscope (SEM) with energy dispersive spectrometer (EDS) as well as a multi-functional Tribometer. Effect of WS2 contents on the microstructure, microhardness and tribological properties were studied. And the corresponding wear mechanism was discussed. Results indicate that the hardness of the coating (about 900HV0.2) is significantly improved compared with substrate (370HV0.2). Coefficients of friction and wear rates of these coatings have been significantly reduced. Besides, laser-clad coating using the mixed powders of 50%Ni-30%TiN-20%WS2 has good anti-wearing and friction reducing effects, and the main wear mechanisms of that are abrasive wear and micro-plowing.
TL;DR: In this article, a powder-delivery laser powder deposition (LPD) process was used to obtain AlSi10Mg alloy with maximum density using Taguchi method, and the results were analyzed based on the signal-to-noise (S/N) ratios and analyses of variance (ANOVA).
Abstract: In this study, AlSi10Mg alloy were prepared by powder-delivery laser powder deposition (LPD) process. In order to obtain AlSi10Mg alloy with maximum density, LPD parameters were optimized using Taguchi method. Results were analyzed based on the signal-to-noise (S/N) ratios and analyses of variance (ANOVA). The optimal combination of parameters was laser power of 150 W, scanning speed of 400 mm/min, powder feeding rate of 0.78 g/min and shielding gas flow rate of 7 L/min. The dominant parameter was the laser power which contributes 49.43% to the relative density. Additionally, the regression equation was established based on the output parameter (relative density) and the four input process parameters, and validated by the obtained results. From the experiments, sample with density higher than 99% was obtained. The investigation will help to establish an efficient process for AlSi10Mg alloy fabricated by LPD.
TL;DR: Results indicated that the Au/CdS-NH2GO/EDC-NHS/IgM film shows high potential sensitive and stronger binding towards DENV E-protein.
Abstract: An optical sensor for the dengue virus (DENV) E-protein based on cadmium sulfide quantum dots composited with amine functionalized graphene oxide (CdS-NH2GO) thin film was successfully developed. A specific monoclonal antibodies (IgM) were covalently attached to CdS-NH2GO via EDC/NHS coupling to sense targeted E-proteins. The SPR sensor exhibited an excellent detection limit (0.001 nM/1 pM) with sensitivity of 5.49° nM−1 for the detection of DENV E-protein. The binding affinity, as well as the performance of the Au/CdS-NH2GO/EDC-NHS/IgM film, was successfully obtained at 486.54 nM−1 in detecting DENV E-proteins. These results indicated that the Au/CdS-NH2GO/EDC-NHS/IgM film shows high potential sensitive and stronger binding towards DENV E-protein.
TL;DR: In this article, a randomly packed powder-bed model by sequential addition method was established mathematically and physically to simulate the condition of the interaction between the laser beam and powder particles.
Abstract: In this paper, a randomly packed powder-bed model by sequential addition method was established mathematically and physically to simulate the condition of the interaction between the laser beam and powder particles. The ray-tracing calculation was used to analyze laser absorptivity and irradiance distribution occurring on powder particle surface as well as the influence of reinforcements on the laser energy absorption during selective laser melting additive manufacturing of pure AlSi10Mg, SiC/AlSi10Mg and TiB2/AlSi10Mg materials. The simulation results reveal that addition of reinforcements enhanced the interactions of laser beam with powder particles, which were illustrated by an increase of laser ray track spots on the particles surface. A respective absorptivity fluctuated from 0.37 to 0.59 and from 0.34 to 0.49 for the randomly packed SiC/AlSi10Mg and TiB2/AlSi10Mg, both of which were significantly enhanced with respective to that of AlSi10Mg powder. The addition of ceramic reinforcement particles can significantly improve the absorption irradiance of laser for powder-bed of pure AlSi10Mg, while the SiC reinforcement was more effective in enhancing this effect than TiB2. The influence of different absorption irradiance on the melt pool dimensions and surface morphologies were studied experimentally to verify the reliability of this simulation.
TL;DR: In this article, a physics-based process model of laser powder-fed additive manufacturing (LPF-AM), a class of directed energy deposition, is established, which can perform an efficient prediction of the melt pool dimension, wetting angle, dilution, process heating/cooling rates and clad 3D profiles from single-track to multi-track and multi-layer deposition, and has the potential to be employed for the fast process optimization and controller design.
Abstract: A physics-based process model of laser powder-fed additive manufacturing (LPF-AM), a class of directed energy deposition, is established in this paper. The model can perform an efficient prediction of the melt pool dimension, wetting angle, dilution, process heating/cooling rates and clad 3D profiles from single-track to multi-track and multi-layer deposition, and has the potential to be employed for the fast process optimization and controller design. The novelty of the model lies in three fronts: (1) the melt pool geometry variation as the liquid melt pool bead spreading on the solid surface is counted by the wetting angle alternation, in which the dynamic wetting angle is computed based on the Hoffman-Voinov-Tanner law; (2) the heat accumulation effect in the multi-track, multi-layer scanning is compensated by adding the accumulated temperature field to the initial temperature field of the following layers/tracks. The accumulated temperature is calculated by summing up the transient temperature solutions of the prior layers/tracks based on the superposition principle; and (3) the feeding powder distribution is incorporated into the transient thermal field simulation of the multi-layer and multi-track deposition process by analytically coupling the powder mass flows and laser heat flux, in which the powder mass flow is expressed as an equivalent heat flux. Experiments were conducted to validate the built model. The single-track measurements (clad height, clad width, dilution and wetting angle) show that the prediction error of the built model is less than 14%. The multi-track and multi-layer measurements also indicate that the model can perform a high accuracy dimension prediction of the built features. Besides, a sensitivity analysis was conducted based on the built model and the results show that the powder feed rate is the most sensitive parameter that substantially varies the clad height, followed by the process speed, whereas the specific heat has the least sensitivity.
TL;DR: In this article, the authors investigated the effects of the process parameters on the quality characteristics of the ceramic coatings on Ti6Al4V substrates, which were prepared by laser cladding using nanoparticle TiC powder as pre-placed material.
Abstract: In laser cladding process, the quality characteristics of the coatings are directly affected by laser cladding process parameters. In this work, in order to investigate the effects of the process parameters on the quality characteristics of the ceramic coatings on Ti6Al4V substrates, which were prepared by laser cladding using nanoparticle TiC powder as pre-placed material, five single factors (laser power, scanning speed, pre-placed powder thickness, laser spot diameter and multi-track overlapping ratio) and four interactions related to laser power were selected as influencing factors, and then multi-track cladding experiments with L27(313) orthogonal array designed by Taguchi method were carried out to obtain the geometric characteristics (coating thickness, coating width and height difference) and mechanical property (micro-hardness) of the coatings. Based on experimental results, the influence extents of all factors on quality characteristics were ranked by signal-to-noise (S/N) ratio, and the significances of all factors on quality characteristics were evaluated by using P-value from the analysis of variance (ANOVA). Then the effects of the significance factors on quality characteristic were analyzed in detail, and the optimal process parameters were selected. Finally, a prediction model based on support vector machine (SVM) was developed for the quality characteristics of the cladding coatings. The results showed that the pre-placed powder thickness, laser spot diameter and laser power were the most crucial process parameters. The prediction model based on SVM method can correctly describe the relations between cladding process parameters (input variables) and quality characteristics of coatings (output characteristics), with the correlation coefficient CC > 0.94. This research work gives a guideline for the selection of appropriate process parameters for laser cladding of high-quality coatings using nanoparticle TiC ceramic powder as starting material.