Showing papers in "Optics and Laser Technology in 2018"

A combination chaotic system and application in color image encryption

Abstract: In this paper, by using Logistic, Sine and Tent systems we define a combination chaotic system. Some properties of the chaotic system are studied by using figures and numerical results. A color image encryption algorithm is introduced based on new chaotic system. Also this encryption algorithm can be used for gray scale or binary images. The experimental results of the encryption algorithm show that the encryption algorithm is secure and practical.

Review on thermal analysis in laser-based additive manufacturing

Abstract: Laser-based Additive Manufacturing (LAM) has been widely used in different industries. However, the quality and repeatability of the components and parts produced by LAM have hindered the spread of this technique. The better understanding of the LAM underlying mechanism can provide insight into acquiring high-quality products. Among researches on underlying physics, there are efforts to study the thermal behavior, as one important part of the complex mechanisms, and its influence on the product quality. This review is presented to comprehensively analyze different approaches to study the thermal behavior. The relationship between thermal behavior and product quality is identified and some recommendations for future research are discussed.

[INVITED] Recent advances in surface plasmon resonance based fiber optic chemical and biosensors utilizing bulk and nanostructures

Abstract: Surface plasmon resonance has established itself as an immensely acclaimed and influential optical sensing tool with quintessential applications in life sciences, environmental monitoring, clinical diagnostics, pharmaceutical developments and ensuring food safety. The implementation of sensing principle of surface plasmon resonance employing an optical fiber as a substrate has concomitantly resulted in the evolution of fiber optic surface plasmon resonance as an exceptionally lucrative scaffold for chemical and biosensing applications. This perspective article outlines the contemporary studies on fiber optic sensors founded on the sensing architecture of propagating as well as localized surface plasmon resonance. An in-depth review of the prevalent analytical and surface chemical tactics involved in configuring the sensing layer over an optical fiber for the detection of various chemical and biological entities is presented. The involvement of nanomaterials as a strategic approach to enhance the sensor sensitivity is furnished concurrently providing an insight into the diverse geometrical blueprints for designing fiber optic sensing probes. Representative examples from the literature are discussed to appreciate the latest advancements in this potentially valuable research avenue. The article concludes by identifying some of the key challenges and exploring the opportunities for expanding the scope and impact of surface plasmon resonance based fiber optic sensors.

Pulsed Nd:YAG laser beam drilling: A review

Abstract: Laser beam drilling (LBD) is one of non contact type unconventional machining process that are employed in machining of stiff and high-strength materials, high strength temperature resistance materials such as; metal alloys, ceramics, composites and superalloys. Most of these materials are difficult-to-machine by using conventional machining methods. Also, the complex and precise holes may not be obtained by using the conventional machining processes which may be obtained by using unconventional machining processes. The laser beam drilling in one of the most important unconventional machining process that may be used for the machining of these materials with satisfactorily. In this paper, the attention is focused on the experimental and theoretical investigations on the pulsed Nd:YAG laser drilling of different categories of materials such as ferrous materials, non-ferrous materials, superalloys, composites and Ceramics. Moreover, the review has been emphasized by the use of pulsed Nd:YAG laser drilling of different materials in order to enhance productivity of this process without adverse effects on the drilled holes quality characteristics. Finally, the review is concluded with the possible scope in the area of pulsed Nd:YAG laser drilling. This review work may be very useful to the subsequent researchers in order to give an insight in the area of pulsed Nd:YAG laser drilling of different materials and research gaps available in this area.

Exploiting chaos-based compressed sensing and cryptographic algorithm for image encryption and compression

Abstract: This paper presents a solution for simultaneous image encryption and compression. The primary introduced techniques are compressed sensing (CS) using structurally random matrix (SRM), and permutation-diffusion type image encryption. The encryption performance originates from both the techniques, whereas the compression effect is achieved by CS. Three-dimensional (3-D) cat map is employed for key stream generation. The simultaneously produced three state variables of 3-D cat map are respectively used for the SRM generation, image permutation and diffusion. Numerical simulations and security analyses have been carried out, and the results demonstrate the effectiveness and security performance of the proposed system.

Hybrid laser arc welding: State-of-art review

Abstract: Hybrid laser arc welding simultaneously utilizes the arc welding and the laser welding, in a common interaction zone. The synergic effects of laser beam and eclectic arc in the same weld pool results in an increase of welding speed and penetration depth along with the enhancement of gap bridging capability and process stability. This paper presents the current status of this hybrid technique in terms of research, developments and applications. Effort is made to present a comprehensive technical know-how about this process through a systematic review of research articles, industrial catalogues, technical notes, etc. In the introductory part of the review, an overview of the hybrid laser arc welding is presented, including operation principle, process requirements, historical developments, benefits and drawbacks of the process. This is followed by a detailed discussion on control parameters those govern the performance of hybrid laser arc welding process. Thereafter, a report of improvements of performance and weld qualities achieved by using hybrid welding process is presented based on review of several research papers. The succeeding sections furnish the examples of industrial applications and the concluding remarks.

Effect of laser remelting on microstructure and properties of WC reinforced Fe-based amorphous composite coatings by laser cladding

Abstract: The WC reinforced Fe-based amorphous composite coatings were prepared by laser cladding with rectangular spot. The effect of laser remelting on the microstructure and properties of composite coatings was investigated. The results showed that laser remelting can reduce the cracks and porosities of the cladding coating and improve its surface quality. Large amounts of crystalline phases were precipitated at the top of the cladding and remelting coatings. However, the microstructure at the top of the remelting coating was finer compared to that at the top of the cladding coating. With increasing distance from the surface of substrate, the amorphous phase appeared within the remelting coating and large amounts of carbides rich in Fe and Mo, Fe23B6, γ-Fe and Cr9.1Si0.9 phases were also precipitated in the remelting coating. As a result, the corrosion resistance of the remelting coating was higher than that of the cladding coating. The microhardness of the remelting coating was approximately 1.13 times higher than that of the cladding coating.

Microstructure and wear resistance of laser cladded Ni-Cr-Co-Ti-V high-entropy alloy coating after laser remelting processing

Abstract: An attempt, combined with the technologies of laser cladding and laser remelting, has been made to develop a Ni-Cr-Co-Ti-V high entropy alloy coating. The phase composition, microstructure, micro-hardness and wear resistance (rolling friction) were studied in detail. The results show that after laser remelting, the phase composition remains unchanged, that is, as-cladded coating and as-remelted coatings are all composed of (Ni, Co)Ti2 intermetallic compound, Ti-rich phase and BCC solid solution phase. However, after laser remelting, the volume fraction of Ti-rich phase increases significantly. Moreover, the micro-hardness is increased, up to ∼900 HV at the laser remelting parameters: laser power of 1 kW, laser spot diameter of 3 mm, and laser speed of 10 mm/s. Compared to the as-cladded high-entropy alloy coating, the as-remelted high-entropy alloy coatings have high friction coefficient and low wear mass loss, indicating that the wear resistance of as-remelted coatings is improved and suggesting practical applications, like coatings on brake pads for wear protection. The worn surface morphologies show that the worn mechanism of as-cladded and as-remelted high-entropy alloy coatings are adhesive wear.

Influence of scan strategy and molten pool configuration on microstructures and tensile properties of selective laser melting additive manufactured aluminum based parts

Abstract: Selective laser melting additive manufacturing of the AlSi12 material parts through the re-melting of the previously solidified layer using the continuous two layers 90° rotate scan strategy was conducted. The influence of the re-melting behavior and scan strategy on the formation of the “track-track” and “layer-layer” molten pool boundaries (MPBs), dimensional accuracy, microstructure feature, tensile properties, microscopic sliding behavior and the fracture mechanism as loaded a tensile force has been studied. It showed that the defects, such as the part distortion, delamination and cracks, were significantly eliminated with the deformation rate less than 1%. The microstructure of a homogeneous distribution of the Si phase, no apparent grain orientation on both sides of the MPBs, was produced in the as-fabricated part, promoting the efficient transition of the load stress. Cracks preferentially initiate at the “track-track” MPBs when the tensile stress increases to a certain value, resulting in the formation of the cleavage steps along the tensile loading direction. The cracks propagate along the “layer-layer” MPBs, generating the fine dimples. The mechanical behavior of the SLM-processed AlSi12 parts can be significantly enhanced with the ultimate tensile strength, yield strength and elongation of 476.3 MPa, 315.5 MPa and 6.7%, respectively.

Numerical and experimental investigation into the subsequent thermal cycling during selective laser melting of multi-layer 316L stainless steel

Abstract: Subsequent thermal cycling (STC), as the unique thermal behavior during the multi-layer manufacturing process of selective laser melting (SLM), brings about unique microstructure of the as-produced parts. A multi-layer finite element (FE) model was proposed to study the STC along with a contrast experiment. The FE simulational results show that as layer increases, the maximum temperature, dimensions and liquid lifetime of the molten pool increase, while the heating and cooling rates decrease. The maximum temperature point shifts into the molten pool, and central of molten pool shifts backward. The neighborly underlying layer can be remelted thoroughly when laser irradiates a powder layer, thus forming an excellent bonding between neighbor layers. The contrast experimental results between the single-layer and triple-layer samples show that grains in of latter become coarsen and tabular along the height direction compared with those of the former. Moreover, this effect become more serious in 2nd and 1st layers in the triple-layer sample. All the above illustrate that the STC has an significant influence on the thermal behavior during SLM process, and thus affects the microstructure of SLMed parts.

Experimental analysis of Nd-YAG laser cutting of sheet materials – A review

Abstract: Cutting of sheet material is considered as an important process due to its relevance among products of everyday life such as aircrafts, ships, cars, furniture etc. Among various sheet cutting processes (ASCPs), laser beam cutting is one of the most capable ASCP to create complex geometries with stringent design requirements in difficult-to-cut sheet materials. Based on the recent research work in the area of sheet cutting, it is found that the Nd-YAG laser is used for cutting of sheet material in general and reflective sheet material in particular. This paper reviews the experimental analysis of Nd-YAG laser cutting process, carried out to study the influence of laser cutting parameters on the process performance index. The significance of experimental modeling and different optimization approaches employed by various researchers has also been discussed in this study.

Effect of Ni content on stainless steel fabricated by laser melting deposition

Abstract: The novel stainless steel + x wt.% Ni (x = 0, 3.05, 6.10, 9.15) specimens were successfully fabricated by laser melting deposition, aiming at investigating the influence of Ni content on stainless steel structure and property. The effects of Ni content on phase compositions, microstructure, microhardness, wear and electrochemical corrosion resistance of as-deposited stainless steel were studied systematically using XRD, OM, SEM, microhardness tester, friction-wear tester and potentiodynamic polarization measurement, respectively. Experimental results showed that with the increase of Ni content, the constituent phase of the as-deposited specimen changed from ferrite phase (specimen for x = 0) to austenite phase (specimen for x = 9.15). The microstructure growth followed the principle of dendrite growth. However, the dominant microstructure varied from equiaxed dendrite to columnar dendrite with increasing Ni content. Phase transition from ferrite phase to austenite phase with the addition of Ni content resulted in the decrease of microhardness value from 643HV to 289HV. Meanwhile, the wear resistance of as-deposited specimens decreased gradually with the increasing of Ni content, which might be attributed to the fact that the wear resistance is proportional to microhardness according to Archard's law. It was noted that corrosion resistance of as-deposited stainless steel was extremely improved with the increase of Ni content. The higher Ni content specimen (specimen for x = 9.15) exhibited the best corrosion resistance among the tested specimens based on corrosion rate, which was one order of magnitude lower than that of the lower Ni content specimens (specimens for x = 0, 3.05).

Characterization of Al0.5FeCu0.7NiCoCr high-entropy alloy coating on aluminum alloy by laser cladding

Abstract: Al0.5FeCu0.7NiCoCr high-entropy alloy (HEA) coatings were synthesized on aluminum by laser cladding, aiming at enhancing surface properties. Samples were characterized by using scanning electron microscopy with spectroscopy (SEM/EDS), X-ray diffraction, laser induced breakdown spectroscopy (LIBS), microhardness. The results showed that the HEA coatings exhibited good metallurgical bonding to the matrix by using optimized laser processing parameters. The HEA coatings were composed of fcc + bcc phases. All the composed elements can be noted in mapping through the calibration of the plasma, and the plasma of the collected Al confirmed that come from substrate dilution. The intensity change of Al-II reflected the depth variety of the cladding layer. The microstructure of clad layer was consisted of dendrite. The microhardness of HEA layer reached 750HV0.2 that was about 8 times larger than that of the substrate.

Controllable superhydrophobic aluminum surfaces with tunable adhesion fabricated by femtosecond laser

Abstract: In this study, a facile and detailed strategy to fabricate superhydrophobic aluminum surfaces with controllable adhesion by femtosecond laser ablation is presented. The influences of key femtosecond laser processing parameters including the scanning speed, laser power and interval on the wetting properties of the laser-ablated surfaces are investigated. It is demonstrated that the adhesion between water and superhydrophobic surface can be effectively tuned from extremely low adhesion to high adhesion by adjusting laser processing parameters. At the same time, the mechanism is discussed for the changes of the wetting behaviors of the laser-ablated surfaces. These superhydrophobic surfaces with tunable adhesion have many potential applications, such as self-cleaning surface, oil–water separation, anti-icing surface and liquid transportation.

Compact passive Q-switching of a diode-pumped Tm,Y:CaF 2 laser near 2 μm

Abstract: Lasing was realized near a wavelength of 2 μm with a compact linear cavity by using a fiber-coupled 792-nm laser diode as the pump source and a Tm3+,Y3+ co-doped CaF2 crystal. By employing broadband graphene oxide (GO) as the saturable absorber (SA), a passive Q-switching Tm,Y:CaF2 laser was implemented for the first time. When the transmission of the output couple (OC) was 2%, the maximum average output power was measured to be 400 mW with a corresponding repetition rate of 20.22 kHz and a pulse width of 1.316 μs. A maximum continuous-wave (CW) output power of more than one watt was obtained with slope efficiency of 51.5%.

Influence of Dy doping on key linear, nonlinear and optical limiting characteristics of SnO2 films for optoelectronic and laser applications

Abstract: In the present work, pure and dysprosium (Dy) doped SnO2 films have been fabricated through sol-gel spin coating technique. Strong influence of Dy doping is observed on structural, morphological, vibrational, linear and nonlinear optical properties of SnO2 films. X-ray diffraction study revealed that deposited films exhibit tetragonal crystal structure with preferentially grown along (2 0 0) plane. With increase of doping concentration in SnO2, the crystallite size decreases while dislocation density and lattice distortion ratio increases. The characteristics Raman peaks of doped SnO2 thin films broaden, shifted and intensity decreases as compared to pure film which confirm the bonding between Dy and SnO2. Optical study shows that the prepared thin films are highly transparent and absorption increases with doping concentrations owing to increase of defects states. It is also observed that the optical band gap first increases and then lessens with rise of Dy-doping concentration which attributed to the Burstein-Moss (BM) effect. Additionally, dielectric constant and refractive index first decreasing with small doping concentration (1–3%) due to increase of carrier concentration, and then increases for higher doping (5–7%) due to increase of defect in SnO2 lattice. The values χ 3 and β obtained by Z-scan measurement are observed in range of 0.31 × 10−7 to 1.28 × 10−7 and 1.27 to 5.32 × 10−4 cm W−1, respectively. The limiting threshold of pure and Dy doped SnO2 nanostructured films were calculated to be in the range of 5.37–11.18 kJ/cm2.

Image compression-encryption algorithms by combining hyper-chaotic system with discrete fractional random transform

Abstract: Based on hyper-chaotic system and discrete fractional random transform, an image compression-encryption algorithm is designed. The original image is first transformed into a spectrum by the discrete cosine transform and the resulting spectrum is compressed according to the method of spectrum cutting. The random matrix of the discrete fractional random transform is controlled by a chaotic sequence originated from the high dimensional hyper-chaotic system. Then the compressed spectrum is encrypted by the discrete fractional random transform. The order of DFrRT and the parameters of the hyper-chaotic system are the main keys of this image compression and encryption algorithm. The proposed algorithm can compress and encrypt image signal, especially can encrypt multiple images once. To achieve the compression of multiple images, the images are transformed into spectra by the discrete cosine transform, and then the spectra are incised and spliced into a composite spectrum by Zigzag scanning. Simulation results demonstrate that the proposed image compression and encryption algorithm is of high security and good compression performance.

Numerical simulation and experimental validation of residual stress and welding distortion induced by laser-based welding processes of thin structural steel plates in butt joint configuration

Abstract: Thin plates are extensively used in automotive, shipbuilding, and railway industries. Welding technology is the main assembling method to manufacture thin plate structures because of its high productivity and ease of use. Consequently, residual stress and distortion induced by welding are an inevitable part of the manufacturing process in welding thin plate structures. Relatively low stiffness, and a high amount of heat input are the main reasons for distortion of the welded structures. In order to decrease the heat input, laser-based welding processes that generate highly localized heat with a very high intensity can be a good choice as an alternative to traditional fusion welding. To predict residual stress and distortion in welding thin plate structures, a three dimensional, thermo-metallurgical-mechanical finite element method was developed. The results of three different laser-based welding processes including aspects of Autogenous Laser Welding (ALW), Cold Wire Assisted Laser Welding (CWLAW), and Hybrid Laser-Arc Welding were compared with traditional Submerged Arc Welding (SAW) from both predicted and experimental perspectives. SYSWELD commercial code was used for the simulations in which both large and small deformation theories were employed to predict the residual stress and the final deformation. Experiments were executed to verify the simulation results. A digital high-resolution microscope was used to visualize and measure the weld cross- sectional shape and bead geometry. To measure the residual stress, an X-ray diffractometer was employed. A digital Vernier Caliper and a 3D laser-handheld scanner were used to measure displacement in the z-direction. Moreover, the mechanical properties of welds obtained by different welding processes were also verified by tensile and micro-hardness tests. It was concluded that lower heat input can markedly influence the final distortion of the welded structure. This conclusion can strongly support the idea of replacing traditional arc welding method with a laser-based one. Simulation and experimental results were matched fairly.

An empirical-statistical model for laser cladding of Ti-6Al-4V powder on Ti-6Al-4V substrate

Abstract: In this article, Ti-6Al-4V powder alloy was directly deposited on Ti-6Al-4V substrate using laser cladding process. In this process, some key parameters such as laser power (P), laser scanning rate (V) and powder feeding rate (F) play important roles. Using linear regression analysis, this paper develops the empirical-statistical relation between these key parameters and geometrical characteristics of single clad tracks (i.e. clad height, clad width, penetration depth, wetting angle, and dilution) as a combined parameter (PαVβFγ). The results indicated that the clad width linearly depended on PV−1/3 and powder feeding rate had no effect on it. The dilution controlled by a combined parameter as VF−1/2 and laser power was a dispensable factor. However, laser power was the dominant factor for the clad height, penetration depth, and wetting angle so that they were proportional to PV−1F1/4, PVF−1/8, and P3/4V−1F−1/4, respectively. Based on the results of correlation coefficient (R > 0.9) and analysis of residuals, it was confirmed that these empirical-statistical relations were in good agreement with the measured values of single clad tracks. Finally, these relations led to the design of a processing map that can predict the geometrical characteristics of the single clad tracks based on the key parameters.

Discrimination of soft tissues using laser-induced breakdown spectroscopy in combination with k nearest neighbors (kNN) and support vector machine (SVM) classifiers

Abstract: In this paper, discrimination of soft tissues using laser-induced breakdown spectroscopy (LIBS) in combination with multivariate statistical methods is presented. Fresh pork fat, skin, ham, loin and tenderloin muscle tissues are manually cut into slices and ablated using a 1064 nm pulsed Nd:YAG laser. Discrimination analyses between fat, skin and muscle tissues, and further between highly similar ham, loin and tenderloin muscle tissues, are performed based on the LIBS spectra in combination with multivariate statistical methods, including principal component analysis (PCA), k nearest neighbors (kNN) classification, and support vector machine (SVM) classification. Performances of the discrimination models, including accuracy, sensitivity and specificity, are evaluated using 10-fold cross validation. The classification models are optimized to achieve best discrimination performances. The fat, skin and muscle tissues can be definitely discriminated using both kNN and SVM classifiers, with accuracy of over 99.83%, sensitivity of over 0.995 and specificity of over 0.998. The highly similar ham, loin and tenderloin muscle tissues can also be discriminated with acceptable performances. The best performances are achieved with SVM classifier using Gaussian kernel function, with accuracy of 76.84%, sensitivity of over 0.742 and specificity of over 0.869. The results show that the LIBS technique assisted with multivariate statistical methods could be a powerful tool for online discrimination of soft tissues, even for tissues of high similarity, such as muscles from different parts of the animal body. This technique could be used for discrimination of tissues suffering minor clinical changes, thus may advance the diagnosis of early lesions and abnormalities.

Sensitive zone parameters and curvature radius evaluation for polymer optical fiber curvature sensors

Abstract: Polymer optical fibers (POFs) are suitable for applications such as curvature sensors, strain, temperature, liquid level, among others. However, for enhancing sensitivity, many polymer optical fiber curvature sensors based on intensity variation require a lateral section. Lateral section length, depth, and surface roughness have great influence on the sensor sensitivity, hysteresis, and linearity. Moreover, the sensor curvature radius increase the stress on the fiber, which leads on variation of the sensor behavior. This paper presents the analysis relating the curvature radius and lateral section length, depth and surface roughness with the sensor sensitivity, hysteresis and linearity for a POF curvature sensor. Results show a strong correlation between the decision parameters behavior and the performance for sensor applications based on intensity variation. Furthermore, there is a trade-off among the sensitive zone length, depth, surface roughness, and curvature radius with the sensor desired performance parameters, which are minimum hysteresis, maximum sensitivity, and maximum linearity. The optimization of these parameters is applied to obtain a sensor with sensitivity of 20.9 mV/°, linearity of 0.9992 and hysteresis below 1%, which represent a better performance of the sensor when compared with the sensor without the optimization.

Investigation on the parameter optimization and performance of laser cladding a gradient composite coating by a mixed powder of Co50 and Ni/WC on 20CrMnTi low carbon alloy steel

Abstract: In this study, a gradient composite coating was manufactured on 20CrMnTi alloy steel by laser cladding. The laser power, cladding scan velocity and powder flow rate were selected as influencing factors of the orthogonal cladding experiments. The influencing factors were optimized by the comprehensive analysis of Taguchi OA and TOPSIS method. The high significant parameters and the predicted results were confirmed by the ANOVA method. The macromorphology and microstructures are characterized by using laser microscope, SEM, XRD and microhardness tester. Comparison tests of wear resistance of gradient composite coating, 20CrMnTi cemented quenching sample and the 20CrMnTi sample were conducted on the friction-wear tester. The results show that the phases are γ-Co solid solution, Co 3 B, M 23 C 6 and etc. The interlayers and wear-resisting layer also contain new hard phases as WC, W 2 C. The microhardness of the gradient coating was increased to 3 times as compared with that of the 20CrMnTi substrate. The wear resistance of the gradient composite coating and 20CrMnTi cemented quenching sample was enhanced to 36.4 and 15.9 times as compared with that of the 20CrMnTi.

Densification behavior and mechanical properties of nanocrystalline TiC reinforced 316L stainless steel composite parts fabricated by selective laser melting

Abstract: Metal matrix composite parts produced using selective laser melting have superior mechanical properties to those produced using traditional powder metallurgy. In this study, nanocrystalline TiC reinforced 316L stainless steel composite parts were fabricated using selective laser melting, and the effects of the TiC mass fraction, particle size, and processing parameters on the relative density, microhardness, and mechanical properties of the TiC/316L composites were investigated. The results show that the relative density of the fabricated parts is related to the laser power and exposure time, and increases when these parameters are increased. The greater the mass fraction of nano-TiC added, the more severe the degree of spheroidization and the lower the density of the resulting material. The microhardness of the 316L stainless steel parts is enhanced by the nano-TiC particles, and increases with increasing nano-TiC mass fraction. The tensile strength is improved with longer exposure time and with the addition of 2 wt% nano-TiC particles. Compared with pure 316L, the microhardness of the TiC/316L composite parts fabricated with 2 wt% 40 nm TiC enhanced from HV0.3 = 219.1 to 277.6, and the ultimate tensile strength significantly increased from 627.5 to 748.6 MPa. The strengthening mechanism of TiC particles is the refinement of the grain size of the 316L matrix, and the greater amount of TiC particles added, the better the grain refinement of 316L.

Experimental investigation into metal micro-patterning by laser on polymer-metal hybrid joining

Abstract: Surface modification pretreatment on laser direct joining of glass fibre reinforced polyamide to steel was studied to assess its effect on the joint's mechanical performance. The steel part was structured by laser radiation to accomplish a proper mechanical interlock when joining with the polymer. In a second step, the opposite side of the micro-structured metal was irradiated by a continuous wave (cw) fibre laser system until reaching the melting temperature of the polymer in both materials interface. The metal micro-structuring was produced by two different laser sources (nanosecond pulses (ns) and cw) in order to study the effect of different groove geometries on the joint's failure force under tensile-shear tests. The impact of structure density and clamping pressure was also assessed. A tight dependence of aspect ratio and recast material height of patterns on joint’s failure force was found for the micro-patterns that were produced by nanosecond pulses. The greatest strength was achieved in the case of patterns produced by ns-pulses. The trend concerning the effect of structure density was validated for the patterns that were produced by ns-pulses and cw-radiation. The changes in clamping pressure did not evidence a significant influence on the joint quality. The morphological features of the detached surfaces showed that the micro-geometric structure aspect ratio has a meaningful effect on the failure mode in the case of structures that were generated by nanosecond pulses.

A novel double perovskite tellurate Eu 3+ -doped Sr 2 MgTeO 6 red-emitting phosphor with high thermal stability

Abstract: A series of novel double perovskite tellurate red-emitting phosphors Sr 2 MgTeO 6 : x Eu 3+ ( x = 0.05–0.40) were successfully synthesized by a high-temperature solid-state reaction method. The phase structure, photoluminescence properties and thermal stability of the phosphor were investigated in detail. The phosphor shows dominant emission peak at 614 nm belonging to the 5 D 0 → 7 F 2 electric dipole transition under 465 nm excitation. The luminescence intensity keeps increasing with increasing the content of Eu 3+ to 25 mol%, and the critical transfer distance of Eu 3+ was calculated to be 12 A. The quenching temperature for Sr 2 MgTeO 6 :0.25Eu 3+ was estimated to be above 500 K. This spectral feature reveals high color purity and excellent chromaticity coordinate characteristics. Therefore, Eu 3+ -doped Sr 2 MgTeO 6 phosphors are potential red phosphors for blue chip-based white light-emitting diode and display devices.

Ti6Al4V lightweight lattice structures manufactured by laser powder bed fusion for load-bearing applications

Abstract: Additively manufactured (AM) lattice structures allow complex-shaped and custom parts, with superior design that cannot be produced by traditional methods For medical implants, AM lattice structures are aimed at matching the elastic modulus of bone while providing strength and allowing bone in-growth for long-term stability In this study, relatively thick struts are investigated in an attempt to match the properties of cortical bone, which is meant for the internal structural integrity of the implant, while a smaller lattice may be used for near-surface parts of an implant In this work we investigate additively manufactured lattice samples produced by Laser Powder Bed Fusion (LPBF) of Ti6Al4V ELI, with samples having approximately 50% regular porosity In particular, we experimentally compare two designs: diagonal and rhombic MicroCT-based static loading simulations are used to highlight stress hotspots in the two designs, to highlight possible failure locations Physical compression testing to initial failure and subsequent microCT highlight the locations of initial failure, which correlate well with the simulation stress hotspots Both designs show excellent strength (120–140 kN failure load) and effective compressive elastic modulus corresponding well to simulations Differences between microCT-based simulations of the produced lattices and those of ideal design parameters can be attributed mainly to surface roughness, and slightly thinner manufactured struts of the as-built lattices, with similar trends for the two model designs These results validate experimentally that both designs are suitable for load-bearing applications

CFRTP and stainless steel laser joining: Thermal defects analysis and joining parameters optimization

Abstract: Experiments with different joining parameters were carried out on fiber laser welding system to explore the mechanism of CFRTP/stainless steel joining and the influence of the parameters on the joining quality. The thermal defect and the microstructure of the joint was tested by SEM, EDS. The joint strength and the thermal defect zone width was measured by the tensile tester and the laser confocal microscope, respectively. The influence of parameters such as the laser power, the joining speed and the clamper pressure on the stainless steel surface thermal defect and the joint strength was analyzed. The result showed that the thermal defect on the stainless steel surface would change metal’s mechanical properties and reduce its service life. A chemical bonding was found between the CFRTP and the stainless steel besides the physical bonding and the mechanical bonding. The highest shear stress was obtained as the laser power, the joining speed and the clamper pressure is 280 W, 4 mm/s and 0.15 MPa, respectively.

Determination of melt pool dimensions using DOE-FEM and RSM with process window during SLM of Ti6Al4V powder

Abstract: Selective laser melting (SLM) shows a positive prospect as an additive manufacturing (AM) technique for fabrication of 3D parts with complicated structures. A transient thermal model was developed by the finite element method (FEM) to simulate the thermal behavior for predicting the time evolution of temperature field and melt pool dimensions of Ti6Al4V powder during SLM. The FEM predictions were then compared with published experimental measurements and calculation results for model validation. This study applied the design of experiment (DOE) scheme together with the response surface method (RSM) to conduct the regression analysis based on four processing parameters (exactly, the laser power, scanning speed, preheating temperature and hatch space) for predicting the dimensions of the melt pool in SLM. The preliminary RSM results were used to quantify the effects of those parameters on the melt pool size. The process window was further implemented via two criteria of the width and depth of the molten pool to screen impractical conditions of four parameters for including the practical ranges of processing parameters. The FEM simulations confirmed the good accuracy of the critical RSM models in the predictions of melt pool dimensions for three typical SLM working scenarios.

Effect of dual laser beam on dissimilar welding-brazing of aluminum to galvanized steel

Abstract: In this investigation, the joining of two types of galvanized steel and Al6022 aluminum alloy in a coach peel configuration was carried out using a laser welding-brazing process in dual-beam mode. The feasibility of this method to obtain a sound and uniform brazed bead with high surface quality at a high welding speed was investigated by employing AlSi12 as a consumable material. The effects of alloying elements on the thickness of intermetallic compound (IMC) produced at the interface of steel and aluminum, surface roughness, edge straightness and the tensile strength of the resultant joint were studied. The comprehensive study was conducted on the microstructure of joints by means of a scanning electron microscopy and EDS. Results showed that a dual-beam laser shape and high scanning speed could control the thickness of IMC as thin as 3 µm and alter the failure location from the steel-brazed interface toward the Al-brazed interface. The numerical simulation of thermal regime was conducted by the Finite Element Method (FEM), and simulation results were validated through comparative experimental data. FEM thermal modeling evidenced that the peak temperatures at the Al-steel interface were around the critical temperature range of 700–900 °C that is required for the highest growth rate of IMC. However, the time duration that the molten pool was placed inside this temperature range was less than 1 s, and this duration was too short for diffusion-control based IMC growth.

Influence of processing parameters on surface texture homogeneity using Direct Laser Interference Patterning

Abstract: Surface functionalities in the field of tribology, wettability, biocompatibility and holographic marking introduced by well-defined surface structures strongly depend on the surface texture homogeneity and quality. This work presents strategies for the fabrication of homogeneous periodic surface microstructures employing the Direct Laser Interference Patterning (DLIP) technology with the fundamental transverse mode (TEM00) emitted from a nanosecond laser source. Ti6Al4V substrates are structured using line-like patterns with spatial periods of 7.20 µm, 5.82 µm and 4.31 µm. The impact of various DLIP process parameters such as laser fluence, pulse overlap, hatch distance and spatial period on the produced surface microstructures is introduced and the consequences on the surface texture homogeneity are discussed. Large-area analysis of micro structures is carried out through white light interferometry and scanning electron microscopy. A quantitative measurement scheme of the pattern homogeneity, based on topographical properties such as kurtosis, standard deviation and mean structure height was introduced. Furthermore, the influence of a second modulation arising from the employed hatch distance has been identified. A quantitative parameter, the surface error percentage, has been introduced and employed for the characterization of pattern homogeneity. It was found that specially for larger spatial periods and surfaces treated at high laser fluence, pulse-to-pulse overlaps and a short hatch distance, the overall surface texture homogeneity could be improved up to ∼80–90%.