Low Scanning Speed Research Articles

Rapid prototyping of noncontact microwave microfluidic devices for sensing applications

Microfluidics is an innovative technological platform with a vast potential to streamline processes in biology, chemistry, and biomedical fields. Microfluidic integrated biosensors attract much attention due to extreme miniaturization, low sample consumption, and increased homogeneity in mixing conditions, leading to enhanced sensitivity. Nowadays, many researchers focus on inexpensive and flexible laser production of polymer-based microfluidic devices for sensing applications due to their ease of production and rapid processing benefits. In this article, we present some key factors for the simple and rapid production of microfluidic components of the microwave sensor by using the CO2 laser ablation technique. The technique does not require any cleanroom or complex laboratory setups and provides short fabrication times for prototyping. It is observed that, at high laser power (30 W) and low scan speed (125 cm s−1), both the channel depth and the surface roughness increase greatly as opposed to channel waviness. It is also demonstrated that heat treatment is a viable method to reduce the channel roughness with a trade of channel depth. In the second section, prepared channels are bonded onto the split ring resonators (SRRs) fabricated using polymethyl methacrylate as a substrate. Power reflection measurements from SRR are performed using a continuous flow system that injects 100 mM glucose solutions into the channels. Change of dielectric constant due to glucose loading generates a meaningful resonance frequency shift, showing a possible use scenario of the device as a biosensor.

Diverse microstructure of Ti6.5Al2Zr1Mo1V fabricated via electron beam selective melting

Ti6.5Al2Zr1Mo1V was fabricated via electron beam selective melting (EBSM) with different process parameters to study the diversity of microstructure. Results demonstrate that samples with a flat surface can be obtained when the ratio of beam current to scanning speed fluctuated between 5.0 and 7.5 as other parameters were fixed. Basketweave structure and Widmanstatten structure were observed to co-exist in EBSM-built samples under different parameters, while martensite phase α′ was more likely to form under low beam current and high scanning speed. Samples with a mixture of (α′ + α + β) phases possess a higher strength and lower plasticity than that with fully lamellar (α + β) phases due to the stress concentration at the α′/β interface in inhomogeneous microstructure.

Tailored grain morphology via a unique melting strategy in electron beam-powder bed fusion

This study presents a unique melting strategy in electron beam-powder bed fusion of Alloy 718 to tailor the grain morphology from the typical columnar to equiaxed morphology. For this transition, a specific combination of certain process parameters, including low scanning speeds (400–800 mm/s), wide line offsets (300–500 μm) and a high number of line order (#10) was selected to control local solidification conditions in each melt pool during the process. In addition, secondary melting of each layer with a 90° rotation with respect to primary melting induced more vigorous motions within the melt pools and extensive changes in thermal gradient direction, facilitating grain morphology tailoring. Four different types of microstructures were classified according to the produced grain morphology depending on the overlap zone between two adjacent melt pools, i.e., fully-columnar (overlap above 40 %), fully-equiaxed (overlap below 15 %), mixed columnar-equiaxed grains, and hemispherical melt pools containing mixed columnar-equiaxed grains (overlap ~20–25 %). The typical texture was <001>; however, the texture was reduced significantly through the transition from the columnar to equiaxed grain morphology. Along with all four different microstructures, shrinkage defects and cracks were also identified which amount of them reduced by a reduction in areal energy input. The hardness was increased through the transition, which was linked to the growth of the γʺ precipitates and high grain boundary density in the fully-equiaxed grain morphology.

Direct laser metal deposition additive manufacturing of Inconel 718 superalloy: Statistical modelling and optimization by design of experiments

Direct laser metal deposition (DLMD) technique is used for additive manufacturing (AM) of Inconel 718 Ni-based superalloy using full factorial design. A 1 kW fiber laser is applied with a coupled coaxial nozzle head. Laser scanning speed (2.5–5.0 mm/s), powder feed rate (17.94–28.52 g/min), and scanning strategies (Unidirectional, Bidirectional) were considered as the input process variables while geometrical dimensions (height, width average), standard deviation of microhardness, and the stability of additively manufactured walls were determined as process responses. The influence of process parameters on the responses variations were studied by analysis of variance (ANOVA). Results indicated that low scanning speed and high powder feed rate caused to increase in height and average width of AM samples. Due to microstructural phases, the microhardness changes have an unstable trend. Results show that a stable wall was obtained in low scanning speed and unidirectional scanning pattern. In order to achieve a desired condition for the DLMD additive manufacturing process, optimization was conducted based on the applied statistical analyses. The scanning speed of 2.5 mm/s, the powder feed rate of 28.52 g/min, and unidirectional scanning pattern were identified as the optimum conditions.

Multi-objective optimization of support structures for metal additive manufacturing

Electron-beam melting (EBM) is a rapidly developing metal additive manufacturing (AM) method. It is more effective with complex and customized parts manufactured in low volumes. In contrast to traditional manufacturing, it offers reduced lead time and efficient material management. However, this technology has difficulties with regard to the construction of overhang structures. Production of overhangs using EBM without support structures results in distorted objects, and the addition of a support structure increases the material consumption and necessitates post-processing. The objective of this study was to design support structures for metal AM that are easy to remove and consume lower support material without affecting the quality of the part. The design of experiment methodology was incorporated to evaluate the support parameters. The multi-objective optimization minimizing support volume and support removal time along with constrained deformation was performed using multi-objective genetic algorithm (MOGA-II). The optimal solution was characterized by a large tooth height (4 mm), large tooth base interval (4 mm), large fragmented separation width (2.5 mm), high beam current (6 mm), and low beam scan speed (1200 mm/s).

Influences of Temperature Field on Microstructural Characteristics of Laser Cladding Al2O3-13wt.%TiO2 Coating Prepared by Plasma Spraying

To explore effects of temperature field in laser cladding on structure of ceramic coating prepared by plasma spraying, a finite element model of continuous moving three-dimensional temperature field of laser cladded Al2O3-13wt.%TiO2 coating prepared by plasma spraying was constructed by the parametric design language of ANSYS finite element software to analyze temperature field during laser cladding. According to analysis results, it is very difficult to realize complete remelting of the whole preset ceramic coating during laser cladding when it is thick, which is related with the relatively low thermal conductivity of the ceramic materials. The whole coating can be divided into remelting zone, sintering zone and residual plasma spraying zone according to temperature field distribution in the zone of cladding. Given the optimal technological parameters, relatively thick remelting zone and sintering zone could be gained under the relatively low laser cladding power and relatively low scanning speed. Experimental results demonstrated that the ceramic coating after cladding formed remelting zone with small-sized and dense isometric crystals, sintering zone and lamellar residual plasma spraying zone. Moreover, the calculated results of thickness of the remelting zone and sintering zone conformed well to experimental values. This proved that the constructed finite element model is accurate and reliable.

Simulation of Primary Particle Development and Their Impact on Microstructural Evolution of Sc-Modified Aluminum Alloys during Additive Manufacturing

The microstructures of additively manufactured Sc- and Zr-modified aluminum alloys are significantly influenced by the nucleation role of solid intermetallic particles in undercooled liquid. To replicate such effects, a precipitation model relying on L12-Al3Sc particles is developed. An initiation criterion is proposed based on the precipitation kinetics of primary particles to address solute trapping under high solidification rates. Avrami’s equation is then used to estimate the progress of precipitation. The model is integrated into a cellular automata (CA) analysis to simulate the resulting solidified microstructure, in that the precipitation model is performed implicitly within the CA cells. It is shown that, in accordance with the experimental findings, the proposed simulation approach can predict the distinct fine- (FG) and coarse-grained (CG) zones at the fusion boundary and the meltpool core, respectively. The model can also deliver the reported enhancement of the FG zone under lower scanning speed and higher platform temperatures. These findings are explained in terms of particle number densities at different meltpool regions. Moreover, a semi-2D simulation with a very small cell size is suggested to address the extremely fine grain structure within the FG zone.

Design of Experiments and Optimization of Laser-Induced Graphene.

Realization of graphene-based sensors and electronic devices remains challenging, in part due to integration challenges with current fabrication and manufacturing processes. Thus, scalable methods for in situ fabrication of high-quality graphene-like materials are essential. Low-cost CO2 laser engravers can be used for site-selective conversion of polyimide under ambient conditions to create 3-D, rotationally disordered, few-layer, porous, graphene-like electrodes. However, the influences of non-linear parameter terms and interactions between key parameters on the graphitization process present challenges for rapid, resource-efficient optimization. An iterative optimization strategy was developed to identify promising regions in parameter space for two key parameters, laser power and scan speed, with the goal of optimizing electrode performance while maximizing scan speed and hence fabrication throughput. The strategy employed iterations of Design of Experiments Response Surface (DoE-RS) methods combined with choices of readily measurable parameters to minimize measurement resources and time. The initial DoE-RS experiment set employed visual response parameters, while subsequent iterations used sheet resistance as the optimization parameter. The final model clearly demonstrates that laser graphitization through raster scanning is a highly non-linear process requiring polynomial terms in scan speed and laser power up to fifth order. Two regions of interest in parameter space were identified using this strategy: Region 1 represents the global minimum for sheet resistance for this laser (∼16 Ω/sq), found at a low scan speed (70 mm/s) and a low average power (2.1 W) . Region 2 is a local minimum for sheet resistance (36 Ω/sq), found at higher values for scan speed (340 mm/s) and average power (3.4 W), allowing ∼5-fold reduction in write time. Importantly, these minima do not correspond to constant ratios of average laser power to scan speed. This highlights the benefits of DoE-RS methods in rapid identification of optimum parameter combinations that would be difficult to discover using traditional one-factor-at-a-time optimization. Verification data from Raman spectroscopy showed sharp 2D peaks with mean full-width-at-half-maximum intensity values <80 cm–1 for both regions, consistent with high-quality 3D graphene-like carbon. Graphene-based electrodes fabricated using the parameters from the respective regions yielded similar performance when employed as capacitive humidity sensors with hygroscopic dielectric layers. Devices fabricated using Region 1 parameters (16 Ω/sq) yielded capacitance responses of 0.78 ± 0.04 pF at 0% relative humidity (RH), increasing to 31 ± 7 pF at 85.1% RH. Region 2 devices (36 Ω/sq) showed comparable responses (0.88 ± 0.04 pF at 0% RH, 28 ± 5 pF at 85.1% RH).

Analysis of Laser Surface Hardening of GM246 Cast Iron

Laser surface modification technology is one of the most advanced technologies, which uses laser to modify the characteristics of the surface to offer superior performance for various industrial applications. In this study, laser surface hardening behavior of GM246 case iron was investigated. Result shows that excellent laser surface hardening of GM246 cast iron need low power density and scanning speed. With power of 2500 W, scanning speed of 300 mm/min and power density of 2500 W/cm2, the laser surface hardening of GM246 cast iron achieved the hardness of 790HV, which was 2-3 times higher than the hardness of base metal. Also, the depth of laser surface hardening case achieved 0.9 mm and the hardening case demonstrated three subzones.

Internal Stress Evolution and Subsurface Phase Transformation in Titanium Parts Manufactured by Laser Powder Bed Fusion—An In Situ X‐Ray Diffraction Study

Laser powder bed fusion (LPBF) is a metal additive manufacturing technology, which enables the manufacturing of complex geometries for various metals and alloys. Herein, parts made from commercially pure titanium are studied using in situ synchrotron radiation diffraction experiments. Both the phase transformation and the internal stress buildup are evaluated depending on the processing parameters. For this purpose, evaluation approaches for both temperature and internal stresses from in situ diffraction patterns are presented. Four different parameter sets with varying energy inputs and laser scanning strategies are investigated. A combination of a low laser power and scanning speed leads to a more homogeneous stress distribution in the observed gauge volumes. The results show that the phase transformation is triggered during the primary melting and solidification of the powder and subsurface layers. Furthermore, the stress buildup as a function of the part height during the manufacturing process is clarified. A stress maximum is formed below the part surface, extending into deeper layers with increasing laser power. A temperature evaluation approach for absolute internal stresses shows that directional stresses decrease sharply during laser impact and reach their previous magnitude again during cooling.

Powder bed laser sintering of copper-doped hydroxyapatite: Numerical and experimental parametric analysis

Additive manufacturing (AM), especially powder bed laser sintering (PBLS), has been an increasingly popular field since the 1980s. Direct SLS is particularly challenging with ceramic materials due to their low thermal conductivity, high melting point, and brittle mechanical behaviour. In addition, they require longer processing times for a reliable sintering degree. In this work, the impact of some crucial parameters in SLS applied to a copper-doped hydroxyapatite bioceramic was studied. Incorporating copper ions into the hydroxyapatite matrix by thermal treatment can stimulate blood vessel formation, simultaneously improving the material's mechanical integrity and antibacterial properties. Moreover, it facilitates laser power absorption by the material at the laser wavelength. Thin films were prepared with controlled thicknesses using dip-coating on glass substrates, and they were irradiated by an ytterbium laser (1.070 µm wavelength). Experimental laser irradiation was systematically compared to numerical models to predict the maximum temperature produced on the film surface by laser irradiation. The evaluated parameters are the absorptivity from the copper concentration, the film thickness, and the laser source (scanning velocity and power). Combining low laser scanning speeds with low film thickness and optimised absorption tuned by the copper concentration has made possible the development of well-sintered ceramics by the PBLS technique. • SLS on Cu-doped HAP films has been experimentally and numerically investigated. • The injected power density controls the local processing temperature. • Key parameters are copper concentration, film thickness, laser scan rate, and power. • The temperatures predicted from numerical models corroborate the film morphologies. • Optimal conditions for SLS processing can be obtained from this approach.

Selective Direct Laser Writing of Pyrolytic Carbon Microelectrodes in Absorber-Modified SU-8.

Pyrolytic carbon microelectrodes (PCMEs) are a promising alternative to their conventional metallic counterparts for various applications. Thus, methods for the simple and inexpensive patterning of PCMEs are highly sought after. Here, we demonstrate the fabrication of PCMEs through the selective pyrolysis of SU-8 photoresist by irradiation with a low-power, 806 nm, continuous wave, semiconductor-diode laser. The SU-8 was modified by adding Pro-Jet 800NP (FujiFilm) in order to ensure absorbance in the 800 nm range. The SU-8 precursor with absorber was successfully converted into pyrolytic carbon upon laser irradiation, which was not possible without an absorber. We demonstrated that the local laser pyrolysis (LLP) process in an inert nitrogen atmosphere with higher laser power and lower scan speed resulted in higher electrical conductance. The maximum conductivity achieved for a laser-pyrolyzed line was 14.2 ± 3.3 S/cm, with a line width and thickness of 28.3 ± 2.9 µm and 6.0 ± 1.0 µm, respectively, while the narrowest conductive line was just 13.5 ± 0.4 µm wide and 4.9 ± 0.5 µm thick. The LLP process seemed to be self-limiting, as multiple repetitive laser scans did not alter the properties of the carbonized lines. The direct laser writing of adjacent lines with an insulating gap down to ≤5 µm was achieved. Finally, multiple lines were seamlessly joined and intersected, enabling the writing of more complex designs with branching electrodes and the porosity of the carbon lines could be controlled by the scan speed.

Modeling and experimental validation of additively manufactured tantalum-titanium bimetallic interfaces

Bimetallic structures processed via laser-based additive manufacturing (AM) efficiently combine multiple materials in single components, which are difficult to achieve using traditional methods. However, limited understanding exists on how processing parameters influence the resulting microstructures and thermal profiles of base material during processing, affecting component performance. To this end, we present a combined numerical and experimental study on the effects of input laser power and scanning speed on the heat-affected-zone (HAZ) and fusion-zone (FZ) of a tantalum-titanium bimetallic structure, two compatible materials that are challenging to process traditionally and are desirable in a bimetallic system. We demonstrate that a wide array of track characteristics can be achieved by varying the laser power and scanning speed. The HAZ and FZ microstructures' width and depth within the underlying Ti6Al4V substrate can be estimated within 6–19% of the experimentally determined values using a 3D transient-thermal finite element analysis (FEA) model, with the most significant errors occurring at low scanning speeds. Adjusting the absorptivity input to the model improves prediction to within 1–11% difference of the HAZ/FZ dimensions and corresponding temperatures relative to the experimental dimensions across a broad range of laser power and scanning speeds. Our results indicate that the underlying temperatures achieved in bimetallic components can be predicted accurately using a detailed FEA approach, aiding larger-scale approaches towards improved process modeling and manufacturing of bimetallic structures using laser-based AM.

Real-time Topography and Hamaker Constant Estimation in Atomic Force Microscopy Based on Adaptive Fading Extended Kalman Filter

In this study, a novel technique based on adaptive fading extended Kalman filter for atomic force microscopy is proposed to directly estimate the topography of a sample surface without needing any control system. While in conventional imaging techniques, the scanning speed or the bandwidth is limited due to a relatively large settling time, the method proposed in this research is able to address this issue and estimate the topography throughout transient oscillation of the microcantilever. With this aim, an estimation process using an adaptive fading extended Kalman filter (augmented with forgetting factor) as the system observer is designed and coupled with the system dynamics to obtain sample topography. Obtained results demonstrate that the sample height is estimated by this algorithm with high accuracy and a relatively high scanning speed. Moreover, the observer is able to identify the topography and Hamaker constant simultaneously. Therefore, the presented approach can compensate for the low scanning speed of the classical imaging method as well as eliminate the need for a closed-loop controller.

Electron beam melted TiC/high Nb–TiAl nanocomposite: Microstructure and mechanical property

To enhance the process stability and densification, semi-melt step has been introduced when fabricating the TiC/high Nb–TiAl nanocomposite via electron beam melting. The homogenous TiAl matrix microstructure with dispersed nano-scale carbides was realised. During the EBM melt, most TiC nanoparticles dissolved and Ti2AlC formed with near-spherical and rod-like shapes. The particles had an influence on solidification behaviour and the subsequent microstructural degradation. High Nb–TiAl nanocomposites with 1.2 wt% TiC addition exhibited a duplex microstructure with dispersed carbides, while a nearly lamellar microstructure (carbide-free) was found in samples with 0.6 and 0.8 wt% TiC. Furthermore, a lower scanning speed resulted in higher relative density, greater Al loss, increased α2-phase but reduced carbide fractions. The microhardness of 433 ± 10 HV0.2, ultimate tensile strength of 657 ± 155 MPa and fracture toughness of 8.1 ± 0.1 MPa√m in 1.2 wt% TiC/high Nb–TiAl nanocomposite processed by EBM are very promising. In addition, the compressive yield strength of 1085 ± 55 MPa, fracture strength of 2698 ± 34 MPa and strain to fracture of 26.1 ± 1.0%, are superior to those processed by conventional means. The strengthening and toughening mechanisms have been interpreted on the basis of crack path observation.

Investigation on efficiency and quality for ultrashort pulsed laser ablation of nickel-based single crystal alloy DD6

The high processing efficiency and quality are constant pursuits for modern manufacturing industry. This paper investigated the ablation efficiency and quality of ultrashort pulsed laser ablation of DD6 single crystal alloy based on experiments and theoretical analysis. The experimental results showed that the ablation rate increases with the increase of laser fluence and with the decrease of scanning speed and scanning width, while the ablation efficiency decreases with the increase of laser fluence. A relatively flat and low melted zone ablation surface could be obtained by employing a low laser fluence and high scanning speed. The influence of laser parameters on the ablation diameter, equivalent energy density, and heat accumulation effect was analyzed based on the theory of laser ablation and heat conduction. The theoretical analysis revealed the material removal transforms from plasma or vaporization removal to melt ejection with the pulse energy increases and the scanning speed decreases, which can explain the formation mechanism of surface morphology very well. In addition, the scanning strategy of high efficiency and quality was proposed based on the theoretical analysis and experimental results.

Additively manufacturing-enabled hierarchical NiTi-based shape memory alloys with high strength and toughness

ABSTRACT A hierarchical microstructure was obtained, including the unique interlaced dual-phase structure, the solidified molten pool, the coarse columnar B2 grains and fine equiaxed B19’ grains, and a great many nanoparticles, during laser powder bed fusion (LPBF) of NiTi alloys. The effect of laser processing parameter on the growth of nanoparticles was assessed. A combination of low laser power and high scanning speed was conducive to the formation of fine granular nanoparticles with a more uniform distribution. Subsequently, effects of rotation angle between adjacent layers on the compressive deformation behaviour of LPBF-processed NiTi alloys were studied. At a small rotation angle (6–36°), the samples could exhibit an excellent combination of high compressive fracture strength and ductility (e.g. 3094 MPa/39.85%). Meanwhile, samples with small rotation angle tended to get a large strain span for the martensite transformation stage and a large deformation capacity (e.g. 4.64% and 9.25% for θ = 6° and σmax = 800 MPa).

Effect of Nd:YAG laser welding on microstructure and mechanical properties of Incoloy alloy 800

Incoloy alloy 800 is a superalloy particularly suited to aggressive corrosive environments. Both weld quality and productivity may be enhanced when joining parts by laser beam welding (LBW). The current paper describes joining of Incoloy alloy 800 plates (4 mm thickness) by laser welding (Nd:YAG). The laser scan speed was varied between 0.5 and 2 m/min for a constant power input (laser). The evolution of the microstructure was investigated utilizing both traditional and advanced microscopic techniques. The results indicated an hourglass shaped fusion zone which was slightly larger on the top surface. Elongated columnar but fine equiaxed dendrites were present in the fusion zone. Significant phase transformation occurred because of a higher cooling rate that is typical with laser welding. An uneven and planar distribution of dislocations associated with subgrain boundaries were observed adjacent to Laves phases. The formation of Laves phases at the lowest scanning speeds reduced the mechanical properties. Mechanical testing showed that the joints failed in the weld zone at the lower scanning speeds because of the presence of the Laves phases. Ductile fracture was demonstrated at the higher scanning speeds whereas brittle fracture occurred at the lower scanning speeds.

Numerical simulation and experimental study of pulsed CO2 laser-induced micro-channels on poly-ether sulfone (PES) polymer

TEA CO2 laser pulses were used to create micro-channels on PES samples with various low fluences and scanning speeds in 16–50 J/cm2 and 23–45 µm/s ranges, respectively. Different micro-channels were created with 142–342 µm widths and 85–440 µm depths which has been 3-dimensionally simulated using ABAQUS software based on the finite element method and CIN heat source. The sharp spike (~85 ns FWHM) and long tail (~3.8 µs) parts of the laser pulses were mathematically modeled with individual Gaussian profiles. A good agreement has been found between the simulated and experimental results. Namely, the maximum relative errors of the depth and opening width of the grooves remain below 11.5% and 12.3%, respectively. However, the corresponding mean values of these relative errors do not exceed 4.1% and 7.5%, respectively.

Ultra‐fast, selective, non‐melting, laser sintering of alumina with anisotropic and size‐suppressed grains

AbstractIn this paper, we report an ultra‐fast sintering phenomenon of alumina achieved by the scanning laser irradiation method. Using CO2 laser irradiation, we found that micrometer‐sized alumina powder (d50 = 1.2 µm) can be sintered close to full density within a few tens of seconds. The microstructure of laser‐sintered alumina was different from that of the furnace‐sintered alumina. The relative density and grain size of the laser‐sintered alumina gradually decreased from the center of the laser beam to the edge. Anisotropy of the grain size was measured along and perpendicular to the scanning direction. This anisotropy decreased as the scanning speed decreased from 0.1 mm/s to 0.01 mm/s. The sintering master curve of grain size versus relative density, which reflects the sintering mechanism, was found to be affected by the laser scanning speed. When the laser scanning speed was 0.1 mm/s, grain size suppression was found for the almost fully dense alumina. However, at lower scanning speed (e.g., 0.01 mm/s), there was significant grain growth in the regions where the relative density was greater than 90%. These results clearly indicate that alumina can be sintered, in the solid‐state, to a high density in a short time using scanning laser and the microstructure is different from the furnace‐sintered alumina.