Rapid Laser Processing Research Articles

Influence of buoyancy on phase separation during laser melting of Silicon and Iron ore

Phase separation is a well-known effect in liquid-liquid interactions, which can also occur during laser-related processes such as laser melting and laser alloying. However, the mechanism of phase separation between immiscible liquids on a millimeter scale during rapid laser processes has not been fully investigated, in which the extent of buoyancy’s contribution to it has remained unclear. Therefore, this investigation focused on the effect of buoyancy on liquid phase separation during the laser melting of silicon (Si) and iron ore. A simplified 2D numerical model was established to simulate the motion of a single Si liquid droplet in iron ore melt with and without the impact of gravity, respectively. The rise velocity of the droplet was calculated and analyzed under the effect of gravity. In addition, the phenomena of simultaneous laser remelting of Si and iron ore in layers were recorded with a high-speed camera, and the element and phase distributions of the target nugget were analyzed by Scanning Electron Microscopy/Energy Dispersive Spectroscopy (SEM/EDS). By combining the simulation, high-speed imaging, and SEM/EDS analysis, the effect of buoyancy on phase separation has been qualitatively analyzed. This investigation revealed that buoyancy is not the main driving force of liquid-liquid phase separation during rapid laser processing.

(Invited) Laser Processing of Solid-state Electrolytes for All-Solid-state Lithium Batteries

Solid-state electrolytes (SSEs) with high ionic conductivity, wide electrochemical stability window and operating temperature window, are promising to replace flammable organic liquid electrolytes for high energy/power density and safe battery systems. However, the processing of SSE components in all-solid-state lithium batteries (ASSLBs) is challenging due to the intrinsic brittleness, air sensitivity, high sintering temperature (for garnet-type SSEs), and poor solid-solid contact. Here, using garnet-type SSEs as a model system, we report rapid laser processing to tackle these processing challenges. First, rapid laser sintering can be used to densify porous LLZO green body with minimal Li loss. Reactive laser sintering can be used to synthesize pure LLZO phase from precursor mixtures. Local laser heating is capable of generating dense/porous bilayers or gradient porous structures. It provides versatile tunability to generate various grain structures to be linked with ion transport properties. Second, laser heating or pulse laser ablation can be used to treat the surface to remove contaminates (Li2CO3, etc.) or generate 3D interfaces that helps to reduce interfacial resistance. Finally, ultrafast laser sintering is beneficial for co-sintering of cathode/SSE to facilitate solid-solid contact while minimizing side reactions. With direct laser energy absorption, extremely fast heating and cooling rates, highly tunable laser parameters, promising scalability, and great integrability, laser-based processing could be an ideal manufacturing approach for ASSLBs. Despite the above benefits, challenges such as temperature gradient induced crack formation will also be discussed in this presentation.

Rapid Laser Processing of Thin Sr‐Doped LaCrO3–δ Interconnects for Solid Oxide Fuel Cells

Rapid Laser Processing of Thin Sr‐Doped LaCrO_{3–<i>δ</i>} Interconnects for Solid Oxide Fuel Cells

Microstructure Transformation in Different Regions of Zr61.4Cu27.8Al4Ni6Y0.8 Bulk Metallic Glass Induced by Rapid Laser Welding

An experimental study is performed on the microstructure transformation induced by rapid laser welding in the different regions of Zr61.4Cu27.8Al4Ni6Y0.8 bulk metallic glass (BMG). The laser input energy has a remarkable influence on the microstructure and microhardness of the Zr-based BMGs. The microstructures in different regions of as-welded joints are diverse. Crystallization happens in heat-affected zone (HAZ) with crystalline dendritic phase of CuZr, which results in the deterioration of the microhardness to 434.9 ± 17.1 HV in HAZ, much lower than that of parent material as 517 ± 5.0 HV. Meanwhile, the element profiles indicate that intragranular segregation of Cu element occurs during the crystallization process. In the center of molten zone (MZ), the structure is fully amorphous and its hardness is close to that of parent material. In the region transiting from MZ to HAZ, some nano-grains with an average size of 20–50 nm are identified. In addition, several flower-like nanostructured grains of Y2O3 phase with a size ranging from 50 to 80 nm are formed in MZ’s matrix. The nanocrystallization is believed to be responsible for the enhancement of the Vickers hardness up to 560.1 ± 8.4 HV in this region. Rapid laser processing induces three kinds of microstructures in Zr61.4Cu27.8Al4Ni6Y0.8 bulk metallic glasses, i.e., the severe crystallization of CuZr phase in heat affected zones (HAZ), the nano-grains in the region transiting from molten zone (MZ) to HAZ, and the fully amorphous structure in the center of MZ, which consequently results in the diverse microhardness in spatial distribution.

A Novel Laser 3D Printing Method for the Advanced Manufacturing of Protonic Ceramics.

Protonic ceramics (PCs) with high proton conductivity at intermediate temperatures (300–600 °C) have attracted many applications in energy conversion and storage devices such as PC fuel/electrolysis cells, PC membrane reactors, hydrogen pump, hydrogen or water-permeable membranes, and gas sensors. One of the essential steps for fulfilling the practical utilization of these intermediate-temperature PC energy devices is the successful development of advanced manufacturing methods for cost-effectively and rapidly fabricating them with high energy density and efficiency in a customized demand. In this work, we developed a new laser 3D printing (L3DP) technique by integrating digital microextrusion-based 3D printing and precise and rapid laser processing (sintering, drying, cutting, and polishing), which showed the capability of manufacturing PCs with desired complex geometries, crystal structures, and microstructures. The L3DP method allowed the fabrication of PC parts such as pellets, cylinders, cones, films, straight/lobed tubes with sealed endings, microchannel membranes, and half cells for assembling PC energy devices. The preliminary measurement of the L3DP electrolyte film showed a high proton conductivity of ≈7 × 10−3 S/cm. This L3DP technique not only demonstrated the potential to bring the PCs into practical use but also made it possible for the rapid direct digital manufacturing of ceramic-based devices.

Selective laser melting vitrification of amorphous soft magnetic alloys with help of double-scanning-induced compositional homogeneity

Recently, selective laser melting (SLM) of Fe-based soft magnetic bulk metallic glass (BMG) is garnering great attention because it can yield both superior magnetic properties such as high permeability and low core loss and near-net shaping of 3-dimensional complex components. However, full vitrification of BMGs with high saturation magnetization above 1.2 T has never been realized because cooling rates are limited and compositional inhomogeneity induced by rapid laser processing causes severe undesirable crystallization. In this work, a double scan strategy has been employed with the aim of amorphous phase fraction enhancement as well as densification. We have shown that double scanning effectively fills voids generated due to partial melting of powders, and leads to relative density of up to 96% and corresponding saturated magnetization of 1.22 T. More importantly, the double scan strategy stimulates reflow in the melt pool, securing compositional uniformity, and eventually enhances amorphous phase fraction to a value as high as 47%. As a consequence, coercivity has been significantly decreased, which in turn reduces core loss and increases permeability.

Facile One Step Rapid Laser Reactive Processing of Protonic Ceramic Electrochemical Cells

Greenhouse gas emissions are becoming more and more serious issue with fossil fuels combustion. Renewable energy sources are the key to solve this problem. Protonic ceramic electrochemical cell (PCEC) is a high-efficiency and cost-effective device for the conversion of renewable electricity into storable fuels (e.g., hydrogen). Because the poor sintering properties of protonic ceramics, conventional furnace sintering methods for PCECs are usually ineffective, which needs long-term and high-temperature firing. A new one-step rapid laser reactive sintering method was developed for achieving fully densified protonic ceramic electrolyte films [1]. Motived by the discovery of rapid laser processing method , we fabricated PCEC single cells through one-step rapid laser scanning. In this cell, the BaCe0.7Zr0.1Y0.1Yb0.1O3-δ (BCZYYb) was selected as electrolyte materials duo to the high ionic conductivity at relatively low temperatures [2]. (BCZYYb) with NiO cermet materials (40:60 wt%) were selected as fuel electrode. BaCe0.6Zr0.3Y0.1O3-δ (BCZY63) was selected oxygen electrode scaffold for further nanoscale phase catalyst infiltration. The porous fuel electrode layer of cell was prepared by 3D printing from the paste comprised of the mixed powders of NiO and BCZYYb stoichiometric amounts precursor solids (BaCO3, CeO2, ZrO2, Y2O3, and Yb2O3). The electrolyte was spray coated on the fuel electrode surface. The coating slurry was composed of BCZYYb stoichiometric amounts precursor solids, 1 wt% NiO was added in it as sintering aid. Then, the scaffold pastes of BCZY63 stoichiometric amounts precursor solids was spray coated on the top surface of BCZYYb green layer. Laser irradiation on the surface of this green single cells in few seconds. Those precursor solids converted into pure BCZYYb phase (both in fuel electrode and electrolyte layer) and BCZY63 phase (scaffold) by solid-state reactive during the laser scanning processing. The fuel electrode layer and oxygen electrode scaffold layer exhibited expected nanoporous microstructure. The BCZYYb electrolyte layer was fully densified with a thickness of ~20 μm, and bond together with the porous electrodes tightly without crack and curvature. The active oxygen electrode material BaCo0.4Fe0.4Zr0.1Y0.1O3−δ nanoparticles were infiltrated into the porous BCZY63 scaffold and calcinated at moderate temperatures. A protonic ceramic electrochemical cell was manufactured successfully with Ideal sandwich structure. This cell exhibited a moderate electrochemical performance. Keywords: Rapid Laser sintering, Protonic ceramic fuel cell, Solid-state reactive sintering, 3D printing.

Surface-Enhanced Raman Spectroscopy of Graphene Integrated in Plasmonic Silicon Platforms with Three-Dimensional Nanotopography

Integrating graphene with plasmonic nanostructures results in multifunctional hybrid systems with enhanced performance for numerous applications. In this work, we take advantage of the remarkable mechanical properties of graphene to combine it with scalable 3D plasmonic nanostructured silicon substrates, which enhance the interaction of graphene with electromagnetic radiation. Large areas of femtosecond laser-structured arrays of silicon nanopillars, decorated with gold nanoparticles, are integrated with graphene, which conforms to the substrate nanotopography. We obtain Raman spectra at 488, 514, 633, and 785 nm excitation wavelengths, spanning the entire visible range. For all excitation wavelengths, the Raman signal of graphene is enhanced by 2-3 orders of magnitude, similarly to the highest enhancements measured to date, concerning surface-enhanced Raman Spectroscopy (SERS) of graphene on plasmonic substrates. Moreover, in contrast to traditional deposition and lithographic methods, the fabrication method employed here relies on single-step, maskless, cost-effective, rapid laser processing of silicon in water, amenable to large-scale fabrication. Finite-difference time-domain simulations elucidate the advantages of the 3D topography of the substrate. Conformation of graphene to the Au-decorated silicon nanopillars enables graphene to sample near fields from an increased number of nanoparticles. Due to synergistic effects with the nanopillars, different nanoparticles become more active for different wavelengths and locations on the pillars, providing broadband enhancement. Nanostructured plasmonic silicon is a promising platform for integration with graphene and other 2D materials, for next-generation applications of large-area hybrid nanomaterials in the fields of sensing, photonics, optoelectronics, and medical diagnostics.

Distribution Characteristics and Reinforcing Behavior of (Ti, Nb)C Reinforced Particle in the Coating Fabricated by Laser Rapid Cladding

(Ti, Nb)C reinforced Fe-based laser coatings were prepared with normal and high scanning velocities of the laser beam. The distribution characteristics of reinforced particles in the coatings were investigated. The mechanical properties of coatings were tested. The results showed that the morphologies of the microstructure and the reinforced particle changed dramatically at high solidification rate due to rapid laser processing compared with that prepared by normal processing. Two kinds of particles were observed in the coating. One was (Ti, Nb)C multiple carbide particle with the size of micron and sub-micron scales, in which a mass of dislocations were found. Another was nano-sized particle including α-Fe and (Ti, Nb) C obtained by rapid solidification. The microstructure of the coatings was highly refined and a large number of twin crystals were found in matrix. The results of mechanical properties test revealed that the wear resistance of the coating was improved by rapid laser processing, compared with that of the coating prepared with normal speeds. The above-mentioned conclusion indicated that rapid laser cladding can promote not only the processing efficiency but also the mechanical properties of the coating.

Improving quality and performance properties of chemical coatings on steels and alloys by laser treatment

The subject of this paper is the Ni-P chemical coatings on steels and alloys. The research goal is to determine the capabilities of improving the quality and performance properties of the coatings under the rapid laser processing. Metal physical research methods - optical and electron-probe microscopy, hardness measurement, X-ray and electron microprobe analysis - are used. Anti-friction properties of the irradiated coatings are determined under testing on the tribometer. The study results have shown that the laser irradiation of chemical coatings can increase the hardness of the steel surface layers, advance the adherence strength of the coating to the steel substrate, lower the friction factor, and enhance the wearability of the coated steels.The results obtained allow reasonably choose modes of laser processing for chemical coatings leading to the consolidation and degassing of the steel surface layers, the increase of the coating adhesion to the substrate, the improvement of the surface morphology, the formation of a relatively perfect texture in the steel surface layers, and to the reduction of the burnout of alloying elements from the surface layers of materials.The studies show that the laser treatment of chemical coatings improves the quality of the surface layers of steels and alloys, increases the strength of coating adhesion to the metal substrate, increases the hardness, decreases the friction factor, and increases the wear resistance of steels with chemical coatings.

Flexible supercapacitor fabrication by room temperature rapid laser processing of roll-to-roll printed metal nanoparticle ink for wearable electronics application

We introduce a rapid and low-temperature laser annealing process of roll-to-roll (R2R) printed metal nanoparticle (NP) ink on a polymer substrate as an alternative to the conventional thermal annealing process using expensive and time consuming lengthy furnace. Due to the confined heating induced by the focused laser, R2R printed Ag NP film is selectively turned into a continuous conductive film without heating the whole substrate. As a result, the damage on the underlying polymer substrate, as well as the processing time required for the annealing, is significantly reduced by the laser annealing compared to the conventional thermal annealing. The resultant laser annealed Ag NP film also exhibits superior electrical and mechanical properties in comparison to the thermal annealed sample. The laser annealed Ag NP film is further applied to the flexible supercapacitor as the current collector in order to confirm the excellence of laser annealed Ag NP film in the fabrication of practical devices.

Numerical controlled two optical paths CO2 laser die-cutting technology

A CO2 laser die-cutting system, which does not need die board any more, is a new technique for manufacturing packing box. Two optical paths, the galvanometer scanning system and the flying optical system, are used to satisfy different processing needs. The scanning system is composed of galvanometer scanning mirrors and F-θ lens. And the flying optical system is driven by two servo motors. This paper presents the software and hardware design of the laser die-cutting system, the difference between the two optical paths, as well as the relationship among the cutting speed, thickness of wrapping paper and laser power. The cutting speed and thickness of wrapping paper are linearly increased by the incremental laser power, while the cutting speed is hyperbolically decreased by the incremental thickness of wrapping paper when the laser power is constant. The amount of incision is reduced by 20% and the processing time by 40% when tested by a low power RF CO2 laser die-cutting system using the optimized program. This technique is also used for the reference of other rapid laser processing systems.

49.3: Mechanism and Advanced Application of Rapid Laser Processing on SnO2 Thin Films for FPD Manufacture

AbstractA Nd:YAG laser processing on a SnO2‐system thin films for FPD manufacturing is investigated as an alternative to photolithographic etching on ITO. Because of the difficulty in realizing a low energy process on SnO2 due to a high melting point, we experimentally found the proper deposition condition and composition of SnO2‐system thin films. By considering two physical mechanisms, namely, plasmon oscillation and inverse bremsstrahlung process, we achieved satisfactory laser processing using only 2 J/cm2 of laser energy. This result leads to the possibility of high‐speed electrode patterning suitable for FPD mass production.

Unusual size-dependent magnetization in near hemispherical Co nanomagnets on SiO2 from fast pulsed laser processing

Nanosecond pulsed laser melting of ultrathin metal films can lead to self-organized arrays of spherical nanoparticles. We have applied this technique to assemble arrays of nanoparticles of the soft elemental ferromagnet Co on SiO2. Surface morphology studies by using scanning electron microscopy and atomic force microscopy established that the nanoparticles were nearly hemispherical with an average contact angle of ∼104±22°. Magnetic properties of these nanoparticles in the size range of 30–250nm diameter were investigated by magnetic force microscopy under zero applied field in conjunction with simulations of the magnetic tip-particle interaction. Particles up to 180nm diameter were found to be single domain with the magnetization direction oriented predominantly in-plane for the smaller particles (⩽75nm) and out-of-plane for the larger particles (⩽180nm). Multidomain behavior was observed for particles larger than 180nm. Magnetic hysteresis measurements at room temperature confirmed that the arrays consisted of a mixture of in-plane and out-of-plane orientations. Microstructural analysis by transmission electron microscopy revealed that the nanoparticles had a granular microstructure with the average grain size increasing with particle size. This size-dependent magnetic orientation is inconsistent with the expected in-plane orientation due to shape anisotropy. We suggest that a size-dependent residual strain and the microstructure formed by rapid laser processing determine the orientation of nanomagnets. This idea was supported by the significant increase in in-plane orientation of larger particles following thermal annealing. These studies suggest that anisotropic nanomagnets of near hemispherical polycrystalline particles with desired magnetic orientation can be prepared by fast laser thermal processing.