Spot Melting Research Articles

In-melt electron analysis to accelerate process exploration of ceramics: Electron beam melting of TiB2

To enhance the versatility of electron beam powder bed fusion (EB-PBF), a widely utilized additive manufacturing (AM) technique for metallic materials, we propose a novel paradigm aimed at facilitating the exploration of the process parameters for less-studied materials, such as ceramics. The high melting points and poorly understood thermal properties of ceramics have constrained the comprehension of their melting behavior. In this study, titanium diboride (TiB2) sintered bodies were subjected to spot melting under four distinct electron beam currents and four different exposure times. By introducing a novel in-melt electron analysis (IMEA) approach, the various stages of melting were clearly identified. The analysis and interpretation of IMEA signals were found to be consistent with experimental observations on the spot-melted surface of TiB2. IMEA demonstrates significant potential for real-time process window optimization and quality assurance for challenging and novel materials.

A Systematic Approach to Optimize Parameters in Manufacturing Complex Lattice Structures of NiTi Using Electron Beam Powder Bed Fusion Process

Herein, the quality and accuracy to manufacture delicate parts from NiTi powder using electron beam powder bed fusion (EB‐PBF) technology is investigated. Therefore, benchmarks with thin cylinders and thin walls are designed and fabricated using two distinct scan strategies of EB‐PBF manufacturing (i.e., continuous melting and spot melting) with different process parameter sets. After these optimizations, four different lattice structures (i.e., octahedron, cell gyroid, sheet gyroid, and channel) are manufactured and characterized. It is shown both continuous melting and spot melting modes are able to manufacture lattices with relative densities over 97%. And as‐built lattice structures exhibit an excellent pseudoelasticity up to 8% depending on the design of the structure, e.g., the channel structure shows more deformation recoverability than the cell gyroid. This is attributed to the integrity of geometry as well as compressive mode of the mechanical loading. Of course, the compressive strength and ultimate compressive strength also increase with the increasing volume fraction. Moreover, the spot melting can be used as an engineering tool to customize a delicate beam‐shaped structure with a superior pseudoelasticity.

Quantification of melt pool dynamics and microstructure during simulated additive manufacturing

The dynamics of laser spot melting and metallic alloy solidification are investigated through synchrotron x-ray radiography, 3D electron backscatter diffraction data, and computational fluid dynamics (CFD) simulations on a model NiMoAl alloy. Solidification velocities are measured from in-situ images to validate a CFD model of the spot melt. TriBeam tomography is used to reconstruct the melt pool in 3D, characterize the microstructure, and validate the CFD model melt pool dimensions. 3D geometrically necessary dislocation (GND) density calculations reveal extensive deformation at the sample surface. GND calculations integrated with the CFD model reveal that the halo of small, equiaxed grains adjacent to the fusion line is a result of recrystallization that occurred in the heat affected zone. By combining in-situ and ex-situ data modalities across a variety of temporal and spatial length scales, the microstructure formation mechanisms and their relationship to melt pool solidification are quantified.

Numerical modelling of high-power laser spot melting of thin stainless steel

Numerical modelling is an important scientific tool in laser materials processing to study different melting, evaporation, and solidification phenomena. It can assist in understanding why certain defects are formed, and thus may provide solution paths for how to decrease certain defects and to increase the quality of a product. Laser spot melting in heat conduction mode represents a simple case and is an excellent first step to build and test solvers prior to moving on to more complicated cases such as laser keyhole welding of thick plates. Modelling of laser spot melting requires only a limited computational domain and allows more complex physics to be added gradually. In this work, a thin 3.0 mm thick stainless steel plate was melted with high-power fiber laser and numerically simulated using a native and custom-build solver based on the VOF method within OpenFOAM. The process was captured with a high-speed imaging camera and simulation results are compared with the experimental results. It was found that temperature-dependent surface tension plays a vital role in controlling melt flow directions within melt pool.

Assessing the viability of high-frequency spot melting for super duplex stainless steel 2507 via electron beam powder bed fusion

This study investigates the use of Electron Beam Powder Bed Fusion (PBF-EB) spot melting on SDSS 2507, a material known for its high tensile strength, corrosion resistance, and welding properties. Spot melting, a localized melting technique, utilize a stationary beam to create melt pools before rapidly repositioning to form new ones, offering precise control over material properties in additive manufacturing. We conducted a design of experiments with 32 samples and analysed them using SEM, XRD, EBSD, optical microscopy, nanoindentation and statistical modelling.Elevated PBF-EB processing temperatures significantly influence microstructure and phase composition. XRD analysis identified the presence of the detrimental sigma phase. EBSD analysis revealed a composition primarily consisting of austenite (63 %) and sigma phase (33.5 %), with residual ferrite (3.5 %). Statistical modelling demonstrated that a combination of spot-time, spot distance, focus offset, and layer thickness was the most reliable predictor for density while area energy proved to be the most accurate predictor for hardness, with R2adj values of 0.766 and 0.802, respectively.Our study confirms that PBF-EB is capable of processing SDSS 2507 through spot melting, resulting in high-density samples at high productivity rates. The presence of sigma phase shows a need for post build heat treatment to achieve the desired phase distribution. This research enhances the understanding of the process and also holds promise for industrial applications.

In-situ preparation of (Ti,Al) codoped blue PEO ceramic coating on magnesium alloy and chromogenic mechanism

In this paper, the blue ceramic coating was prepared in situ on the surface of AZ31 magnesium alloy using Ti and Al composite salt as electrolyte by PEO technology. The results show that the light wave response range of the prepared ceramic coating is all in 430–470 nm with different n(Ti)/n(Al) atomic percentage in the electrolyte, but the blue color saturation of the ceramic coating increases with the increase of n(Ti)/n(Al) ratio. XRD and XPS analysis show that Ti exists in the form of Ti4+ and Ti3+, Al exists in the form of Al2O3, and a small amount of Ti3+ ions occupy the Al3+ lattice in the form of replacement solution, forming (Al2-xTix)O3 solid solution. This is the chromogenic mechanism of PEO-MgO ceramic coating changing from off-white to blue. Finally, due to the PEO plasma discharge generated on the surface of magnesium matrix in the micron level spot melting pool, the formation of the blue material of Al2O3 doped with Ti and the oxidation and sintering of magnesium matrix at high temperature synchronously, thus achieving in situ color ceramic treatment on the surface of magnesium alloy with low melting point.

Laser Spot Melting on Ti-6Al-4V Substrates: A Study on Thermal History and Keyhole Porosity

In situ monitoring techniques have been applied to laser spot welding experiments to study specific phenomena that also occur in metal additive manufacturing processes. Without the interference of powder particles and their interaction with the laser beam, melt pool signatures and pore evaluation can be monitored, which can help in understanding their effect on the end results in laser spot welding and in metal additive manufacturing. One in situ monitoring technique is thermography which uses infrared cameras to acquire surface temperatures in real time. However, one of the main challenges for infrared cameras is finding the unknown emissivity value of printed parts. Another challenge is that thermography cannot monitor the dynamics under the surface of the substrate. A new method was proposed by combining X-ray imaging and infrared imaging to estimate the emissivity and monitor subsurface phenomena. The method consisted of measuring the melt pool size in X-ray images and comparing it to infrared images. The proposed method was tested by analyzing X-ray and infrared images from laser spot melting experiments on Ti-6Al-4V substrates. Ti-6Al-4V is widely used in metal additive manufacturing processes because of its attractive mechanical properties consequently estimating its emissivity is important. The laser power and laser dwell time were varied for each experiment, and the process was observed in real-time using X-ray and infrared images. The objective was to achieve a confidence interval of the emissivity value for Ti-6Al-4V. In addition, an emissivity value was selected from the obtained confidence interval, which enabled the analysis of the thermal history of the surface of the substrate. Furthermore, the resulting emissivity was used to correct the reading of the temperatures and to estimate the melt pool size in the infrared images. The selected emissivity value of 0.5 from the confidence interval gave an accurate estimation of the melt pool size with an overall average error percentile with the melt pool size measured with the X-ray images of approximately 6.5%. After the temperature correction, solidification time, solidification rates and cooling rates were also calculated from the infrared images using the thermal history. Lastly, it has been observed that the size of the pore generated by the keyhole could affect the surface dynamic of the substrates, concluding that defects under the surface might be detected using thermal images from infrared cameras.

Preparation of oral solid dosage forms based on homogenized spot melting technique

Given the benefits of high printing precision and capability, the selective laser sintering technique has been used to manufacture medicines and implants with unique engineering and functional properties. Using homogenized beams with a reduced thermal gradient and a larger diameter as an alternative energy source, the thermal stability and production efficiency of powder bed fusion would be improved. Herein, a novel homogenized spot melting (HSM) technology for pharmaceutical preparation was developed in this study. The melting behavior of typical pharmaceutical polymers under a homogenized spot was determined. A crystalline polymer with a low melting point was used as a solid binder, and the HSM printability and formation of drug-loaded formulations were explored. Oral solid dosage forms with different morphological and dissolution designs were prepared and evaluated under optimal formulation and process conditions. It was observed that HSM reduced the surface temperature distribution of the powder bed and improved the printability of drugs and excipients. Crystalline PEG 8000 with suitable flowability and heat conduction efficiency in the molten state was preferable for HSM printing. Incorporating 40% PEG 8000 as a solid binder was an effective strategy for HSM processing of unfused or unstable powders. Solid preparations with different structures and dissolution behaviors were successfully printed, suggesting that HSM is a promisingtechnique for personalized medicine.

Texture evolution as a function of scan strategy and build height in electron beam melted Ti-6Al-4V.

Metal additive manufacturing (AM) enables customizable, on-demand parts, allowing for new designs and improved engineering performance. Yet, the ability to control AM metal alloy microstructures (i.e., grain morphology, crystallographic texture, and phase content) is lacking. This work performs corroborative neutron diffraction and large-scale electron backscatter diffraction (EBSD) measurements to assess crystallographic texture in electron beam melted (EBM) Ti-6Al-4V as a function of scan strategy and build height. Texture components for one raster and two spot melt scan strategies were evaluated using a triclinic specimen symmetry to capture all possible texture components, which were found to be considerably different than previously reported values from studies employing orthotropic specimen symmetry. This finding highlights the importance of a standard method and best practice for assessing textures produced by AM. Texture was found to vary between scan strategies, but changed minimally as a function of build height. Parent phase β-Ti reconstructions obtained from as-built crystallographic orientations revealed spot melt scan strategies produced finer equiaxed/columnar grains with clear 001 β build direction fiber textures, whereas the raster scan strategy produced large columnar grains and a weaker 001 β build direction fiber texture. The observed grain morphologies agree with those predicted by solidification theory for the thermal gradients and solidification velocities experienced during the build process. The presence of a strong 001 β fiber orientation (typical of cubic solidification) produced by spot melting was found to correlate with a previously unreported fiber texture in the as-built condition and colony microstructures. The fiber texture was weakly observed for the raster scan strategy, and 001 β oriented grains preferentially transformed into α' martensite with orientations between and . This shift in product α-Ti orientations has not yet been reported, and further work is recommended to understand these crystallographic signatures in the context of solid-state phase transformations. The presence of the fiber texture is proposed as a useful diagnostic for evaluating the solidification or transformed microstructure condition (e.g., grain morphology and texture) of Ti-6Al-4V AM builds via accessible techniques like laboratory X-ray diffraction.

New data on absolute age, petrology and potential of ore mineralization within Murzinsky intrusive massif (northwestern Altai)

The geological, petrogeochemical data, absolute age dating and information about endogenetic ore mineralization of Murzinsky intrusive massif of Altai are presented. Comparison of rock compositions and melanocratic inclusions suggests that gold potential of deep spot melting is related to hybrid melts forming as basalt and crust acidic magma mixed. Along with skarn, the ore field could host copper-gold-porphyry mineralization. Gold was supplied from acidic melting as a result of amphibolites and lower crust greywacke melting.

Relative Density of Mold Steel H13 Fabricated by Hybrid Laser Spot Melting

Relative Density of Mold Steel H13 Fabricated by Hybrid Laser Spot Melting

Numerical study of molten metal melt pool behaviour during conduction-mode laser spot melting

Molten metal melt pools are characterised by highly non-linear responses, which are very sensitive to imposed boundary conditions. Temporal and spatial variations in the energy flux distribution are often neglected in numerical simulations of melt pool behaviour. Additionally, thermo-physical properties of materials are commonly changed to achieve agreement between predicted melt-pool shape and experimental post-solidification macrograph. Focusing on laser spot melting in conduction mode, we investigated the influence of dynamically adjusted energy flux distribution and changing thermo-physical material properties on melt pool oscillatory behaviour using both deformable and non-deformable assumptions for the gas-metal interface. Our results demonstrate that adjusting the absorbed energy flux affects the oscillatory fluid flow behaviour in the melt pool and consequently the predicted melt-pool shape and size. We also show that changing the thermo-physical material properties artificially or using a non-deformable surface assumption lead to significant differences in melt pool oscillatory behaviour compared to the cases in which these assumptions are not made.

Geometry-independent microstructure optimization for electron beam powder bed fusion additive manufacturing

The ability to manipulate the formation of microstructure is one of the potential advantages of additive manufacturing. Yet, the additive manufacturing process is riddled with complex interactions between processing parameters, geometry, and spot melting sequence which makes the task of controlling microstructure challenging. This paper proposes a method to solve the microstructure texture optimization problem by leveraging established optimization techniques and increasingly fast and accurate analytical heat transfer models. Respectively, we apply two different optimization algorithms, genetic algorithm and concurrent greedy line search, in order to induce arbitrarily shaped microstructure regions and we use a heat transfer model to evaluate the fitness of solutions in an iterative approach that is far more efficient than pure trial and error. The objective of the optimization algorithm is to control local thermal conditions – hence microstructure formation – during the melting process by manipulating the order and the dwell time of all the points of the infill pattern sequence. We then analyze the optimized sequence to determine important path characteristics that affect the microstructure formation. Through examples, we show that relative order and frequency, as measured by weighted average and variance of spot order, are important factors that influence the final characteristics.

High speed laser cladded Ti-Cu-NiCoCrAlTaY burn resistant coating and its oxidation behavior

To improve the high temperature oxidation resistance and burn resistance performance of titanium alloy, Ti-Cu-NiCoCrAlTaY composite coating was designed and deposited on TC4 alloy using a novel high speed laser cladding technology. The chemical composition, constituent phases, microstructure and morphology of the coating were characterized by EDS, XRD, SEM and 3D laser microscope respectively. The oxidation behavior of laser-cladded Ti-Cu-NiCoCrAlTaY coating and TC4 titanium alloy was analyzed at 800 °C. It was found that the functional coating has good oxidation performance attributed to the formation of dense double layered composite oxide scales. The flame-retardant functions of TC4 substrate and Ti-Cu-NiCoCrAlTaY coating were evaluated through laser spot melting test. The high thermal conductivity of copper and high anti-oxidation of NiCoCrAlTaY promote the flame retardant performance. The formation of TiCu eutectic transition zone in front of the substrate also helps to delay the combustion process.

Influence of scan strategy on porosity and microstructure of Ti-6Al-4V fabricated by electron beam powder bed fusion

Ti-6Al-4V is of high value in biomedical, aerospace, and industrial sectors and is ideal for additive manufacturing (AM) because of its poor machinability. In electron beam powder bed fusion of Ti-6Al-4V, a raster scan is commonly used and often results in porosity that is detrimental to the fatigue strength. In this paper, we demonstrate that spot melting can significantly minimize porosity but produces a coarser microstructure compared to raster melting. Process parameters can be optimized to achieve minimal porosity with tailored microstructures. A finite element method was used to rationalize these observations.

Contour design to improve topographical and microstructural characteristics of Alloy 718 manufactured by electron beam-powder bed fusion technique

Additive manufacturing (AM) processes are being frequently used in industry as they allow the manufacture of complex parts with reduced lead times. Electron beam-powder bed fusion (EB-PBF) as an AM technology is known for its near-net-shape production capacity with low residual stress. However, the surface quality and geometrical accuracy of the manufactured parts are major obstacles for the wider industrial adoption of this technology, especially when enhanced mechanical performance is taken into consideration. Identifying the origins of surface features such as satellite particles and sharp valleys on the parts manufactured by EB-PBF is important for a better understanding of the process and its capability. Moreover, understanding the influence of the contour melting strategy, by altering process parameters, on the surface roughness of the parts and the number of near-surface defects is highly critical. In this study, processing parameters of the EB-PBF technique such as scanning speed, beam current, focus offset, and number of contours (one or two) with the linear melting strategy were investigated. A sample manufactured using Arcam-recommended process parameters (three contours with the spot melting strategy) was used as a reference. For the samples with one contour, the scanning speed had the greatest effect on the arithmetical mean height (Sa), and for the samples with two contours, the beam current and focus offset had the greatest effect. For the samples with two contours, a lower focus offset and lower scan speed (at a higher beam current) resulted in a lower Sa; however, increasing the scan speed for the samples with one contour decreased Sa. In general, the samples with two contours provided a lower Sa (∼22 %) but with slightly higher porosity (∼8 %) compared to the samples with one contour. Fewer defects were detected with a lower scanning speed and higher beam current. The number of defects and the Sa value for the samples with two contours manufactured using the linear melting strategy were ∼85 % and 16 %, respectively, lower than those of the reference samples manufactured using the spot melting strategy.

The Microstructural Evolution and Wear of Weld Deposited M2 Steel Coating After Laser Spot Melting

This paper is devoted to studying the microstructural evolution and wear of the laser pulse remelted spot patterns on the weld deposited M2 steel coating. The energy of laser pulse was changed by changing the pulse parameters to obtain optimal structure of the irradiated spot. As shown, the remelted metal macroscopically consists of fusion and heat-affected zones each of them containing different phases and structures. The fusion zone is composed of two structural components so that one of which (A) has a dendrite-cellular type of structure and contains δ-iron, retained austenite, and carbides. The other one (B) is composed of austenite, martensite, and eutectic carbides. The microstructure of laser-irradiated spot obtained at pulse duration 10 ms was optimal from the viewpoint of wear. Sliding wear tests showed high wear resistance of laser-irradiated pattern as compared to that of as-deposited metal.

Energy absorption during pulsed electron beam spot melting of 304 stainless steel: Monte-Carlo simulations and in-situ temperature measurements

The absorption coefficient during pulsed, conduction-mode electron beam spot melting of 304 stainless steel was measured at different combinations of accelerating voltage [60,80] kV, beam current [10,15,20] mA, pulse length [0.6–12] mS and beam inclination angle [0, 15, 35, 55, 65]°. Ignoring evaporative and radiative heat loss, the absorption coefficient was determined directly by fitting in-situ thermocouple measurements to an analytical function, with an average adjusted R-square fit parameter of 0.9996 over the 103 measurements. The absorption coefficient was found to be insensitive to both beam current and accelerating voltage, but decreased with increasing inclination angle. Measurements are compared to estimates generated from Monte-Carlo electron trajectory simulations using the CASINO software, with good agreement for all process parameter combinations, experimentally demonstrating the capability of Monte-Carlo methods to estimate local electron beam heat transfer.

Nanojoint Formation between Ceramic Titanate Nanowires and Spot Melting of Metal Nanowires with Electron Beam.

Construction of nanoarchitectures requires techniques like joint formation and trimming. For ceramic materials, however, it is extremely difficult to form nanojoints by conventional methods like merging. In this work, we demonstrate that ceramic titanate nanowires (NWs) can be joined by spot melting under electron beam (e-beam) irradiation (EBI). The irradiation fuses the contacted spot of titanate NWs yielding an intact nanojoint. Nanojoints with different morphologies can be produced. The joint structures consist of titanium dioxide (TiO2) rutile, anatase, and titanate phases in the direction away from the e-beam melting spot. The titanate binds to anatase via a crystallographic matching coherent interface (the oxygen atoms at the interface are shared by the two phases) and the anatase solidly binds to the rutile joint. The resulting rutile joint is stable at high temperatures. Additionally, it is demonstrated that the heat production from EBI treated rutile can be utilized to break metal NWs (Ag, Cu, and Ni) apart by spot melting. The required e-beam intensity is considerably mild (75 pA/cm2) which allows visual access and control over the NW melting. Direct melting of Ag and Cu is not applicable under EBI due to their high thermal conductivity even with high current density (500 pA/cm2). Our findings reveal that ceramic nanojoint formation and spot melting at nanoscale are applicable if the properties of nanomaterials are understood and properly utilized.

Mechanistic Investigations of Uncatalyzed and Ruthenium(III) Catalyzed Oxidation of Vanillin by Periodate in Aqueous Alkaline Medium

The kinetics and mechanism of uncatalyzed and ruthenium(III) catalyzed oxidation of vanillin (Van) by periodate were studied in alkaline medium at 298 K, and at constant ionic strength of 0.3 mol·dm−3. The reaction exhibits 1:1 stoichiometry ([Van]:[periodate]). The reaction shows first-order kinetics in [periodate] and [Ru(III)] and less than unit order with respect to [Van] and [OH−]. The ionic strength and dielectric constant of the medium did not affect the rate significantly. The main products were identified by spot tests, melting temperature and FT-IR. From the effect of temperature on the reaction rate, the Arrhenius and activation parameters have been calculated. The catalytic constant (K C) was also calculated for Ru(III) catalysis at different temperatures. Plausible mechanisms have been proposed and rate laws explaining the experimental results are derived. Kinetic studies suggest that the active species of periodate and Ru(III) were [H2IO6]3− and [Ru(H2O)5OH]2+, respectively. The reaction constants involved in the different steps of the mechanism were calculated. The activation parameters with respect to the slow step of the mechanism, along with the corresponding thermodynamic quantities, were determined and discussed.