Single Track Research Articles

Justification of technological modes for the formation of a stable single track at a thickness of a 30-μm layer of INCONEL 718 alloy

In selective laser melting (hereinafter - SLP), a single layer is created from a set of single tracks. The influence of the characteristics of the melt bath on the quality of con-struction of three-dimensional parts from various materials has been widely studied. Thus, finding the optimal scan speed is a trade-off between performance and quality of the build process. For certain printing factors (each material/equipment/part) it is nec-essary to find this optimum and this is one of the possible ways to improve the structure. The material used in this study was metal powder with a particle size of 10 to 45 μm. Chemical composition of INCONEL 718 powder in % by mass: Cr=17.79; Ni=53.5; Mo=3.12; Mo = 3.01; Ti=0.85; Nb=5.12. In this work, single tracks were created on a base platform made of the same material. At the same time, the power was changed in the range of 100...150 W in steps of 10 W, and the speed - in the range of 1300...3500 mm/s in steps of 100 mm/s. A total of 108 printing modes of single tracks, located at a distance of 1.5...2 mm from each other, were investigated. The thickness of the layer used in the experiments is 30 μm. A nomogram of printing parameters of single tracks made of INCONEL 718 alloy with a layer thickness of 30 microns was constructed. From the analysis of the nomogram, it was established that at the selected powers and scan-ning speeds of 1800...3400 mm/s, a stable track is formed, and when the speed is re-duced, spattering and remelting of the base metal is formed. It should be noted that samples with an overlap of 0.05 and 0.06 form an unstable, discontinuous track with droplet formation when the scanning speed is increased. The range of rational energy density of 37...41 J/mm3 was established for the construction of parts from the Inconel 718 alloy with a layer thickness of 30 μm.

Measuring the Cooling Behavior of Melt Pools in L-PBF by Pyrometry.

This study aims to measure the cooling rates or, more precisely, the cooling durations of single laser tracks by pyrometry within the laser powder bed fusion (L-PBF) process. Two-color, as well as one-color pyrometers are tested within this work. Regarding the second, the emissivity of the investigated 30CrMoNb5-2 alloy is determined in-situ within the L-PBF system in order to measure temperature instead of arbitrary units. This is done by heating up printed samples and verifying the measured pyrometer signal by comparing it to values obtained by thermocouples attached to the samples. In addition, the precision of two-color pyrometry is verified for the given setup. Following the verification experiments, single laser track experiments are conducted. The obtained signals prove to be partially distorted mainly due to by-products such as smoke and weld beads arising from the melt pool. To encounter this problem, a new fitting method is presented and experimentally validated. Melt pools resulting from different cooling durations are analyzed by EBSD. These measurements show areas of extreme deformation or potential amorphization correlating with the cooling durations. The obtained cooling duration can be used for the validation of simulations as well as for the correlation of corresponding microstructure and process parameters.

Influence of Novel Beam Shapes on Laser-Based Processing of High-Strength Aluminium Alloys on the Basis of EN AW-5083 Single Weld Tracks

The commonly used Gaussian intensity distribution during the laser-based processing of metals can negatively affect melt pool stability, which might lead to defects such as porosity, hot cracking, or poor surface quality. Hot cracking is a major factor in limiting production rates of high-strength aluminium alloys in laser-based processes such as welding or the powder bed fusion of metals (PBF-LB/M). Going away from a Gaussian intensity distribution to ring-shaped profiles allows for a more even heat distribution during processing, resulting in more stable melt pools and reduced defect formations. Therefore, the aim of this study is to investigate the influence of different laser beam profiles on the processing of high-strength aluminium alloys by using a multicore fiber laser, allowing for in-house beam shaping. Single weld tracks on the aluminium alloy EN AW-5083 are produced with varying laser powers and weld speeds, as well as different beam profiles, ranging from Gaussian intensity distribution to point/ring profiles. The molten cross sections are analyzed regarding their geometry and defects, and the surface roughness of the weld tracks is measured. By using point/ring beam profiles, the processing window can be significantly increased. Hot cracking is considerably reduced for weld speeds of up to 1000 mm/s compared to the Gaussian beam profile. Furthermore, the melt pool width and depth are more stable, with varying parameters for the point/ring profiles, while the Gaussian beam tends to keyhole formation at higher beam powers. Finally, a strong decrease in surface roughness for the point/ring profiles, accompanied by a significantly reduced humping effect, starting even at lower beam powers of 200 W, can be observed. Therefore, these results show the potential of beam shaping for further applications in laser-based processing of high-strength aluminium alloys.

Spreading Behavior and Hot Cracking Mechanism of Single Tracks in High Strength Al–Cu–Mg–Mn Alloy Fabricated by Laser Powder Bed Fusion

Spreading Behavior and Hot Cracking Mechanism of Single Tracks in High Strength Al–Cu–Mg–Mn Alloy Fabricated by Laser Powder Bed Fusion

Optimization of processing parameters and microstructure evolution of (TiB+La2O3)/Ti6Al4V manufactured by laser melting deposition

Due to the intrinsically ultrahigh cooling rate and thermal gradient during laser melting deposition (LMD), columnar-to-equiaxed transition (CET) of grains has been a significant challenge in titanium-based alloys. In this study, two strategies, including the optimization of processing parameters and the addition of ceramics particles, were utilized to promote the CET of Ti6Al4V. The optimal processing parameters of Ti6Al4V were confirmed by response surface methodology (RSM). The width of prior β grains effectively decreases under the minimum dilution of single track. Besides, different contents of TiB2 and La2O3 were added to Ti6Al4V powder and the in situ (TiB + La2O3)/Ti6Al4V composites were manufactured using the identified optimal processing parameters. In situ TiB whiskers segregating at the grain boundaries tailor the coarse columnar to equiaxed grains with La2O3 particles dispersed in the composites. With increasing formation of the reinforcements, equiaxed grain size decreases from 23.3 to 11.9 μm. The ultimate tensile strength of the components was improved by 19.6% and 26.4% compared to that of Ti6Al4V. This work provides systematic solutions to suppress the coarse columnar grains and refine the microstructure for titanium-based alloys.

The one-dimensional potential energy function that is analogous to a two-dimensional track

When learning about potential energy functions, students are sometimes told that the potential energy function is analogous to that of a particle sliding along a frictionless roller coaster track or wire confined to a vertical plane with peaks and valleys of the track corresponding to unstable and stable equilibrium points. However, motion along a track with height z(x) is a constrained two-dimensional motion, not a one-dimensional motion, so the exact nature of this analogy may be unclear. We show that the horizontal motion of a point mass sliding along a frictionless track z(x) and subject to a uniform gravitational field is equivalent to the motion of a particle in one dimension characterized by an “analogous potential energy” function UE(x), which generally depends on the total energy of the system (and thus on the initial conditions). We derive a general expression for UE(x) in terms of z(x) and the total energy and show that the equilibrium points of the actual potential energy U(x)=mgz(x) are also static equilibrium points for UE(x) with the same stability. However, UE(x) may have additional dynamic equilibrium points that are not present for U(x). As an example, we derive UE(x) for a double well track and determine the period of oscillations on that track. The results show that in general a single track corresponds to many different analogous potential energy functions, each with a different value for the total energy.

Process Map Definition for Laser Metal Deposition of VDM Alloy 780 on the 316L Substrate

VDM Alloy 780 is a novel Ni-based superalloy that allows for approximately 50 °C higher operating temperatures, compared to Inconel 718, without a significant decrease in mechanical properties. The age hardenable NiCoCr Alloy combines increased temperature strength with oxidation resistance, as well as improved microstructural stability due to γ′-precipitation. These advantages make it suitable for wear- and corrosion-resistant coatings that can be used in high temperature applications. However, VDM Alloy 780 has not yet been sufficiently investigated for laser metal deposition applications. A design of experiments with single tracks on 316L specimens was carried out to evaluate the influence of the process parameters on clad quality. Subsequently, the quality of the clads was evaluated by means of destructive and non-destructive testing methods, in order to verify the suitability of VDM Alloy 780 for laser metal deposition applications. The single-track experiments provide a basis for coating or additive manufacturing applications. For conveying the results, scatter plots with regression lines are presented, which illustrate the influence of specific energy density on the resulting porosity, dilution, powder efficiency, aspect ratio, width and height. Finally, the clad quality, in terms of porosity, is visualized by two process maps with different mass per unit lengths.

Tectonic dismemberment of Shona Hotspot volcano: Insights from Sites 698, 699, 701, and 703 bulk-rock Sr-Nd-Pb-Hf isotopic geochemistry

A genetic link between the Georgia-Islas Orcadas and Meteor guyots on opposite sides of the South Atlantic was proposed based on seafloor morphology and tectonic reconstructions. Here we test this model with geochemistry. We present new major and trace element and Sr, Nd, Pb, Hf radiogenic isotope data from volcanic and sedimentary rocks from Meteor Rise (ODP Site 703) and Georgia-Islas Orcadas Rise (ODP Sites 698, 699, and 701). Site 701 samples have slightly depleted isotopic compositions similar to southern Mid-Atlantic Ridge (SMAR) basalts, representing the upper mantle. Site 698, 699 and 703 volcanic rocks have initial Sr-Nd-Pb-Hf isotope ratios ((87Sr/86Sr)i = 0.70278–0.70660; (143Nd/144Nd)i = 0.51217–0.51283; (206Pb/204Pb)i = 18.09–18.75; (176Hf/177Hf)i = 0.28246–0.28299), extending from the Shona Hotspot track field (consisting of Richardson guyot, Agulhas Ridge and Meteor guyot samples) towards Proterozoic continental crust. These data support derivation from a common mantle plume, having formed contemporaneously as a single continuous hotspot track, which was subsequently divided by a ridge jump. Modelling of the isotope data show that binary mixing between an average Shona anomaly composition and an upper continental crustal component with a composition similar to the Site 698 sandstones can explain the data by 10–30% upper crustal assimilation to generate the composition of the Site 698, 699 and 703 volcanic rocks. Therefore, our geochemical data confirm the dismemberment of the Shona Hotspot track by a ridge jump and subsequent seafloor spreading.

A novel thermo-geometrical model for accurate keyhole porosity prediction in Laser Powder-Bed Fusion

AbstractWhen performing Laser Powder-Bed Fusion, undesired physical phenomena, such as balling, preballing and keyhole, must be avoided in order to achieve high-quality products. To date, keyhole-free process parameters can be identified either using demanding empirical methods or complex numerical simulations, while only a few analytical models can be found in literature for this purpose. In this work, state-of-the-art analytical models for predicting keyhole porosity were summarized and proved to be rather inaccurate because they are only based on thermodynamic principles, whereas they neglect the geometry and both the kinetics and kinematics of the keyhole cavity, which do also influence cavity collapse and porosity formation. Here an innovative physics-based semi-analytical model for predicting the formation of keyhole-related porosities was conceived, in which both thermodynamic and geometrical factors are taken into account. The proposed model was validated by performing single tracks experiments on Ti6Al4V according to a full factorial DoE on laser power and scanning speed. Produced samples were cross-sectioned and analyzed to evaluate keyhole porosity formation. The comparison between experimental data and model predictions confirmed the higher accuracy of the new model with respect to state of the art models. Besides improving the understanding of the keyhole phenomenon, the proposed model may provide a novel, effective and simple tool for fast process parameter optimization in industry.

Systematic approach to process parameter optimization for laser powder bed fusion of low-alloy steel based on melting modes

In the metal additive manufacturing (AM) process of laser powder bed fusion (LPBF), there are a limited number of materials suitable for producing parts with high density and desired mechanical properties. To establish novel materials, it is essential to determine optimized process parameters in order to overcome process-related challenges and mitigate defects such as lack of fusion, keyholing, and balling. Scaling laws based on thermophysical properties and process parameters can be used to transfer knowledge from other materials or LPBF systems. In this work, a scaling law is used to adjust process parameters for single-track experiments over a wide range, which are laser power PL (100–1000 W), scan speed vs (300–2500 mm/s), and laser spot size ds (0.08–0.25 mm). Compared to existing studies, the parameter range is thus extended towards large laser spot sizes and high laser powers. The scaling law used is based on the calculation of the normalized enthalpy frac{Delta H}{{h}_{s}}. The ratio of the deposited energy density DeltaH and the melting enthalpy hs correlates with the dimensions of the melt pool. According to the aspect ratio {delta }_{mathrm{c}} of the melt pool of each single track, the respective melting mode—conduction, transition, and keyhole mode—was identified. The process parameters of the single tracks in transition mode were used to optimize the density of the LPBF specimens with varying hatch distance hd (0.06–0.12 mm), resulting in specimens with a relative density of > 99.8%. The proposed methodology can accelerate the process parameter finding for new alloys and avoid process-related defects.Graphical

Linear Stability of Reversing a Car-trailer Combination

In this paper, we investigate the reverse motion of a car-trailer combination. The single track model of the vehicle is used with quasi-static tire model to design a simple linear feedback controller that can achieve stable reversing motion along a straight path. The linear stability of the closed-loop system is analyzed by constructing stability charts in the plane of the control gains. The effect of the reversing speed of the vehicle on the stability is also shown. In order to validate the theoretical results, laboratory experiments are carried out using a small-scale vehicle and a conveyor belt.

Multi-physics modeling for laser powder bed fusion process of NiTi shape memory alloy

Due to its excellent shape memory effect and super elasticity, NiTi Shape Memory Alloy (NiTi SMA) has broad application prospects in aerospace, ship, biomedicine and other fields. Laser powder bed fusion (L-PFB) has proven to be a feasible way to fabricate NiTi with a complex and precise structure. In this study, a 3D transient multi-physics model based on the computational fluid dynamics (CFD) model is proposed, which incorporates the effects of convective heat transfer and radiation heat transfer on the forming quality of parts and mechanical models such as thermal buoyancy. The temperature field and stress field distribution during the L-PBF forming process of NiTi alloy were studied by using this multi-physics model. Furthermore, the influence of different process parameters on the shape of the molten pool was analyzed, and a nonlinear regression equation was proposed to predict the size of the molten pool. The proposed model is verified by experimental results with a prediction error of 3 %−8 %. Both numerical and experimental results demonstrate that under the process parameters of P= 125 W and V= 500 mm/s, the shape of the molten pool is stable and the NiTi single track is continuous. This work illustrates the reliability of the established simulation method and provides a timesaving approach to optimize the L-PFB process parameters of nickel-titanium alloy.

Engineering dislocation‐rich plastic zones in ceramics via room‐temperature scratching

AbstractIn this communication, we demonstrate a simple but powerful method to engineer dislocations into large plastic zones in various single‐crystal ceramic materials via room‐temperature scratching. By using a Brinell indenter with a diameter of 2.5 mm, we successfully produced plastic zones with a width and depth of ∼150 µm in a single scratch track, while the length of the scratch track can be arbitrarily long depending on the sample size. Increasing the number of repetitive scratching cycles increases the dislocation density up to ∼1013 m−2 without visible crack formation. The outlined experimental procedure is showcased on single‐crystal SrTiO3, MgO, ZnS, and CaF2 to demonstrate the general applicability of this technique. In light of the increasing research interest in dislocation‐tuned functional and mechanical properties in ceramics, our method will serve as a simple, fast, and robust technique to pave the road for scaling up the required large plastic zones for dislocation engineering in ceramics.

Effects of gas flow speed on bead geometry and optical emissions during laser powder bed fusion additive manufacturing

PurposePowder bed fusion processes are common due to their ability to build complex components without the need for complex tooling. While additive manufacturing has gained increased interest in industry, academia and government, flaws are often still generated during the deposition process. Many flaws can be avoided through careful processing parameter selections including laser power, hatch spacing, spot size and shielding gas flow rate. The purpose of this paper is to study the effect of shielding gas flow on vapor plume behavior and on final deposition quality. The goal is to understand more fully how each parameter affects the plume and deposition process.Design/methodology/approachA filtered-photodiode based sensor was mounted onto a commercial EOS M280 machine to observed plume emissions. Three sets of single tracks were printed, each with one of three gas flow rates (nominal, 75% nominal and 50% nominal). Each set contained single-track beads deposited atop printed pedestals to ensure a steady-state, representative build environment. Each track had a set power and speed combination which covered the typical range of processing parameters. After deposition, coupons were cross-sectioned and bead width and depth were measured. Finally, bead geometry was compared to optical emissions originating in the plume.FindingsThe results show that decreasing gas flow rate, increasing laser power or increasing scan speed led to increased optical emissions. Furthermore, decreasing the gas cross-flow speed led to wider and shallower melt pools.Originality/valueTo the best of the authors’ knowledge, this paper is among the first to present a relationship among laser parameters (laser power, scan speed), gas flow speed, plume emissions and bead geometry using high-speed in situ data in a commercial machine. This study proposes that scattering and attenuation from the plume are responsible for deviations in physical geometry.

Post-Craft

Unlike many academic publications, which start with an introduction from the editors setting out their argument, process, themes, and implications, Post-Craft unfolds more like an album, where the compilation is formed with a poetic and aesthetic sense. Without the usual guideposts, the reader is left to make their own connections and conclusions between the entries, an experience that is both welcome, engaging, and at times disorienting. Indeed, the Sternberg Press publication series is aptly titled ‘EP,’ short for ‘extended play,’ a term used in the music industry to indicate a recording that is longer than a single track, but shorter than a full album.

Experimentally mapping the oriented-to-misoriented transition in laser powder bed fusion Ti-10%Mo alloys

Understanding the oriented-to-misoriented transition (OMT) and its origins is critical to additive manufacturing design processes. The Ti – 10 wt.% Mo alloy was printed at laser scan speeds ranging from 500 mm/s to 2500 mm/s and volumetric energy densities (VED) ranging from 50 J/mm3 to 150 J/mm3. A technique for rapidly mapping the OMT over the design space using X-ray diffraction was developed with electron backscattered diffraction verification. Mapping of the OMT revealed two independent transitions as functions of scan speed and VED respectively. Cross sections of in-situ single track scans at constant VED revealed the scan speed based OMT to be caused by a decrease in penetration depth and larger equiaxed grain zones during weld pool solidification.

Growing child horizons: paradoxes and research prospects

Introduction. The issue of studying the process of growing up of a growing child in the realities of our time is of particular relevance and significance. A number of contradictions can be clearly seen (changes in the space of the child's functioning, the absence of a single track of growing up, the presence of tendencies towards the manifestation of disharmonious forms of behavior). Materials and Methods. The purpose of our study is the theoretical substantiation and development of the conceptual foundations for growing children growing up at the distance of childhood, taking into account the specifics of different educational environments. Among the key tasks, we focused, firstly, on describing the numerous cross-section of domestic and foreign works that are closely related to childhood and adulthood against the backdrop of constantly changing sociocultural practices, and secondly, to identify specific dynamic changes in emerging educational environments. problems, focusing on the main contradictions generated by the very process of growing up; thirdly, to develop the main conceptual provisions of the psychological and pedagogical analysis of the growing child growing up in educational organizations. The article is based on sociological and psychological-pedagogical studies of the problems of growing up of growing children, carried out by modern Russian and foreign scientists. Methods used: phenomenological and problem analysis. Results. An analysis of our studies (2015-2021), studies of domestic and foreign specialists made it possible to state the following conclusions: – We consider the maturation of a modern child in an educational environment as a cyclical process of constant change in the structure of his subjective and objective characteristics, including the formation of an image of adulthood in a child during ontogenesis, its development and implementation, as well as the reflection of the development of adulthood by children in the psychological and pedagogical space of participants in the educational process (parents, teachers). – The concept of the psychology of growing up a child is considered as a theoretical system that includes structure, typology, dynamics, research methods, a model that develops psychological technologies aimed at the favorable passage of age and educational crises by students (transition from “childhood” to “adult” state, in in which a growing person will have to independently determine its semantic content, showing behavior independent of the direct influence of circumstances). Discussion and Conclusions. The data obtained made it possible to substantiate the importance and objectivity of the scientific positions defended in the future. In connection with the new challenges of objective reality in modern educational environments, the search for predictors of successful maturation of growing young people, this area of research seems to be quite relevant, requiring further study.

The Imprint of Clump Formation at High Redshift. II. The Chemistry of the Bulge

In Paper I, we showed that clumps in high-redshift galaxies, having a high star formation rate density (ΣSFR), produce disks with two tracks in the [Fe/H]–[α/Fe] chemical space, similar to that of the Milky Way’s (MW’s) thin+thick disks. Here we investigate the effect of clumps on the bulge’s chemistry. The chemistry of the MW’s bulge is comprised of a single track with two density peaks separated by a trough. We show that the bulge chemistry of an N-body + smoothed particle hydrodynamics clumpy simulation also has a single track. Star formation within the bulge is itself in the high-ΣSFR clumpy mode, which ensures that the bulge’s chemical track follows that of the thick disk at low [Fe/H] and then extends to high [Fe/H], where it peaks. The peak at low metallicity instead is comprised of a mixture of in situ stars and stars accreted via clumps. As a result, the trough between the peaks occurs at the end of the thick disk track. We find that the high-metallicity peak dominates near the mid-plane and declines in relative importance with height, as in the MW. The bulge is already rapidly rotating by the end of the clump epoch, with higher rotation at low [α/Fe]. Thus clumpy star formation is able to simultaneously explain the chemodynamic trends of the MW’s bulge, thin+thick disks, and the splash.

Influence mechanism of laser delay on internal defect and surface quality in stitching region of 316L stainless steel fabricated by dual-laser selective laser melting

Multi-laser stitching additive manufacturing technology is an effective solution to break through the size limitation in single-laser additive manufacturing based on a powder-bed process, where excellent metallurgical bonding and high surface quality of the multi-laser stitching region (overlap) are the critical issues to ensure the final forming quality. The above metallurgical bonding and surface quality are not only affected by common process parameters but also sensitive to laser delay (including on and off delay) parameters because they influenced the starting and end regions of melt tracks. In this study, the influence of laser delay parameters on the forming quality of a single 316L stainless steel melt track was first investigated, thereby obtaining an optimization range of laser delay parameters. Then, the influence mechanism of laser delay on the internal pore defects and surface quality in the dual-laser stitching region was systematically studied. The results show that with the increase of laser on delay, there are four kinds of internal defects in the stitched region, namely keyhole, irregular pore, large-size continuous pore and non-overlap. In addition, due to the high energy density at the starting/end point of the melt tracks, powder denudation and solidified bulge were observed near the stitching line, which leads to the undulation problem with layer-by-layer accumulation on the surface in the stitching region. It is found that the surface undulation with a height of 202 μm and a width of 723 μm still exists at the optimized laser delay parameters (porosity of 0.96 %), which means new process strategies are also needed to be developed besides optimization of laser on/off delay parameters. In addition, a trade-off should be made between the low porosity and high surface quality due to the different influence trends of laser delay on them. This study provides a theoretical basis and technical support for reducing internal defects and improving surface quality in the stitching region fabricated by multi-laser selective laser melting (SLM).

Additive manufacturing of Ti-6Al-4V alloy by micro-laser metal wire deposition with pulsed wave emission: processability and microstructure formation

In this work, the micro-laser metal wire deposition (μLMWD) with ms-pulsed wave emission and low duty cycles was utilized to build the Ti-6Al-4V thin walls. The work first investigated the influence of the process parameters on single track stability and geometry. With the developed processing conditions thin walls with multiple layers were produced. The μLMWD produced thin walls were characterized by fine grain size expected to be due to the columnar to equiaxed transition (CET) in the produced wall. Fine columnar grains formed in the bottom region of wall due to the restriction of melt pool size and large cooling speed, while equiaxed grain formation and further refinement were achieved in the middle region, attributed to the intermittent stirring force that broke dendritic arms and increased nucleation events before solid–liquid interface. From the bottom to top region microstructures transferred from acicular α′ to short α lamella constituting basketweave structure, and the periodic heating and cooling generating by pulsed laser reduced the acicular α′ at higher cooling rate and decreased α size. The forming of equiaxed grain and fine grain and microstructure increased the wall microhardness.