Laser Direct Metal Deposition Research Articles

Comprehensive Distortion Analysis of a Laser Direct Metal Deposition (DMD)-Manufactured Large Prototype Made of Soft Martensitic Steel 1.4313

Additive manufacturing (AM) by using direct metal deposition (DMD) often causes erratic distortion patterns, especially on large parts. This study presents a systematic distortion analysis by employing numerical approaches using transient–thermal and structural simulations, experimental approaches using tomography, X-ray diffraction (XRD), and an analytical approach calculating the buckling distortion of a piston. The most essential geometrical features are thin walls situated between massive rings. An eigenvalue buckling analysis, a DMD process, and heat treatment simulation are presented. The eigenvalue buckling simulation shows that it is highly dependent on the mesh size. The computational effort of the DMD and heat treatment simulation was reduced through simplifications. Moreover, artificial imperfections were imposed in the heat treatment simulation, which moved the part into the buckling state inspired by the experiment. Although the numerical results of both simulations are successful, the eigenvalue and DMD simulation cannot be validated through tomography and XRD. This is because tomography is unable to measure small elastic strain fields, the simulated residual stresses were overestimated, and the part removal disturbed the residual stress equilibrium. Nevertheless, the heat treatment simulation can predict the distortion pattern caused by an inhomogeneous temperature field during ambient cooling in an oven. The massive piston skirt cools down and shrinks faster than the massive core. The reduced yield strength at elevated temperatures and critical buckling load leads to plastic deformation of the thin walls.

Investigations on mass flow rate of rotary vane feeder for direct metal laser deposition

Investigations on mass flow rate of rotary vane feeder for direct metal laser deposition

Effects of TiC addition on the interface stability, microstructure, and mechanical properties of IN718 fabricated by laser direct metal deposition: A combined experimental, DFT and MD study

In this study, we reveal the impact of the addition of TiC in the IN718 superalloys at both atomic and micron scales through density functional theory (DFT), molecular dynamics (MD), and experimental analysis. From the micro scales, the addition of TiC can effectively mitigate the segregation behavior of Nb and Mo atoms, promote heterogeneous nucleation, reduce grain size, and thus improve mechanical properties. From the atomic scales, the effect of alloying elements (Fe, Cr, Mo, Nb, Co) on the stability of the TiC/γ-Ni interface was investigated through first principles. Co-doping interface was more stable than other interfaces by MD calculations, followed by Cr and Fe-doping models. The heat of segregation results inferred that TiC can effectively mitigate the segregation behavior of Nb and Mo atoms in the TiC/γ-Ni interface, it is mutually verified with the experimental results. Furthermore, the interface energy values theoretically illustrated that TiC particles could promote the heterogeneous nucleation of γ-Ni, this behavior of TiC particles was verified by experiment results. This investigation results provide reference information in the study of ceramic particle reinforced alloys at atomic and micron scales.

Experimental study of SS316L, Inconel 625, and SS316L-IN625 functionally graded material produced by direct laser metal deposition process

Three types of walls were produced by the direct laser metal deposition (DLMD) process; SS316L, Inconel 625 (IN625), and SS316L-Inconel 625 FGM. The thin walls were deposited on an AISI 4130 austenitic steel substrate in five layers with a length of 2 cm. The solidification behavior, secondary dendrite arm spacing (SADS) value, chemical composition, and hardness of samples were studied. Microstructures were evaluated using optical microscopy (OM) images, scanning electron microscopy (SEM), EDS Line, EDAX, and Map analyses. OM and SEM images showed an acceptable bonding between the layers in all samples. The main solidification was equiaxed dendritic and columnar dendritic in most parts. The growth of dendrites was perpendicular to the substrate. Some dendrites grew epitaxially at the interface of two sequential layers. The standard deviation of SDAS value for SS316L, IN625, and SS316L-IN625 FGM was 0.63, 0.71, and 0.73, respectively. The lowest value of SDAS was obtained in layer one, while the highest value was obtained in layer five of the thin walls. The average SDAS values for SS316L, IN625, and SS316L-IN625 FGM were 4.40, 4.53, and 4.76 µm, respectively. Therefore, the difference between the SDAS values was not significant. EDAX and Map analyses showed that the segregation of Nb and Mo to the dendritic boundary and the formation of eutectic, secondary phases, and brittle Laves phases have occurred. Additionally, the segregation of Nb and Mo to the dendritic boundary in the SS316L-IN625 FGM sample was higher than SS316L and IN625 samples. The microhardness values oscillated significantly and decreased by moving away from the substrate (in the build direction). The microhardness values of different points of the SS316L-IN625 FGM walls were in the range of 218–278 HV. EDS line scan, microstructure, and microhardness analyses indicated the successful fabrication of the SS316L-IN625 FGM by the DLMD process.

Tailoring of the Microstructure and Mechanical Properties of High Nitrogen Steel Repaired by Underwater Laser Direct Metal Deposition

Tailoring of the Microstructure and Mechanical Properties of High Nitrogen Steel Repaired by Underwater Laser Direct Metal Deposition

A review of energy efficiency and Machine learning analysis for additive manufacturing of direct laser metal deposition

Additive Manufacturing (AM) is an innovative industrial process that utilizes layering of materials to create unique products with an unprecedented level of flexibility. To maximize the benefits of AM, it is crucial to understand the precise utilization of laser energy. This review provides a concise overview of the Directed Laser Metal Deposition (DLMD) process, which includes an analysis of input parameters and the effective use of laser power, along with the impact of laser synchronous preheating processes. Various input parameters such as travel speed, hatch spacing, powder feed rate, and the standard of distance influence the calculation of volumetric energy density (VED). VED is important for Clad bed geometry, including dilution (D), height (H), width (W) of AM wall, and clad bead stability (ΔH). In the field of manufacturing, Machine Learning (ML) is a commonly used subset of Artificial Intelligence (AI) to improve the quality of processes, expedite production, and reduce costs. Specifically, in Metal Additive Manufacturing (MAM), ML techniques are leveraged to optimize various process parameters, resulting in the production of high-quality, defect-free products. This review provides a detailed explanation of the step-by-step implementation process of ML and its classification within a fundamental structure.

Research on gas pore formation and inhibition mechanism of high nitrogen steel during laser direct metal deposition

Nitrogen pore formation is an inherently tricky problem that limits the application of high nitrogen steel (HNS) in various fields. In the present study, a CA-LBM coupling model was proposed to understand the nitrogen pore formation mechanism during laser direct metal deposition (DMD) of HNS. Based on the proposed model and theoretical analysis, the effects of pulse frequency and shielding gas nitrogen content on the porosity were clarified systematically. Results showed that after the onset of solidification, the ferrite phase with extremely low nitrogen solubility precipitated first, inducing the continuous enrichment of nitrogen in the residual liquid phase, which in turn provided the prerequisite for nitrogen pore nucleation. The application of quasi-continuous-wave (QCW) laser mode accelerated the molten pool solidification, and shortened the nitrogen supersaturated region, allowing more nitrogen to be solid dissolved in the matrix. On this basis, the porosity was inhibited to a certain extent. Compared with the high-frequency pulse, the low-frequency pulse showed better porosity inhibition. In addition, following the classic nucleation theory, nitrogen segregation and nitrogen solubility synergistically dominated nitrogen pore formation. The nitrogen partial pressure, determined by the shielding gas nitrogen content, played a dual role in porosity defects. Elevated nitrogen partial pressure served to increase nitrogen solubility while promoting the nitrogen absorption process to intensify nitrogen segregation. However, due to the short duration of the molten pool, the nitrogen absorption process could not be fully processed. Nitrogen solubility enhancement was the key factor in inhibiting porosity during the DMD process.

The dynamic carbon footprint modeling for laser direct metal deposition based on processing states

The Laser Direct Metal Deposition (LDMD) process offers notable advantages and obtains wide application in aerospace, defence equipment and other industrial sectors. However, the characteristics of multiple-inputs and low-efficiency in the process will bring about high carbon footprint. Additionally, the carbon footprint fluctuates with processing states and equipment systems owing to the discontinuous process in LDMD involving the layer-by-layer deposition and the laser-powder coupling. This paper investigated dynamic carbon footprint based on the resource and energy consumption from the process-oriented standpoint in LDMD process, which quantified the processing time, power distribution and material consumption of each processing state for every sub-system. In this research, the discontinuous process was divided into effective processing state, rapid moving state and transformed delay state and the processing time of each state were estimated with process parameters. Besides, the operating state time and power distribution of five sub-systems were estimated combining the equipment triggering mechanism and the processing state time. The orthogonal experiment was carried out to deposit the 316L stainless steel powder into parts with the size of 15 mm*15 mm*10 mm under the given process parameter conditions (Vf ∈ [8,12] g/min, P ∈ [600,1000] w, Vs ∈ [500,900] mm/min). The results show that carbon footprint of deposited parts fluctuates in the range of 3624.68–15759.08 g under parameter combinations and the low carbon footprint parameter-interval is obtained. The average carbon footprint of effective processing state, the transformed delay state and the rapid moving state account for 55%, 40% and 5% respectively, while the carbon footprint of powder supply sub-system contributes to 68% among the five sub-systems. This research revealed and qualified the dynamicity of carbon footprint at the levels of processing states, process parameters and sub-systems, offering potential for carbon footprint reduction in advanced manufacturing processes.

Electrochemical passivation behavior and surface chemistry of 316 L stainless steel coatings on NV E690 steel fabricated by underwater laser direct metal deposition

The underwater direct metal deposition (UDMD) was employed to deposit 316 L stainless steel (SS316L) coatings on NV E690 steel. The chemical composition gradient from monolayer to trilayer SS316L induces an in-situ phase transformation, thereby enhancing the corrosion resistance. The steady-state passive film grew linearly with the applied potential and exhibited a bilayer structure: a high resistivity barrier layer and a low resistivity outer layer. The growth kinetics of the UDMD fabricated SS316L coatings align with the point defect model. Passive film is enriched in Cr while depleted in Fe and Ni, whereas the altered zone is enriched in Ni.

Oxygen Uptake of Ti6Al4V during Direct Metal Deposition Process

The efficient fabrication of titanium components using laser direct metal deposition (DMD) is gaining significant importance in the aerospace and medical sectors. The DMD process must be appropriately designed to address the issue of oxidation, as titanium exhibits a high affinity for oxygen. The carrier gas flow and shield gas flow, which have been considered secondary factors so far, are shown to exert a substantial influence on the gas dynamics of the DMD process. By varying these parameters, it is possible to identify the influence of the gas volume flows on the oxidation behavior exhibited during the DMD process. To quantify the oxygen uptake in titanium structures during buildup, hot carrier gas extraction is employed. Experiments are conducted using both a three-jet and a coaxial nozzle to assess the influence of nozzle geometry. Additionally, the experiments are conducted within a shielding gas chamber to demonstrate the benefits of such a chamber in mitigating oxidation. Finally, the study reveals that by appropriately combining the parameters of carrier gas volume flow, shield gas volume, and travel speed, it is possible to fabricate titanium components, which fulfill the requirements regarding oxygen content of aerospace and medical applications even without the utilization of a shielding gas chamber.

Effect of different feedstocks on the microstructure and mechanical properties of HSLA steel repaired by underwater laser direct metal deposition

Underwater laser direct metal deposition (UDMD) technique shows great potential for the on-site repair of damaged structures in the ocean. In this study, aiming at the possibility of flexible feedstock substitution, two powders with different properties are employed to repair the preprepared HSLA steel plates using UDMD. The combined effects of alloy compositions and UDMD processing on the repair performance including microstructure, mechanical properties and corrosion behavior, are systematically studied. The results show that the localized laser melting/solidification and rapid underwater cooling effect significantly increase the cooling rates, and thus lead to the formation of fine-grained lath martensite and acicular ferrite. The high Ni content in the sample repaired with ultra-high strength (UHS) powder contributes to the interlath austenite. Compared with that of the sample repaired with high strength (HS) powder, the microhardness of the sample repaired with UHS powder is high due to the solid solution strengthening and grain boundary strengthening. In addition, the tensile properties of the UDMD samples exceed the marine steel requirement (yield strength ≥690 MPa). The acceptable impact toughness of the UDMD samples is due to the existence of acicular structures and high fraction HAGBs. Furthermore, the UDMD samples present a better corrosion resistance in comparison with the substrate. The experimental findings demonstrate the employment feasibility of powder substitution on the UDMD repair of complex steel structures in the ocean.

Optimization of process parameters for gas-powder flow behavior in the coaxial nozzle during laser direct metal deposition based on numerical simulation

Optimization of process parameters for gas-powder flow behavior in the coaxial nozzle during laser direct metal deposition based on numerical simulation

Correction to: Process and materials design via statistical modeling for Inconel-625/tungsten carbide wear-resistant composite coatings fabricated by laser direct metal deposition technique

Correction to: Process and materials design via statistical modeling for Inconel-625/tungsten carbide wear-resistant composite coatings fabricated by laser direct metal deposition technique

Forming Behavior of Additively Manufactured Al/Ti Material Compounds Produced by Cold Spraying

Cold spraying has great potential for additive manufacturing, especially of oxidation-sensitive metals, because the material is not melted and significantly higher deposition rates can be achieved than with conventional additive manufacturing processes such as selective laser melting or direct metal deposition. Titanium is regarded as a high-performance engineering material due to its unique combination of properties, including good corrosion resistance, biocompatibility and high strength at comparatively low density. However, due to its high price, it appears reasonable for many applications to use material compounds in which titanium is only used on the surface of the workpiece, while less expensive materials such as aluminum are used for the remaining volume. In the present work, cold sprayed pure titanium coatings were deposited on Al substrates and then formed to defined 3-dimensional final contours by die forging and rotary swaging. Different porosities were selectively set in order to evaluate their influence on the coating adhesion and cohesion in the forming process. Pre-consolidation of the coatings and the use of Al/Ti interlayers proved to be promising strategies.

Study of microstructure and mechanical properties and residual stresses of 24CrNiMo steel prepared by selective laser melting and laser melting deposition

Selective laser melting (SLM) and laser direct metal deposition (LMD) have shown promise in advanced manufacturing. However, limited research fabricating the same material using these methods, particularly regarding mechanical properties and residual stresses. In this study, 24CrNiMo blocks were prepared using SLM and LMD and subjected to stress relief annealing (SR). The microstructure, residual stresses, and mechanical properties were investigated using SEM, XRD, EBSD, mechanical testing, and μ-X360n residual stress analysis. The results showed that the microstructure of both blocks composed of α-Fe. However, due to different thermal histories, there were differences in grain size between the SLM and LMD specimens. SLM specimens exhibited higher dislocation density, resulting in increased tensile strength and yield strength, while the LMD samples had higher proportions of high-angle grain boundaries (HAGBs), providing enhanced plasticity. LMD-SR specimens exhibited stronger texture and higher content of HAGBs in the <111> direction, further improving plasticity. Both as-deposited blocks exhibited high residual stresses, ranging from 450 MPa to 580 MPa for SLM and 20 %–50 % of SLM values for LMD. After SR treatment, the strength of both specimens decreased due to a reduction in dislocation density, but the increased content of HAGBs improved plasticity. Additionally, the residual stresses in both specimens significantly decreased, transitioned from tensile stresses to compressive stresses, greatly enhancing their wear resistance. Compared to the as-deposited specimens, the SLM-SR and LMD-SR specimens exhibited a reduction in weight loss due to wear by 46.1 % and 75.2 %, respectively, indicating a significant improvement in wear resistance.

Effects of scanning methods on cracking, microstructures and microhardness of Inconel 625 parts formed by direct laser metal deposition

This study aims at investigating the effects of scanning methods on the stress distribution and microstructures of Inconel 625 thin-walled part fabricated by direct laser metal deposition. The results showed that with the single direction scanning (SDS) method, the residual stress at both the ends of the thin wall was relatively high while the stress at the middle was smaller with a stress difference of about 1800 MPa. In contrast, with the reverse direction scanning (RDS) method, the residual stress in the thin wall was distributed relatively evenly, with a stress difference of about 350 MPa between both the ends and the center. The experimental results showed that, in the SDS method, cracks occurred at both ends and in the middle of the thin wall, whereas in the RDS method, warping and cracks phenomena were eliminated. The microstructure of the Inconel 625 in the forming layer is characterized by a columnar crystal structure that has a small length and grows perpendicularly to the scanning direction. This growth is continuous between the forming layers. In both cases, the microhardness increases with the height of the formed layers. The microhardness values are relatively uniform with values ranging from 420 to 450 HV.

Effect of laser direct metal deposition process on the microstructure and mechanical properties and temperature and stress fields of 24CrNiMo

Effect of laser direct metal deposition process on the microstructure and mechanical properties and temperature and stress fields of 24CrNiMo

Experimental and response surface study on additive manufacturing of functionally graded steel-inconel wall using direct laser metal deposition

Experimental and response surface study on additive manufacturing of functionally graded steel-inconel wall using direct laser metal deposition

Study on the mechanism of crack fomation in Inconel 625 formed by direct laser metal deposition

Study on the mechanism of crack fomation in Inconel 625 formed by direct laser metal deposition

Enhanced wear and corrosion resistance of the laser direct metal deposited AISI 316L stainless steel by in-situ interstitial N alloying

To meet the applicability in aggressive environments, the wear and corrosion resistance of additively manufactured 316L stainless steel can be improved by alloying with N. In this work, the in-situ interstitial N alloying of 316L with varying amount of CrxN is first manufactured at ambient environment utilizing the rapid cooling character of laser direct metal deposition (DMD). Combined effects of CrxN addition and DMD processing parameters on the relative density, dissolved N content, microstructure, microhardness, wear performance and corrosion behavior are systematically investigated. The results show that the relative density of the DMD 316L decreases with increasing additive amount of CrxN. A full density 316L sample with a high N content of 0.5 wt% is obtained. The N alloying transforms the solidification mode of DMD 316L from “AF” to “A”, resulting in a fully austenitic phase. The interstitial N promotes the formation of planar dislocations, nano-stacking faults and nano-twins during DMD. As the CrxN addition increases, both the microhardness (278–312 HV) and wear resistance are significantly enhanced owing to the dislocation strengthening and interstitial N solid solution strengthening. Compared with CrxN-free DMD 316L, the DMD 316L with CrxN addition presents superior pitting corrosion resistance. The increasing CrxN addition progressively improves the pitting corrosion resistance due to the positively synergistic effect Cr-N on the stability and repassivation ability of the passive film. This work provides a practical and cost-effective approach for manufacturing advanced 316L with exceptional properties.