High-speed Deposition Research Articles

Process development and heat flow analysis for thin walls made of aluminum using extreme high-speed laser material deposition (EHLA3D)

Extreme high-speed laser material deposition (EHLA) is an adapted variant of directed energy deposition (DED-LB-P/M), also known as laser material deposition, and has been developed for the efficient manufacturing of thin layers with high deposition speeds. With precise control of the energy input into the powder gas jet and the substrate, EHLA allows deposition speeds of up to 200 m/min and weld beads as thin as 25 μm. Advantages include a smaller melt pool and a heat-affected zone, allowing the processing of difficult-to-weld material combinations. The development of EHLA for additive manufacturing (EHLA3D) aims to produce highly customized components with improved structural accuracy compared to standard LMD at increased build rates compared to laser powder bed fusion (PBF-LB/M). A promising application is complex lightweight structures for the aerospace industry. However, there is a lack of systematic investigation on lightweight materials processed with EHLA3D at feed rates >20 m/min. In this work, a specially designed tripod machine (maximum feed rate 200 m/min) was used to investigate the buildup of aluminum in process regimes at 30 m/min. After confirming the existing single-track parameters, the tracks were metallographically examined and checked for pores, cracks, and bonding defects. The process was applied to thin-wall geometries and line energies as well as return-times that were varied. To gain an understanding of process-induced heat development, the process was monitored using thermography. Since the process shows geometry-specific heat flow patterns, guidelines have been developed that enable the buildup using different process adaptions.

Fundamentals of simultaneous machining and coating (SMaC) through combination of extreme high-speed laser material deposition (EHLA) and turning

Simultaneous machining and coating (SMaC) is a novel hybrid technology developed by the Fraunhofer Institute for Laser Technology ILT that combines additive manufacturing through extreme high-speed laser material deposition (EHLA) with a simultaneously engaged turning process. In the present work, the parallelization of the two subprocesses is successfully demonstrated. For the first time, systematic investigations into the influence of residual heat from the deposition process on the machining process and the properties of the resulting coating, respectively, are conducted. The study specifically examines geometric deviations, surface roughness, and tool wear. One of the main parameters affecting the residual heat introduced into the turning process is the distance between the tool center points of the EHLA deposition head and the turning tool Δz. This parameter is identified as a primary factor influencing the dimensional accuracy of the coating geometry. The results show that SMaC not only offers potential for increasing the productivity of the process chain but also has a positive effect on the service life of the cutting tools involved, potentially improving the workability of hard coating materials. Improvements in terms of the attainable surface roughness are also observed. These investigations provide a basis for research into further aspects of the SMaC process, such as adaptive tool path control methods to enhance dimensional accuracy and the influence of induced compressive stresses in processing highly brittle coating materials.

Thermal features and its effect on the properties of AISI 4140 fabricated by conventional and extreme high-speed laser material deposition

The extreme high-speed laser material deposition (EHLA) process has the potential to enable additive manufacturing for mass production by overcoming the limitations of slow scanning speed in conventional laser material deposition (LMD) processes. Thermal features are the key factors to link process and properties. A sound understanding of process-thermal-property relationships is essential for performance control and process optimization of a deposited component. In this study, we studied the thermal characteristics within a single layer and among layers for continuous processing using the numerical method, and reveal the mechanism of microstructure and hardness changes of AISI 4140 material formed by EHLA and LMD processes through the analysis of thermal properties and temperature history results. The grain size and hardness evolution for both processes during single-layer cladding and continuous forming processes were investigated. The results revealed that the grain refinement effect in continuous LMD processing is stronger than that in EHLA process (from 30.0 μm for single layer to 3.2 μm for multi layers vs. from 18.6 μm for single layer to 2.2 μm for multi layers). Similar hardness values were obtained by LMD and EHLA processes, with mean values of 511 HV and 472 HV, respectively. The yield and tensile strengths of EHLA were superior to the conventional cast material, but inferior to those of the conventional material quenched and tempered at lower temperatures. The enhanced tensile results of EHLA process were found similar to those prepared through conventional method with quench and tempering at 600 °C.

Improvement of High Temperature Wear Resistance of Laser-Cladding High-Entropy Alloy Coatings: A Review

As a novel type of metal material emerging in recent years, high-entropy alloy boasts properties such as a simplified microstructure, high strength, high hardness and wear resistance. High-entropy alloys can use laser cladding to produce coatings that exhibit excellent metallurgical bonding with the substrate, thereby significantly improvement of the wear resistance of the material surface. In this paper, the research progress on improving the high-temperature wear resistance of high entropy alloy coatings (LC-HEACs) was mainly analyzed based on the effect of some added alloying elements and the presence of hard ceramic phases. Building on this foundation, the study primarily examines the impact of adding elements such as aluminum, titanium, copper, silicon, and molybdenum, along with hard ceramic particles like TiC, WC, and NbC, on the phase structure of coatings, high-temperature mechanisms, and the synergistic interactions between these elements. Additionally, it explores the potential of promising lubricating particles and introduces an innovative, highly efficient additive manufacturing technology known as extreme high-speed laser metal deposition (EHLMD). Finally, this paper summarizes the main difficulties involved in increasing the high-temperature wear resistance of LC-HEACs and some problems worthy of attention in the future development.

Optimization design and interface characteristics research of high damping NiTi - Nickel-Aluminum Bronze functional gradient composite coating additively manufactured by high-speed laser-directed energy deposition

The near-equatomic NiTi shape memory alloy demonstrates exceptional damping performance due to its distinctive low-temperature self-cooperative martensitic internal friction. This study successfully fabricated NiTi-NAB (Nickel-Aluminium bronze shape memory alloy) functionally graded composite coatings with excellent metallurgical bonding between layers on Q235 steel substrates by designing an appropriate interlayer structure and employing the high-speed laser-directed energy deposition (LDED). Through comprehensive evaluation of the composite coating's performance and the numerical simulations of heat transfer within the molten pool, we elucidated the impact of process parameter levels on the microstructure and phase transformation characteristics of the NiTi alloy coating (NTC). The phase composition and phase interface characteristics of the NTC surface and bonding interface were analyzed using an electron probe microanalyzer and transmission electron microscopy, while dynamic thermomechanical analysis was employed to evaluate the damping performance of the NTC. The results indicate that an optimal parameter combination area still exists within the NTC-LDED process parameter window, even with equal laser energy density. Insufficient parameter levels can lead to an increase of micro-defects within the NTC, consequently causing a deterioration in both the cohesion and deformation resistance of the coating. Excessively high parameter levels can lead to significant element loss and residual stress, which in turn contributes to an increase in microcracks within the coating. A considerable quantity of reaction product mixture phases was formed at the interface between NTC and NAB, tending to align coherently with the NAB phase interface. The NTC, prepared with optimal process parameters, exhibits exceptional damping performance with a damping ratio of 0.498 at internal friction equilibrium, rendering it highly promising for applications in surface erosion protection for fluid machinery.

Design of laser-powder coupling for high-speed laser direct energy deposition

High-speed laser direct energy deposition (DED-LB) is developed to enhance deposition efficiency while maintaining build quality, compared to conventional DED-LB. The core of designing high-speed DED-LB involves formulating the laser-powder coupling, through optimizing nozzle structural and deposition process parameters. This study developed an analytical model to delineate the coupling mechanisms between laser beam and discontinuous coaxial powder stream (DCPS) comprised of individual single powder streams (SPSs). A data pretreatment method, involving gray processing, normalization, and renormalization of the thermal images successively, was applied to validate the model. Simulation results indicate that the DCPS spot size and SPS particle temperature distribution are predominantly influenced, respectively, by the nozzle structural and deposition process parameters. Through jointly designing the nozzle structural and deposition process parameters, a high deposition rate of high-speed DED-LB, which is 1.7 times that of conventional DED-LB, was achieved. This paper pioneers a new design methodology for high-speed DED-LB.

Microstructure and properties of K648 superalloy additively manufactured by extreme high-speed laser metal deposition

Microstructure and properties of K648 superalloy additively manufactured by extreme high-speed laser metal deposition

Achieving a High Thermally Conductive One Micron AlN Deposition by High Power Impulse Magnetron Sputtering plus Kick.

High-power impulse magnetron sputtering (HiPIMS) plus kick is a physical vapor deposition method that employs bipolar microsecond-scale voltage pulsing to precisely control the ion energy during sputter deposition. HiPIMS plus kick for AlN deposition is difficult since nitride deposition is challenged by low surface diffusion and high susceptibility to ion damage. In this current study, a systematic examination of the process parameters of HiPIMS plus kick was conducted. Under optimized main negative pulsing conditions, this study documented that a 25 V positive kick biasing for AlN deposition is ideal for optimizing a high quality film, as shown by X-ray diffraction and transmission electron microscopy as well as optimal thermal conductivity while increasing high speed deposition (25 nm/min) and obtaining ultrasmooth surfaces (rms roughness = 0.5 nm). HiPIMS plus kick was employed to deposit a single-texture 1 μm AlN film with a 7.4° rocking curve, indicating well oriented grains, which correlated with high thermal conductivity (121 W/m·K). The data are consistent with the optimal kick voltage enabling enhanced surface diffusion due to ion-substrate collisions without damaging the AlN grains.

Microstructure and Microhardness of High-Strength Aluminium Alloy Prepared Using High-Speed Laser Fabrication

As a recently developed high-strength aluminium alloy used specifically for laser additive manufacturing, AlMgMnSc alloy possesses superior mechanical properties and excellent processability. Extreme high-speed laser deposition (EHLD) is a novel surface-modification technique, which is characterised by high depositing speed, rapid cooling, rate and minimal dilution rate. To offer a new method for surface repairing high-strength aluminium alloys, an AlMgMnSc alloy coating, containing two deposition layers, is prepared on a 6061 aluminium-alloy axle using the EHLD technique. Meanwhile, the microstructure, composition distribution, and microhardness variation of the fabricated coating are studied. The results reveal that the coating is dense and crack-free, which is well-bonded with the substrate. Additionally, layer 1 is mainly composed of large columnar and equiaxed grains, while layer 2 consists of a fully equiaxed grain structure with an average grain size of about 4.5 μm. Moreover, the microhardness of the coating (about 104~118 HV) is similar to the substrate (about 105 HV), proving the feasibility of repairing high-strength aluminium alloys using AlMgMnSc alloy powders through the EHLD technique.

Rapid Alloy Development Using Calphad Simulation and Powder Blends in Direct Energy Deposition

The ongoing commercialization of additive manufacturing (AM) has necessitated the need to tailor alloy chemistry as well as exploit AM process particularities such as freedom of design, print geometry and high cooling rates to meet functional application requirements. Alloys such as hot-work tool steels, including H11, are well suited for machining and tooling applications. In this work, the authors investigated and compared high-speed direct energy deposition with laser beam source (HS DED-LB/M) processability of a reference H11 alloy and its modified form (H11m). The modification of the alloy was intended to minimize the amount of retained austenite (RA) in as-built microstructure and reduce post-heat treatment steps. The investigative approach included Calphad simulation, rapid alloy blending (modified powder) and process parameter optimization to produce dense parts for microstructure characterization and mechanical properties testing. The results show that while H11 achieved a high relative density > 99.85%, H11m still had cracks parallel to the building direction. The amount of RA was equally reduced from 4.08% in H11 to 1.23% in the H11m. H11 had a comparatively superior average microhardness (591 HV0.5) to H11m (561.5 HV0.5), which can be attributed to the more carbide presence. The martensitic strengthening effect between H11 and H11m can be described as similar.

Effect of hot isostatic pressing on microstructure and properties of high chromium K648 superalloy manufacturing by extreme high-speed laser metal deposition

High chromium superalloys have good overall mechanical properties and are widely used in critical hot-end components. The current manufacturing process still faces the problem of low forming efficiency. Extreme high-speed laser metal deposition (EHLMD) is a new and efficient additive manufacturing technology that can quickly and directly shape the direct forming of difficult-to-process materials. However, EHLMD still possesses some inter-layer defects in EHLMD alloy due to its excessively fast scanning speed, implying that there is potential for further improvement in its properties. Hot isostatic pressing (HIP) as a post-heat treatment is primarily used for the removal of defects in additive manufacturing components. In this study, the defects, microstructure, and properties of the EHLMD K648 superalloy using Micro-CT, XRD, SEM and TEM under HIP treatment were investigated. The results show that the porosity of the HIP EHLMD K648 superalloy decreased, and slender needle-shaped α-Cr phase, γ′ phase and coarse M6C carbides were precipitated. The tensile strength of the HIP EHLMD K648 superalloy increased by about 240 MPa. However, its plasticity was reduced. To further improve the plasticity of the HIP EHLMD K648 superalloy, subsequent heat treatment was carried out. The outcomes of this study are expected to promote the manufacturing of high-quality chromium superalloys and the development of EHLMD technology.

Investigation on different laser beam profiles in high-speed directed energy deposition

High-speed directed energy deposition via laser beam (HS-DED-LB) represents a novel powder-based approach for the additive manufacturing of metals. By significantly increasing the feed rate compared to conventional processes, a more economical production can be achieved. Within this study, the influence of different laser beam profiles (Gaussian and Top-Hat) on the resulting properties of 316L stainless steel specimens made by HS-DED-LB was investigated. All parameters except the laser beam profiles were held constant. The manufactured specimens were analyzed regarding their microstructure, microhardness, and relative density. Due to the different laser beam profiles, different melt pool geometries existed, which resulted in variances of the specimen’s properties.

Investigation on different laser-powder alignments and their influence on part properties in high-speed Directed Energy Deposition

Efficient high-speed directed energy deposition via laser beam (HS DED-LB) requires precise knowledge of the powder focus location and diameter. The alignment of the laser and powder focus ensures maximum powder efficiency and minimizes potential defects caused by unmolten powder due to insufficient power input during the laser-powder interaction time. The focal characteristics, such as diameter or focus position, are dependent on the nozzle used and are affected by the powder gas jet parameters, like shielding gas- or carrier gas flow. This study analyses the effects of individual powder gas jet parameters on the focal position and -diameter. Additionally, the impact of different laser-powder alignments (unaligned and aligned) for HS DED-LB is investigated by adjusting the laser focus to the measured powder focus position. The analysis of these different settings focuses on the sample’s height, relative density, and microhardness.

High-speed direct energy deposition as a high-throughput design tool for laser-based additive manufacturing

A wide range of additive manufacturing (AM) processing conditions can be rapidly realized within a single specimen via high-speed direct energy deposition laser based (DED-LB), due to a variety of cooling conditions and in-situ powder mixing. Since existing approaches are inefficient in exploring the vast material and process design space in AM, high-speed DED-LB can be employed as a novel technology for high-throughput alloy design tool. However, an evaluation of the process transferability of the high-speed DED-LB process with respect to the currently dominating metal AM technologies, namely laser powder bed fusion (PBF LB/M) and conventional DED-LB, is required. In this study, high-speed DED-LB is applied for the high-throughput sample production, using the nickel alloy IN718 as reference material as well as the AM processes PBF LB/M and DED-LB as reference processes. The resulting microstructures are characterized and compared using optical microscopy and large-area scanning electron microscopy (SEM) analysis combined with energy-dispersive X-ray spectroscopy (EDS). Furthermore, a model for calculation of the volumetric energy density is developed to compare the applied AM processes. The significant influence of the processing conditions on the solidification behavior of the investigated material allows for efficient exploration of the microstructure and phase composition. Specific high-speed DED-LB-process conditions achieved the average solidification cell size and laves phase content as observed in the PBF LB/M- and DED-LB -produced counterparts. The applicability of the high-speed DED-LB process for rapid alloy and process development, i.e., process transferability, is critically evaluated. The results show that high-speed DED-LB can be used to emulate cooling conditions of PBF-LB/M and DED-LB and, therefore, be used as tool for rapid alloy development.

Microstructure evolution and corrosion behavior of TC11 laser melt deposition additive components after post-heat treatment

The TC11 components were produced using a high-power, high-speed laser metal deposition (LMD) process. Subsequent post-heat treatment significantly improved the microstructures and corrosion resistance of the components. The results showed that the microstructure of the as-deposited component primarily comprised α Widmanstatten microstructure and mesh basket-weave microstructure. After post-heat treatment, the original interlayer zone disappeared in the deposition direction, and the microstructures were transformed from α’ to α phase. The aspect ratio of the α phase decreased, and the α grain boundary (αGB) became spheroidized. The tensile strength decreased but plasticity increased significantly. Overall, the corrosion resistance was improved in both directions, with greater improvements observed in the deposition direction. Phase ratio, grain size and KAM value are all factors affecting the corrosion resistance, but for the deposited direction, the significant improvement of the corrosion resistance is mainly due to the weakening of the charged galvanic corrosion effect between the non-interlayer zone and interlayer zone.

Process development and process adaption guidelines for the deposition of thin-walled structures with IN718 using extreme high-speed directed energy deposition (EHLA3D)

Extreme high-speed directed energy deposition (EHLA) is a modified variant of the laser based directed energy deposition (DED-LB) and is being applied as an efficient coating process for rotational symmetric components. Characteristics of EHLA processes are feed rates of up to 200 m/min, which result in smaller weld bead deposition and thinner layer thicknesses compared to conventional DED-LB. When transferred to additive manufacturing, this characteristic utilizes the potential of depositing thin-walled filigree structures at deposition rates, which are comparable to typical DED-LB processes (EHLA3D). The results of this work were achieved with an EHLA3D machine, which is a modified CNC-type machine capable of operating feed rates with vf = 30 m/min. In this work, process parameters were developed for the deposition of thin-walled filigree structures with the Ni-based superalloy IN718. Single tracks with constant feed rates and a variation in the beam diameter and powder mass flow were deposited and analyzed regarding the resulting weld bead dimension and dilution zone. Then, process parameters were selected and transferred to the deposition of thin walls, and guidelines of the parameter adaption toward thin-walled deposition were defined. Two parameter sets were developed to assess the feasible wall-thicknesses deposited by EHLA3D. Depending on the developed parameter sets, wall thicknesses between 300 and 500 μm are achieved. To characterize the resulting thin-walls, surface roughness measurements and metallographic cross sections were conducted.

Microstructure evolution and mechanical properties of high-chromium superalloy manufacturing by extreme high-speed laser metal deposition at different aging temperatures

Extreme High-Speed Laser Metal Deposition (EHLMD) is an efficient additive manufacturing technology that can quickly form difficult-to-machine materials. However, the rapid melting and solidification of EHLMD has the characteristic of forming a metastable microstructure. This study examines the effect of different aging temperatures on the microstructure and properties of EHLMD K648 superalloy. It is found that the formation of long needle-like α-Cr phase and γ' phase at lower aging temperatures (750 °C and 800 °C) is more beneficial for improving the strength of EHLMD K648 superalloy. The tensile strength was highest at 750 °C (1236 MPa) but its elongation was low (9.4 %). As the aging temperature increased (850–900 °C), the α-Cr phase transformed into rods and small particles, resulting in a decrease in tensile strength and an increase in elongation. At 900 °C, the tensile strength was 918 MPa and the elongation was 21.0 %. With further increase in aging temperature (>900 °C), coarse carbide and α-Cr phase precipitated in EHLMD K648 superalloy, causing its tensile strength and elongation to decrease. When the aging temperature reached 1000 °C, the tensile strength and elongation decreased to 790 MPa and 13.3 %, respectively.

Crystal grain size effects and crystallinity dynamics during supersonic particle impacts

We examine the effect of crystal grain size on particle impacts with substrates at supersonic speeds, which are commonly used in producing metal and ceramic coatings. Large-scale atomistic simulations are utilized to examine the impact outcomes of 60 nm nickel particle impacts on nickel substrates, with mean crystal grain sizes varied from 5 nm to 30 nm, representing nanoparticles commonly formed in vapor phase synthesis processes. We observe that smaller grain particles have higher critical strains and lower Young’s moduli than their larger grain counterparts due to having a larger fraction of grain boundaries. Smaller grain particles also experience a greater degree of heating and amorphization during higher speed impacts, while defect formation and propagation are hindered. We also provide insight into experimentally observed losses in crystallinity during high-speed deposition processes; in all cases a rapid loss of crystallinity occurs at impact, followed by recrystallization, with the net result being a decrease in crystal grain sizes.

Investigation of GH3625 alloy: Contrasting microstructures, mechanical properties, and corrosion performance via conventional and extreme high speed laser material deposition

The GH3625 nickel alloy, known for its exceptional mechanical properties and corrosion resistance, has been widely adopted. Nonetheless, the current additive manufacturing (AM) of GH3625 alloy presents compromised strength and significant segregation, thus limiting its potential applications. To address these challenges, the utilization of the extreme high-speed laser material deposition (EHLA) process with its rapid cooling capabilities has been investigated, aiming to enhance grain refinement and suppress segregation. In this study, a comparative analysis was conducted between GH3625 nickel alloy sample fabricated by conventional laser material deposition (LMD) and the EHLA technique. The investigation covered thermal processes, microstructural evolution, mechanical properties, and corrosion resistance. The EHLA-fabricated specimen exhibits a refined microstructure and elevated dislocation density attributed to the rapid solidification process. This leads to an impressive ultimate tensile strength of 1005 MPa, surpassing the LMD-deposited counterpart by 20 %. The Clyne-Kurz model outperforms the classic Scheil model in evaluating AM processes sensitive to cooling rates. Notably, the EHLA sample demonstrates reduced Nb segregation compared to the LMD sample. Furthermore, the formation of the precipitated Laves phase is reduced, and the concentrations of Nb and Mo within the dendritic structure are increased in the EHLA sample. Consequently, enhancements in pitting corrosion resistance and the protective effectiveness of passive films are observed.

High-speed deposition of silicon nitride thick films via halide laser chemical vapor deposition

High-speed deposition of silicon nitride thick films via halide laser chemical vapor deposition