Effect of Laser Power on Wear Characteristics of Ti-6A-4V Alloy Fabricated by Selective Laser Melting

Selective laser melting (SLM) is an important advanced additive manufacturing technology. The existing SLM products cannot fully meet the requirements of high-precision and strength of the mechanical component because of their defects. The TiAlN/TiN multilayer coating can improve the surface property of SLM products. The present work aims to explore the influences of different process parameters of SLM on the property of TiAlN/TiN multilayer coating plating on the 361L specimen and the mechanism of these influences. Taking laser power, scanning speed, and scanning space as factors, an orthogonal experiment was designed. The TiAlN/TiN multilayer coating specimens can be obtained by plating on the 361L specimen, fabricated by the process parameters of SLM on the orthogonal experiment. The surface topographies and properties of TiAlN/TiN multilayer coating were tested, the influences of SLM process parameters on TiAlN/TiN multilayer coating were analyzed, and the optimal process parameter was obtained. The electron microscope images revealed that the surface morphology of TiAlN/TiN multilayer coating plating on the SLM specimen was relatively flat, and there were some macro-particles in different sizes and pin holes dispersed on it. The thickness of the TiAlN/TiN multilayer coating was 2.77–3.29 μm. The microhardness value of coating SLM specimen was more than four times that of the uncoated SLM specimen and the wear rates of the uncoated specimen were 2–4 times that of the corresponding coating specimen. The comprehensive analysis shows that the laser power had the greatest influence on the comprehensive property of the coating. The primary cause of the influence of SLM process parameters on the properties of the TiAlN/TiN multilayer coating was preliminarily discussed. When the laser power was 170 W, the scanning speed was 1,100 mm/s, and the scanning space was 0.08mm, the TiAlN/TiN multilayer coating plating on the SLM specimen had the best comprehensive property.

Effect of process parameters on the formation of single track in pulsed laser powder bed fusion

The interest of high speed steel (HSS) for wood cutting tools remains very important because of their good tool edge accuracy and easy grinding. The main problem is their low resistance to both mechanical and chemical wearing. Resistance of HSS cutting tools to wearing is a primary concern in the applicability of the HSS cutting tools to a wood cutting operation. In order to increase their performance, a laser melting and cladding applied on the tool edges is presented in this paper. First, the annealed AISI M2 bar was melted, and the M2 powder was cladded onto the AISI L2 substrate by a laser beam. The microstructure and microhardness of the M2-clad and M2-melted were characterized. Second, their wear resistance was tested for cutting wood. The experimental results showed that the microstructures on the clad zone (CZ) of M2-clad and melted zone (MZ) of the M2-melted reveal fine and homogeneous iron dendritic structure, in which whole primary carbides were completely dissolved during laser cladding and melting. The energy dispersive spectroscopy (EDS) analysis indicated that the M2-clad reveals CZ microstructure with more uniform distribution of fine carbides compared to MZ microstructure. The M2-clad and M2-melted, which present almost the same microhardness, have larger microhardness compared to the M2-conventional. The results of wearing tests showed that the M2-clad and M2-melted cutting tools are better in wear resistance, edge roughness, and suffer less edge fractures than the M2-conventional peeling tool. Laser melting and cladding are considered to be valuable techniques to improve the performance of the M2 high speed steel cutting tools for wood machining application.

Process parameters and powder spreading quality are important factors for aluminum matrix composites (AMCs) prepared using laser powder bed fusion (LPBF). In this study, a Box-Behnken Design (BBD) was used to optimize the process parameters, and near-spherical β-SiC was selected to improve the quality of powder spreading. The rationality of parameter optimization was verified by testing the density of samples prepared using different laser power levels. Al4C3 diffraction peaks were found in XRD patterns, which indicated that interface reactions occurred to form good interface bonding between the Al matrix and the SiC particles. The tensile strength and plasticity of LPBF α-SiC/AlSi10Mg were lower than that of LPBF AlSi10Mg, which was mainly due to the poor fluidity of the powder mixtures and powder spreading quality. For LPBF β-SiC/AlSi10Mg, the tensile strength increased and elongation decreased slightly compared to LPBF α-SiC/AlSi10Mg. The data in this study were compared with the data in other studies. In this study, LPBF AlSi10Mg and LPBF β-SiC/AlSi10Mg not only showed the inherent high strength of their LPBF parts, but also had relatively high plasticity. Matching between strength and plasticity was mainly dependent on the scanning strategy. Most studies use uni-directional or bi-directional scanning strategies with a certain rotation angle between layers. A chessboard scanning strategy was used in this study to form a coarse remelted connected skeleton inside the material and significantly improve plasticity. This study lays a theoretical and experimental foundation for the controllable preparation of SiC-reinforced AMCs using LPBF.

Selective laser melting (SLM) is an additive manufacturing technique in which complex parts can be fabricated directly by melting layers of powder from a CAD model. SLM has a wide range of application in biomedicine and other engineering areas and it has a series of advantages over traditional processing techniques. A large number of variables including laser power, scanning speed, scanning line spacing, layer thickness, material based input parameters, etc. have a considerable effect on SLM process materials. The interaction between these parameters is not completely studied. Limited studies on balling effect in SLM, densifications under different processing conditions, and laser re-melting, have been conducted that involved microstructural investigation. Grain boundaries are amongst the most important microstructural properties in polycrystalline materials with a significant effect on the fracture and plastic deformation. In SLM samples, in addition to the grain boundaries, the microstructure has another set of connecting surfaces between the melt pools. In this study, a computational framework is developed to model the mechanical response of SLM processed materials by considering both the grain boundaries and melt pool boundaries in the material. To this end, a 3D finite element model is developed to investigate the effect of various microstructural properties including the grains size, melt pools size, and pool connectivity on the macroscopic mechanical response of the SLM manufactured materials. A conventional microstructural model for studying polycrystalline materials is modified to incorporate the effect of connecting melt pools beside the grain boundaries. In this model, individual melt pools are approximated as overlapped cylinders each containing several grains and grain boundaries, which are modeled to be attached together by the cohesive zone method. This method has been used in modeling adhesives, bonded interfaces, gaskets, and rock fracture. A traction-separation description of the interface is used as the constitutive response of this model. Anisotropic elasticity and crystal plasticity are used as constitutive laws for the material inside the grains. For the experimental verification, stainless steel 316L flat dog bone samples are fabricated by SLM and tested in tension. During fabrication, the power of laser is constant, and the scan speed is changed to study the effect of fabrication parameters on the mechanical properties of the parts and to compare the result with the finite element model.

Purpose The laser powder bed fusion (L-PBF) process has gained increasing interest in investment casting (IC) due to its suitability for small-batch production. This study aims to optimize L-PBF process parameters for Polystyrene (PS200), focusing on their effects on hardness and density to produce high-quality investment casting patterns. Design/methodology/approach A comprehensive characterization of PS200 was conducted. A three-factor face-centered central composite design (FC-CCD) was used to analyze the effects of laser power (LP), laser speed (LS) and skin-hatch distance (SHD) on the hardness and density of PS200 components. Findings Powder characterization shows moderate flowability and low ash residue. LP and SHD were identified as the most influential factors. Hardness and density increased with higher LP, whereas LS and SHD showed an inverse effect. Optimized parameters improved hardness by 6.9% and density by 7.5%, with a significant LP−SHD interaction, reducing surface roughness (Ra) from 17 to 14 µm (17.7% improvement) and enabling high-quality PS200 patterns. Research limitations/implications This study is limited to a specific machine-material combination, restricting generalizability to other L-PBF systems. Future work should explore additional process parameters, L-PBF platforms and long-term stability in investment casting. Originality/value Qualifying new materials requires an in-depth understanding of machine-material process parameters. This study introduces a systematic approach to qualifying Polystyrene (PS200) for L-PBF. It establishes its process parameters, contributing to adopting L-PBF to produce high-quality investment casting patterns.

The use of components fabricated by laser powder bed fusion (LPBF) requires the development of processing parameters that can produce high-quality material. Manipulating the most commonly identified critical build parameters (e.g., laser power, laser scan speed, and layer thickness) on LPBF equipment can generate acceptable parts for established materials and moderately intricate part geometries. The need to fabricate increasingly complex parts from unique materials drives the limited research into LPBF process control using underutilized parameters, such as atmosphere composition and pressure. As presented in this review, manipulating atmosphere composition and pressure in laser beam welding has been shown to expand processing windows and produce higher-quality welds. The similarities between laser beam welding and laser-based AM processes suggest that this atmosphere control research could be effectively adapted for LPBF, an area that has not been widely explored. Tailoring this research for LPBF has significant potential to reveal novel processing regimes. This review presents the current state of the art in atmosphere research for laser beam welding and LPBF, with a focus on studies exploring cover gas composition and pressure, and concludes with an outlook on future LPBF atmosphere control systems.

Laser Powder Bed Fusion (LPBF) is an additive manufacturing (AM) technique with growing industrial applications. Variations in laser power, scan speed, and thermal conditions can lead to defects such as porosity, cracks, and deformations. Effective Real-time monitoring and control in LPBF are crucial for ensuring process stability, defect mitigation, and part quality consistency as well as improving production efficiency. Existing LPBF process monitoring and control research often focuses on the performance of the algorithms, such as prediction accuracy and decision-making optimization without addressing real-time implementability and discussing the trade-offs between algorithm complexity and computation feasibility. Evaluation of computational resources is essential for advanced monitoring and control algorithm implementation. For real-time data processing and control, Field Programmable Gate Array (FPGA) is an ideal computing platform for sub millisecond applications. In LPBF AM, melt pool image (MPI)-based process monitoring with machine learning has been widely studied for part quality prediction and control. This paper conducts computing performance evaluation for FPGA implementation of real-time MPI-based LPBF process monitoring. More specifically, latency and resource utilization are analyzed for various advanced analytical algorithms. Two case studies illustrate this evaluation: (1) High-Level Synthesis (HLS)-based analysis of MP feature extraction and (2) High-Level Synthesis for Machine Learning (HLS4ML)-based evaluation of neural network inference for anomaly detection. These cases demonstrate the applicability of FPGA-based solutions to in-process advanced data analytics during LPBF, providing insights for researchers and engineers to develop scalable and efficient real-time control systems for LPBF.

Current production of dense Nd-Fe-B permanent magnets is restricted to the powder metallurgical way consisting of powder production, pressing and magnet field alignment, sintering and post processing. This method allows the production of simple shaped magnets with superior magnetic performance. Bonded magnets show a higher geometrical flexibility on the expense of magnetic performance due the mixing with non-magnetic polymer with a volume content of up to 50%. Additive Manufacturing by means of laser powder bed fusion (LPBF) offers the opportunity to overcome design restrictions of conventional production techniques and allows new strategies for the application-oriented product development. LPBF is characterized by a layer-by-layer local melting of powder on a built platform by a focused laser beam, which is scanned across the powder. New powder is applied on top of melted material afterwards and the melting process is continued. Local melting, rapid solidification, directional heat transfer and several re-melting and re-heating cycles control the microstructural development of metals during LPBF. For this reason, achievable microstructures and properties differ in general significantly from such ones, which can be obtained from conventional fabrication processes.We applied laser powder bed fusion to commercial Nd-lean MQPTM-S powder from Magnequench for the additive manufacturing of Nd-Fe-B bulk permanent magnets. Samples were manufactured on a “M2 cusing” machine from Concept Laser GmbH under protective Argon atmosphere and an Oxygen content below 0.2%. Nd-Fe-B behaves very different compared to established materials during LPBF and the resulting magnetic performance is mainly controlled by the energy input from the laser beam and depends on the processing parameter laser power PL, laser scan velocity vL and hatch distance hy. The latter one represents the offset of neighbouring laser scan lines [1].The impact of processing parameter laser power and scan velocity on coercivity is shown in Figure 1 (a). It is obvious, that Hc is enhanced, when laser power increases or scan velocity decreases – in other words, if the energy input raises. A similar behaviour was observed for remanence Br and maximum energy product (BH)max. However, the enhancement of magnetic performance is limited by a material specific maximum allowed limit of processibility, at which the samples will be increasingly destroyed. For optimized processing parameter a coercivity of 920 kA/m (1.16 T), a remanence of 0.63 T and a maximum energy product of 63 kJ/m3 is obtained. Thereby, Br and (BH)max represent the highest reported values for additively manufactured permanent magnets so far. The demagnetization branch of the hysteresis curve for a magnet with optimized magnetic properties is shown in Figure 1 (b) and compared to the initial MQPTM-S powder and a polymer bonded magnet from the powder, which is produced by injection molding with a loading factor of 60 vol.%. The coercivity of the powder is 700 kA/m and is slightly reduced by injection molding. However, LPBF leads to an unexpected enhancement of coercivity and the value of the powder is exceeded by 30% without the addition of any rare earth containing eutectics or other post processes.The composition of the used material exhibits 20 wt.% of rare earth, which is equivalent to 8 at.% and is in the range of α-Fe/Nd2Fe14B nanocomposites [2]. These are typically prepared by melt spinning and show coercivities of 400 – 600 kA/m for comparable compositions [2,3], e.g rare earth content between 8 and 9 at.%. These values are clearly exceeded by our LPBF-processed Nd-Fe-B magnets.The link between LPBF-processing and enhanced magnetic performance is the microstructure of the magnets and the microstructural development is controlled – as described above – by several factors. In the case of LPBF-processed Nd-Fe-B magnets we obtained a unique fine-grained microstructure with a grain size between 60 and 600 nm.Our results demonstrate, that improved magnetic performance can be achieved by LPBF of Nd-Fe-B bulk permanent magnets with an optimized coercivity, which is unexpected high for the given Nd-lean composition. This offers new perspectives for the development of new manufacturing processes for the production of improved Nd-Fe-B permanent magnets. **

Effect of laser power in laser powder bed fusion on Ni content and structure of Nitinol

This study was set to fundamentally investigate the characteristics of austenite reversion occurring in maraging steels additive-manufactured by laser powder bed fusion (L-PBF). The maraging steel samples manufactured under different L-PBF process conditions (laser power P and scan speed v) were subjected to heat treatments at 550°C for various durations, compared with the results of the austenitized and water-quenched sample with fully martensite structure. The L-PBF manufactured samples exhibited the martensite structure (including localized austenite (γ) phases) containing submicron-sized cellular structures. Enriched alloy elements were detected along the cell boundaries, whereas such cellar structure was not found in the water-quenched sample. The localized alloy elements can be rationalized by the continuous variations in the γ-phase composition in solidification during the L-PBF process. The precipitation of nanoscale intermetallic phases and the following austenitic reversion occurred in all of the experimental samples. The L-PBF manufactured samples exhibited faster kinetics of the precipitation and austenite reversion than the water-quenched sample at elevated temperatures. The kinetics changed depending on the L-PBF process condition. The enriched Ni element (for stabilizing γ phase) localized at cell boundaries would play a role in the nucleation site for the formation of γ phase at 550°C, resulting in the enhanced austenite reversion in the L-PBF manufactured samples. The variation in the reaction kinetics depending on the L-PBF condition would be due to the varied thermal profiles of the manufactured samples by consecutive scanning laser irradiation operated under different P and v values.

Laser Powder Bed Fusion (LPBF) is a metal additive manufacturing technology (AM) that uses high power laser to melt powder layer by layer to create mechanical parts. LPBF several advantages, including short manufacturing time, freedom to design complex geometries and user-friendly customization. It is widely used in the manufacture of high-value parts in aerospace, automotive and biomedical industries. Due to the nature of the layer-by-layer process, partially melted powder is attached to the as-built part surface during LPBF, resulting in a significant increase in surface roughness. Furthermore, initial surface roughness of final part is different with locations since quantity of powder adhesion varies depending on building angle. Increase of surface roughness due to attached metal powder can cause out of dimensional tolerance that designed. Such dimensional inaccuracy can lead to failure or breakage of the mechanical parts. Therefore, surface post-treatment is essential to reduce surface roughness with minimizing dimensional change. Conventional mechanical and chemical treatments for surface finishing have limitations such as limited tooling range and surface damage due to the use of strong acids and long-time of processing. Electropolishing, based on electrochemical reactions, is suitable for improving the roughness of LPBF manufactured parts with complex geometries. Thickness reduction can be predicted by controlling the applied voltage and processing time. Also, surfaces in contact with the electrolyte is polished without geometric restrictions. Studies have been reported that analyze the change in surface roughness after electropolishing to improve the roughness of alloys manufactured with LPBF. However, for application to real parts, it is necessary to conduct basic research to optimize the electropolishing conditions to obtain satisfactory surface roughness with minimal thickness reduction by considering the effect of dimensional changes during electropolishing. In this study, we electropolished Hastelloy X fabricated by LPBF. Four types of electrolytes were selected for electropolishing. We measured surface roughness and thickness reduction with respect to applied voltage and processing time. With such results, optimized condition to reduce the surface roughness with minimal thickness changes are discussed. Then, these conditions were applied to LPBF specimen with different building angles. Surface roughness and weight changes were measured to compare polishing efficiency to each electrolyte.

7075 aluminum alloy powders were used as raw materials. The selective laser melting single tracks forming experiment of 7075 aluminum alloy was carried out at scanning speed of 50–700 mm s−1, laser power of 80–100 W. The continuity and dimensional uniformity of selective laser melting 7075 aluminum alloy single tracks were characterized by OM and SEM. The influence law of laser power and scanning speed on the continuity and dimensional uniformity of selective laser melting 7075 aluminum alloy single tracks were revealed. The results show that: when the laser power was increased from 80 to 100 W and the scanning speed of 50–700 mm s−1, the continuity and dimensional uniformity of selective laser melting 7075 aluminum alloy single tracks were improved, the morphology was changed from discrete irregular particles to continuous single line. When the laser power was 80 W, the continuity of selective laser melting 7075 aluminum alloy 3D printing single tracks was deteriorated, but the dimensional uniformity was improved, with the increases of scanning speed from 100 to 700 mm s−1. When the laser power was 100 W, the continuity and dimensional uniformity of the 7075 aluminum alloy selective laser melting 3D printing single tracks were improved with the increases of scanning speed from 50 to 300 mm s−1; the continuity and dimensional uniformity of the 7075 aluminum alloy selective laser melting 3D printing single tracks reduced with the increase of scanning speed from 500 to 700 mm s−1. Laser power has a great impact on the continuity and dimensional uniformity of 7075 aluminum alloy selective laser melting 3D printing single tracks, high laser power and low scanning speed are beneficial to obtaining continuous and dimensional homogeneous of the 7075 aluminum alloy single tracks.

High-temperature shape memory alloys (HT-SMAs) are required in specific automotive, aerospace or energy applications [1], [2]. Common binary Ni-Ti SMAs are characterized by a limited transformation temperature and, thus, cannot be used for applications operating at 100°C or above. Ternary elements (Pt, Au, Hf, Zr) can be added to increase the transformation temperature [3]. The ternary Ni-Ti-Hf alloy is currently the most promising candidate material, however, pronounced brittleness and high costs due to the significant amount of Hf hinders its technological breakthrough. Alternative HT-SMAs are Co-Ni-Ga Heusler alloys. These materials undergo a first-order magnetostructural transformation (FOMST) from high-temperature B2-ordered austenite to tetragonal L10 low-temperature martensite [4]. A fully reversible superelastic response up to 500°C as well as excellent cyclic stability up to temperatures of 100°C have been reported for single-crystals [5]. However, polycrystalline Co-Ni-Ga suffers from intergranular cracking and a premature failure after several transformation cycles due to the anisotropic volume change of randomly crystallographic orientated grains.Many efforts in the fields of grain boundary and microstructure engineering have been done to synthesize HT-SMAs with favorable grain boundary configuration in order to fully prevent intergranular cracking and premature failure. It was reported that a columnar-grained microstructure with strong <001> texture and straight low-angle grain boundaries can overcome the structural and functional limitations in Cu-based SMAs [6].Additive manufacturing (AM) is a very promising technique to synthesize HT-SMA since it allows a direct microstructure design. Selective laser melting (SLM) and directed energy deposition (DED) are two common AM techniques for metallic alloys. During the SLM process, pre-alloyed powder is molten layer-by-layer using a laser system operating under inert gas atmosphere to prevent oxidation. Microstructure can be directly tailored by different processing parameters like laser power, scanning velocity and scanning path. In contrast to the powder-bed based SLM, DED is a powder-stream based process using nozzles to directly transfer the powder material into a focused laser beam. Similar to the SLM process the microstructure can be directly tailored by varying the processing parameters such as laser power and scanning speed.In our present work, we compare the microstructure and magnetic properties of Co49Ni21Ga30 alloys processed by SLM and DED with single crystals as well as polycrystalline material prepared by conventional casting. The preferred columnar-grained microstructure could be obtained by proper choice of processing parameters for the different AM techniques [7], [8]. Fig. 1 shows the microstructure of Co-Ni-Ga fabricated by SLM. The electron backscatter diffraction (EBSD) analysis of the cross-section shows a polycrystalline columnar-grained microstructure along the building direction (BD) [7]. A similar columnar-grained microstructure is also observed in the DED processed material [8]. In addition, the DED sample is characterized by a strong <001> texture along BD. Due to these highly anisotropic microstructures, AM processed Co-Ni-Ga obtained by both, SLM and DED, shows excellent HT-SMA properties without any post-processing [7], [8].To study the FOMST in more detail, temperature and field-dependent magnetization measurements were performed. Fig. 2 shows the temperature-dependent magnetization of additively processed samples, polycrystalline material in the as-cast condition and in a single crystalline state for different orientations. The SLM sample reveals the largest transition width and thermal hysteresis while the DED sample provides for a transformation behavior being very similar to the cast and single crystalline counterparts. Since the transformation behavior depends on parameters such as grain size, residual stresses, defects and precipitates [9] the influence of the processing parameters on these parameters is essential to understand the FOMST and functional properties in Co-Ni-Ga in more detail.This work was supported by the ERC Advanced Grant "CoolInnov" (No 743116), the CRC/TRR 270 “HoMMage” (DFG). TN acknowledges funding by DFG (No 398899207). **

Experimental study and neural network model based prediction of layer thickness influence on LPBF IN625 single track geometry