Powder Bed Research Articles

Experimental Study and Random Forest Machine Learning of Surface Roughness for a Typical Laser Powder Bed Fusion Al Alloy

Surface quality represents a critical challenge in additive manufacturing (AM), with surface roughness serving as a key parameter that influences this aspect. In the aerospace industry, the surface roughness of the aviation components is a very important parameter. In this study, a typical Al alloy, AlSi10Mg, was selected to study its surface roughness when using Laser Powder Bed Fusion (LPBF). Two Random Forest (RF) models were established to predict the upper surface roughness of printed samples based on laser power, laser scanning speed, and hatch distance. Through the study, it is found that a two-dimensional (2D) RF model is successful in predicting surface roughness values based on experimental data. The best and minimum surface roughness is 2.98 μm, which is the minimum known without remelting. More than two-thirds of the samples had a surface roughness of less than 7.7 μm. The maximum surface roughness is 11.28 μm. And the coefficient of determination (R2) of the model was 0.9, also suggesting that the surface roughness of 3D-printed Al alloys can be predicted using ML approaches such as the RF model. This study helps to understand the relationship between printing parameters and surface roughness and helps print components with better surface quality.

Height-resolved emission spectroscopy and high-speed imaging of the TiAl6V4 vapor plume under laser powder bed fusion conditions

Optical emission spectroscopy is increasingly used as an in situ monitoring technique during laser powder bed fusion (LPBF) because plume emission holds elemental information not found in other in situ sensing techniques. This work explores the shape, stability, and temperature of the emission plume above the melt pool of Ti6Al4 V undergoing laser scans under LPBF-like processing conditions, using high-speed video and height-resolved spectroscopy to study the details of plume dynamics. Optical emission spectroscopy is conducted in the 480 nm to 525 nm region, where Ti emission is strong, with 0.3 mm vertical resolution above the baseplate. The Boltzmann plot method is used to determine temperature at each probed elevation, which indicates that the hottest location of the plume is occasionally elevated 0.3 mm to 0.6 mm above the scanning surface. The results show that the plume shape, stability, temperature, and spectra are highly dependent on the processing conditions. We highlight some of the complexities of optical emission spectroscopy and discuss potential challenges for implementing optical emission spectroscopy across an entire build.

Experimental Investigation on Novel Lattice Structure Parts of IN718 Made by Laser Powder Bed Fusion for Enhanced Specific Flexural Strength

Experimental Investigation on Novel Lattice Structure Parts of IN718 Made by Laser Powder Bed Fusion for Enhanced Specific Flexural Strength

STUDY ON THE INFLUENCE OF 1 AND 15μm PITCH VALUES ON THE APPARENT NANOMECHANICAL PROPERTIES OF LASER POWDER BED FUSION-PRODUCED CuCrZr ALLOY

Material deformation due to nanoindentation is well known. However, the deformation of a material, indentation cavity, and piled-up region drastically increases and nanohardness significantly decreases if the nanoindentation is performed in such a way that the deformation of one nanoindentation affects the others. This situation arises in various materials when they are subjected to tribological application such as pantograph assembly in electric trains and contact between the electrical power supply plug and pins. This situation has been addressed in this study and the quantitative reduction in nanohardness has been evaluated in detail. In this work, the nanoindentation was performed on the laser powder bed fusion (LPBF) CuCrZr alloy specimen under a load condition of 4500[Formula: see text][Formula: see text]N. This test was conducted at 100 points with an array of [Formula: see text] at a 1[Formula: see text][Formula: see text]m pitch value. Two significant findings were identified in this work. First, the indentation impression was smaller and the corresponding nanohardness and contact stiffness values were higher in the first column of 10 nanoindentations and the first row of 10 nanoindentations. The remaining 80 nanoindentations displayed contrasting behavior compared to the initial 20 nanoindentations due to the prior deformation of nearer regions. Nanohardness value decreased parabolically from the low deformation to the high deformation region. This finding was validated by increasing the pitch to 15[Formula: see text][Formula: see text]m under the 4500[Formula: see text][Formula: see text]N load conditions. The piled-up region around the impression of indentation changed from a semi-circular shape at a 15[Formula: see text][Formula: see text]m pitch value to a cone shape at a 1[Formula: see text][Formula: see text]m pitch value. These findings will be beneficial for industries during the design of materials and will help reduce material failures resulting from tribological activities.

Low temperature powder bed fusion of polyamide 6: transient process characteristics and process-dependent part properties

AbstractThe powder-based additive manufacturing of high-melting polyamides is impeded by unfavorable fracture properties and oxidation tendencies, limiting the technical applicability and the reuse of unfused powder. Overcoming these limitations through new processing strategies provides the opportunity for significantly extending the range of materials applicable for powder bed fusion processes. Based on fractal, locally quasi-simultaneous exposure strategies, a mesoscale compensation of thermal and crystallization-induced shrinkage is obtained, enabling the non-isothermal processing and stable layer formation of polyamide 6 at powder bed temperatures of 25 °C, 50 °C, and 75 °C. Thermographic in situ investigations reveal the layerwise quenching of discrete layers, leading to cooling rates exceeding − 250 K s−1 at 130 °C. Based on microscopic, mechanical, thermal, and spectroscopic investigations, insights into the structure formation and corresponding mechanical properties can be obtained, yielding reduced fractions of α-PA6 while increasing the elongation at break. The inherent layerwise quenching promotes the formation of microspherulitic morphologies while minimizing oxidation-induced material degradation, reflected in infrared spectroscopic material characteristics. Relying on obtained findings, process optimization strategies can be derived that enable the processability of high-melting polyamides at reduced temperatures, reducing the energy consumption of the build process while adapting underlying material characteristics based on accelerated intermediate cooling conditions.

Corrosion behavior of additively manufactured M300-CuCr1Zr by multi-material laser-based powder bed fusion

Additive manufactured parts of thermally-conductive CuCr1Zr and high-hardness M300 tool steel were fabricated via a single step multi-material Laser-based Powder Bed Fusion (PBF-LB). The corrosion properties of two interface configurations, CuCr1Zr built on M300 and M300 on CuCr1Zr, were evaluated using the electrochemical polarization resistance measurement, weight loss method and galvanic corrosion current measurement via a Zero Resistance Ammeter. The interface microstructure of the dissimilar bi-metallic parts fabricated by multi-material PBF-LB is tunable. The printing configuration influences the defect size and density and interface microstructure, which affect the global corrosion rate of the fabricated parts. Electrochemical measurements were performed on the fabricated parts in oxygen-saturated and chloride-containing water at elevated temperature, complimented by post-mortem characterizations. The interface configuration with M300 on CuCr1Zr has a slightly lower corrosion rate than that of CuCr1Zr on M300. Unexpectedly, galvanic corrosion occurred only locally in the interface region between M300 and CuCr1Zr materials. Beyond the interface regions, there is no clear sign of galvanic corrosion. Pitting and intergranular corrosion in CuCr1Zr material is the dominant corrosion mechanism. Both base materials beyond the interface region underwent localized pitting, particular in CuCr1Zr. Intergranular corrosion in CuCr1Zr is governed by sub-surface defects like pores and microcracks formed during printing.

Accelerating Laser Powder Bed Fusion: The Influence of Roller-Spreading Speed on Powder Spreading Performance

The powder spreading process is a fundamental element within the laser powder bed fusion (PBF-LP) framework given its pivotal role in configuring the powder bed. This configuration significantly influences subsequent processing steps and ultimately determines the quality of the final manufactured part. This research paper presents a comprehensive analysis of the impacts of varying spreading speeds, which are enabled by different roller configurations, on powder distribution in PBF-LP. By utilizing extensive Discrete Element Method (DEM) modelling, we systematically examine how spreading speed affects vital parameters within the spreading process, including packing density, mass fraction, and actual layer thickness. Our exploration of various roller configurations has revealed that increasing spreading speed generally decreases packing density and layer thickness for non-rotating, counter-rotating, and forward-rotating rollers with low clockwise rotational speeds (sub-rolling) due to powder dragging. However, a forward-rotating roller with a high clockwise rotational speed (super-rolling) balances momentum transfer, enhancing packing density and layer thickness while increasing surface roughness. This configuration significantly improves the uniformity and density of the powder bed, providing a technique to accelerate the spreading process while maintaining and not reducing packing density. Furthermore, this configuration offers crucial insights into optimizing additive manufacturing processes by considering the complex relationships between spreading speed, roller configuration, and powder spreading quality.

Microstructure and mechanical properties of TiB2/Al-5Cu composites fabricated by multi-material laser powder bed fusion

This study compares the fabrication of aluminum matrix composites (AMCs) using multi-material laser powder bed fusion (MM-LPBF) with that of conventional methods. The MM-LPBF AMCs exhibit a lamellar structure with a microhardness of 90±2 HV0.05 in the soft zone and 126±2 HV0.05 in the hard zone. The microhardness of the LPBF AMCs is 97±1 HV0.05. Compression tests show that the MM-LPBF AMCs have anisotropic properties with a compressive yield strength of 155±2 MPa along the building direction and 186±4 MPa along the scanning direction. In comparison, the LPBF AMCs have a compressive yield strength of 171±4 MPa. The fracture morphology shows that a single crack in the lamellar composite is accompanied by a deflection of the crack angle. In summary, this work showcases the potential of the MM-LPBF technique for tailoring material properties on demand.

Optimum Oxygen Concentration in Powder Bed Fusion Using Laser Beam for Building of Sc-containing Aluminum Alloy Powder.

Optimum Oxygen Concentration in Powder Bed Fusion Using Laser Beam for Building of Sc-containing Aluminum Alloy Powder.

Development of a 7000 series aluminium alloy suitable for laser-based Additive Manufacturing

High strength aluminium alloys are of significant interest for laser-based Additive Manufacturing as they can provide a high specific strength but have limited assembly possibilities due to poor weldability and the presence of large intermetallic particles challenging the conventional manufacturing route. Increasing the geometrical freedom by enabling their use with laser-based Additive Manufacturing would create new possibilities. This study investigates the possibilities of using an aluminium 7000 series alloy with Laser Powder Bed Fusion (L-PBF) and secondly for comparison with Direct Energy Deposition (DED). The chemical composition targets 5.1–6.1 wt% Zn and 2.1–3.9 wt% Mg. The level of Zn and Mg in the powder was increased to 10 wt% Zn and 3 wt% Mg to compensate for the expected evaporation during the laser-based AM process and guarantee a sufficient Zn and Mg content for precipitation strengthening. Solidification cracking in the initial alloy composition was resolved by the addition of 1 wt% Zr and 1 wt% V. For L-PBF, a study of the impact of the laser spot size showed a larger spot size is beneficial to improve the process stability. A study of the capability of preheating and of slowing down the process showed both further improve the process stability as well which is required to manufacture successfully larger parts to characterise the quasi-static tensile properties. For optimal process parameters for a fast process, meaning a scan speed of 700 mm/s, a yield stress of 425 ± 7 MPa and an ultimate tensile strength of 442 ± 5 MPa was obtained after a homogenisation and ageing heat treatment. In the as built state, the strength was significantly lower. For optimal process parameters for a slow process, meaning a scan speed of 250 mm/s, a yield stress of 398 ± 11 MPa and an ultimate tensile strength of 440 ± 16 MPa were obtained in as built state. For DED the mechanical properties of the alloy showed to be significantly dependent on process parameters. An excessive energy input results in more Zn and Mg evaporation and decreased cooling rates. Such parameters also impact the process stability of DED throughout the build cycle. Limiting the energy input resulted in dense samples and stable build cycles which after a heat treatment to peak ageing reached a yield stress of around 400 MPa and an ultimate tensile stress of around 440 MPa in the X- and Z-direction.

Effect of Laser Powder Bed Fusion Parameters on the Evolution of Melt Pool, Densification, Microstructure, and Hardness in 420 Stainless Steel Parts

Laser powder bed fusion (LPBF) involves depositing, melting, and solidifying metal powder particles layer by layer to create 3D components. In this study, a deep fundamental understanding on how process parameters—laser power, scan speed, and hatch spacing—affect the melt pool, densification, microstructure, hardness, and thermal behavior of 420 stainless steel (420SS) parts produced by such technology is provided. The conducted investigation considers five levels of laser power and hatch spacing, and four scan speeds. Optimal single tracks, based on geometry and profile, are achieved with laser powers between 40 and 80 W and a scan speed of 10 mm s−1. In the multitrack analysis, it is indicated that a dense, smooth surface is obtained with a hatch spacing of 250 μm, corresponding to an overlapping rate of ≈30%. The 420SS samples show high densification (≈99%) and low surface roughness (≈3.62 μm). The microstructure consisted of martensite laths and retained austenite. The hardness and thermal conductivity of the samples are measured at 540 HV and 15.3 W m−1 K−1, respectively. In this study, the understanding of the process–structure–property relationships in LPBF of 420SS is expanded.

Enhanced electrical and mechanical properties of additively manufactured pure copper with green laser

The effort to improve the additive manufacturing (AM) of copper, which is essential in various industrial sectors, has led to the exploration of green laser powder bed fusion (GL-PBF). By using a high-energy green laser, we overcome the challenges posed by the high reflectivity of copper, which has previously hindered achieving the desired component densities and functionalities through AM. This study uncovers the key role of GL-PBF process parameters on the densification, microstructure, surface roughness, mechanical properties, and electrical conductivity of pure copper parts. Our findings demonstrate that optimizing GL-PBF parameters can achieve copper components with over 99.9 % relative density and 98 % international annealed copper standard (IACS) electrical conductivity. The combination of comprehensive experiments and finite element modeling also reveals how the critical role of defect morphology in affecting electrical conductivity. This work contributes to the broader application of AM technologies, especially for high-reflectivity metals, and also provides new insights into how these defects affect conductivity and should be controlled during the AM process.

Tensile Properties and Coefficient of Thermal Expansion of Laser Powder Bed Fusion Fabricated IN718‐YSZ Compositionally Graded Composite

The microstructure, tensile properties, and thermal expansion characteristics of a laser powder bed fusion (LPBF) manufactured compositionally graded composite with 0.5–8 wt% yttria‐stabilized zirconia (YSZ) reinforced Inconel 718 are investigated. Along the composition gradient, which is perpendicular to the build direction, in all cross sections, the YSZ segregates at the melt‐pool boundaries and the IN718 matrix has randomly oriented equiaxed grains. Cross sections with >2 wt% YSZ contain significant porosity (>2%) and solidification cracks, which reduces their strength and ductility significantly. In the section with 1.5 wt% YSZ, the YS, UTS, and ductility are 819 ± 30, 1008 ± 40, and 7.4 ± 0.4 MPa, which matches well with that of LPBF fabricated YSZ‐free IN718. Dilatometry measurements on sections with 0.5–1.5 wt% YSZ in the temperature range of 25–1200 °C indicate that their coefficient of thermal expansion (CTE) is intermediate to that of IN718 and YSZ. Finally, the variations in CTE with temperature are discussed in detail by considering the microstructural evolution in the composite with changes in temperature.

Grain boundary crystallography and segregation in Ni-based superalloy INC738 manufactured by electron-beam powder bed fusion in as-built and annealed conditions

The excellent high-temperature properties of Ni-based superalloy INC738 are due to its hierarchical microstructure, making it an ideal engineering material for high-temperature applications. Engineering parts are now increasingly made via electron beam powder bed fusion (EPBF), an additive manufacturing technique suitable for such hard-to-weld Ni-based superalloys, due to lower thermal gradients and unmatched scan path control. The thermal cycles induced by EPBF impact characteristics of the γ-matrix, γ’ precipitates, secondary phases such as carbides, grain boundary (GB) solute segregation and, in turn, properties including GB cohesion and strength. However, a more thorough understanding of the GB microstructure evolution with focus on GB chemistry and character is required to optimise properties. We systematically investigate texture, grain structure, GB habit planes, and GB segregation in INC738 fabricated with linear versus random EPBF scanning strategies. We show that random scanning is a suitable strategy to inhibit cracking, refine grains, and decrease segregation of Cr, Mo, C, and B at GBs. For both scanning strategies, γ/γ GBs predominantly terminate on {100} planes and are decorated with C, B, Mo, and W. Upon 2 h annealing at 1180 °C and 1250 °C, the GB character and texture are shown to remain stable despite a reduction in GB interfacial excess. After 24 h annealing at 1250 °C, GB segregation and depletion are nearly eradicated, while static recrystallisation is observed with a predominant formation of annealing twins and GBs terminating on {111} planes. These findings are critical for defect-free additive manufacturing of INC738 and similar grades for superior high-temperature performance.

Impact of Surface Finishing on Ti6Al4V Voronoi Additively Manufactured Structures: Morphology, Dimensional Deviation, and Mechanical Behavior

Additively manufactured medical devices require proper surface finishing before their use to remove partially adhered particles and provide adequate surface roughness. The literature widely investigates regular lattice structures—mainly scaffolds with small pores to enhance osseointegration; however, only a few studies have addressed the impact of surface finishing on the dimensional deviation and the global and local mechanical responses of lattice samples. Therefore, the current research investigates the impact of biomedical surface finishing (i.e., corundum sandblasting and zirconia sandblasting) on Voronoi lattice structures produced by laser powder bed fusion (LPBF) with large pores and different thicknesses on the surface morphology and global and local mechanical behaviors. MicroCT and SEM are performed for the assessment of dimensional mismatch and surface evaluation. The mechanical properties are investigated with 2D digital image correlation (DIC) in quasi-static compression tests to estimate the impact of surface finishes on local maps of strain. In the quasi-static tests, both the global mechanical performances, as expected, and local 2D DIC strain maps were mainly affected by the strut thickness, and the impact of different surface finishings was irrelevant; on the contrary, different surface finishing processes led to differences in the dimensional deviation depending on the strut thickness. These results are relevant for designing lattice structures with thin struts that are integrated into medical prostheses that undergo AM.

Enhanced high-temperature mechanical properties and strengthening mechanisms of chemically prepared nano-TiC reinforced IN738LC via laser powder bed fusion

Fabrication of high-strength nickel-based composites to meet the demanding service requirements in aerospace environments is a significant challenge. This paper introduces the wet chemical method to prepare the nano-TiC reinforced IN738LC. In contrast to the conventional ball milling approach, this method attains superior attachment of nanoparticles. By employing a full-factorial experimental design, the correlation between Laser-powder bed fusion (L-PBF) processing parameters and the porosity, micro-hardness, and high-temperature tensile strength of as-built samples was examined. The results indicate that the optimal processing parameters are a laser power of 225 W, scanning speed of 750 mm/s, and hatch space of 0.09 mm, with a Volumetric energy density (VED) of 111.1 J/mm3. Compared to IN738LC, the chemically prepared TiC-IN738LC exhibits a 45 % increase in room temperature tensile strength (400 MPa) and a 65 % increase in high-temperature tensile strength (120 MPa). Compared with ball-milled TiC-IN738LC, the chemically prepared samples present superior microstructure with more equiaxed grains. The morphological analysis of the tensile samples reveals that the presence of dimples are crucial in enhancing the ductility properties. Furthermore, this study identifies the Orowan strengthening mechanism and the grain refinement strengthening mechanism as the principal mechanisms of reinforcement by nano-ceramics.

On the Effect of Cooling Parameters on Solidification Structure in NdFeB Alloys

The elaboration of suitable NdFeB‐based permanent magnets is essential for high‐performance electrical machines in a number of applications. In this respect, the understanding of the relationship between heat transfer phenomena and the final solidified microstructure is the key to the control of the grain size and the improvement of the magnetic properties. The problem is even more acute with the emergence of new manufacturing processes, such as the laser powder bed fusion, where the cooling rates are much higher than those encountered in the standard strip casting process and where the microstructure can be considered as fixed from the fabrication step. The objective of the present work is to identify correlations between interstructural spacings in the solidified alloys and cooling conditions. This study is based on a methodology coupling experimental and numerical simulation approaches featuring three solidification processes: strip casting, arc melting, and laser fusion. The obtained results cover more than four orders of magnitude in terms of cooling rates R and allow to propose a reliable empirical relationship between the interstructural spacing λ and R of the form λ [μm] = 83 R [K s−1]−0.36. This relation can thus be used to estimate cooling rates from metallographic observations.

Laser directed energy deposition remanufacturing of LPBF-processed TA15 parts: Hybrid process interface induced microstructure inheritance and mechanical performance

The laser additive hybrid manufacturing technology, which combines the precision of Laser Powder Bed Fusion (LPBF) and the flexibility of Laser Directed Energy Deposition (LDED), provides an effective solution for efficient forming and remanufacturing of large, complex components. The bonding zone (BZ) between LPBF and LDED forming regions is crucial for the final component performance. This study utilized LDED to remanufacture annealed LPBF substrates and investigated the microstructure and mechanical properties of TA15 alloy remanufactured parts. Results shows that a gradient microstructure forms at the bonding zone (BZ), where the bottom region exhibits a mixed structure including transitional β phase (βt), lamellar α and secondary α phase (αs). The top region shows a "ghost structure" of fine needle-like α phases. The mechanical property matched the microstructure well, as the hardness in the upper BZ reaches up to 463 MPa, whereas the LFZ exhibits the lowest hardness at 401 MPa. As the angle between the LDED region edge and tensile direction increases, the tensile strength first increases and then stabilizes, while elongation increases initially and then decreases. At a tilt angle of 60°, the strength peaks at 1098 MPa; at a 30° angle, the elongation reaches a maximum of 10.336%. All samples fracture at the LPBF zone, indicating that the formation of fine lamellar α phases in the BZ contributes to its higher strength compared to LPBF substrate and LDED deposition zones.

Effect of Powder Spreading Parameters on Laser Absorption Behavior and Processability of High‐Strength Aluminum Alloy Fabricated by Laser Powder Bed Fusion

Laser powder bed fusion (LPBF) of rare‐earth‐modified high‐strength aluminum alloys presents a novel approach for manufacturing complex components with enhanced structural performance, particularly in aerospace applications. This study fabricates Al–Mg–Sc–Zr specimens using various powder spreading parameters to explore their impact on laser processability. The investigation reveals that varying the powder layer thickness from 30 to 70 μm yields the smallest irradiation diameter of 135 μm at an optimal thickness of 50 μm, attributable to effective multiple reflections, high laser absorption rates, and stability. With an optimal laser power of 400 W, a scanning speed of 600 mm s−1, and a hatching spacing of 60 μm, the sample produced at 50 μm layer thickness achieves a relative density of 99.23%, a top surface roughness of 15.42 μm, and a refined grain size of 1.67 μm. Following aging at 325 °C for 4 h, this sample exhibits a tensile strength of 518 MPa and an elongation of 15.6%. The findings establish a theoretical basis for controlling the morphology and properties of high‐strength aluminum alloys in laser additive manufacturing.

Simulation-assisted prediction of residual stress-induced failure during powder bed fusion of metals using a laser beam

Simulation-assisted prediction of residual stress-induced failure during powder bed fusion of metals using a laser beam