Powder Bed Research Articles

Laser powder bed fusion of GH4099 Ni-based superalloy under a static magnetic field with tailored microstructure and enhanced mechanical performance

ABSTRACT In the present work, the static magnetic field (SMF) was applied in the L-PBF process of a typical γʹ strengthening Ni-based superalloy of GH4099 concerning the as-built and heat-treated conditions. The SMF during the L-PBF process can effectively refine the cellular str ucture, refine the grain size, promote the columnar to equiaxed transition (CET), and reduce the dislocation density. After the solution-aging procedure, the SMF samples exhibited a refined grain structure, suggesting that the tailored microstructure is inherited after the solution-aging treatment. The tensile test results show that by applying the SMF during the L-PBF process, the ductility can be notably improved on both building planes under the as-built and heat-treatment conditions, and the anisotropy along different directions can be reduced. It reveals that the SMF in L-PBF can be an effective method to modulate the microstructure and improve the comprehensive mechanical properties for γʹ strengthening Ni-based superalloys.

Effect of current on the tribological behavior of Cu-Fe-P immiscible alloy produced by laser powder bed fusion

Cu-based immiscible alloys have significant potential application value in the field of electrical contacts. This study investigated the tribological behavior of Cu-Fe-P immiscible alloys produced via laser powder bed fusion (LPBF) under current-carrying conditions. The alloys consist of softer ε-Cu phase and harder Fe-rich phases. The Fe-rich phase acts as a protective reinforcement during current-carrying friction and wear tests, improving the wear resistance of the alloy. With the increasing current, the coefficient of friction initially rose and then decreased, whereas the wear rate showed a gradual increase. At low currents (0, 2, 3 and 5 A), mechanical wear predominantly governs the wear mechanism. As the current increases, the mechanical wear gradually transitions from adhesive wear to abrasive wear, accompanied by weak oxidative wear. At higher currents (7 A and 10 A), the wear mechanism is dominated by arc erosion wear and oxidative wear. Notably, when the current exceeded 2 A, an oxide film consisting of CuO, Fe2O3, and Fe3O4 formed, enhancing the frictional properties of the alloy. Once the current surpassed 5 A, the arc discharge occurred at high currents, forming molten phases and arc erosion pits on the worn surface of the Cu-Fe-P immiscible alloy.

Manufacturing and aging behavior of CuCr1Zr powder: Analysis and modelling of close-coupled gas atomization of CuCr1Zr and its impact on the melt beam disintegration and analysis powder oxidation kinetics

Powder bed-based additive manufacturing methods represent an increasingly vital role in industrial applications. Specifically, there has been considerable focus on highly reflective metals, such as CuCr1Zr, in recent years. However, current research primarily revolves around developing appropriate manufacturing parameters e.g. laser powder bed fusion (PBF/LB-M) and assessing the corresponding mechanical and electrical properties of CuCr1Zr. The impact of manufacturing routines and oxidation behavior of CuCr1Zr powder are seldom discussed in additive manufacturing. Therefore, the present study addresses the analysis of powder production and the oxidation behavior of CuCr1Zr powder via close-coupled gas atomization to analyze the disintegration of a CuCr1Zr melting jet during gas atomization of CuCr1Zr by using a high-speed camera. Critical conditions for secondary disintegration were calculated as a function of the initial gas pressure. Additionally, calorimetric measurements and isothermal oxidation experiments were conducted to quantify oxide formation and growth. According to the results, initial oxide formation occurs after 42 days with CuCr1Zr powder at room temperature in a nitrogen atmosphere. Subsequently, oxide growth follows a logarithmic law, associated with the formation and conversion of Cu2O to CuO.

Effect of geometric defects on the mechanical properties of additive manufactured Ti6Al4V lattice structures

Lattice structures realized by additive manufacturing (AM) have the great potential for a broad range of engineering applications. However, the lattice structures are involved in geometric defects. This paper focuses the effect of geometric defects on the mechanical properties of Ti6Al4V lattice structures manufactured by laser powder bed fusion (L-PBF), three cell topologies, i.e., body centered cubic with vertical struts (BCCZ), face centered cubic with vertical struts (FCCZ), and face and body centered cubic with vertical struts (FBCCZ) were studied. X-ray computed tomography was used to extract the shape and the distribution of process-induced geometric defects of these three kinds of samples. Probability density distributions of geometric defects in each layer were also established to analyze the effect of the printing sequence on geometric defects. Then these distributions of geometric defects were inputted into Abaqus to build the modified statistical models to study the effect of geometric defects on mechanical properties. It is shown that the deviation of the cross-section radius exhibits normal distribution and the deviation of the center axis offset exhibits logarithmic distribution. And the middle layer of the sample has a better manufacturing precision. The modified statistical model can predict the mechanical properties within an error of 5 %. The strut thickness deviation had a more significant effect on the mechanical properties than the strut waviness.

Fatigue properties of a Ti–5Al–5Mo-5 V–3Cr alloy manufactured by electron beam powder bed fusion

AbstractAdditive manufacturing (AM) is a modern way of manufacturing structures, which tends to have fewer design limitations than those manufactured by conventional processes such as casting or forging. A combination of high-strength materials and small and complex structures opens up a wide range of potential applications, especially in the fields of medicine and aerospace. Titanium and its alloys show a very beneficial combination of density and mechanical properties. One of these alloys is the metastable β titanium alloy Ti– 5Al–5Mo–5 V–3Cr (Ti-5553), which is currently used mainly for large forged structures like landing gears of airplanes. In this study, for the first time the fatigue behavior of electron beam powder bed fused (PBF-EB) Ti-5553 was investigated with a focus on the defects created by the layer wise manufacturing. To understand the defect structure and its respective influence on the fatigue behavior, all specimens were scanned prior to fatigue testing using a state-of-the-art µ-focus CT. The specimens were subjected to two heat treatment procedures commonly used in technical applications, which were aiming for high strength (solution treated and aged—STA) as well as high ductility (beta annealed, slow cooled and aged—BASCA). Results indicate that the fatigue strength of PBF-EB manufactured Ti-5553 is significantly reduced compared to conventionally manufactured Ti-5553. The main reason for this are defects, which have varying critical effects depending on the heat treatment of the specimen and the defect size, shape, location and type.

Characterizing the as-built surface topography of Inconel 718 specimens as a function of laser powder bed fusion process parameters

Purpose The ability to use laser powder bed fusion (LPBF) to print parts with tailored surface topography could reduce the need for costly post-processing. However, characterizing the as-built surface topography as a function of process parameters is crucial to establishing linkages between process parameters and surface topography and is currently not well understood. The purpose of this study is to measure the effect of different LPBF process parameters on the as-built surface topography of Inconel 718 parts. Design/methodology/approach Inconel 718 truncheon specimens with different process parameters, including single- and double contour laser pass, laser power, laser scan speed, build orientation and characterize their as-built surface topography using deterministic and areal surface topography parameters are printed. The effect of both individual process parameters, as well as their interactions, on the as-built surface topography are evaluated and linked to the underlying physics, informed by surface topography data. Findings Deterministic surface topography parameters are more suitable than areal surface topography parameters to characterize the distinct features of the as-built surfaces that result from LPBF. The as-built surface topography is strongly dependent on the built orientation and is dominated by the staircase effect for shallow orientations and partially fused metal powder particles for steep orientations. Laser power and laser scan speed have a combined effect on the as-built surface topography, even when maintaining constant laser energy density. Originality/value This work addresses two knowledge gaps. (i) It introduces deterministic instead of areal surface topography parameters to unambiguously characterize the as-built LPBF surfaces. (ii) It provides a methodical study of the as-built surface topography as a function of individual LPBF process parameters and their interaction effects.

Topology-defined bioactive properties of porous Ti-6Al-4V scaffolds produced by laser powder bed fusion

The effect of the design of additively printed Ti porous structures on their bioactive properties is elucidated by in vitro testing. 3D-printed scaffolds with pores defined by several bioinspired triply periodic minimal surfaces as well as by a strut model have been engineered. Cell proliferation, angiogenesis and osteogenesis have been studied with the help of multipotent mesenchymal stromal cells. The elementary unit size and pore design can notably modify bioactive properties of porous structures. The models providing maximal bioactive activity of developed scaffolds are discussed.

Assessing the Corrosive Effects of Unmelted Particles in Additively Manufactured Ti6Al4V: A Study in Simulated Body Fluid

This study investigates the corrosion behavior of Grade 23 Ti6Al4V alloys produced through laser powder bed fusion (L-PBF) when exposed to simulated body fluid at room temperature, focusing on the role of unmelted particles. This research aims to understand how these microstructural features, resulting from the additive manufacturing process, influence the corrosion resistance of the alloys. It was observed that unmelted particles serve as critical sites for initiating localized corrosion, including pitting, which significantly compromises the material’s overall durability. Electrochemical testing and detailed surface analysis revealed that these particles, alongside other defects such as voids, exacerbate the susceptibility to corrosion in biomedical environments where high material reliability is paramount. Weight loss measurements conducted over exposure periods of 48 h, 96 h, and 144 h demonstrated a progressive increase in corrosion, correlating with the presence of unmelted particles. These findings underscore the importance of optimizing L-PBF processing parameters to minimize the formation of unmelted particles, thereby enhancing corrosion resistance and extending the operational lifespan of Ti6Al4V implants in biomedical applications.

Laser powder bed fusion in-situ alloying of W-Y alloy: Microstructure, mechanical properties and cracking suppression

The microcracks caused by impurity oxygen are recognized as one of the main challenges in additive manufacturing of tungsten. In this study, yttrium was incorporated into the tungsten matrix to suppress crack formation, and W-Y alloys with minimal cracks were successfully obtained by laser powder bed fusion (LPBF). It is found that during the LPBF process, yttrium combines with impurity oxygen to generate intergranular and intragranular precipitated particles in situ, which effectively suppress cracking behavior due to impurity oxygen. Furthermore, these intracrystalline nanoprecipitate are cubic Y2O3 particles that have formed a semi-coherent interface with the tungsten matrix. These dispersed particles significantly improved the mechanical properties of W-Y alloy. The results offer a corresponding strategy for crack suppression of tungsten alloys in laser additive manufacturing processes, and would provide a benificial additive manufacturing strategy to other refractory alloys.

Flexural performance of high strength-to-weight ratio strut-based and surface-based lattice-structured Inconel-718 parts manufactured by laser powder bed fusion

Flexural performance of high strength-to-weight ratio strut-based and surface-based lattice-structured Inconel-718 parts manufactured by laser powder bed fusion

Effect of laser power during laser powder bed fusion on microstructure of joining interface between Tungsten and AISI 316L steel

This study investigates the deposition of tungsten (W) onto a 316L steel substrate by laser powder bed fusion (L-PBF), to optimize process parameters and analyze the interface between W and 316L. To obtain high-density W structure (98.89%), the optimal laser power was 350 W, and scan speed was 500 mm/s, but these parameters cause significant dilution of W in the W-316L interface; as a result, Fe7W6 intermetallics form, despite L-PBF being a non-equilibrium solidification process. These intermetallics which are brittle could degrade joint strength. By reducing laser power below 250 W, the dilution of W can be mitigated, and potentially minimize formation of intermetallics and increase joint stability for advanced manufacturing applications.

Unveiling the cellular microstructure–property relations in martensitic stainless steel via laser powder bed fusion

Unveiling the cellular microstructure–property relations in martensitic stainless steel via laser powder bed fusion

A comprehensive study of LPBF parameter influence in 316L stainless steel mechanical properties, macrostructure, and printability

Additive manufacturing, particularly using Laser Powder Bed Fusion (LPBF) technologies with 316L stainless steel, has proven highly promising in biomedical engineering due to the material’s exceptional mechanical properties and biocompatibility. This study, which is a foundational step towards developing porous bone implants, focuses on assessing the influence of a broad range of parameters - spot size, scanning speed, laser power, and energy density - on the mechanical performance and structural integrity of 316L stainless steel parts across three distinct specimen geometries: fully dense parallelepipedic, fully dense cubic, and cellular (lattice) specimens. By analysing 17 different parameter sets and producing over 150 specimens, a thorough series of experimental tests were conducted, including flexural tests, compression tests, hardness tests, macroscopic evaluation of the surface of fully dense specimens, and macroscopic evaluation of the lattice structures.e in powder accumulation within the pores of cellular structures, with higher energy densities (100 J/mm3) leading to a significantly greater retention compared to lower energy densities (66 J/mm3). This underexplored phenomenon has significant implications for the selection of parameters in the fabrication of bone implants. Further research is needed to refine LPBF printing parameters and enhance the quality of porous bone implants.

Improvements in mechanical property and corrosion resistance of Ti-6.5Al-2Zr-1Mo-1V fabricated by laser powder bed fusion using cost-effective modified hydride-dehydrided powder

Due to higher mechanical properties and shorter fabrication time, Ti-6.5Al-2Zr-1Mo-1V (TA15) fabricated by laser powder bed fusion (LPBF) is gaining increasing attention. However, the high cost of raw powder limits its wide application. In this study, TA15 is fabricated by LPBF using cost-effective modified HDH powder (LPBF-ed modified HDH). Microstructure, mechanical properties, and corrosion resistance of the fabricated sample are investigated and compared systematically with sample fabricated by LPBF using gas atomization (GA) spherical powder (LPBF-ed GA). The result shows that both two samples can achieve full density at the optimized process parameters and consist of α′ phase. But compared with LPBF-ed GA sample, the volumetric energy density (VED) of LPBF-ed modified HDH decreases about 60 % (41.15 vs. 94.65 J/mm3), which makes the LPBF-ed modified HDH sample exhibit finger grain size (decreasing from 0.231 μm to 0.129 μm). Such differences together with different interstitial element content result in LPBF-ed modified HDH samples exhibiting higher mechanical properties and corrosion resistance compared with LPBF-ed GA sample, namely tensile strength and elongation improves about 10 % (from 1286.1 MPa to 1353.7 MPa) and 100 % (from 5.8 % to 11.2 %), respectively, while corrosion current density (Icorr) and passivation current density (Ip) reduces about a half (from 2.98 × 10−8 A/cm2 and 4.07 × 10−6 A/cm2 to 1.03 × 10−8 A/cm2 and 2.54 × 10−6 A/cm2, respectively). Furthermore, the cost analysis result indicates that the cost of modified HDH powder was reduced by 60 % compared with GA powder (50 vs. 120 $/kg). Cost-effective raw materials together with a good combination of tensile strength and elongation and excellent corrosion resistance make LPBF-ed modified HDH parts exhibit broad application prospects, especially in the fields of aviation and maritime.

Evading intermediate temperature embrittlement of FeCoCrNiMn high entropy alloy via N-doping

High entropy alloys (HEAs) exhibit high strength and excellent ductility at both room and low temperatures. The loss of ductility with increasing the tensile temperature above room temperature has been widely observed in single phase face-centered cubic structured HEAs. In this work, a N and Si doped FeCoCrNiMn-(N,Si) HEA with preexisting nano-sized Cr2N particles was fabricated by laser powder bed fusion (LPBF) and subsequent cold-rolling and annealing treatment. Tensile testing was conducted on the alloy at 298 K, 573 K, 773 K, 873 K, and 973 K, respectively. It has been shown that the FeCoCrNiMn-(N,Si) alloy with preexisting Cr2N phase exhibits a steady ductility with increasing the tensile temperature. The intermediate temperature embrittlement is evaded in the FeCoCrNiMn-(N,Si) alloy via N-doping. The widely reported loss of ductility with increasing deformation temperature was avoided in present FeCoCrNiMn-(N,Si) HEA by shifting fast segregation of element Cr from GBs into preexisting Cr2N phase due to the high affinity between N and Cr elements, leading to the increases in the content and size of Cr2N particles after high temperature deformation.

Application of impact-based and laser-based surface severe plastic deformation methods on additively manufactured 316L: Microstructure, tensile and fatigue behaviors

Applying post-processing methods can play a crucial role in addressing defects inherent in the as-built state of additively manufactured materials. This study comprehensively examined the effects of various post-processing techniques, including surface severe plastic deformation (SSPD) methods such as severe shot peening (SSP), ultrasonic shot peening (USP), ultrasonic nanocrystal surface modification (UNSM), and laser shock peening (LSP), combined with stress relieving (SR) on the tensile properties and fatigue behavior of laser powder bed fusion (LB-PBF) stainless steel AISI 316L specimens. Experimental characterization was carried out, focusing on microstructure, porosity, surface texture, hardness, residual stresses, monotonic tensile properties, and rotating bending fatigue behavior. The results demonstrated an excellent combination of enhanced strength and ductility after applying SR and SSPD treatments. Additionally, the post-processing methods significantly improved fatigue behavior by increasing strength, closing subsurface pores, surface layer nanocrystallization and hardening, inducing compressive residual stresses, and modifying the surface texture. Notably, in the high-cycle fatigue regime at the lowest stress amplitude, the SR + UNSM treated specimens exhibited the greatest improvement in fatigue life, followed by SR + USP, SR + SSP, SR + LSP, and SR, when compared to the as-built state.

Optimizing AlSi10Mg Part Quality Aspects in Laser Powder Bed Fusion: A Literature Review

Optimizing AlSi10Mg Part Quality Aspects in Laser Powder Bed Fusion: A Literature Review

Powder bed fusion of solid and permeable Crofer 22 APU parts for applications in chemical process engineering

AbstractAdditive manufacturing of metals has attracted significant attention across various industries. However, its adoption in certain chemical and energy sectors remains constrained by the absence of optimized alloys tailored for high temperatures and corrosive environments. This study explores the laser-based powder bed fusion processing of Crofer 22 APU, a high-temperature, corrosion-resistant alloy ideal for applications such as methane steam reforming reactors, high-temperature fuel cells, and palladium membrane supports. Systematic optimization of laser parameters including laser power, hatch distance, point distance, and building angles was conducted for both dense and porous objects. Dense parts achieved a relative density of 0.9999 and surface roughness of Sa= 41.27±1.48 on a 45$$^\circ$$ ∘ overhang. Porous samples showed a porosity range of 28.655.5% and surface roughness Sa 22.2 $$\upmu$$ μ m to 45.9 $$\upmu$$ μ m as hatch distance increased from 0.12 mm to 0.16 mm. Additionally, an 8YSZ coating applied via screen printing demonstrated the impact of hatch distance and laser power on surface quality. The combination of additive manufacturing of Crofer 22 APU and screen printing of 8YSZ simplifies the preparation of metallic supports for Pd-based membranes, reducing fabrication time and cost by shortening the number of preparation steps. This technique offers a promising approach for scaling up membranes and membrane reactors.

Assessment of the mechanical and functional properties of nitinol alloys fabricated by laser powder bed fusion: Effect of strain rates

Laser Powder Bed Fusion-fabricated (LPBFed) nitinol shape memory alloys (SMAs), which undergo solid-solid phase transitions between austenite and martensite, are increasingly utilized in various technical fields and are subjected to a wide range of strain rates during service. This study pioneers the investigation of a comprehensive range of strain rates (3.16 × 10−6-10°/s), encompassing the strain rates used in quasi-static tensile tests reported in the existing literature, to understand their effects on the deformation mechanisms of LPBFed nitinol SMAs. Utilizing multi-scale characterization, including macroscopic mechanical evaluation, mesoscale analysis of deformation surfaces, and microscale examination of microstructure, we reveal distinct deformation behaviors at different strain rates. At lower strain rates, the mechanical behavior exhibits little sensitivity to changes in the strain rates, with stress-induced martensite transformation or martensite detwinning and variant reorientation being the primary deformation mechanisms. However, at higher strain rates, we observe significant variability in mechanical response, dominated by dislocation-induced slip and reduced occurrence of stress-induced martensitic transformation. This study provides the first comprehensive database for the engineering applications of LPBFed Nitinol SMAs and offers critical insights into optimizing mechanical and functional assessments for these advanced materials.

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.