Powder Reuse Research Articles

Revealing effects of powder reuse for LPBF-fabricated NiTi shape memory alloys

Revealing effects of powder reuse for LPBF-fabricated NiTi shape memory alloys

Effects of Powder Reuse and Particle Size Distribution on Structural Integrity of Ti-6Al-4V Processed via Laser Beam Directed Energy Deposition

In metal additive manufacturing, reusing collected powder from previous builds is a standard practice driven by the substantial cost of metal powder. This approach not only reduces material expenses but also contributes to sustainability by minimizing waste. Despite its benefits, powder reuse introduces challenges related to maintaining the structural integrity of the components, making it a critical area of ongoing research and innovation. The reuse process can significantly alter powder characteristics, including flowability, size distribution, and chemical composition, subsequently affecting the microstructures and mechanical properties of the final components. Achieving repeatable and consistent printing outcomes requires powder particles to maintain specific and consistent physical and chemical properties. Variations in powder characteristics can lead to inconsistencies in the microstructural features of printed components and the formation of process-induced defects, compromising the quality and reliability of the final products. Thus, optimizing the powder recovery and reuse methodology is essential to ensure that cost reduction and sustainability benefits do not compromise product quality and reliability. This study investigated the impact of powder reuse and particle size distribution on the microstructural and mechanical properties of Ti-6Al-4V specimens fabricated using a laser beam directed energy deposition technique. Detailed evaluations were conducted on reused powders with two different size distributions, which were compared with their virgin counterparts. Microstructural features and process-induced defects were examined using scanning electron microscopy and X-ray computed tomography. The findings reveal significant alterations in the elemental composition of reused powder, with distinct trends observed for small and large particles. Additionally, powder reuse substantially influenced the formation of process-induced defects and, consequently, the fatigue performance of the components.

Effect of Powder Reuse on Powder Characteristics and Properties of DED Laser Beam Metal Additive Manufacturing Process with Stellite® 21 and UNS S32750

In this work, the influence of powder reuse up to three times on directed energy deposition (DED) with laser processing has been studied. The work was carried out on two different gas atomized powders: a cobalt-based alloy type Stellite® 21, and a super duplex stainless steel type UNS S32750. One of the main findings is the influence of oxygen content of the reused powder particles on the final quality and densification of the deposited material and the powder catch efficiency of the laser deposition process. There is a direct relationship between a higher surface oxidation of the particles and the presence of oxygen content in the particles and in the as-built materials, as well as oxides, balance of phases (in the case of the super duplex alloy), pores and defects at the micro level in the laser-deposited material, as well as a decrease in the amount of material that actually melts, reducing powder catch efficiency (more than 12% in the worst case scenario) and the initial bead geometry (height and width) that was obtained for the same process parameters when the virgin powder was used (without oxidation and with original morphology of the powder particles). This causes some melting faults, oxides and formation of undesired oxide compounds in the microstructure, and un-balance of phases particularly in the super duplex stainless steel material, reducing the amount of ferrite from 50.1% to 37.4%, affecting in turn material soundness and its mechanical properties, particularly the hardness. However, the Stellite® 21 alloy type can be reused up to three times, while the super duplex can be reused only once without any major influence of the particles’ surface oxidation on the deposited material quality and hardness.

The Effect of Powder Re-Use on the Coalescence Behaviour and Isothermal Crystallisation Kinetics of Polyamide 12 within Powder Bed Fusion.

Polymer powder bed fusion (PBF) is becoming increasingly popular for the fabrication of lightweight, high-performance parts, particularly for medical and aerospace applications. This study investigates the effect of powder re-use and material aging on the coalescence behaviour, melt flowability, and isothermal crystallisation kinetics of polyamide-12 (PA-12) powder. With increased powder re-use, a progressive reduction in melt flowability and material coalescence is observed; at 200 °C, the particle consolidation time increases from 15 s in virgin powder to 180 s in powder recovered from build 6. The observed changes in the behaviour of PA-12 were attributed to polycondensation and cross-linking; these aging phenomena also create structural defects, which hinder the rate and extent of primary crystallisation. At an isothermal crystallisation temperature of 165 °C, the crystallisation half-time increased from 12.78 min in virgin powder to 23.95 min in powder re-used across six build cycles. As a result, the commonly used Avrami model was found to be unsuitable for modelling the crystallisation behaviour of aged PA-12 powder, with the co-efficient of determination (R2) reducing from >0.995 for virgin powder to as low as 0.795 for re-used powder. On the other hand, an alternative method, the Hay model, is able to successfully track full phase transformation within re-used powder (R2 > 0.99). These results highlight the importance of selecting the most appropriate model for analysing the crystallisation kinetics of PA-12 powder re-used across multiple build cycles. This understanding is crucial for obtaining the strong mechanical properties and dimensional precision required for the fabrication of functional, end-use parts within PBF.

Influence of Inconel 625 alloy powder reusing on feedstock characteristics and mechanical properties of deposited parts

Low utilization efficiency of powders limits the large-scale application of Laser Melting Deposition (LMD) and discussions on this topic are far from enough. So, this study was done with the aim to enhance powder reuse. Changes of Inconel 625 powders (compositions, morphology, size, flowability and sphericity etc.) in the 4 times of reusing were clarified. And the resulted effects on microstructures, inclusions and mechanical properties (microhardness and tensile properties) of deposited parts were also elucidated. It was found that reused powders were severely oxidized and indicated poorer flowability, with particle sizes increased after 1 and 2 times of reusing while decreased after 3 and 4 times of reusing. Number densities of inclusions in the deposited parts increased while grain sizes decreased in the powder reusing. Obvious changes in microhardness and tensile strength in deposited parts were not seen but the ductility only slightly decreased. The obtained results were meaningful to indicate that powder reusing was feasible, which would help save resources and reduce costs, thus to promote the competition of LMD.

Powder degradation as a consequence of laser interaction: A study of SS 316L powder reuse on the laser directed energy deposition process

The feedstock capture efficiency on powder laser directed energy deposition (L-DED) is becoming a big challenge in the industrial use of the L-DED process for the manufacturing of large-scale AM parts. The powder capture efficiency is dependent on process optimization and the toolpath. The current literature presents a vast range of usual powder efficiency, between 3% and 32% and in some specific cases exceeding 90%. In L-DED, the powder-gas jet stream interacts with the laser beam adding material locally onto the substrate. Part of this material is captured by the melt pool. The not captured material that is affected by the laser beam suffers degradation. In the literature, there is a lack of studies related to powder reuse in the L-DED process. This paper presents a comprehensive study on the consequence of laser interaction with SS 316L metal powder particles during the L-DED process using a range of different powder characterization techniques to assess the powder morphology, size distribution, chemical composition, followability, and density. The study was conducted within eight powder reuse cycles, without adding virgin material to the powder batch. Reduction of particle size distribution range, increase in circularity, and improvement in the powder flowability were identified as consequences of powder reuse. The result of laser interaction with particles was further explored by scanning electron microscopy, presenting the continuous modification of the particles across the eight reuse cycles. The oxygen content on the particles was also measured to access the O2 pick-up as a consequence of particle heating.

Powder Reuse and Regeneration by the Infiltration Technique in Electron Beam Melting (EBM)-powder Bed Fusion (PBF) Additive Manufacturing

Powder Reuse and Regeneration by the Infiltration Technique in Electron Beam Melting (EBM)-powder Bed Fusion (PBF) Additive Manufacturing

Re-use of polyamide-12 in powder bed fusion and its effect on process-relevant powder characteristics and final part properties

Powder bed fusion (PBF) is an additive manufacturing technique capable of fabricating highly complex, individualised, and lightweight polymer components. However, to maximise the potential of PBF, in terms of both economic efficiency and environmental sustainability, a successful powder re-use strategy is essential. During a build, ageing and degradation processes affect the re-usability of un-sintered powder, so used powder is usually refreshed with virgin material before re-use. This study considers the effectiveness of using a 70:30 refresh ratio in a specific PBF technique: laser sintering (LS). Across a total of seven printing cycles, polyamide-12 (PA-12) powder refreshed with 30 % virgin material after each build, revealed a 4.5 °C increase in melting temperature. There was also a 20 % reduction in particle flowability, which may be related to the presence of fine satellite particles and considerable particle cracking. This deterioration in powder quality resulted in a 5.8 % increase in total part porosity, and an 11 % reduction in the ultimate tensile strength of fabricated parts, over the seven build cycles. A Pearson correlation test indicated that the reduction in powder flowability was the most significant (p-value of 0.005) cause for the loss of part strength; emphasising that the revolution powder analyser could be a useful complimentary technique for determining the quality of used powder within laser sintering. Nonetheless, compared to previous studies which re-used 100 % aged PA-12 powder, without refreshing with any virgin material, the observed reduction in part strength is relatively modest. This suggests that a 70:30 refresh ratio offers a good compromise between maintaining part performance, particularly for non-critical applications, without having to add an unnecessary amount of virgin powder. Therefore, this study reveals the relationship between the deterioration of powder properties and reductions in part strength; yet highlights the benefits of operating with a 70:30 refresh ratio when re-using PA-12 powder across multiple build cycles.

Effects of Ni-based powder reuse on porosity, surface quality and reproducibility of thin-walled structures in Laser Powder Bed Fusion process

Inconel 718 alloy parts were manufactured by a laser powder bed fusion (PBF-LB) process using virgin and reused nickel-chromium powder produced by an argon gas atomization. PBF-LB is an emerging technology for the additive manufacturing of metallic end-products with complex shapes. At the same time, optimization of the PBF-LB parameters and powder reuse/recycling evaluation are required to achieve high-quality manufactured superalloy products for a critical manufacturing sector, such as aeronautical and aerospace applications. This paper focused on studying the effects of virgin and reused powders after 10 iterations on the powder properties and material density, surface roughness/topography of the PBF-LB-built superalloy parts, as well as repeatability of thin-walled structures. Results showed that the oxygen content and particle size of the reused powder increased. In addition, the micro-porosity and surface roughness values varied depending on the amount of reused powder. The quality and repeatability of the thin-walled structures are improved after increasing the number of builds.

Environmental and Economic Sustainability Impacts of Metal Additive Manufacturing: A Study in the Industrial Machinery and Aeronautical Sectors

Metal additive manufacturing has emerged as a promising alternative to conventional manufacturing in various industries, offering advantages like complex geometries and reduced material waste. However, there is a research gap in the form of comparative and industry-specific investigations and case studies to comprehensively assess the environmental and economic impact of metal additive manufacturing.This study focuses on two significant sectors, industrial machinery and aeronautics, to understand how metal additive manufacturing influences environmental and economic sustainability compared to conventional manufacturing. Therefore, taking a life cycle approach, the environmental and economic impacts of this technology are evaluated and compared to conventional manufacturing through representative case studies in the two sectors using life cycle assessment and life cycle cost methodologies.The economic evaluation reveals that metal additive manufacturing reduces the total cost for aeronautical components by 33.2 %, even considering several post-processing operations. While for industrial machinery parts, this cost increases by 79.3 % due to high machine and material cost. However, this technology reduces the potential environmental impact by more than 60 % for both sectors, mainly due to reduced material consumption. The use phase for aeronautical components further contributes to environmental and economic benefits, with significant fuel and CO2 emissions savings. The results emphasize the sector-dependent nature of metal additive manufacturing's environmental and economic impact and underscore the importance of a life cycle perspective for informed decision-making.Some critical points for sustainable adoption of metal additive manufacturing in each sector are equipment investment, the post-processing applied, the material selected or, for the aeronautical industry, the impact of the use phase. Nevertheless, future developments are needed to address powder reuse, optimization, certification, and the social impact of metal additive manufacturing.

Recycling selective laser melting alloy powder on cobalt chromium-to-ceramic bond strength

Statement of problemReusing the powder in selective laser melting machines after multiple cycles is a cost-effective procedure for dental laboratories. However, information on the metal-ceramic bond strength of the framework fabricated by using recycled powder is lacking. PurposeThe purpose of this in vitro study was to investigate how the bonding agent and repeated alloy powder reuse affected the metal-ceramic bond strength of cobalt chromium frameworks fabricated by using selective laser melting. Material and methodsFour square and 40-bar-shaped cobalt chromium frameworks were fabricated by selective laser melting. Half were produced by using virgin alloy powder (Group V; nsquare=2, nbar=20), and half with 30-times reused powder (Group R; nsquare=2, nbar=20). The particle size of each powder was measured by using scanning electron microscopy, and its phase composition was characterized by using radiograph diffraction. Each group was divided into 2 subgroups (Group W [Wash Opaque] and Group N [NP-Bond]) according to the brand of bonding agent used. After ceramic application, the metal-ceramic bond strengths were evaluated by using 3-point bend tests. The bonding agents’ chemical composition was analyzed by using radiograph fluorescence. Bond strength data were analyzed by using a 2-way analysis of variance (α=.05). ResultsMean ±standard deviation bond strengths did not differ significantly (P>.05) between Groups V (31.25 ±4.65) and R (30.88 ±4.78). Group W (35.34 ±1.78) had significantly higher bond strength than Group N (26.80 ±1.74; P<.001). Radiograph diffraction analysis found that the phase composition of all powders was similar. The bonding agent in Group W contained cerium, whereas, that in Group N did not. ConclusionsMetal-ceramic bond strength was unaffected by alloy powder reuse. However, the bonding agent brand may affect the bond strength of cobalt chromium frameworks fabricated by using selective laser melting.

An all-encompassing study on the joint effect of powder feedstock characteristics and manufacturing process parameters on the densification and mechanical properties of additively manufactured nickel alloy 718

Laser-powder bed fusion (L-PBF) is a commonly employed additive manufacturing (AM) technique in manufacturing 3D metallic parts with complex geometries from powder materials. It is a complex process with more than 100 process parameters affecting the properties of fabricated parts. Studies on AM of nickel alloy 718 are currently focusing on investigating the effect of the process parameters and heat treatment on final part properties. Nevertheless, the effect of different powder characteristics such as particle size distribution (PSD), the presence of fine particles, powder reuse, and moisture content has not been studied comprehensively in the literature. In this study, two types of powder: virgin and recycled, as well as four parameters: PSD, which is represented by the median particle size and the particle size range, moisture content, and volumetric energy density (VED), were studied. To reduce experimental cost and burden, statistical design of experiment (DOE) techniques were utilized. Then, the measured results were analyzed using analysis of variance (ANOVA) to ascertain the effect of the different powder characteristics on multiple quantities of interest (QoIs). Different densification and mechanical tests were performed, and their outputs were studied as the QoIs. This study revealed that VED, powder type, PSD range, and median are the most common significant factors for most QoIs. Meanwhile, moisture content had a significant effect only on the Charpy impact energy. Besides, the study showed that the presence of fine particles <20μm improved the densification of the fabricated parts but reduced the mechanical properties.

Study on the influence of oxygen content evolution on the mechanical properties of tantalum powder fabricated by laser powder bed fusion

In this work, the influence of reuse times on the properties of tantalum powder and its laser powder bed fusion (LPBF) product was investigated. For this purpose, a batch of tantalum powder was reused up to 16 times, and the particle size distribution, flowability, surface topography, and other characteristics of the powder were studied after different reuse times. The mechanical properties of the finished product samples were also tested. Results from the powder reuse showed that the particle size distribution of tantalum powder changed from 30.1 μm to 33.8 μm, and the oxygen content increased from 310 ppm to 450 ppm. The density and fracture strain of tensile specimens decreased from 16.57 g/cm3 to 16.48 g/cm3 and from 37.9% to 11.6%, respectively. The ultimate tensile strength and microhardness decreased after reaching a peak, ranging from 504 MPa to 614 MPa, and 227 HV to 245 HV, respectively. In addition, it was found that the oxides were mainly tantalum pentoxide, along with monovalent and bivalent oxides. The change in tensile properties was likely related to the interstitial solution of oxygen atoms. This study provides a reference for the reusability of LPBF tantalum powder.

Comparative analysis and characterization of used and unused Alsi10mg powders

Reducing waste through powder reuse is one way to overcome the economic barrier brought on by the high cost of metal additively produced components. As a result, this study aimed to thoroughly characterize four AlSi10Mg metal powders from two various manufacturers, used and unused, as well as sieved and un-sieved. Analysis of various parameters such as the static angle of repose (AOR), particle shape, particle size distribution, and the angle of internal friction (AIF) were calculated. Based on AOR and flowrate, it was found that the virgin powder from the first manufacturer has better flow characteristics and shape than the other powders. It was showed that Virgin powder, used sieved powder, and used un-sieved powder of manufacturer 2, have higher AIF values than the Virgin powder of manufacturer 1, implying that they can sustain lateral stresses better. According to the experiment, sieved, previously used powders can still be employed in additive manufacturing.

Maraging steel powder recycling effect on the tensile and fatigue behavior of parts produced through the laser powder bed fusion (L-PBF) process

Additive manufacturing (AM) has advanced the manufacturing industry and has been employed in a wide range of industrial applications, including aerospace, automotive, medical, and die-casting equipment. To ensure the cost-effectiveness of the AM process, unfused powder must be recycled even if its characteristics may change after each cycle, making essential the validation of powder quality and component mechanical performances. Despite the research published to date, predicting the mechanical performance of printed parts issued from reused powder remains challenging since it is dependent on many AM process variables. Until now, no research has looked at the impact of powder recycling on the fatigue behavior of maraging steel components. This study investigates the impact of maraging steel powder reuse on powder characteristics, as well as on the tensile and fatigue properties of printed components. Our results indicate that the powder particle size distribution increased after eight powder reuses, particle morphology showed the presence of aggregates, broken particles, and shattered and deformed particles, while powder apparent density remained constant. Powder reusing had no significant impact on the surface roughness of as-built specimens. Although there was a slight decrease in mechanical properties over reuse cycles, tensile and fatigue performance remained globally stable, while the standard deviation of fatigue stress became narrower after eight cycles. Finally, fractography revealed that the fatigue fracture surfaces of components manufactured from an eight-time recycled powder have more fusion defects and carbon inclusions than the parts made from virgin powder.

Influence of oxygen content on melt pool dynamics in metal additive manufacturing: High-fidelity modeling with experimental validation

In the metal additive manufacturing process, the exposure to oxygen and its incorporation into the melt pool are usually deemed unfavorable, but cannot be completely eliminated. Yet, the understanding of this inevitable process remains limited. This work aims to shed light on the effect of oxygen content on melt pool dynamics through multiphysics thermal-fluid flow simulations of the laser powder bed fusion process. Our simulations reveal that oxygen sources from the powder, base plate and oxygen absorption from the atmosphere influences the melt pool dynamics. Although changes in oxygen content barely affect melt pool dimensions, they induce huge differences in the melt pool dynamics and the corresponding material composition distribution within the melt pool. Moreover, our model further clarifies and explains observed experimental phenomena. We demonstrate that the melt pool flow characteristics are responsible for the formation of oxygen-rich streaks observed in experiments regardless of inward or outward Marangoni circulation, while previous experimental studies attributed that to the outward circulation. Additionally, we show that sulfur content minimizes the effect of oxygen on Marangoni flow in iron alloys, and thus leads to the apparent consistency of surface roughness for additively manufactured iron alloys. This work is a fundamental development towards modeling for additive manufacturing under reactive atmospheres and provides unprecedented details on the effects of oxygen on melt pool dynamics. Consequently, this work can further offer practical guidance on powder reuse and adjusting manufacturing parameters for reused powders, thereby improving the sustainability of additive manufacturing.

Toward a sustainable laser powder bed fusion of Ti 6Al 4 V: Powder reuse and its effects on material properties during a single batch regime

Titanium alloy Ti6Al4V is the most used titanium alloy due to its high specific strength, ductility, corrosion resistance, and weldability. Currently, this alloy is produced with a density above 99% with laser welding-based additive manufacturing processes. However, the costs of titanium powder are high, and for critical components, the excess powder is usually not reused. In this work, we characterized the powder and additively manufactured Ti6Al4V parts by reusing the powder of a single batch to determine the impact on morphology, chemical composition, melt pool viscosity, density, microstructure, and tensile and impact strength. We aimed to determine the limits of powder reuse to increase sustainability and reduce the carbon footprint of Laser Powder Bed Fusion (L-PBF). We found that the powders pick up oxygen after each cycle to form an oxide layer up to 20 nm, causing a change in the optical and thermal properties of the titanium powders. This change affected the laser absorption and, with this, the melt pool properties. The powders reused after 18 cycles were responsible for a drop in the relative density of 0.1%. However, the tensile properties remained unchanged. The reused powders also presented a small shift in particle size distribution that did not affect the sphericity and increased flowability. In this work, we proved that the powders of Ti6Al4V alloys could be reused up to 18 cycles without any modification to the tensile properties but with a decrement in the impact strength of 30% for vertical- and 12% for horizontal stress-relieved specimens and 19% and 16% for furnace-annealed specimens, respectively.

Mechanical properties of laser powder directed energy deposited NASA HR-1 superalloy: Effects of powder reuse and part orientation

The feasibility of NASA HR-1 powder reuse for laser powder directed energy deposition (LP-DED) of thin-walled structures in the as-built surface condition was investigated in this study. Although continuously reusing the powder five times slightly reduced the number of fine particles in the powder and increased the mean particle size, changes in powder rheological properties were negligible. The similarities in powder flow between all reused conditions resulted in no variation in surface roughness, defects’ size and spatial distributions, and microstructure of the as-deposited parts and, thus no differences on tensile and fatigue properties. The effects of different specimen orientations, loading direction being perpendicular or parallel to the building direction, on mechanical properties were also investigated. While no change in tensile strength was noted, tensile ductility was lower for the parallel specimens because of surface micro-notches being perpendicular to the loading direction, which led to an early onset of fracture. Due to accelerated crack initiation from these micro-notches, parallel specimens were also less resistant to fatigue failures. The fatigue failures always initiated from the specimen surfaces, and all specimens experienced a ductile fatigue crack growth mechanism characterized by clear striations on the fracture surface.

Sustainability assessment of feedstock powder reuse for Directed Laser Deposition

In this paper, the results of a sustainability assessment for the study of the reuse of un-melted feedstock powder in Directed Laser Deposition are reported. Ti6Al4V ELI powder was employed as material for the study and the un-melted powder was collected and reused as raw material for subsequent cycles of deposition. A total of three deposition cycles were completed and data for a Life Cycle Assessment were compiled. From the experimental work results, the un-melted powder suffered minimal changes that did not affect the critical characteristics analysed. The Life Cycle Assessment showed that reusing the powder, and consequently reducing the total mass of raw material consumed, resulted in significant environmental benefits. All the categories considered saw approximately a 15%–25% environmental impact reduction when reusing the powder as compared to a scenario when only virgin material is used. Most of the environmental footprint was seen in the production of the powder as compared to the transportation and manufacturing stages. The production phase, when reusing and when using only virgin powder, accounted for 89% and 95% of the total environmental impact respectively. This meant the environmental benefits due to the lower mass of powder used far outweighed the increase in water and energy required for the powder reuse process in the manufacturing stage. Thus, feedstock powder reuse in Directed Laser Deposition process is seen to have a significant environmental benefit as compared to the usage of virgin powder alone.

Cyclic Deformation Behavior of Additive-Manufactured IN738LC Superalloys from Virgin and Reused Powders.

In laser powder bed fusion (L-PBF), most powders are not melted in the chamber and collected after the printing process. Powder reuse is appreciable without sacrificing the mechanical properties of target components. To understand the influences of powder reuse on mechanical performance, a nickel-based superalloy, IN738LC, was investigated. Powder morphology, microstructure and chemical compositions of virgin and reused powders were characterized. An increase in oxygen content, generally metallic oxides, was located on the surface of powders. Monotonic tensile and cyclic fatigue were tested. Negligible deterioration in strength and tensile ductility were found, while scattered fatigue performance with regard to fatigue life was shown. Deformation and fatigue crack propagation mechanisms were discussed for describing the powder degradation effects.