Powder Batches Research Articles

Influence of print-chamber oxygen content on the microstructure and properties of 3D-printed 316L

Abstract Samples of 316L stainless steel have been prepared using laser-powder bed fusion from the same batch of powder using different print-chamber oxygen levels, ranging from 50 ppm to 1500 ppm. The oxide particle density is found to increase with oxygen content, while the cell structure is invariant with oxygen level and the grain size shows a relatively sharp transition for measured oxygen levels of above 450 ppm. Based on the microstructural observations it is suggested that the increasing oxygen levels leads to a transition in the solidification pattern. Samples printed at the higher oxygen level show higher strength and lower mechanical anisotropy than samples with a coarser grains structure printed at lower oxygen levels. The main influence of the higher oxide particle content on thermal stability is on the kinetics of recrystallization during isothermal annealing at 1000 °C.

A Simulation Study on Sieving as a Powder Deposition Method in Powder Bed Fusion Processes.

Powder deposition of even and homogeneous layers is a major aspect of every powder bed fusion process. Powder sieving is commonly performed to powder batches outside of the PBF machine, prior to the part manufacturing stage. In this work, sieving is examined as a method of powder deposition rather than a method to solely filter out agglomerates and oversized particles. Initially, a DEM powder model that has been validated experimentally is implemented, and the sieving process is modelled. The sieving process is optimized in order to maximize mass flow, duration of its linear stage and total mass sieved during linearity. For this, a Taguchi design of experiments with subsequent analysis of variance is deployed, proving that the larger the initial powder loaded in the sieve, the larger the sieve stimulation necessary, both in terms of oscillating frequency and amplitude. The sieve's aperture shape is also evaluated, proving that the more sides the canonical polygon has, the less the mass flow per aperture for the same maximum passing particle size. Then, the quality of the layer produced via controlled sieving is examined via certain layer quality criteria, such as the surface roughness, layer thickness deviation, surface coverage ratio and packing density. The findings prove that controlled sieving can outperform powder deposition via a non-vibrated doctor blade recoater, both in terms of layer surface quality and duration of layer deposition, as proven by surface skewness and kurtosis evaluation.

Influence of pressure and powder characteristics on the properties and microstructure of Colmonoy-5 alloy sintered by spark plasma sintering

This study investigates the microstructure and final properties of Colmonoy-5, a nickel-based hardfacing alloy, consolidated via spark plasma sintering (SPS) as an alternative to traditional welding deposition on stainless steel substrates. Two batches of Colmonoy-5 alloy powders with different particle sizes used for sample processing. Sintering occurred at 900 °C under pressures of either 50 MPa or 60 MPa for 15 min. The evaluation of the sintered samples included density measurement through Archimedes' method, morphology assessment via confocal microscopy, phase composition analysis by X-ray diffraction (XRD), microstructural examination using scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), and hardness testing by Vickers method. Findings indicate that SPS is an effective technique for producing Colmonoy-5, achieving satisfactory densification. The study also reveals that the initial morphology of the precursor powders can influence the size of phases precipitated within the nickel matrix. Sintering pressure of 50 MPa seems to be the most effective in processing Colmonoy-5 via SPS.

Effect of Astroloy powder characteristics on mechanical properties of Powder-HIP components

Astroloy, Ni-based superalloy, with a high-volume fraction of γ', is beneficial for high temperature applications but, at the same time, has limited forgeability. For this reason, powder metallurgy (PM) is the only viable processing route for this alloy. In particular, Near Net Shape powder-HIPping (NNSHIP) is attracting much interest since it offers a possible solution to the high cost of PM production by reducing the amount of post-process forging and machining steps. However, this method still has some issues to overcome, such as the presence of prior particle boundaries (PPBs) decorated with carbides and/or oxides, which drastically reduce the material's mechanical properties. Many studies have attempted to solve this issue by optimizing HIP cycles and heat treatments (HTs), although powder characteristics, more specifically interstitial content, affect PPB presence and mechanical properties of HIP + HTed material. Additionally, powder boron content can have a major effect on material microstructure and mechanical properties. In this work, four powders with different particle size distribution (PSD), oxygen, carbon and boron content were studied. In doing so, the four powder batches and their HIP + HTed samples were fully characterized in terms of chemical composition, grain size and γ' system, and these properties were linked to the mechanical properties of the samples in order to define optimized powder characteristics. The optimized powder demonstrated more than 23 vol % of tertiary γ' due to a high boron content (259 ppm), a carbon content below 160 ppm, and an oxygen content below 150 ppm. With these characteristics, HIP + HTed Astroloy component obtained an improvement, with respect to the aeronautical AMS 5852B standard, of 7 % in ultimate tensile strength (UTS), 3 % in yield strength (YS), 84 % in elongation, 29 % in impact toughness and 22 % in hardness at room temperature. Additionally, at high temperatures, 760 °C, values are around the standard demands with an increase of 2 % in YS and a decrease of 7 % in UTS and 28 % in elongation, being the last one the best result obtained among the tested powders; also impact toughness at 760 °C presents a value close to room temperature requirements with 30 J.

On the potential of eddy current characterization of the ferritic content of recovered 316L powders after LaserPowder bed fusion fabrication

An original container was designed to measure the ferritic content of powder batches by the Eddy Current (EC) technique. As opposed to the standard X-Ray Diffraction (XRD) or Electronic BackScatter Diffraction (EBSD) methods, the EC measurements can be implemented on powder batches of significant sizes, say a hundred grams or so. Using a methodology based on the multiple recycling of an initially ferrite-free virgin powder, it was shown that the EC signals are sensitive to the ferritic content of the recovered powder. On the other hand, in the frequency range scanned by the sensor, the EC signals are virtually independent on the oxygen concentration within the tested powder.

Insights into the assessment of spreadability of stainless steel powders in additive manufacturing

This work investigates the link between the single particle and bulk flow properties of stainless steel (SS316L) powders and their spreading behaviour for additive manufacturing (AM) application. Two different batches of SS316L powders, noted to have significantly different spreading behaviour in AM machines, were investigated. The two batches had almost identical particle size, morphology and bulk flow properties as quantified by angle of repose, Hausner ratio, Carr index and basic flow energy; however one of the batches did not consistently flow during Hall and Carney flow tests and also had very poor spreadability when evaluated using an in-house spreading rig. The flow and spreading behaviours of the poorly spreading batch significantly improved and became almost identical to the good batch when tested following drying, either in a vacuum oven or a freeze dryer. Elemental analysis revealed that batches had some small but significant differences in chemical composition. This study revealed the complexity of defining a correlation between powder properties and spreading behaviour, and the importance of considering the environmental conditions.

Optimization of the Zhou Tian Formula extraction technology based on AHP-CRITIC method and analysis of transfer efficiency of key components based on HPLC fingerprinting.

Zhou Tian Formula (ZTF) is an antidepressant traditional Chinese medicine utilized widely in clinical settings for the treatment of patients with depression. However, shortcomings persist in its extraction technology and quality control. This study aimed to propose a methodology for ZTF extraction technology based on the analytic hierarchy process (AHP)-criteria importance through intercriteria correlation (CRITIC) method and to establish a quality control framework for the efficient transfer of index components. Firstly, we analyzed the chemical components of ZTF and determined the optimal extraction technology. Secondly, we calculated the transfer efficiency of the index components during the conversion of water decoction to extract powder and subsequently to granules. Thirdly, we established HPLC fingerprints for 15 batches of ZTF water decoction, extract powder, and granules. We employed SIMCA software to analyze the chemicals responsible for variations in quality among different batches of ZTF granules. We determined the optimal extraction process. The average transfer efficiency of ferulic acid, puerarin, mirificin, isoferulic acid, and calycosin during the conversion of water decoction to extract powder and subsequently to granules exceeded 41%. The HPLC fingerprints of ZTF exhibited a similarity exceeding 0.890. Variable importance in projection values indicated that calycosin, ferulic acid, and puerarin were the primary contributors to quality variations. The AHP-CRITIC method, coupled with an orthogonal array design, could be used for exploring extraction technology. In addition, the rules governing the transfer of index components from water decoction to extract powder, and subsequently to granules, could be applied for the evaluation and quality assessment of ZTF.

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.

Impact of Electron Beam Melting process recycling on defects and microstructure of Ti-6Al-4V powders

Metal powders are used as the feedstock material during the Electron Beam Melting processes. The process involves using an electron beam as the energy source to produce intricate parts with complex shapes in a layer-by-layer production system. The electron beam is directed by information from an STL file, and the process takes place in a pre-heated chamber that is maintained under vacuum. Once the production cycle is complete, the process yields the desired components along with a certain amount of residual powders that were not melted.To improve process efficiency and reduce costs associated with powder atomization, it is feasible to reuse the excess powder for subsequent production cycles. Prior to starting a new cycle, the excess powder is initially sieved to ensure a more uniform powder batch, and subsequently, the sieved powder can be mixed with other virgin powder to decrease oxygen content.This study examines the microstructure and defects present in a batch of virgin powders produced through plasma atomization and a batch of powders that were reused five times and mixed with Ti-6Al-4V grade 23 (ELI powders) at each cycle. The ELI powders are characterized by a low oxygen content.The results of the analysis indicate a connection between the powder atomization process and the formation of porosities in virgin powders resulting from trapped gas, as well as surface irregularities, including the presence of satellites. With an increase in the number of reuses, there is a reduction in the number of satellites, potentially due to surface partial melting due to the pre-heating of the EBM chamber, leading to rougher surfaces on the recycled particles.The microstructure of virgin powders is predominantly characterized by a fine acicular α’ phase, known as martensitic, formed due to the rapid cooling rate during the atomization process. Conversely, recycled powder tends to exhibit a coarser grain microstructure due to lower cooling rates. However, it is common to observe particles with a microstructure similar to that of newly manufactured powders, indicating that each individual particle has undergone a distinct thermal history.

Using ultrasonic atomization to recycle aluminium bronze chips for additive laser directed energy deposition

In the post-processing of large maritime components, a considerable amount of waste in the form of milling and grinding chips is produced. At the same time, additive manufacturing technologies have shown great potential in producing high-volume parts for maritime applications, allowing novel design approaches and short lead times. In this context, this study presents a sustainable approach to recycle and use aluminium bronze waste material, generated during post-processing of large cast ship propellers, as feedstock for laser-powder directed energy deposition. The recycling technology used to produce powder batches is inductive re-melting in combination with ultrasonic atomization. The derived metal powders are characterized using digital image analysis, powder flowability tests, scanning electron microscopy as well as energy dispersive X-ray spectroscopy. Compared to conventional metal powders produced by gas atomization, the recycled material shows excellent sphericity and a powder size distribution with a higher content of finer and coarser particles. Metallographic sections of deposited additively produced specimens show an increased hardness and reduced ductility, but also competitive densities and higher yield and ultimate tensile strength compared to cast material. The process chain shows high potential for the maritime sector to enable circular and sustainable manufacturing.

Preparation and Optimization of Ivabradine Hydrochloride Mouth-Dissolving Tablet

The aim of the present work was the preparation and optimization of mouth-dissolving tablets (MDTs) of Ivabradine hydrochloride by using natural super disintegrants. The tablets were prepared using microcrystalline cellulose as diluent and aspartame as a sweetening agent along with Natural super disintegrants. The natural super disintegrants used in this study were Guar Gum and Banana powder. By using natural superdisintegrants we had saved the environment and protected our bodies from the harmful effect of synthetic superdisintegrants. The tablet was prepared by the direct compression method. The 6mm of punch was used and the tablet weight is 110 mg. The tablets were evaluated for weight variation, hardness, friability, wetting time, disintegration time (DT), and dissolution study. Different concentration of superdisintegrants was used in this formulation as 6%, 8%, and 10%. The three batches of guar gum and 3 batches of banana powder were prepared i.e., a Total of six batches were prepared. From the results obtained, it can be concluded that the tablet formulation prepared with 10% banana powder i.e., 10 mg showed fast and higher drug release (98.66%) during in vitro dissolution study. Also, the hardness, friability, dissolution rate, and assay of prepared tablets (batch F6) were found to be acceptable according to standard limits. The result was the F6 batch was optimized batch from all the batches.

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.

Safety and quality evaluations of liquid milk and infant formula products in China in 2022

AbstractMilk serves two nutritional functions: it provides nutrition while also maintaining a healthy intestinal microenvironment. Thus, the safety and quality of milk products are critical for consumers' health. To evaluate liquid milk and infant formula products in China, we analyzed nine indices of 294 batches of pasteurized milk (PM), 92 batches of ultra‐high temperature milk (UHT), and 20 batches of infant formula milk powder (IF) collected from 21 provinces in 2022. All PM, UHT, and IF samples were satisfactory concerning aflatoxin M1 contamination, contamination by heavy metals, and residues of veterinary drugs and pesticides. The contents of lactoferrin, α‐lactalbumin, β‐lactoglobulin, furosine, and lactulose in the majority of samples met the group standards. Moreover, the contents of lactoferrin, α‐lactalbumin, and β‐lactoglobulin were higher in PM than in UHT, while furosine and lactulose contents showed the opposite trend. The findings concerning the safety and quality of milk products in China provide important insights to aid consumer preferences for milk products.

Influences of processing temperatures on the nature of polarization phenomena in 85% (Bi0.5Na0.5)TiO3-15%BaTiO3 with different strategies of bismuth oxide non-stoichiometry

Adding excessive metal oxide doping to a powder batch is a known way to compensate for the loss of volatile cation species during high temperature sintering. An important case in the piezoelectric ceramics is the bismuth oxide in the lead-free ferroelectric ceramic bismuth sodium titanate (BNT). Building from the earlier knowledge about excessive bismuth oxide's influences on the properties of BNT, we further note that varying the sintering temperature can both control the distribution of excessive Bi3+ and impact the relaxor/normal ferroelectric behaviors and corresponding phase transition. In addition to the nature of polarization, the sintering temperature also significantly manipulates the electrical conductivity. A hypothetical mechanism for the resistive grain boundary is proposed, based on inferences from electrical—microstructure—processing relations in 85% Bi0.5Na0.5TiO3-15% BaTiO3 with batched Bi2O3 excess and acceptor Mg2+ in a co-doped strategy.

Cracking susceptibility of maraging parts manufactured by laser powder bed fusion additive manufacturing: study on the powder characteristics and baseplate preheating influence

ABSTRACT Maraging steel 300 processed by laser powder bed fusion (PBF-LB/M) is widely used for manufacturing inserts and moulds with conformal cooling channels. For such applications, high fracture toughness and strength are required to withstand thermal fatigue and any defect like pores, lack of fusion and cracks should be avoided so that the durability of the mould is not reduced. Maraging steel is prone to be cracked due to thermal gradients which arise during PBF-LB/M. Moreover, it was recently observed that slight variations in composition led to the crack’s presence, which implied lower mechanical properties. In this study, two powder batches, from the same powder producer, were employed with the same processing parameters. The effect of small changes in minor elements composition of the powder batch on cracking was studied and the preheating temperature was varied to significantly reduce the crack density. The presence of cracks significantly reduced the ductility of the parts.

Electrospun HPMC/PEO-blend orodispersible films: how slight batch differences affect the crucial mechanical properties

Orodispersible films comprise a promising dosage form with a wide range of advantages compared to conventional formulations. The electrospinning process can significantly enhance the relevant characteristics of orodispersible films, e.g., the dissolution rate and the ease of administration. This study involved the use of two types of hydroxypropyl methylcelluloses of low molecular weight obtained from three different manufacturers as the matrix. The SEM, FTIR, RAMAN, and DSC analyses revealed comparable values for all the fabricated materials. However, the mechanical properties of the fibers differed significantly, with electrospun Methocel E5/PEO proving to be particularly brittle. This is probably caused by the different arrangements of substituted methoxy- and hydroxypropyl groups of studied HPMCs. It is hoped that this paper will serve as an example of the extent to which slight differences between HPMC powder batches can dramatically alter the key properties of electrospun orodispersible films.

Influence of powder size on defect generation in laser powder bed fusion of AlSi10Mg alloy

The particle size distribution (PSD) often changes as powders are cycled for recycled and different powder batches are used, challenging a critical aspect of quality assurance in the Laser Powder Bed Fusion (LPBF) process. It is therefore important to understand how powder PSD affects the processability of powder in the context of LPBF. In this work, a batch of AlSi10Mg powder was sieved into four sets of powder with controlled PSD (D50 ranging from 16 μm to 76 μm). Single-track and cuboid samples were made from powders with variations in laser power whiling fixing other laser processing parameters constantly. It is shown that coarser powders are much more sensitive to changes in laser power in terms of melt pool characteristics, defect population and size, showing significant improvements in relative density upon increasing laser power. The simulations reveal with the combination of low laser power and coarse powders, pores mainly originate from insufficient melting of powders at the sides of melt pools due to insufficient and inhomogeneous absorption of laser energy. It is possible to achieve nearly fully-dense parts when processing coarse powders given that the incident laser beam energy is sufficient.

Cadmium telluride for high-efficiency solar cells

Problems of the synthesis of cadmium telluride powders having required purity and grain size distribution for high-efficiency solar cells have been analyzed. A test batch of powders has been synthesized and used for the manufacture and study of thin-film solar cell specimens exhibiting parameters compliant with the best worldwide standards. The phase composition of the powders has been studied using X-ray diffraction. Structural analysis and elemental composition measurements have been carried out using electron microscopy. The effect of free tellurium phase in the powders on the endurance of devices manufactured from the powder has been described. We show that excess tellurium in the film specimens whose atoms are predominantly localized along grain boundaries may cause temporal degradation of the electrical properties of the manufactured solar cells due to changes in the parameters of the crystalline structure of the cadmium telluride phase which are caused in turn by changes in the stoichiometric composition of the material. Structural studies of the film specimens have not revealed differences in the film structure before and after endurance tests. A new cadmium telluride powder process route has been developed, proven and tested taking into account the advantages and drawbacks of the previously used process and experiments confirming the correctness of the technical solutions chosen have been conducted.

Computational investigation of particle segregation in capsule filling for hot isostatic pressing

Particle segregation, which is defined as location-dependent congregation of particles of similar size in a powder batch, can happen during the capsule filling step of hot isostatic pressing (HIP). Segregation can lead to microstructural and macrostructural flaws of the post-HIP compact. Since a systematic study of segregation with respect to filling parameters is not reported in the literature, the current work computationally investigates the effects of the geometry of the HIP capsule, the particle size distribution of the powder batch, the vibration frequency, amplitude and duration on segregation using discrete element method simulations. The results prove that cone shaped capsules are more prone to segregation, particularly if the direction of the flow of the particles is towards the tip of the cone. Particle size distributions with larger particles are more susceptible to segregation too. Moreover, higher frequencies and amplitudes increase segregation to different extents. Vibration duration initially reduces the segregation by a small amount and then reaches to an asymptote at a characteristic duration.

Influence of a prolonged shelf time on PA12 laser sintering powder and resulting part properties

In the laser sintering technology, the semi-crystalline polymer material is exposed to elevated temperatures during processing, which leads to serious material ageing for most materials. This has already been investigated intensively by various authors. However, the ageing of the material at ambient temperatures during shelf life has not been the focus so far. The need to analyse the shelf life can be derived from an ecological and economic point of view. This work is focusing on the shelf life of PA2200 (PA12). To reduce the potential influences of powder production fluctuations, two different powder batches stored for 5.5 years and 6.5 years are investigated and compared to a reference powder produced 0.5 years before these investigations. Multiple powder analyses and part characterisations have been performed. A significant yellowing and molecular chain length reduction can be derived from the measurement results. Whereas the influence on mechanical part performance was minor, the parts built with the stored powders are more yellowish. As it is most likely that this is due to the consumption of polyamide stabilisers, it can be assumed that these parts will be subject to significantly faster ageing. Therefore, it is still not recommended to use the stored powders for critical parts or light intense and humid environments.