Powder Batches Research Articles

Influence of temperature and time factor on process of spraying of metallic powders in a plasma atomizer

The development of additive technologies is hampered by the almost complete absence of domestic systems for the production of metal powders. A prototype installation of a plasma atomizer was developed and manufactured, which makes it possible to obtain low-tonnage batches of metal powders of various chemical compositions. However, when the technology was transferred from the laboratory to production, a number of additional issues arose associated with a decrease in the quality of commercial products as the time of continuous spraying increases. It was found that the reason for this is the formation of powder deposits on the walls of the spray chamber and the increase in its temperature. Using the method of mathematical modelling, the maximum permissible temperature of the walls of the spraying chamber was determined, ways of stabilizing the quality of the powder during industrial production were shown.

Single track scanning experiment on the hypereutectic aluminium alloy Al-8%Zn-7%Ni-3%Mg

Solidification path, hot tearing susceptibility and processability by L-PBF of the hypereutectic aluminium alloy Al-8%Zn-7%Ni-3%Mg were investigated. It was shown that the alloy has an advantageous hot tearing resistance due to formation of an adequate amount of the [(Al)+Al3Ni] eutectic and a reduced effective solidification range. In that sense, it may be valid for L-PBF. To prepare a feedstock for L-PBF, we produced chips which were subsequently grinded by high-energy ball milling into a 100 µm fine powder batch. The powder contained irregular shape particles that may have led to failure in fabrication of regular single tracks at a laser power of 170-250 W and scanning speed of 200-350 mm/s. Whilst from on-top view all the tracks had defects like balling and irregularity, their cross-sections also revealed a high degree of penetration into 5052 alloy substrate. Most structures showed a level of mixing of 5/1 between the substrate and the experimental alloy. The most successful track obtained at 250 W and 250 mm/s showed an inhomogeneity in distribution of the alloy-rich regions. Meanwhile, no defects and no primary Al3Ni phase were observed. The present study serves as an initial one for further research which may be focused on producing of a finer powder, assessment of different layer thicknesses and fabrication of bulk specimens.

Batch and Fed-Batch Ethanol Fermentation of Cheese-Whey Powder with Mixed Cultures of Different Yeasts

Eight yeast strains of Lachancea thermotolerans, Kluyveromyces marxianus, and Kluyveromyces waltii have been tested for their ability to ferment lactose into ethanol in mashes containing 10% (w/v) cheese whey powder (CWP). The K. marxianus NCAIM Y00963 achieved 3.5% (v/v) ethanol concentration at 96–120 h of fermentation. The ethanol production by the selected lactose-positive strains and the well-known ethanologenic Saccharomyces cerevisiae (Levuline Fb) in mixed culture was also investigated at different CWP concentrations and inoculation techniques in batch mode. The mixed culture in an equal ratio (1:1) of cell counts of K. marxianus and S. serevisiae showed an increase in lactose conversion rate. The two yeast strains in a ratio of 3:1 (three-quarters of K. marxianus and a quarter of S. cerevisiae in a total of 4.5 × 1010 cells) resulted in 72.33% efficiency of lactose bioconversion and 7.6% (v/v) ethanol production at 17.5% (w/v) of CWP concentration. In the repeated inoculation process, with the addition of three-quarter part of 3:1 ratio of mixed culture (3.3 × 1010 cells of K. marxianus) into 150 mL CWP mash at initiation and the rest quarter part (1.2 × 1010 cells of S. cerevisiae) at 24 h, 8.86% (v/v) ethanol content with 87.5% efficiency of lactose conversion was reached. Both the ethanol concentration and efficiency of bioconversion were increased to 10.34% (v/v) and 92%, respectively, by combination with fed-batch fermentation technology. Our results can serve a very good basis for the development of industrial technology for the utilization of cheese whey.

Effects of powders and process parameters on density and hardness of A357 aluminum alloy fabricated by selective laser melting

Additive manufacturing processes based on the local fusion of a powder bed, such as selective laser melting (SLM), are a valid alternative to conventional technologies and a growing number of industrial sectors are currently relying on these processes for the production of different components. However, there are still some limits in using SLM and they are often related to the feedstock material. For this reason, in the present work, the effects of powder properties and pre-treatments, as well as process parameters, on the fabrication of aluminum alloy A357 samples were investigated. Two different batches of powder were considered in order to evaluate the effects of particles shape and size in the as-received condition and after two different pre-treatments: 60 °C for 3 h and 200 °C for 1 h. Selective laser-melted samples were produced in the conditions described above and were then characterized in terms of density, phase and chemical composition, defects, and hardness. The results showed a correlation between powder conditions in terms of morphology and pre-treatment on the properties of SLM A357 aluminum alloy components.

Incremental solidification (toward 3D-printing) of metal powders by transistor-based microwave applicator

Incremental solidification (IS) of small batches of metal powders is a fundamental process in various additive-manufacturing (AM) and 3-D printing (3DP) operations. Here we show the feasibility of an IS process implemented by a compact, all-solid-state microwave applicator. In this compact scheme, the localized microwave-heating (LMH) process is conducted in a nitrogen shielding environment, and hence the microwave power is reduced to only ∼0.1 kW (compared to ∼1 kW in a previously reported magnetron-based IS process). This shielding prevents the plasma excitation (which intercepted most of the microwave power in the previous experiments in air atmosphere), and hence significantly improves the efficacy of the LMH-IS process. This paper introduces the compact LMH-AM concept, and its novel implementation by a transistor-based microwave system. Experimental and theoretical results of the LMH-AM process applied to bronze- and iron-based powders are presented. The powder is provided to the LMH interaction region in small batches, on demand. A contactless magnetic confinement is demonstrated for ferromagnetic powder batches. The experimental products obtained are tested, and their mechanical properties are evaluated. The potential applicability of the solid-state LMH technology to full AM and 3DP processes is discussed.

Application of SPS consolidation and its influence on the properties of the FeAl20Si20 alloys prepared by mechanical alloying

The FeAl20Si20 alloy was prepared by a combination of short-term mechanical alloying and spark plasma sintering. The processing parameters either of the mechanical alloying or spark plasma sintering were optimized to yield the maximal mechanical properties of the alloy. For the mechanical alloying, two amounts of powders batch (5 g or 20 g) were compared. The spark plasma sintering regimes combined pre-pressing prior heating and vice versa, direct and pulse current flow. The MA + SPS alloys exhibited ultrafine-grained microstructure composed of FeSi, Fe3Si and Fe3Al2Si3 phases (with an average crystallite size of approximately 30 nm) with a presence of randomly distributed Al2O3 particles (with diameters ranging from 5 to 100 nm). The FeSi, Fe3Si phases were supersaturated by Al, which resulted in an increase of lattice parameters. The hardness of the compact alloys reached up to approximately 1100 HV 0.1 for both the powder batches. The 20 g samples showed a standard deviation nearly half the of 5 g powder batches and the 20 g prepared by a regime combining pre-pressing prior heating up to consolidation temperature using pulse current flow resulted in the highest compressive strength of 2008 MPa. Combination of pre-pressing prior heating-up also reduced the increase of the Fe3Al2Si3 phase weight fraction especially in the 5 g alloys that otherwise had a tendency to microstructural coarsening.

The effect of metal EOS 316L stainless steel additive manufacturing powder recycling on part characteristics and powder reusability

ABSTRACTDirect metal laser sintering (DMLS) is a powder bed fusion (PBF) process commonly used within the medical device and aerospace industries to fabricate high value, complex components. Powder material used in the DMLS process can be costly and it is rare for a single build to require a full batch of powder. The un-melted powder, which differs in particle size and morphology from virgin powder, is often recycled for further builds. This work presents a study of the effects that recycling a stainless steel metal powder used in the DMLS process has on finished parts. Hence, in this paper, powder material characteristics, such as particle size, particle morphology and bulk chemical composition have been monitored throughout the recycling process. An analysis of parts manufactured via DMLS on an EOS M280 demonstrate the negative effect of powder recycling on part quality in terms of surface roughness, part density, hardness and dimensional accuracy. Results from this research provide an insight to the effect that recycling AM powders has on the powder characteristics and on the quality of the parts produced.

3D Shape Analysis of Powder for Laser Beam Melting by Synchrotron X-ray CT

The quality of components made by laser beam melting (LBM) additive manufacturing is naturally influenced by the quality of the powder bed. A packing density <1 and porosity inside the powder particles lead to intrinsic voids in the powder bed. Since the packing density is determined by the particle size and shape distribution, the determination of these properties is of significant interest to assess the printing process. In this work, the size and shape distribution, the amount of the particle’s intrinsic porosity, as well as the packing density of micrometric powder used for LBM, have been investigated by means of synchrotron X-ray computed tomography (CT). Two different powder batches were investigated: Ti–6Al–4V produced by plasma atomization and stainless steel 316L produced by gas atomization. Plasma atomization particles were observed to be more spherical in terms of the mean anisotropy compared to particles produced by gas atomization. The two kinds of particles were comparable in size according to the equivalent diameter. The packing density was lower (i.e., the powder bed contained more voids in between particles) for the Ti–6Al–4V particles. The comparison of the tomographic results with laser diffraction, as another particle size measurement technique, proved to be in agreement.

Electrospark Dispersion in Nanopowder Production for Additive Technologies

A laboratory electrospark system permits the creation of an overvoltage in the gap between dispersible electrodes. Conductive nanopowder may be produced by an electrospark method with a considerable overvoltage in the electrode gap. The production of small powder batches for additive technology by this means is promising and economical.

Phase formation in cemented carbides prepared from WC and stainless steel powder – An experimental study combined with thermodynamic calculations

Cemented carbides prepared from mixes of WC and stainless steel powder have been proposed as possible alternatives to WC-Co. However, phase formation in such systems is not well described in the literature, in particular with regard to the possible formation of Cr-carbides. In this work, cemented carbides have been prepared from batches of coarse WC powder and 20 wt% AISI 360 L stainless steel powder, considering different carbon black additions to vary the final carbon contents to 4.9, 5.64, 5.75 wt% C. Both experimental results and thermodynamic calculations show that no classical two phase area – containing only WC and metallic binder- can be expected in these alloys. (Cr, Fe)-carbides are observed at all carbon contents in equilibrium with eta phases and binder, and at the highest carbon content also with graphite. As a consequence of the formation of (Cr, Fe)-carbides the amount of metallic binder decreases significantly, and the composition of the binder changes drastically. The binder phase in the sintered materials constitute an Fe-15Ni alloy with about 5 wt% Cr and 2 wt% W in solid solution, which is more similar to a maraging steel rather than a stainless steel. Both thermodynamic calculations and experimental results confirm that the maximum amount of Cr that can be retained in the metallic binder is around 5 wt% Cr which implies that, after sintering, the stainless steel properties will be lost.

Additive Manufacturing: Assessing Metal Powder Quality Through Characterizing Feedstock and Contaminants

The quality of powder feedstock for additive manufacturing (AM) metal powder bed fusion methods can significantly affect the quality of parts built from it. Particle size distribution (PSD) and shape factors influence flowability as well as the thickness and uniformity of each powder layer in the build box. For high-performance applications such as aerospace, medical, power generation and military, it becomes important to identify critical additional factors: the types, numbers and sizes of particulate contaminants that may be present in the powder. This is true for virgin, used and blended powders. Contaminants may be introduced during powder manufacture (e.g., ceramic insulation fragments from gas atomization equipment), handling (building insulation, talc) or possibly during the build process itself. Contaminants contained within a batch of powder can be physically built into an additive part when they are incorporated into the melt pool, and they can remain as discrete particulates or non-fused interfaces that act as stress concentrators. Their presence may decrease fatigue life by increasing the likelihood of fatigue crack initiation. This article describes three methods to rapidly and quantifiably characterize powder feedstock. (1) Computer-controlled scanning electron microscopy (CCSEM) provides quantitative size and shape parameters, as well as fine surface details from individual images on a particle-by-particle basis in large populations of powder. (2) Energy-dispersive spectroscopy (EDS) can be included, providing insights into variations within a batch of powder, as well as contaminant compositions. (3) For critical applications, the heavy liquid separation (HLS) method physically extracts low-density contaminants from a sample of powder metal down to part-per-billion detection limits to allow direct examination of contaminants and enhance identification and prevention of their sources. Altogether, these methods permit direct comparisons among powder metal samples. Better quantification of powder characteristics aids determination of suitability for end uses.

Quality assessment of licorice extract powder through geometric linear quantified fingerprint method combined with multicomponent quantification and chemometric analysis

Licorice extract powder, the aqueous extract of licorice, has been widely used as a common raw material in both pharmaceutical and food fields. Its quality evaluation is of great significance but still a big challenge due to complex chemical components. In this study, a rapid and efficient HPLC-DAD method for fingerprint profiling and multiple components determination was developed and validated to assess the quality consistency of licorice extract powder. The chromatographic fingerprints at five wavelengths were fused into a synthesized fingerprint to avoid one-sidedness of single wavelength. Then, quality grades of 72 batches of licorice extract powders from different manufacturers were successfully discriminated by geometric linear quantified fingerprint method, in which both qualitative and quantitative evaluation parameters were obtained. Principle component analysis revealed that samples from different manufacturers can be clustered according to the contents of six main components, same as the fingerprint evaluation results. Furthermore, the fingerprint-efficacy relationship among the components as well as the antioxidant activity in vitro was investigated by partial least squares model, which offered significant medicinal efficacy information. The present study established a powerful and reliable method to monitor the quality consistency of licorice extract powder.

Developing New Materials for Electron Beam Melting: Experiences and Challenges

Lack of industrially available materials for additive manufacturing (AM) of metallic materials along with the promises of materials with improved or unique properties provides a strong drive for developing new process/material combinations. As powder bed technologies for metallic materials are relatively new to the market, and to some extent are only maturing, developers of new process/material combinations have certain challenges to overcome. Firstly, basic knowledge on the behavior of materials (even those well established for other applications) under extreme conditions of melting/solidification with beam-based AM methods is far from being adequate. Secondly, manufacturing of the equipment is up to date driven by industrial application, thus optimization of the AM machines for small test batches of powders is still belongs to research and development projects. Also, majority of the powder manufacturers are primarily driven by the market development, and even they are well aware of the demands imposed by the powder bed AM machines, availability of small test batches of adequate powders may be problematic or at least quite costly for the R&D oriented users. Present paper describes the experiences in developing new materials for EBM A2 machine by Arcam EBM, modified for operating with powder batches of 100-200 ml and less. In particular it discusses achievements and challenges of working with powders from different materials with specifications far beyond the range suggested by machine manufacturer. Also it discusses the possibility of using blended rather than pre-alloyed powders for achieving both composite-like and alloyed materials in the same part by steering electron beam energy deposition strategy.

Fingermark visualisation with iron oxide powder suspension: The variable effectiveness of iron (II/III) oxide powders, and Tween® 20 as an alternative to Triton™ X-100

The effectiveness of the current UK iron oxide powder suspension formulation, ‘C-IOPS-09’ (Triton X-100 based), for fingermark or latent fingerprint visualization is shown to be affected by variations between batches of the recommended iron oxide powder from Fisher Scientific (I/1100/53). When incorporated into the C-IOPS-09 formulation, a 2015 powder batch resulted in the detection of ∼19% fewer fingermarks, of broadly reduced contrast, when compared to powder suspension prepared with a 2008 batch of the same product. Furthermore, the 2015 powder batch was found to be unsuitable in experimental reduced-surfactant concentration powder suspension, because it caused surface-wide or background staining. The studies in this paper also investigated the use of Tween 20 surfactant as an alternative to the currently utilised Triton X-100, in preparation for the potential unavailability of Triton X-100 in the future. Powder suspensions prepared with Tween 20 surfactant solutions of 4% and 40% were shown to offer similar effectiveness to the currently recommended C-IOPS-09 formulation, when compared using the same batch of Fisher Scientific iron oxide powder (2008 or 2015). The difference between the 2008 and 2015 iron oxide batches was hence also evident with these alternative surfactant solutions. Particle size distribution analysis of the iron oxide powders in Tween 20 and Triton X-100 based surfactant solutions show that the more effective powder exhibits a higher sub-micrometre particle population than the less effective powder. This work leads to an improved specification for powder suspension formulations. This is demonstrated with an example powder suspension formulation which uses a 10% Tween 20 surfactant solution and iron oxide nanopowder (50–100nm) from Sigma Aldrich, which was shown to visualise 27% more fingermarks than the C-IOPS-09 formulation prepared with the 2015 Fisher Scientific powder batch, in a comparative study.

Influence of Morphology of the Press Powder Particles and Thermal Annealing on the Structure and Microhardness of Palladium Obtained by Solid-Phase Sintering

The article is devoted to the investigation of the structure of pressed palladium-barium cathodes. These cathodes are made from a polycrystalline palladium matrix with inclusions of the particles of the activator phase Pd5Ba. The high efficiency and durability of pressed palladium-barium cathodes is ensured by the formation of an active-emission BaO layer on the working surface. The active metal Ba comes from the volume to the surface by diffusion of atoms on the defects of the crystal structure of the palladium matrix. When comparing the electrical parameters of the cathodes, the matrices of which were made from the same fractions but different batches of palladium powder, a considerable spread of electrical parameters was established. There were also revealed significant differences in the roughness of the cathode working surface. These differences affect the uniformity and stability of the emission current. This indicates the need for a detailed study of the characteristics of the initial palladium powder and their effect on the structure of the sintered material, and, consequently, on the physicomechanical properties of its surface. In this paper, the morphological features of eight batches of palladium powder in the initial state and after the purification annealing were studied by the method of electron microscopy. Significant differences in the form of particles and agglomerates of powder from different batches have been revealed. A metallographic analysis of microsections of the palladium samples prepared by solid-phase sintering was carried out. The influence of the morphological features of the particles of the initial powder on the grain size and the mechanical properties of the sintered compact is determined. Studies have shown that to obtain a compact palladium with reproducible and predictable properties, stability of the morphological characteristics of the original powder is necessary.

Stability of antibodies and proteins in camel whey powder treated by Gamma-irradiation during radurisation process

Camel milk and milk derived products have a growing potential in pharmacy, food and biotechnology industry. Its therapeutic value has been investigated and documented in many studies before. The contamination of camel whey powder during manufacturing and transportation may impact economy; re-pasteurisation could cause dramatic effect on antibodies and proteins of camel whey powder. Radurisation (0.4 to 10 kGy) process could be a choice in sterilising camel whey powder. This study aimed to investigate the stability of camel antibodies and proteins in whey powder before and after Gamma-irradiation. Efficacy of radiation dose on microbial content was also studied. Four batches of hyper immune camel whey powder containing antibodies against Propionibacterium acnes were subjected to six Gamma-radiation doses (1.5, 3, 4.5, 6, 7.5 and 9 kGy). Results revealed marked decline in the total microbial count (3-5 log cycles) after escalating the doses of irradiation. Minor effect on antibody activity (7.4 % reduction) was observed after treating the whey by 9 kGy. Moreover, the concentration of total camel IgG was reduced by 13% using the same irradiation dose. In addition, no effect on major whey proteins (Lactoferrin, Casein, and α-lactoalbumin) was revealed in protein identification using SDS-PAGE. In conclusion, using 9 kGy dose of Gamma-irradiation for sterilising camel whey powder is effectively reducing bacterial contamination with limited effects on antibodies activity and protein stability.

Characterisation and heat treatment of chloride-contaminated and humidified PuO2 samples

To mimic the reactions that have occurred between plutonium dioxide (PuO2) and degraded polyvinyl chloride during prolonged storage, batches of PuO2 powders with varying specific surface area (4–38 m2 g−1) were exposed to dry hydrogen chloride gas forming a surface-sorbed exchangeable chloride species that was readily leached by dilute caustic solution. One batch was also humidified under a 95% relative humidity atmosphere. Heat treatment at temperatures between 100 and 950 °C steadily reduced the leachable chloride content at least when the initial leachable chloride surface coverage was calculated to be > 0.5 monolayer (ML). Variations between samples are attributed to differences in surface area as well as production route and period of interim storage in air or humidified atmospheres. The data are consistent with surface species and reactions proposed in the literature for HCl adsorption on to TiO2. This indicates that it is interactions between hydrogen chloride/chloride and water/hydroxyl species on the PuO2 surface that are key to understanding the behaviour of these materials when heated in a furnace. These data will inform the design of a future thermal stabilisation process for chloride-contaminated PuO2.

Stringent sampling inspection plans using upper envelopes for cell counts

A new type of stringent sampling inspection plan is proposed for cell counts generally in line with a Poisson or a mixed-Poisson type of distribution. The proposed plan is based on setting an upper envelope estimated from the sample counts which should remain below the given microbiological limit m. We used Monte-Carlo simulation methodology to evaluate the proposed plans and showed that the lot acceptance criterion using the upper envelope improves consumer protection in general. Both two and three class attribute plans are investigated for establishing the upper envelope. Our study reveals that the proposed plans can offer better consumer protection and economy when compared to both two and three class attribute plans. It is also demonstrated that a slightly stringent plan can be found in place of lognormal type variables plans. The limitations of the proposed new plans, and a discussion on alternative stringent rules for batch acceptance are also provided. The new plan was also validated using the APC cell counts observed for 2000 milk powder batches. Our conclusion is that the proposed stringent plans can improve protection to the consumer, particularly for exported food products.

The effect of powder recycling on the mechanical properties and microstructure of electron beam melted Ti-6Al-4 V specimens

Additive manufacturing (AM), also called 3D-printing, is an innovative technology, as the printing of objects is performed by layer-by-layer deposition. A wide variety of materials can be used to produce a variety of shapes that cannot be achieved using any other technology. AM started as a prototyping in plastics, and now it is successfully implemented with metals. AM in metals, first of all, in Titanium alloys, offers the potential to not only generate net-shape, complex geometrical and light-weight objects, but also to achieve enhanced mechanical properties, even better than achieved by traditional mass production, like casting.However, the priority of achieving good non-porous microstructure and the desired mechanical properties is a challenge for the main fields of applications of Titanium AM, such as the aerospace industry and production of medical implants. Thus, the quality of the powder and standardization of the AM process are the top priority. The potential recycling of the Ti-6Al-4 V powder as an inextricable part of the AM process needs to be explored.The influence of powder recycling on Ti-6Al-4 V additive manufacturing, the correct number of cycles, the requirements of the recycling procedures, and possible post processing procedures – are still open questions. This research aims to answer these questions. Two identical test cylinder sets were printed, one from recycled powder and one from the new powder batch. The cylinders were printed by the Arcam EBM A2X machine using a start platform of 210 x 210 mm in size. Electron Beam Melting (EBM) is a well-known effective manufacturing process. This AM technology utilizes high power electron beam to produce layer-by-layer metal parts for various applications, such as fabrication of biomedical implants and aerospace components. The microstructure and mechanical properties of the printed specimens from the two sets (new and recycled Ti-6Al-4 V powder) were investigated before and after heat treatment.

Thermal diffusivity of soda–lime–silica powder batch and briquettes

Thermal diffusivity of soda–lime–silica powder batch and briquettes