Powder Contamination Research Articles

Dense integration of chlorocatechols crosslinked polyphenylene sulfide solid-state separator for Li Metal-Free Batteries

Dry electrode film fabrication technology, known for its environmental friendliness and low energy consumption, is recognized as an effective industrial approach for producing highly dense solid-state electrolytes and pore-free separators. It holds promise for applying thin lithium metal and Li metal-free anodes in ultra-high energy density Li-ions batteries. However, the films produced by this method suffer from issues such as poor toughness, low strength, uneven thickness, and difficulties in rewinding, which limit its widespread adoption in the large-scale manufacturing of lithium batteries. In this study, we propose a hydrothermal process to introduce a chlorocatechol-based cross-linker onto the surface of highly crystalline polyphenylene sulfide (PPS) powder. By employing the dry electrode process, a PPS-based solid-state separator (PPS-SSS) is fabricated, featuring a thin profile (18±2 μm), a smoother surface, and a denser structure, significantly enhancing its mechanical properties. Moreover, the dense integration structure and chlorocatechol groups contribute to a higher Li+ transference number and more effectively inhibit the growth of Li dendrites. Li metal-free batteries, constructed with this separator, a Sn-plated Cu 10 μm foil anode, and a thick high-nickel cathode dry electrode, exhibit high discharge areal and specific capacities (5 mAh cm−2 and 200 mAh g−1, respectively) and pouch battery device energy density exceeding 440 Wh kg−1. Impressively, even in the presence of Cu or Fe powder contamination on the CuSn foil anode or cathode, this separator can still achieve uniform electric field distribution and lithium deposition, demonstrating good cycle stability.

Millimeter-scale macrocapsules with cold energy storage and temperature indication for vaccine storage

This study aims to prepare millimeter-scale macrocapsules with cold energy storage and temperature indication suitable for the requirement of vaccine storage (−25 °C ∼ -15 °C). In these macrocapsules, reversible thermochromic microencapsulated phase change materials (TC-MPCMs) are used as dispersions, and flexible calcium alginate is served as the polymer matrix. Macrocapsules exhibit a particle size distribution from 0.5 mm to 3.0 mm, with a melting temperature of −18.4 °C, a melting enthalpy of 86.0 J/g and an encapsulation efficiency of 45.5 %. After melting of the PCMs (Phase change materials), these macrocapsules can undergo a reversible discoloration, with a color difference of 27.54. Additionally, the volatilization of internal PCMs can also trigger the discoloration reaction. After 100 thermal cycles, the latent heat loss of the macrocapsules is less than 5 %, and the calcium alginate shell material delays the thermal decomposition of internal PCMs. Finally, the storage-release cold energy test shows that at 25 °C, the macrocapsules can maintain the ideal temperature range (−25 °C ∼ -15 °C) for 10.34 min. The millimeter-scale macrocapsules successfully address the issues of ultrafine powder contamination, difficulty in reuse and recycling of micron-scale TC-MPCMs, and show excellent potential for vaccine frozen storage.

Sixty Years of Mechanical Alloying—Past Achievements, Current Challenges, and Future Prospects

Mechanical alloying (MA), a completely solid‐state high‐energy powder processing method, was initially used to develop Ni‐based and Fe‐based superalloys containing oxide dispersions for applications at high temperatures and requiring high strength. MA is currently an established materials process to synthesize a variety of nonequilibrium alloys with unique microstructures and properties. Supersaturated solid solutions, metastable intermediate phases, amorphous alloys, quasicrystalline alloys, nanostructures, and nanocomposites, and high‐entropy alloys are some of the materials developed using MA. These advanced structural and functional materials exhibit great potential with widespread applications. Several new and novel applications have also been recently developed. A major concern in using this technique to produce advanced materials is the inherent contamination experienced by the milled powder. In the present article, the past achievements during the last 60 years and current challenges are described in brief. Methods to decrease powder contamination and ways to reduce the cost of powders produced are also discussed. It is also shown that while the MA concept is straightforward, the outcome of the process can be stochastic, depending on many variables which must be experimentally determined since no comprehensive process model exists. The article concludes with the future prospects of this materials processing technique.

Black powder and mineral deposits in the LPG production and processing line: Analytical study and formation mechanisms

The accumulation of mineral deposits such as black powder causes severe impacts throughout the gas production and transport process. The phenomenon takes place from gas wells to LNG/LPG treatment plants and terminals. The complexity lies in understanding the mechanisms by which these materials are formed in random quantities, as well as their varied nature. The aim of this study is to monitor black powder and other mineral deposits formation in a chain of gas production and processing situated in the south of Algeria and unravel their root causes. To that extent, an analytical study was carried out on four samples of both mineral deposits and black powder taken from an LPG processing and production unit. The adopted analytical approach included an exploration of the textural and structural properties. It also involves a composition characterizations related to the content of metallic elements, moisture, organic and mineral matter. The particle distribution is also determined. The analytical study was conducted using gravimetric determination, XRD, XRF, SEM/EDX and Raman spectroscopy. Particle distribution was given by Laser granulometry technique. The results of the DRX/FRX and EDX characterization primarily revealed that the samples contain a variety of mineral components such as iron oxides; magnetite Fe3O4 and hematite Fe2O3, iron oxy-hydroxide FeO(OH), iron sulphide FeS2, calcite CaCO3, SiO2 and halite NaCl. The presence distribution of these components depends on the location of the sample in gas line. Granulometry study shows that black powder contamination can be spread over a wide spectrum of particle sizes ranging from 1.51 µm to 678.50 µm. This study has allowed to elucidate the nature and distribution of particles deposited at different positions in the LPG production chain and to propose probable mechanisms for their formation.

Assessment of Microbial Contamination and Hygiene Practices of Okra Powders in Public Markets of Yamoussoukro

Background: Okra is one of the most consumed fruit vegetables by Ivorians either fresh or powdered. However, due to a lack of supervision, okra powders are sold under conditions that often leave something to be desired. Objectives: This study aims to assess the level of microbial contamination of okra powders sold in public markets, with a view to preventing any potential health risks for consumers. Methodology: The experimental method is based on a survey within the markets of the city of Yamoussoukro in order to describe the conditions of sale. Samples of okra powders sold in these markets were analyzed. Acquired Results: The survey showed that, most marketers sell their product beyond 10 days. Additionally, okra powders are sold in plastic containers, uncovered. In addition, the analyzes reveal the absence of Salmonella spp. but the presence of yeasts, molds, Staphylococcus aureus and Escherichia coli whose loads varying from 3.5. 103a ± 0.16.103 to 4.8.103a ± 0.49.103 CFU/g, 1.5.104b ± 0.28.104 to 3.2.103a ± 0.32.103 CFU/g and 3.3.103a ± 0.17.103 to 8.103a ± 0.91.103 CFU/g. However, all the okra powders analyzed present an unsatisfactory microbiological quality. Conclusion and Outlook: To avoid any health risk for consumers, traders must be supervised, organized and made aware of good hygiene practices.

Determination of Airborne Release Fractions from Loose Powder Contamination Under Impact Stress

Safety basis calculations support the safety considerations necessary for legacy nuclear facilities as they transition from active use, through limited operations and standby modes, until final disposition is achieved. Many of the calculations are governed heavily by the coefficients presented in DOE-HDBK-3010 in the form of airborne release of radioactive material resulting from penetration of the facility per seismic activity, full facility fires, and/or explosions. The main objective of this study is to validate the original data for airborne release fractions (ARFs) for powder contaminants under impact, as determined in DOE-HDBK-3010. The limited data available for impact experiments was generated at the Rocky Flats Plant in 1987, where the median ARFs for surrogate powder contamination were 4E-4 with a bounding value of 1E-2. However, estimating the level of uncertainty was challenging in the absence of multiple measurements conducted under identical test conditions. Moreover, the uncertainty was significantly increased due to the restricted range of the test conditions. A more modern approach has been developed for the experimental design in this study, utilizing standardized techniques and analytical instruments. An impact apparatus was employed to be able deliver repeatable impact forces up to 369 kg·cm (320 in.·lb.). Cesium chloride was used as the surrogate powder contaminant in these experiments as it is extremely soluble in water and is even more so in the acidic media used to leach/dissolve the air filters for concentration analysis using mass spectrometry The developed approach leveraged multiple international standards and historical documents in an attempt to recreate a valid testing system that can be used for future analysis and to analyze mitigation factors such as contamination fixative technologies. The current ARFs were found to be consistent with the original values in DOE-HDBK-3010, 3.47E-4 and 4E-4, respectively.

Effect of Al content on the microstructure and mechanical alloying behavior of AlCoCuMnNi and Al0.25CoCuMnNi high entropy powders

The concept of high entropy alloys (HEAs) is an emerging subject in materials science and engineering. The presence of at least four elements in equiatomic or near equiatomic composition in HEAs has led to superior properties and vast unexplored alloying space. In this study, we investigated two new HEA powders, AlCoCuMnNi and Al0.25CoCuMnNi, by subjecting mechanically milled (MM) powders to a series of analyses over a 60 h ball milling process. It was found that alloying starts after 20 h of MM and after 45 h, full elemental integration into the host lattice was detected. Meanwhile, further milling to 60 h can cause powder contamination. The High-Resolution Transmission Electron Microscopy (HRTEM) results validated the XRD findings and provided further insights into the substantial influence of Al content on the microstructure and the extent of amorphization within the milled powders. Differential Thermal Analysis (DTA) analysis on the MM powders showed one exothermic peak for AlCoCuMnNi and one for Al0.25CoCuMnNi at high temperatures, which may suggest the formation of the BCC or second FCC phases for these alloys. The results confirmed the significant influence of the increased Al content on increasing both the lattice constant and lattice strain while decreasing thermal stability of the investigated MM powders. The present results provided insights needed for consolidation of such HEA powders.

Microstructural and mechanical characterization of additively manufactured parts of maraging 18Ni300M steel with water and gas atomized powders feedstock

The demand for manufacturing components with complex geometries, good mechanical properties, and material efficiency has surged across various industries, encompassing aerospace, military, nuclear, and naval sectors. Laser powder bed fusion (LPBF), as an additive manufacturing (AM) process, has emerged as a promising method for producing ultra-high mechanical strength alloys, like maraging 300 steel (18Ni300M). However, in numerous studies in the literature concerning the effects of processing parameters on the properties of 18Ni300M steel parts fabricated through LPBF, limited attention has been given to the influence that powder atomization methods may exert on the final properties of these parts. This article investigated the effect of gas atomization (GA) and water atomization (WA) processes on the microstructure of 18Ni300M steel powders and the mechanical properties, microstructure, and chemical composition of LPBF-produced parts. The results revealed significant distinctions in the morphology, aggregation degree, and particle size distribution between the GA and WA powders, which directly influenced the microstructure and affected the amount of defects in LPBF-produced parts. Despite the similar mechanical response found in the WA and GA specimens in the elastic region, the samples produced with the WA batch presented a brittle behavior with a ductility of only 4.06%, whereas the GA parts had an elastoplastic behavior with an elongation of 11.52%. The bulks from the WA batch produced in the LPBF process were compromised due to powder contamination with oxygen, which increased gas porosity and effected fragile oxide particles visible on the fracture surface.

Anti-contamination calibration method for ultra-fine dry chemical agent: Achieving wide measurement range and high measurement accuracy

Achieving real-time measurements of ultra-fine dry chemical agents (UDCA) is extremely challenging, with their complex composition, high injection concentrations, and susceptibility to contamination. In this study, a high-concentration particulate matter measurement method was proposed based on the extinction principle to reduce the powder contamination effect during calibrations. Through theoretical analysis and experimental verification, a functional relationship was established. Calibration experiments were conducted using sodium bicarbonate (SBA) and potassium bicarbonate (PBA) UDCAs, which are the most representative. The results showed that the measurement ranges of SBA and PBA reached 227.15 g/m3 and 122.55 g/m3, respectively. Compared with the uncorrected calibration method, the maximum indicated errors of SBA and PBA with the powder contamination effect corrected were reduced from 11.25% and 22.68% to 5.98% and 9.21%. This method provides a strategy for measuring high concentration powder, especially for achieving the measurement of UDCA in aircraft engine compartments.

Real-Time Optical Detection of Artificial Coating Defects in PBF-LB/P Using a Low-Cost Camera Solution and Convolutional Neural Networks

Additive manufacturing plays a decisive role in the field of industrial manufacturing in a wide range of application areas today. However, process monitoring, and especially the real-time detection of defects, is still an area where there is a lot of potential for improvement. High defect rates should be avoided in order to save costs and shorten product development times. Most of the time, effective process controls fail because of the given process parameters, such as high process temperatures in a laser-based powder bed fusion, or simply because of the very cost-intensive measuring equipment. This paper proposes a novel approach for the real-time and high-efficiency detection of coating defects on the powder bed surface during the powder bed fusion of polyamide (PBF-LB/P/PA12) by using a low-cost RGB camera system and image recognition via convolutional neural networks (CNN). The use of a CNN enables the automated detection and segmentation of objects by learning the spatial hierarchies of features from low to high-level patterns. Artificial coating defects were successfully induced in a reproducible and sustainable way via an experimental mechanical setup mounted on the coating blade, allowing the in-process simulation of particle drag, part shifting, and powder contamination. The intensity of the defect could be continuously varied using stepper motors. A low-cost camera was used to record several build processes with different part geometries. Installing the camera inside the machine allows the entire powder bed to be captured without distortion at the best possible angle for evaluation using CNN. After several training and tuning iterations of the custom CNN architecture, the accuracy, precision, and recall consistently reached >99%. Even defects that resembled the geometry of components were correctly classified. Subsequent gradient-weighted class activation mapping (Grad-CAM) analysis confirmed the classification results.

Effect of blood contamination on marginal adaptation of cold ceramic and MTA angelus: a scanning electron microscopic study

BackgroundThis study aimed to assess the effect of blood contamination on marginal adaptation of cold ceramic (CC) and mineral trioxide aggregate (MTA) Angelus using scanning electron microscopy (SEM).MethodsThis in vitro experimental study was conducted on 24 extracted single-rooted human teeth. After cleaning and shaping, the root canals were filled with lateral compaction technique. The apical 3 mm of the roots was cut, and cavities with 3 mm depth were created at the apex. The teeth were randomly assigned to two group (n = 12) for the application of CC and MTA Angelus as retrograde filling materials. CC and MTA Angelus were prepared by mixing the powder with blood, and applied in the cavities. After 24 h, their marginal adaptation to the canal walls was assessed by SEM. Data were statistically analyzed by t-test (alpha = 0.05).ResultsThe mean marginal gap was 8.98 μm in the CC, and 16.26 μm in the MTA Angelus group; this difference was statistically significant (P < 0.001).ConclusionsThe present in vitro study revealed that following complete blood contamination of powder, CC showed significantly superior marginal adaptation than MTA Angelus as shown by SEM assessment.

Influence of spattering on in-process layer surface roughness during laser powder bed fusion

Laser powder bed fusion (LPBF) based additive manufacturing (AM) holds great promise to efficiently produce high-performance metallic parts. However, LPBF processes tend to incur stochastic melt pool (MP) spattering, which would roughen workpiece in-process surface, thus weakening inter-layer bonding and causing issues like porosity, powder contamination, and recoater intervention. Understanding the consequential effect of MP spattering on layer surface is important for LPBF process control and part qualification. Yet it remains difficult due to the lack of process monitoring capability for concurrently tracking MP spatters and characterizing layer surfaces. In this work, using our lab-designed LPBF-specific fringe projection profilometry (FPP) along with an off-axis camera, we quantitatively evaluate the correlation between MP spattering and in-process layer surface roughness for the first time to reveal the potential influence of MP spatters on process anomaly and part defects. Specifically, a method of automatically and accurately extracting and registering MP spattering metrics is developed by machine learning of the in-situ off-axis camera imaging data. Each image is analyzed to obtain the MP's center location and the spatter count and ejection angle. These MP spatter signatures are registered for each monitored MP across each layer. Then, regression modeling is used to correlate each layer's registered MP spatter signature and its processing parameters with the layer's surface topography measured by the in-situ FPP. We find that the attained MP spatter feature profile can help predict the layer's surface roughness more accurately (> 50 % less error), in contrast to the conventional approaches that would only use nominal process setting without any insight of real process dynamics. This is because the spatter information can reflect key process changes including the deviations in actual laser scan parameters and their effects. The results also corroborate the importance of spatter monitoring and the distinct influence of spattering on layer surface roughness. Our work paves a foundation to thoroughly elucidate and effectively control the role of MP spattering in defect formation during LPBF.

Recycling of silicon from waste PV diamond wire sawing silicon powders: A strategy of Na2CO3-assisted pressure-less sintering and acid leaching

Recycling diamond wire sawing silicon powders (DWSSP) from photovoltaic (PV) silicon wafers production has become an urgent problem. The challenge of recovery is the surface oxidation and contamination of the ultra-fine powder with impurities during the sawing and collection process. In this study, a clean recovery strategy of Na2CO3-assisted sintering and acid leaching was proposed. Due to the Al contamination from the perlite filter aid, the introduced Na2CO3 sintering aid can react with the SiO2 shell of DWSSP to form a slag phase with accumulated impurity Al during the pressure-less sintering process. Meanwhile, the evaporation of CO2 contributed to the formation of ring-like pores surrounded by a slag phase, which can be easily removed by acid leaching. When 15 % Na2CO3 was added, the content of impurity Al in DWSSP could be reduced to 0.07 ppm with a removal rate of 99.9 % after acid leaching. The mechanism suggested that the addition of Na2CO3 can trigger the liquid phase sintering (LPS) process of the powders, and the cohesive force and liquid pressures difference generated during the process facilitated the transportation of impurity Al from the SiO2 shell of DWSSP to the formed liquid slag phase. The efficient silicon recovery and impurity removal of this strategy demonstrated its potential for solid waste resource utilization in the PV industry.

In Situ Inclusion Detection and Material Characterization in an Electron Beam Powder Bed Fusion Process Using Electron Optical Imaging.

Electron Beam Powder Bed Fusion (PBF-EB) is an Additive Manufacturing (AM) method that utilizes an electron beam to melt and consolidate metal powder. The beam, combined with a backscattered electron detector, enables advanced process monitoring, a method termed Electron Optical Imaging (ELO). ELO is already known to provide great topographical information, but its capabilities regarding material contrast are less studied. In this article the extents of material contrast using ELO are investigated, focusing mainly on identifying powder contamination. It will be shown that an ELO detector is capable of distinguishing a single 100 μm foreign powder particle, during an PBF-EB process, if the backscattering coefficient of the inclusion is sufficiently higher than its surroundings. Additionally, it is investigated how the material contrast can be used for material characterization. A mathematical framework is provided to describe the relationship between the signal intensity in the detector and the effective atomic number Zeff of the imaged alloy. The approach is verified with empirical data from twelve different materials, demonstrating that the effective atomic number of an alloy can be predicted to within one atomic number from its ELO intensity.

The Cs-137 radiological accident in Goiânia, Brazil: Conditions and results of the airborne radiometric survey

This paper describes the details of the aeroradiometric operations, the radiation detection system used and discusses the results. The low-altitude survey was carried out over Goiânia a few days after information of the accident was received by the national competent authority, the Brazilian Nuclear Energy Commission (CNEN). Given the little information at the time of the accident and the urgency to respond to the local and federal authorities, an aerial radiometric survey was proposed to evaluate the extent of the contamination and dispersion of the radioactive powder. The city's entire urban area and nearby dwellings centers, plus the two creeks crossing the city were surveyed in two days. The survey found only one additional contamination point 2.8 x 10-4 C/kg/h (1.1 R/h) that had not yet been identified by ground survey crews. Furthermore, no contamination was found along the margins of the Capim Puba Creek and Meia Ponte rivers which could be contaminated due to rainwater common at that time of the year. Detection tests conducted at different altitudes over the main contamination area showed that the Cs-137 gamma radiation could be detected even at altitudes of 350m above the ground. This was much higher than the 40 m - 70 m decided for the overflights. The survey demonstrated that the contamination was restricted to a few locations in the neighborhood of the metal scrap place where the source shield was broken. These locations were under the control of CNEN radiological emergency response personnel. Such a finding was an important indicator to calm down the population and the government authorities. This allowed concentrating attention on the remediation of the known points of high gamma activity.

An improved method to determine the minimum extinguishing concentrations of ultrafine dry powder agents: Taking NaHCO3 and KHCO3 as examples

Ultrafine dry powder agents (UDPAs) are the most potential Halon substitutes due to the high extinguishing effectiveness and excellent environmental friendliness. Nevertheless, the method for obtaining minimum extinguishing concentration (MEC) is flawed and inaccurate. An improved method is proposed by developing the special laser measurement system without powder contamination, the concentration calibration test bench and the cup burner with uniform aerosol generating. The results show that the optimum calibration position is 0.35–0.65 m from the inlet in the y-axis coordinate. More accurate mathematical relationships between the transmittance of the laser measurement system and the NaHCO3 and KHCO3 powders are established, with the errors less than 12%. Upon reaching MECs in the modified cup burner, the flames pulsate, then fade and eventually die. Based on the phenomenon of the sudden change in the transmittance of the laser measurement system at the moment of flame extinguishment, i.e. the “step shape” curve, a more accurate critical criterion point for the MEC is proposed. The measured MECs for methane flames by NaHCO3 (32.2 g/m3) are approximately 4 times that of KHCO3 (8.2 g/m3), consistent with previous studies. The obtained MECs of NaHCO3 and KHCO3 for kerosene flame are verified by 1 m3 total flooding fire extinguishing experiments. The improved method may guide the design of industry fire protection systems based on UDPAs to achieve process safety.

Characterization of Aluminium-based alloy starting powders morphology for the synthesis of rail components through Selective Laser Melting

Additive manufacturing is widely acknowledged as a popular fourth-industrial revolution technology used in the production of parts attributed to its numerous advantages. Hence, Selective Laser Melting of AlSi12 alloy presents a unique advantage in producing components with high density and minimal cracks or the initiation of stress. Selective laser melting is also an excellent technique for prototyping functional components. However, the process requires multiple heating cycles because it undergoes chemical and physical changes which causes variations in the powder performance and characteristics. This may lead to powder inconsistency, reactivity, and contamination. The properties of additively manufactured parts depend on the powder morphology and granulometry thus making the powders have significant advantages over standard production materials, however, there are certain restrictions in additive manufacturing. Hence, this study explores the characterization of aluminum-based alloy starting pre-alloyed powders for the synthesis of rail components using selective laser melting technology. It investigates the morphology of starting powders for the synthesis of rail components through selective laser melting. The powders were weighed accurately by using stoichiometry to make up the desired compositions. The mixing was carried out by the tubular mixer at 49 rpm for the period of 1, 4, and 8 hours, to get a uniform distribution of the alloy constituent in a dry environment at room temperature. This study aims at determining powder fitness before fabrication to ensure consistency and part quality through powder quality control, powder process optimization, and cost reduction. Morphology and qualitative phase analysis of the starting and mixed powders will be examined by X-Ray Diffractometer (XRD), field emission scanning electron microscopy (FESEM, JSM-7600F, Jeol, Japan) equipped with an energy dispersive X-ray spectrometer (EDS). The findings provide valuable insights into optimizing the SLM process for rail component synthesis using aluminum-based prealloyed powders. This study contributes to the advancement of additive manufacturing techniques for the railway industry, and potentially for other industries as well.

Evaluating Aseptic Presentation of Different Medical Device Packaging Configurations.

The Medical Device Regulation (MDR) of the European Union (EU) places greater emphasis on the usability of medical devices, with the goal of eliminating or reducing the risk of infection to patients. As this goal also is applicable to sterile packaging, ANSI/AAMI/ISO 11607-1:2019 introduced a usability evaluation requirement for aseptic presentation of terminally sterilized medical devices. In an effort to reduce contamination risks, this requirement focuses specifically on the sterile barrier system (SBS). However, research is limited on evaluating the usability of SBSs and their performance, from an aseptic presentation standpoint, in clinical settings. To address this research gap, we assessed 14 sterile medical devices with five different SBS configurations to elucidate how SBS configuration (type, size, and number of SBS layers) and user satisfaction levels affect usability. A total of 40 experienced clinical nurses participated in 280 individual trials (20 per SBS configuration), which were conducted in a simulated operating room. Ultraviolet fluorescent powder was used to simulate the contamination process and to evaluate the success or failure of the aseptic presentation. Pouch and tray configurations exhibited the best overall performance, while vent bags performed poorly and were considered less acceptable. Double SBS configurations outperformed single SBS configurations. The study highlighted the importance of appropriate SBS symbols to identify SBS layers, which is another patient safety-related requirement of the EU MDR. The current work also includes an analysis of the powder contamination method used in conducting the usability evaluation.

Mg-Ni-Nb2O5 Composite Produced by High-Pressure Torsion

A Mg-based composite material has been produced by the consolidation at room temperature of a Mg-5wt.% Ni-2wt.% Nb2O5 powder mixture subjected to high-pressure torsion (HPT), one of the processing methods to induce severe plastic deformations. The microstructure, density, and microhardness of the consolidated disks were characterized after the application of up to 30 revolutions in torsion under compression stresses of 3 and 5 GPa. According to the density measurements, the composite was consolidated in full after the application of five revolutions, although disks subjected to only one revolution exhibited densities close to the maximum measured value. On the other hand, grain size and microhardness measurements showed that differences existed at locations near the center and the periphery of the HPT-processed disks. Under the stress of 5 GPa, the grain size in the central regions stabilized at about 0.35 μm after five revolutions, while at the peripherical regions it gradually decreased with an increasing number of revolutions down to about 0.15 μm after 30 revolutions. In turn, the microhardness measured along a diametral cross section steadily increased with the number of revolutions between 1 and 10 revolutions, maintaining a gradient from the center to the periphery in all cases. With the application of 20 and 30 revolutions, only the peripheral regions increased considerably in hardness. It was discovered that the magnesium particles in the initial powder mixture had formed an oxide—hydroxide surface layer, which changed the expected final density of the consolidated material by about 2 to 4.5%. This superficial contamination of the Mg powders did not prevent the material from achieving full consolidation.

Laser Fusion of Powder and Foil – a Multi Material Approach to Additive Manufacturing

Multi material additive manufacturing (MM-AM) is an attractive approach to combine the geometric flexibility in particular of powder bed based AM processes with functional integration. A major limitation of multi-material laser powder bed fusion (MM-LPBF) approaches is the risk of powder contamination. In the present study, the implementation of a concept for manufacturing of multi material parts is demonstrated. A new type of device is contructed, and the new process is tested fundamentally and gradually by experimental means. Aspects investigated include machine and process feasibility, bonding issues, and dilution. Microstructural analysis reveals the successful build of multimaterial basic geometries out of steel powder (316L stainless steel) and both nickel-based alloy and copper foil. This provides a new process whose further research offers high potential for numerous multi-material applications.