Single shear test for powder compact has been suggested to identify shear failure envelope on several powder. Critical state line of power has been estimated directly since dilatancy characteristics can be observed in stress pass on single shear. Uniaxial compaction failure test of powder compact is also conducted to measure shear failure characteristics in lower stress state. It is recognized that variation of cohesion value of powder compacts has clearly depended on compaction pressure. Determination of subsequent yield surface is able to accomplish to identify internal friction angle and cohesion with several green compact density. Results of FEM (Finite Element Method) analysis of powder die compaction with Drucker-Prager CAP model simulates almost proper density distributions of green compact and occurrence of shear stress concentrations in ejection stage. It is concluded that estimation of critical state line using single shear test method becomes useful way to identify shear failure and subsequent yield surface.

Zinc stearate (ZnSt) and N,N’-ethylene bis (stearamide) (EBS) are conventional lubricants for powder metallurgy. While an iron powder mixture containing ZnSt exhibits excellent flowability, its ejection property was found to be inferior to that of a mixture containing EBS. The main purpose of this study was to identify the reason why EBS is superior to ZnSt in the ejection property. To achieve this objective, we attempted to evaluate the “lubricity” and “extrusive property” of the two lubricants separately, as these properties appear to determine their ejection properties. Lubricity was investigated by sliding tests on a uniform lubricant film. The friction coefficient of EBS obtained in this test was larger than that of ZnSt. The extrusive property, which means the ability to fill the gap between the compact and the die wall, was evaluated by an X-ray analysis of the compact surfaces. The results of those measurements indicated that the extrusive property of EBS was greater than that of ZnSt, resulting in the better ejection property.

The relationship between the physical properties and the density of sintered materials has been known until now. In general, the required functions are being met by increasing the density of the sintered material. Powder metallurgy is characterized by the creation of pores on the surface and inside of the material, and are mainly caused by the burning of lubricant during the sintering process. Up to now, there has been little mention of parameters other than the area ratio of pores that are related to density. So this time, we observed how the raw iron powder and lubricant affect the surface condition of the sintered body.

Anodic Ti-based gas diffusion layer (GDL) is the core component of proton exchange membrane (PEM) electrolysis cell. Realizing preparation of large-size ultra-thin porous Ti-based GDL can significantly improve efficiency of hydrogen production from PEM electrolysis water and reduce cost, which has important practical application value. In this work, the porous Ti plates with a size of 400×400 mm, a thickness of 230~330 µm, a porosity of 23~43%, an average pore size of 8~13 µm and a gas permeability of 5~15×10^-4 L/min·Pa·cm² were successfully fabricated through very few processing steps (powder rolling and vacuum sintering). It was proved that the pore structure, thickness and its uniformity of porous Ti plates can be regulated by powder characteristics (e.g. particle size) and rolling parameters (e.g. speed and roll gap) based on changing bite angle. This work provides some useful information and new possibilities for the development of Ti-based GDL.

Brazed characteristics of sintered Fe-Cu-C alloy are investigated focusing on the effect of pores in the sintered metals on the wettability and spreading behavior of filler metals, as well as a penetration of filler metals into a brazing gap to form brazed microstructure. Experiments are conducted using Ag-based alloys filler metals with different wettability. The wetting behaviors of the fillers on the surface of the sintered metals was examined. The result showed that the spreading area decreased with the increase of porosity of the sintered metal due to infiltration of the molten filler into the pore. The penetration of brazing filler into a gap was dependent on behaviors of spreading on the brazing interface and infiltration into microstructure. The relation between the spreading and infiltration is discussed based on the capillary action of molten filler and the effect of alloy elements in the filler metals on the interfacial reaction.

Stainless steel is used in a wide range of applications due to excellent mechanical properties and corrosion resistance. However, there is a difficulty in forming unmachinable small diameter and deep holes since stainless steel is a difficult-to-cut material. Additionally, the application of sintered stainless steel is limited to items that do not require airtightness due to the presence of pores inside the material. Although a method of increasing the density using liquid phase sintering was considered to reduce internal pores of sintered stainless steel, it significantly affects dimensional accuracy and post-processing after sintering because of the generation of large amount of shrinkage. In order to solve the above issues, we developed a high-density green machining method that combines a technique to increase density during powder compaction and a green machining process. We have succeeded in producing a stainless steel sintered material with a density of 95 vol% that does not leak even when evaluated for tightness under high-pressure hydrogen conditions of 70 MPa.

Sintered parts can be mass-produced with high precision and cost-effectiveness, and have a wide range of applications, including in automobiles. Since conventional sintered materials tend to show lower fatigue strength than that of wrought steel, they cannot be applied to high load applications.The effect of homogeneity in the microstructure of sintered materials on fatigue strength has been investigated in many studies. In this paper, we compare fatigue strength between homogeneous and heterogeneous materials. Our study reveals that in a high-density range of about 7.7 g/cm³, cracks occur at the surface starting point, and homogeneous materials have a fatigue life 10 times longer than that of heterogeneous materials.

In this work, powder compaction and solid-state sintering are employed to fabricate iron-based self-lubricating composites containing MoS₂ and graphite. Previous studies have shown that MoS₂ reacts with iron matrices during sintering, making the production of Fe-MoS₂ composites challenging. We hereby demonstrate that a modification in the sintering atmosphere improves the composites' tribological properties due to a synergic effect of retardation of the solid-state reaction and increase of the matrix microhardness related to the nitrogen intake. The composites sintered in a mixed Ar/H₂/N₂ atmosphere exhibited, on average, a lower dry coefficient of friction compared to those sintered in Ar/H₂.

We received a request to develop a piston and pilot case for a new semi-active suspension with a built-in damping force control valve. The built-in valve mechanism is subject to high internal pressure, so each part required high sealing performance and rigidity. A combination piston was adopted due to port specifications, but there were concerns about sealing performance. There were also concerns about pressure resistance due to the complicated oil passages arranged on the seat surface. The pilot case has a complicated seat surface shape, so ensuring flatness was an issue. In this paper, we overcame these issues by setting appropriate conditions by correctly evaluating the performance using CAE analysis and 3D measurement. Here, we will report on the development process, which started with the material and set appropriate conditions.

The demand for motors is increasing, and the needs for down-sizing, weight-saving and higher efficiency of motors are increasing with the progress of electrification of mobility, and improving efficiency of home appliances and industrial equipment. Axial flux motor (AFM) exhibits higher torque with thin shape than radial gap motors, and are attracting attention that meet these needs. For AFM, it is important to form a three-dimensional magnetic circuit, and Soft magnetic composite core (SMC) with high design flexibility in shape is suitable. In this study, in order to increase the opposing area between the stator and rotor, contributing to improved magnetic properties and increasing productivity, we will report on development of core shape that allows a teeth and double flanges to be integrally molded using SMC.

For many years, additive manufacturing has been used to produce new features and production designs to benefit the user and application. AM (Additive Manufacturing) is now moving into the industrialisation phase and companies are investing heavily to install full scale production facilities. There is increasing focus on repeatability, quality, and the overall need to reduce cost to compete with traditional production methods. Here, Hot Isostatic Pressing (HIP), plays a key role.This paper with show examples of cost reduction whilst reducing environmental impact and ensuringproduct quality, with a focus on PBF (Powder Bed Fusion)

The cost of additive manufacturing (AM) processes is today typically higher than traditional manufacturing processes such as casting or machining for series production, particularly of medium and large batches. A fair comparison is often complex, since the true costs of the AM part become only visible after leveraging the design freedom through a Design-for-AM process. Thus, for the analysis of the manufacturing costs of additively manufactured parts versus conventional production methods a simplified cost estimation model based on component volume is introduced. Considering at first the same volume as in the conventional part design, the price for the component using powder bed fusion and sinter-based AM methods is approximated. The resulting, typically higher costs are then transduced into a weight saving requirement for matching the costs of the conventional process. Finally, this requirement is assessed against the typical weight saving potentials of each technology to predict the economic feasibility.

Metal powder is the feedstock for most of the metal additive manufacturing (AM) technologies, including powder bed fusion – laser beam (PBF-LB) and electron beam (PBF-EB), binder jetting (BJT) and powder blown directed energy deposition (DED). However, even if nearly the same alloys systems are used, requirements to the powder feedstock are rather different. Processing conditions during powder-based metal AM differ significantly, depending on technology, hardware solution and process parameters employed. This results in changes in powder properties during manufacturing cycle and especially during its reuse, also having significant impact on the final component properties. This work summarizes recent experimental observations and thermodynamic simulations of the changes in powder properties during the whole life-cycle of metal powder: from its manufacturing through powder handling and AM processing by variety of powder-based metal AM technologies. Generic model of the powder degradation in dependance on alloy composition and AM technology, is elaborated.

In the context of multi-material additive manufacturing (MMAM), Cu-based alloys present inherent chemical and physical properties mismatch with other alloys that often lead to cracking, dimensional mismatch and poor bond performance at the interface. This, combined with the lack of optimized laser parameters for the desired arrangement of materials in the 3D-space present a challenge to achieve functionally distinct regions. IN718, which has been used in the past together with Cu-based alloys, benefits from great chemical affinity of Ni with Cu and, and contrary to 316L, has been rarely explored with Cu alloys in PBF-LB/M. The present work focuses on the feasibility study of printing CuCrZr onto IN718 substrate and the influence of PBF-LB/M process parameters on the morphology and the composition of the meltpool. CuCrZr single tracks were printed onto IN718 buildplate for different set of process parameters including laser power, scan speed and layer thickness.

Recently, the demand for high-quality gas-atomized powders has increased. Some particles in gas-atomized powders contain internal pores, and the presence of these pores may result in the degradation of various properties of the final product manufactured through a specific process. However, the mechanism of the internal pore formation has not yet been elucidated. In this study, various alloy powders were prepared using the gas atomization method, and their internal pores were observed using synchrotron X-ray CT. The results showed that alloys with a wider solid–liquid coexistence temperature range exhibited a higher porosity–volume ratio. This suggests that gas bubbles are more likely to be entrained during secondary droplet breakup. It was also found that introducing a small amount of hydrogen as a reducing agent into the spray gas reduced these quantities.

Commonly, flow rate (ISO 4490, JIS Z 2502, MPIF Standard 3) is used to evaluate powder flow. However, it may not be possible to measure flow rate because powder is not discharged from the orifice, and sometimes flow rate does not correspond to the actual production of parts in terms of productibility or weight variation. To examine the evaluation method of powder flow for die filling, we conducted measurements using evaluation devices (die filling testing devices) which are close to the actual die filling of pressing machines, owned by three powder producing member companies of the Technical Committee for Metal Powders of the Japan Powder Metallurgy Association. In addition, the powders used for this evaluation were those used in actual production by three member companies who manufacture components, from the same committee. As a result, it was found that appropriate quantitative evaluation is possible within the range of standard parameter conditions. On the other hand, it was also found that valid evaluations could not be obtained outside this range. We would like to discuss the possibility of standardization by further limiting parameter conditions.

Metal-organic frameworks (MOFs) are highly effective materials for environmental cleanup, but their small size limits industrial scalability. MOF-based macroscopic architectures offer a solution allowing for their practical use. This study presents a sustainable, scalable method for the in-situ growth of copper benzene-1,4-dicarboxylate (Cu-BDC) MOF on carboxymethyl cellulose (CMC) beads. A 2% w/v CMC solution with aniline and 1,4-benzenedicarboxylic acid (H₂BDC) was dropped into a copper nitrate solution. Cellulose nanofibers (CNFs) were also added to this CMC solution to assess their effects. The resulting beads, sized 1.87±0.16 mm, featured gyrification-like folds with 488.78±1.19 nm Cu-BDC spherical protrusions. Aniline was crucial in forming the folds and spherical protrusions. The presence of CNFs enhanced the beads' mechanical and thermal strength, although higher concentrations of CNFs (>1%) hindered the growth of MOFs. This method offers a viable pathway for scaling MOFs for practical industrial applications.

The glassy volcanic sand produced mainly in the Kyushu region of Japan is called “Shirasu” and is composed of fine particles of silica-based compounds. Rapid heating to about 1000 ℃ makes the Shiras particles to expand and foam. The particles form a balloonlike hollow structure called a “Shiras balloons”. In this study, solidified bodies of shirasu particles were prepared by alkali activation and foamed at low temperatures. The effects of sample preparation conditions, such as the concentration of added NaOH, treatment temperature, and time, on the foaming properties were investigated. The mechanism of low-temperature foaming of silica-based solidified bodies was discussed.

In this study, we investigated the enhancement of sinterability and suppression of sintering aid segregation in the lithium-ion conductor LiTa₂PO₈ (LTPO) through a nano-coating approach with MgO. Our findings reveal that the nano-coating technique significantly improves sinterability, requiring less additive compared to conventional methods. The sintered ceramic exhibited a total lithium-ion conductivity of 8.5×10⁻⁵ S cm⁻¹, highlighting the efficacy of the nano-coating method in enhancing sinterability while mitigating segregation issues.

A new segregation-free iron-based powder mixture with excellent lubricity was developed. The most notable feature of this new powder mixture is superior lubricity compared with mixtures containing conventional lubricants such as zinc stearate. In addition, clean sintered surfaces can be obtained because the new mixture does not contain zinc stearate. These features will contribute to improvement of product quality and the yield rate of sintered parts. The mechanism of the excellent lubricity of this powder mixture was investigated by SEM/EDX analysis of green compact surfaces. The analysis indicated that the ejection force of the compacts made of this powder mixture was reduced by concentration of the lubricant between the compact and the die wall surface during the compaction process.

The flow properties of metal powder premixes are influenced by the selection of powder metallurgy (PM) lubricants, which affect both the chemical composition and physical characteristics of the premix. External factors, such as environmental conditions during mixing, transportation, and storage, as well as blending methods, play a significant role in altering flowability. PM lubricants must sustain optimal flow across a range of conditions, including elevated temperatures, humidity, and shear stress. This study evaluates the influence of lubricant hardness, manufacturing processes, and premix preparation techniques on flow behavior. Statistical analysis was performed to quantify the effects of these variables. Additionally, newly developed lubricants were compared with commercial alternatives using flowmeters, GranuDrum, and die-filling assessments. Results show that the novel lubricants retained superior flow properties under challenging conditions and achieved faster, more stable filling than commercially available products.

Metal powders usually have oxide films on their surfaces. When used in powder metallurgy, these surfaces form oxygen-rich grain boundaries, which could harm the material's performance. We developed a technique to coat metal powders with different metals directly on their oxide-free surfaces under ultra-low oxygen atmosphere. This enables us to form a thin and uniform covering layer on each particle. Even when the content of the coating material is of the order of single wt%, it can greatly improve the material performance through a direct metal-metal interface without oxides in between. By sintering the coated powder, the grain boundary properties, which affect various material properties, can be controlled by this technique. We will show some examples of how this technique can tune the material function.

This research investigated the effect of in-situ TiC formation during the sintering process on the microstructure and mechanical characteristics of a NbTaVTi high entropy alloy (HEA). The study examined the carbon diffusion from the graphite mold and its influence on TiC formation, as well as analyzed how the size and dispersion of TiC particles influence the microstructure and mechanical properties of the alloy. The in-situ TiC-reinforced NbTaVTi HEA displays a microstructure consisting of BCC and FCC TiC phases. This structure shows a significant yield strength of 1.6 GPa and a plastic strain of 34% at room temperature. These outstanding properties of the in-situ TiC-reinforced HEA indicate its potential as a promising material for structural application.

In this paper, microstructure and mechanical properties of equimolar CrFeCoNiMo high entropy alloy (HEA) prepared by mechanical milling (MM) and spark plasma sintering (SPS) process were investigated in detail. The initial and MM powders were sintered 1.8 ks at 1173 to 1373 K by using SPS apparatus. Microstructural observation of the powders and SPS compacts was achieved using scanning electron microscopy (SEM) / electron back scattered diffraction (EBSD). The SPS compact of the initial and MM powders consist of FCC, σ and μ phases. The grain size of the compacts of the MM powders is fine compared with that of the initial powders. The grain sizes of each phase increase with increasing the sintered temperature. The Vickers hardness of the MM powder compacts is higher than that of the initial powder compacts. The Vicker hardness of the compacts of initial and MM powders decreases with increasing the sintered temperature. It is revealed that the hardness of CrFeCoNiMo HEA is attributed to the grain size of each phase composed of the microstructure.

The Harmonic Structure (HS) design was applied to a high entropy CrMnFeCoNi alloy with two different ultrafine-grained (UFG) fractions. The high-temperature deformation behavior of the alloy with those kinds of HS compacts, as well as a homogeneous (Homo) compact, was studied by compression tests at a strain rate of 0.01/s at 1073 K. The stress-strain curves of the Homo and HS compacts exhibited strikingly disparate characteristics, rendering them quite distinctive. The Homo compact exhibited a steady state deformation following the onset of yielding, whereas the two types of HS compacts demonstrated a softening behavior with increasing strain. It is notable that the HS compacts exhibited the formation of a smaller misoriented grain concentration at the UFG network structure, designated as the “Shell,” at the initial stage of deformation. Conversely, the Homo compact exhibited a comparable microstructural alteration only following the occurrence of a substantial strain region. It can thus be posited that the process of dynamic recrystallization occurred at an earlier stage in the HS compacts in comparison to the Homo compacts. In other words, a selective dynamic crystallization occurs at the Shell in the HS compacts at high temperature deformation.

The fabrication of a series of CrMnFeCoNi alloy compacts with homogeneous (Homo) and harmonic structure (HS) via powder metallurgy routes was followed by the subjection of these specimens to high-temperature compression tests at initial strain rates of 1.0×10^-2 s^-1, 1.0×10^-3 s^-1, and 1.0×10^-4 s^-1 at 1073 K and 1173 K. The HS compacts exhibited a well-developed ultra-fine grain (UFG) network structure, designated as the “Shell.” Consequently, the HS-designed specimen exhibited a pronounced reduction in flow stress in comparison to the homogeneous structure counterpart. Moreover, the homogeneous specimens exhibited a strain rate sensitivity value of less than 0.3, while the HS specimens demonstrated a strain rate sensitivity value greater than 0.3, with a value of 0.61 observed at 1173 K. This indicates that the HS specimens displayed pseudo-superplastic deformation behavior. This softening behavior can be attributed to the accumulation of dislocations in the shell region, which leads to dynamic recrystallization. This phenomenon can be understood as hetero-deformation-induced (HDI) softening.

Fe has been identified as a detrimental element in Al alloy systems due to its proclivity to co-precipitate with other elements. The formation of brittle intermetallic phases by Fe impedes the sustainable utilization of Al. Nevertheless, the role of Fe in laser-powder bed fusion (LPBF) processes requires reconsideration. It is noteworthy that the rapid cooling rate (on the order of 10⁵ K/s) provided by LPBF facilitates both the freezing of doping elements and the formation of well-dispersed cellular structures and precipitates. Despite the numerous advantages offered by these sub-structures, the precise microstructure evolution during the LPBF process remains unclear. In order to gain a comprehensive understanding of the phenomenon in question, we first designed and tested several 8xxx series Al alloys with the objective of exploring the ability of these materials to resist high-temperature softening. The second part of the study involved conducting in-situ TEM heating experiments on the LPBF-built AlFeMoSiZr system.

Powder smoke phenomena – a cloud of metallic powder created by electrostatic repulsion – is an inherent issue that has been observed in many high temperature alloys processed by Electron Beam Powder Bed Fusion (EPBF). To date the majority of research addressing this issue has focused on machine modification and process manipulation to prevent overcharging of powder particles, but little has investigated the effects of controlling powder characteristics. A recent body of work from the University of Tohoku has proposed ball milling as a method for mechanically working the surfaces of gas atomized IN718 and TiAl4822 powders to alter their surface oxide layers, thus improving their electrical conductivity. Utilizing microscopy, thermophysical and electrical property analysis, an assessment of the ball milling mechanisms responsible for smoke mitigation have been investigated using a novel γ-TiAl – Ti-48Al-2Nb-3Zr-0.2B – with superior oxidation resistance.

Additively manufactured (AM) α+β titanium alloys produced by laser powder-bed fusion (L-PBF) typically exhibit fine acicular microstructures due to the intrinsically fast-cooling rates of the process. In solute-rich alloys such as Ti-6Al-4V, this extreme grain refinement can severely reduce plasticity (fracture strains < 10%), thereby exposing parts to catastrophic engineering failures. In pursuit of a superior strength-ductility balance, we investigated the L-PBF processing of compositionally lean Ti-alloys containing small fractions of common iron and nitrogen solutes (beyond the standards of commercial purity). Despite their traditionally low wrought strengths, these near-purity alloys are shown to pair well with the grain refinement effects of L-PBF to produce mechanical properties on par with wrought Ti-6Al-4V (yield strengths > 825 MPa, fracture strains > 10%), indicating a strong compatibility with AM processing. Meanwhile these compositions are rare-metal free, and simple to recycle, thereby offering a cheap and sustainable alternative for use in titanium AM.

A low odor anaerobic sealant for sealing pores in cast metal and powder metallurgy parts was prepared using polyethylene glycol dimethacrylate and lauryl methacrylate as the main materials, by exploring the effects of formula composition, stirring time and stirring temperature on the performance of the anaerobic sealant. After optimization, the results show that when the weight percent (wt%) of Dicumyl peroxide is 3.0~3.5%, the wt% of acetophenazine is 0.8~1.0%, the stirring time is 2~2.5 hours, and the stirring temperature is 40⁓60℃, the prepared anaerobic sealant fully meets the sealing requirements of the powder metallurgy parts. It has passed all the requirements of MIL-I-17563 Rev.C and also exhibits excellent resistance to acids, caustics, hydrocarbons and solvents. Furthermore, the prepared anaerobic sealant demonstrates a lower cure shrinkage rate, thereby rendering it highly suitable for a diverse array of applications.

Fe-based nanocrystalline alloy powders Fe₇₇Cu₁Nb₃Si_5.7B_13.3-xCr_x (x = 0, 0.5, 1.0, 1.5, 2.0 at%) was produced by our own unique technology atomization process “Spinning Water Atomization Process (SWAP^Ⓡ)”. The broad peak of amorphous state was retained for up to chromium content 1.5% in above mentioned composition. The increase in coercive force with heat treatment was suppressed with adding chromium content. Additionally, the rate of rise the magnetic flux density due to nanocrystallization from the amorphous state showed a tendency to increase with adding chromium content. The Fe₇₇Cu₁Nb₃Si_5.7B_11.8Cr_1.5 nanocrystalline powder showed Hc = 46.2 A/m and Bs = 1.34 T. The Fe₇₇Cu₁Nb₃Si_5.7B_11.8Cr_1.5 powder exhibited approximately 7% increase in magnetic flux density and 24% decrease in core loss at 1 MHz at Bm = 0.02 T compared to a commercial (Fe_0.97Cr_0.03)₇₆(Si_0.5B_0.5)₂₂C₂ amorphous powder.

With the expanding use of high-performance permanent magnets, such as Nd-Fe-B, in green energy production and e-mobility, comes the need to further investigate contemporary production methods. Field assisted sintering technologies, such as spark plasma sintering and flash spark plasma sintering, have shown promising results with regards to anisotropic texturing, densification, and microstructural fine-tuning, even from non-ideal crushed anisotropic Nd-Fe-B scrap as a starting powder. Optimization of these processes could lead to magnetic performance that matches or exceeds standard commercial magnet production techniques, such as hot deformation. This is due to the fine parameter monitoring and control available with field assisted sintering devices. This study focuses on the optimization of field assisted sintering with commercial MQU-F to demonstrate net-shaping of anisotropic Nd-Fe-B magnets with an intention of transferring the parameters to the deformation of recycled magnet powder.

The development of additive manufacturing (AM) of permanent magnets is rapidly growing due to the competitive advantages they offer. AM of complex shape magnets could revolutionize the design of electrical machines potentially allowing for higher performance. Unfortunately, magnetic performance of AM permanent magnets is often limited due to the use of isotropic powders. In this study, Al-NdFeB composite permanent magnets were fabricated by cold spray AM using anisotropic NdFeB powders. Anisotropic powder can improve magnets’ remanence and energy product via particle alignment and subsequent magnetic anisotropy. The effect of gas temperature on deposition rate and magnet performance was evaluated. Magnetic measurements were performed along three orthogonal directions to quantify the level of anisotropy. It is demonstrated that anisotropic powders partially align itself during the cold spray process in the absence of external magnetic field. This could pave the way for a simple and efficient way of fabricating anisotropic magnets.

The induction thermal plasma (ITP) process, which is a bottom-up physical gas evaporation process, is a promising method for preparing nanoparticles smaller than 300 nm. In this study, the Sm-Co magnetic alloy nanopowders were successfully prepared by the ITP process using a mixture of Sm and Co powders with an atomic ratio of Sm:Co = 1:1.5, and 1:6. Spherical nanoparticles with a mean particle size of approximately 50-56 nm were obtained. The formation of Sm-Co alloy phases according to the mixing ratio of Sm and Co powders was investigated using X-ray diffraction profile and thermomagnetic analysis. This study suggests that the ITP process is a promising new strategy for the preparation of unique magnetic nanopowders.

The low-temperature-phase MnBi (LTP-MnBi) powders were successfully synthesized via an in-house developed low-oxygen induction thermal plasma system, followed by post-annealing treatment. However, achieving high-purity LTP-MnBi alloy remains a challenge due to persistent undesired Mn, Bi and Bi-rich phases post-peritectic reaction during a heat treatment. Here, we employed the in-situ transmission electron microscopy to investigate phase transformation processes dynamically. It is found that micro-sized Bi clusters formed after the heat treatment which can significantly shift the desired Mn:Bi composition and reduce the area fraction of Mn/Bi interface which is essential for an efficient peritectic phase transformation. It sequentially reduces the volume fraction of the desired LTP-MnBi phase in the final product. The in-situ kinetics analysis in this work elucidates the structural evolution and phase transformation mechanisms in Mn-Bi nanopowders, offering useful insights for developing high-performance rare-earth-free permanent magnet.

Achieving appropriate interfacial bonding while avoiding structural damage is the foremost concern in fabricating high-performance carbon nanotube (CNT)/Al matrix composites. In this work, a ceramic coating strategy was developed to enhance the interfacial strength of CNT/Al composites. A continuous SiO₂ layer, approximately 50 nm in thickness, was uniformly coated on the surface of acid-treated CNTs using the sol-gel method. Through the combination of hetero-agglomeration process, spark plasma sintering, and hot extrusion, the SiO₂@CNTs experienced limited structural damage and remained dispersed and singly aligned in the Al matrix. Due to the presence of the amorphous SiO₂ layer between the CNTs and the Al matrix, the CNTs were polygonally deformed and free from interfacial reactions. Consequently, the 2.0 wt.% SiO₂@CNT/Al composites exhibited an increased mechanical performance, indicating enhanced load transfer at the CNT-Al interfaces due to the ceramic coating.

This study discusses strategies and challenges for computational design of sintered materials. In this context, the importance of fast acting reduced order models to efficiently explore the multi-dimensional design space of materials is highlighted. The study also presents an example of a reduced order model for designing pre-alloyed powders that can be densified by using super-solidus liquid phase sintering. The design exercise is based on an integrated computational materials engineering (ICME) framework involving genetic algorithm to optimize the chemical composition of high-speed steels (HSS) to simultaneously improve the sintering response and the resultant properties. Thermodynamic simulations, based on the CALPHAD method, are used to establish microstructural constraints through phase stability at equilibrium. Results of the design exercise in comparison with conventional alloys are presented. We show that new HSS alloys with improved sintering performance can be designed while simultaneously enhancing their performance properties.

Based on previous research data, the High-Density High-Performance Powder Metallurgy (HPM) process has proven to effectively enhance material overall density and mechanical strength at a relatively low processing cost. This study extends previous research by further exploring the fatigue resistance of HPM gears. The experiment will focus on dynamic testing of spur gears with involute teeth using a dynamic testing system. Finite Element Method (FEA) analysis will be employed for supplementary simulation calculations to evaluate the fatigue resistance of pinions manufactured under different processes and to design reasonable parameters. The study primarily compares the fatigue properties among Powder Metallurgy (PM), High-Density High-Performance Powder Metallurgy (HPM), and hobbing gears, analyzing and discussing the test results based on F-N curves.

The use of Cr or Mn as alloying elements plays a prominent role in sintered iron-based materials, as they possess the ability to enhance the strength of materials through the addition of small quantities, due to their high quenching multiples. However, Cr and Mn, which are also a readily oxidisable element, is preferentially oxidised by the presence of H₂O and CO₂ in the atmosphere in the conventional carburising process using hydrocarbon-modified gas. The oxidation of Cr and Mn during carburising represents a significant challenge to address, as it can lead to significant variations in the mechanical strength of sintered and carburised materials. We focused on low-pressure carburisation, which has the potential to suppress Cr and Mn oxidation. This paper will demonstrate such an effect on the tensile properties of Fe-Cr and Fe-(Cr, Mn) sintered steels applied by the low-pressure carburisation.

Powder metallurgical components reveal a high dimensional accuracy while offering a cost efficient and sustainable production. The inherent porosity contributes to a notable weight reduction but also affects the strength and durability. Numerous studies examined the effect of the porosity and the size and shape of individual pores on the fatigue behaviour. However, its effect on yielding behaviour is rarely reported. In this work, uniaxial compaction and dilatometry are used to produce cylindrical samples with different sintering states and densities. Microstructural analyses are performed to evaluate the effect of different sintering conditions on pore morphology and subsequently derive two-dimensional finite element models to virtually assess the effect of the pore morphology and density on strength. The results are compared with corresponding Rastagaev compression tests that are conducted with identical cylindrical samples. Additional three-dimensional simulations are performed based on μ-CT measurements to evaluate the difference between two- and three-dimensional simulation models.

Porous materials, when applied in batteries, require not only functional pores but also a certain level of mechanical strength. Therefore, this experiment attempts to add varying proportions of iron phosphide to the iron slurry, employing a tape casting process to produce thin porous iron-phosphorus sheets. We compare the characteristics (porosity, microstructure, resistance, etc.) and mechanical strength of the specimens resulting from different phosphorus contents. In the experiment, we control the phosphorus ratio in the iron-phosphorus mixture within the range of 0.0wt% to 1.5wt% and manufacture specimens with thicknesses ranging from 0.3mm to 0.6mm. At 1120°C during the sintering process, the phosphorus allows the specimens to reach liquid-phase sintering conditions. The experimental results indicate that a higher proportion of phosphorus significantly improves bonding between powders and enhances mechanical strength.

Uni-axial compression tests were performed to derive yield stress equation, flow rules and coefficient of flow stress of BaTiO₃ sintered compaction. These basic equations and their physical properties were introduced into the FEM. The drooping behavior of the thin-thickness specimen during the sintering was simulated and compared to the experimental drooping, where the specimens were composed of large or small average diameter BaTiO₃, respectively. Resulting simulation drooping quantitatively reproduces that experiment. This result suggests that experimentally derived yield stress equation, non-Newtonian viscoplastic flow rule 𝜎_eq = 𝐹𝜀⁰𝜀̇^0.8 and coefficient of flow stress about several to 1000 GPa s of sintered BaTiO₃ compaction were numerically validated.

Over the last two decades, Spark Plasma Sintering (SPS) has become a major technique for manufacturing advanced materials. But mastering SPS process is complex and, for a better understanding, requires a computational calculation support. SPS simulations are mostly conducted using Finite Element Method (FEM). However, FEM approaches are well-known for being time and cost-consuming due to high computational complexity. On the other hand, the emerging approaches such as Deep Learning (DL) could be considered as a viable alternative to traditional modelling and has proven their effectiveness in many fields. But classic DL methods are not well suited for approximate data based on Partial Differential Equations (PDE). Thereby, the interesting properties of Neural Operator (NO) lies in the ability of the network to implicitly learn the underlying PDE operators hidden in the data. In this study, we investigated the potential of emerging NO approach as a faster alternative to SPS FEM models.

The sintering of engineered components produced from powders can be enhanced by the formation of a liquid phase, but excess liquid leads to distortion and an inability to make net-shape parts. The amount of distortion depends not only on the liquid volume fraction but also on other microstructural parameters, such as grain size, dihedral angle, contiguity, and connectivity. The effects of these parameters on distortion of liquid-phase-sintered tungsten heavy alloys can be evaluated by adjusting alloy compositions and processing conditions. Sintering in microgravity extends the range of compositions that can be evaluated by eliminating settling of grains resulting from the density difference between the solid and liquid phases. In this work, data from recent microgravity experiments on the International Space Station are used for testing model predictions for the effects of microstructural parameters on dimensional stability.

To examine the effects of morphology of metal-ceramic mixtures on the sinterability, a method of simulating the sintering process with no chemical reaction between two dissimilar powder materials is proposed, based on the combined phase-field method (PFM) and discrete element method (DEM). The initial arrangements of dispersed/aggregated particles are prepared with the mixing ratio of two powders changing in the range from 0 to 100%. The calculated results indicate that the sintering shrinkage of powder compacts with dispersed particles is lower than that of aggregated particles, which agrees with the experimental observation in a previous study. It is also confirmed that the grain growth behavior is affected by the dispersion degree of dissimilar particles. The average grain size is decreased with mixing ratio, especially in the case of dispersed particles.

Nowadays, the fabrication of multi-material components with desired geometries and tailored microstructural properties is drawing continuous attention. By laminating or additive manufacturing and subsequent co-sintering, multi-material composites that combine a wide range of favorable properties can be produced. Examples are metal-ceramic laminates and multi-ceramic composites, which not only open the spectrum of material applications but also provide a higher degree of flexibility than single materials. However, undesired deformation that triggers delamination, curvature, cracks or even catastrophic failure frequently occurs during the co-sintering process. To solve these issues, a thermo-mechanical model that predicts densification, deformation, and delamination of multi-material components along the entire co-sintering process was developed. A multi-ceramic composite and a metal-ceramic laminate were selected to test and validate the developed model by experimental investigations. The developed model is proven to effectively describe the deformation, curvature, and stress distribution in the studied material combinations.

Additive manufacturing (AM) of metal components has developed rapidly throughout the last decade. Sinter-based processes hereby offer the implementation of AM within existing powder metallurgical process routes, utilizing similar powders and sintering furnaces. While processes such as binder-jetting or fused-filament-fabrication have disadvantages such as limited resolution accuracy, lithography-based metal manufacturing (LMM) enables the production of filigree, complex structures with low surface roughness. However, layer-by-layer powder deposition induces anisotropic shrinkage during the subsequent sintering process.

In this work, two numerical models are proposed to predict the shrinkage behavior of 316L produced by LMM. Firstly, a kinetic Monte-Carlo model is used to simulate shrinkage and grain growth based on experimentally derived microstructures of green parts. Secondly, a dilatometric study is conducted to derive a constitutive model of sintering on a macroscale that accounts for the effect of density, grain size, temperature and printing direction. The accuracy of both models is shown by comparison with experiments.

Today there is a huge and growing number of additive manufacturing (AM) technologies. Since LPBF as dominating AM technology of metals has limitations in terms of geometries and materials as well as in productivity, sinter-based additive manufacturing (SBAM) processes are becoming increasingly important. Metal Binder Jetting (MBJ) or Fused Filament Fabrication (FFF) are the most well-known SBAM processes. Furthermore, new processes such as MoldJet (MJ), Cold Metal Fusion (CMF) or Lithography-based Metal Manufacturing (LMM) are attracting widespread attention due to their promising properties. In this review, the status of the most important sinter-based processes is highlighted and compared with LPBF. All technologies have pro´s and con´s, therefore a detailed analysis of the main features is the key to select the right technology for the intended application. At the same time, it is becoming apparent that there is still a development need in accompanying processes (e.g., heat treatment, sinter simulation). Future development trends and the market potential of SBAM processes will be discussed.

Additive manufacturing (AM) of metals has undergone rapid technological development over the past 2 decades. While the beginning was strongly influenced by the development of beam-based processes, the sinter-based AM processes have gained more and more diversity and importance for more than 5 years now. This review presents the results of investigations following process developments of selected sinter-based AM processes using elemental powder mixtures to produce WHA parts. The achieved sintering densities, microstructures, purities as well as mechanical properties are compared with the minimum requirements of the current ASTM standard B777 and typical values of the conventional PM route (p/s). Manufactured demonstrators show the advantages and opportunities of the technologies. According to the current state of technical knowledge, a concluding process overview should serve as a decision-making aid for the right choice of technology for the additive manufacturing of WHA products, considering selected criteria as well as the limitations