Powder Injection Research Articles

Manufacturing, high heat flux testing and post mortem analyses of a W-PIM mock-up

Abstract In the framework of the European material development programme for fusion power plants beyond the international thermonuclear experimental reactor (ITER), tungsten (W) is an attractive candidate as plasma facing material for future fusion reactors. The selection of tungsten is owing to its physical properties such as the high melting point of 3420 °C, the high strength and thermal conductivity, the low thermal expansion and low erosion rate. Disadvantages are the low ductility and fracture toughness at room temperature, low oxidation resistance, and the manufacturing by mechanical machining such as milling and turning, because it is extremely cost and time intensive. Powder Injection Molding (PIM) as near-net-shape technology allows the mass production of complex parts, the direct joining of different materials and the development and manufacturing of composite and prototype materials presenting an interesting alternative process route to conventional manufacturing technologies. With its high precision, the PIM process offers the advantage of reduced costs compared to conventional machining. Isotropic materials, good thermal shock resistance, and high shape complexity are typical properties of PIM tungsten. This contribution describes the fabrication of tungsten monoblocks, in particular for applications in divertor components, via PIM. The assembly to a component (mock-up) was done by Hot Radial Pressing (HRP). Furthermore, this component was characterized by High Heat Flux (HHF) tests at GLADIS and at JUDITH 2, and achieved 1300 cycles @ 20 MW/m². Post mortem analyses were performed quantifying and qualifying the occurring damage by metallographic and microscopical means. The crystallographic texture was analysed by EBSD measurements. No change in microstructure during testing was observed.

Rheological and thermal debinding behaviors of silicon nitride in powder injection molding

Abstract In powder injection molding process, it is important to analyze the rheological and thermal debinding behaviors of feedstock, because they can directly affect the final quality of products. Therefore, for the silicon nitride based feedstocks, the rheological and thermal debinding behaviors were investigated and compared between feedstocks prepared with the combination of two types of powders and sintering aid ratios. At first, the optimal solids loading for each feedstock was determined based on the results of the torque rheometer experiment. The viscosity of the feedstocks was measured using the capillary rheometer, and rheological properties were evaluated with the Power Law-Arrhenius model. Silicon nitride (JPN) feedstock with 5 wt% yttria and 2 wt% alumina (JPN+5Y2A) had the highest moldability index among all feedstocks. The powders with sintering aid ratio of 5 wt% yttria and 2 wt% alumina made the feedstocks have a high moldability index. Thermogravimetric experiment was also performed to analyze the pyrolysis behavior of the feedstocks, and the apparent activation energies for each feedstock were obtained using Kissinger method with the thermogravimetric analysis results. Based on the results, the master decomposition curve (MDC) was developed, and the utility of MDC for optimizing the thermal debinding process was verified.

A comprehensive review of extrusion-based additive manufacturing processes for rapid production of metallic and ceramic parts

The extrusion-based additive manufacturing (EAM) technique is recently being employed for rapid production of metals and ceramic components. This technique involves extruding the metal or ceramic material in solid powder form mixed with a binder (i.e., an expendable viscous fluid), which is removed from the part after 3D printing. These technologies rely on the large design freedom allowed and the cost efficiency advantage over alternative metal additive manufacturing processes that are based on high energy beams, such as laser or electron beams. The EAM of metals and ceramics is not yet widespread, but published scientific and technical literature on it is rapidly growing. However, this literature is still less extensive than that on the fused deposition modeling (FDM) of plastics or the selective laser melting (SLM) of metals. This paper aims at filling this gap. FDM and powder injection molding are identified as preceding or enabling technologies for EAM. This paper systematically reviews all aspects of the feedstock EAM processes used for production of complex-shaped parts. The unique characteristics and advantages of these processes are also discussed with respect to materials and process steps. In addition, the key process parameters are explained to illustrate the suitability of the EAM process for diverse application domains.

Design of a transmissive optical system of a laser metal deposition three-dimensional printer with metal powder.

A transmissive optical system of a three-dimensional (3D) printer using the laser metal deposition (LMD) technique with a metal powder is proposed here, together with its design method. An f-number of the focused laser beam emitted from the optical system should be large enough for the laser beam not to be absorbed or reflected by the metal powder injection nozzle. On the other hand, owing to the Lagrange-Helmholtz relation, the f-number should be small enough to form a minute laser spot diameter for high-resolution building. A temperature rise induced by the high-power laser may cause damage or a thermal lens effect on the optical system, which can be reduced by using lenses having plano-surfaces contacting thermally with holders. A formula of the relationship of the thermal lens effect with an f-number of each lens is derived to determine the lens specifications. A formula of longitudinal spherical aberration (LSA) of these lenses is also derived, and the total LSA is shown to be able to be zero with an acceptable f-number of the focused laser beam. The prototype LMD 3D printer with 6kW laser is fabricated and shows favorable properties, such as a minimum building width of 0.3mm and a building speed of over 500cc/h.

Study on the melting characteristics of steel scrap in molten steel

ABSTRACTSteel scrap is of great benefit for environmental protection. In converter steelmaking, bottom carbon injection was applied to enhance the scrap ratio and in EAF steelmaking, submerged carbon powder injection was used to accelerate the smelting of scrap. In these two cases, carbon powder is directly injected into molten metal to improve the scrap melting with effective carburization capacity and intense stirring effect. In this study, the induction furnace experiments were carried out to study the melting characteristics of steel scrap with different carbon contents and bottom-blowing gas flow rates. The results show that larger carbon content and faster fluid flow can promote scrap melting because the carburizing reaction can be accelerated by larger carbon concentration gradient and the heat transfer can be enhanced by larger stirring intensity. Finally, the convective mass transfer coefficient and heat transfer coefficient between steel bar and molten metal were also calculated.

Debinding behaviour of feedstock for material extrusion additive manufacturing of zirconia

ABSTRACTMaterial Extrusion Additive Manufacturing (MEAM) is mainly used for the production of polymeric components. Using feedstocks similar to those of powder injection moulding, MEAM of ceramic components is possible. MEAM with filaments is also called Fused Filament Fabrication. Feedstocks are used as filaments; this imposes new requirements such as flexibility for spooling, stiffness to avoid buckling and constant diameter to ensure a consistent mass flow. Additionally, the binder should be removed without damaging the shaped part. In this paper, the debinding behaviour of MEAM feedstocks with zirconia was investigated. It was observed that higher temperature increases the debinding rate, but cracks occurred; the addition of a surfactant speeds up the debinding rate and reduces cracks; and a mixture of 10% isopropanol and 90% cyclohexane initially decreases swelling during debinding, but the debinding rate and the appearance of cracks is unaffected.

High pulse number thermal shock testing of tungsten alloys produced by powder injection molding

Abstract The investigation of plasma facing materials (PFM) subjected to a large number (≥10,000) of thermal shocks is of interest to determine long term morphological changes which might influence component lifetime in and plasma performance of a fusion reactor. The electron beam facility JUDITH 2 was used to simulate these conditions experimentally. In this study eight different tungsten grades produced by powder injection molding (PIM) were investigated: Two pure tungsten grades, one with 2 wt% Y2O3, three with 1, 2 and 3 wt% TiC, and two with 0.5 and 1 wt% TaC. Samples of 10 × 10 × 4 mm³ were brazed to a copper cooling structure and subjected to 105 thermal shocks of 0.5 ms duration and an intensity of Labs = 0.55 GW/m² (FHF = 12 MWs½/m2) at a base temperature of Tbase = 700 °C. The PIM grades showed damages in general comparable with a sintered and forged pure tungsten reference grade (>99.97 wt% W) that complies with the ITER specifications. One exception was the 2 wt% TiC doped material which failed early during the experiment by delamination of a large part of the surface. The Y2O3 doped material showed a comparatively good performance with respect to crack width (

Simulation on the Two-phase Separation of Powder Injection Molding 316L Stainless Steel

By utilizing the FLUENT software, finite element simulation analysis was performed on the two-phase separation of powder injection molding, and the simulation results were verified through experiment. As indicated in the simulation results, the optimal process parameters for the injection molding of 316L stainless steel sample were to inject at 70 MPa and 140 °C, at an injection speed of 3.49 cm3/s. Under these conditions, the maximum average solid volume fraction in observation area of the sample was 57.68 %. Additionally, it was discovered that while preparing 316L stainless steel was prepared by powder injection molding, the smaller the average porosity of the sample, the greater the Vickers hardness. And then the higher the average solid volume fraction simulated the slighter the two-phase separation between the powder and the binder. DOI: http://dx.doi.org/10.5755/j01.ms.25.3.19137

Mold optimization design of metal powder injection product USB interface based on Mold Flow analysis

Metal powder injection molding technology (metal injection molding, the MIM) can achieve a mass in the small and medium-sized complex shape product preparation, low cost, which is of great significance in promoting the production of products and applications.In this paper, taking the USB interface parts made of 17-4ph stainless steel as an example, through scheme verification, the optimized and reasonable die structure is obtained, the 3d modeling of the parts is carried out with UG, and MoldFlow software is used for MoldFlow analysis.The design cycle is shortened and the design quality is improved.

Investigation of operating parameters on high-velocity oxyfuel thermal spray coating quality for aerospace applications

The coating quality by the high-velocity oxyfuel (HVOF) thermal spray process is greatly dependent on the operating parameters chosen during the operation. Depending on the application, the operating conditions are manipulated to enhance the desired coating property. Enhancement of multiple properties necessitates optimization of the operating conditions. This entails a comprehensive analysis of several coatings deposited at different operating conditions. The design of experiments is an effective method that helps in identifying optimum operating conditions with a reduced number of experiments. In the present study, a 24 factorial design approach is used to establish the relationships between four operating parameters (coating thickness, fuel/oxygen ratio, spraying distance, and powder injection rate) and three coating properties (roughness, microhardness, and contact angle). The results obtained are utilized in identifying the optimum parameters that produce the best coating quality. Furthermore, the study also compares the coating quality obtained by the HVOF thermal spray process with that by chrome plating. The results show that the HVOF thermal spray process produces superior coating quality and it can be a promising environmentally friendly candidate for replacing chrome plating.

Investigation and two-stage modeling of sintering behavior of nano/micro-bimodal powders

Nano/micro-bimodal powders take advantages of both nano- and micro-powders. However, densification of the bimodal powder samples is hardly predictable with conventional sintering models due to their particular shrinkage behaviors. In this study, sintering behaviors of micro-, nano- and nano/micro-bimodal powders were investigated, and a two-stage master sintering curve model was developed. Micro-, nano- and three bimodal powder samples were prepared via powder injection molding process. The samples were sintered using a dilatometer to analyze the densification behavior, and microstructures of the samples with various sintering temperatures were observed. The results demonstrated the sintering mechanism of the bimodal and nano-powder samples could be divided into two stages. Based on observation, the two-stage master sintering curve model was suggested by introducing transition temperature, and sintering activation energy and material parameters were obtained for each region from the dilatometric data. The two-stage master sintering curve model was successfully developed with high accuracy. The model significantly reduced the maximum error of prediction density from 6 to 0.8%. The result indicated the two-stage master sintering curve model could describe the sintering behaviors of the bimodal and nano-powder samples.

Estimation of plasma parameters in the process of micro-scale powder plastic and characteristics of its products

The temperature and density of plasma jets were estimated with a Boltzmann plot and Stark broadening of Ar I (696.54 nm) lines by optical emission spectroscopy (OES) in the process of plasma plastic, and the morphology and microstructure of tungsten (W) powders were investigated by scanning electron microscope (SEM) and x-ray Diffraction (XRD), respectively. The results show that the assumption of local thermodynamic equilibrium (LTE) was invalid at the end of the plasma jets, and earlier than this after the injection of tungsten powder. The temperature and electron density of the plasma jets were up to about T = 6797 K with Qc = 50 slpm and ne = 1.05 × 1016 cm−3 with Qs = 115 slpm at Z = 60 mm, respectively, and both dropped rapidly with the injected tungsten powders of 20 μm. After the plasma plastic process, the spherical tungsten powders were prepared and there were some satellite particles on the surface of the spherical products. The tungsten powders were both composed of a single equilibrium α-W phase with a body centered cubic (bbc) crystal structure before and after plasma treatment.

Professor German updates his views on the present and future outlook for powder injection molding

Professor German updates his views on the present and future outlook for powder injection molding

YiQiFuMai Powder Injection Attenuates Coronary Artery Ligation-Induced Heart Failure Through Improving Mitochondrial Function via Regulating ROS Generation and CaMKII Signaling Pathways.

The YiQiFuMai powder injection (YQFM), a traditional Chinese medicine (TCM) prescription re-developed based on Sheng-Mai-San, is widely applied for the treatment of cardiovascular diseases. However, its potential molecular mechanism remains obscure. The present study was designed to observe the effects of YQFM and underlying mechanisms on coronary artery ligation (CAL)-induced heart failure (HF) and cell hypoxia of 24 h oxygen-glucose deprivation (OGD) in neonatal rat ventricular myocytes (NRVMs). HF was induced by permanent CAL for 2 weeks in ICR mice. The results demonstrated that YQFM significantly attenuated CAL-induced HF via improving the cardiac function, cardiac systolic function, cardiac structure impairment, cardiac histological features and fibrosis. YQFM markedly attenuated mitochondrial dysfunction through improving mitochondrial morphology, increasing mitochondria membrane potential (Δψm), mitochondrial ROS generation and expression of Mitofusin-2 (Mfn2), meanwhile, decreasing phosphorylation of dynamin-related protein 1 (p-Drp1). Mechanistically, YQFM could significantly decrease the expression of isoforms of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase subunit NADPH oxidase 2 (NOX2), p67phox and NADPH oxidase 4 (NOX4), ultimately reducing reactive oxygen species (ROS) generation. In addition, YQFM could down-regulate expression of calcium voltage-gated channel subunit α1C (CACNA1C) and phosphorylation of calmodulin dependent protein kinase II (p-CaMKII). These results suggest that YQFM ameliorates mitochondrial function in HF mice, partially through inhibiting ROS generation and CaMKII signaling pathways. Therefore, the present study provided scientific evidence for the underlying mechanism of YQFM.

Processing of Stainless Steel (SS316L)-Hydroxyapatite (HA) Powder Composite through Powder Injection Molding

The combination of a metallic bioinert material, stainless steel 316L (SS316L) and a bioactive material, hydroxyapatite (HA) can produce a composite material which has superior properties for orthopaedic applications. The main objective of this study is to investigate the effects of sintering temperature and time on the physical and mechanical properties of the sintered part. 50wt.% of SS316L and 50wt.% of HA were mixed with a binder system which consisted of palm stearin (PS) and polyethylene (PE) for 61.0vol.% powder loading. Rheological properties show the pseudoplastic behavior of the feedstock, where viscosity decreases with increasing shear rate. The feedstock was injection moulded into a tensile bar shape while thermal debinding was carried out at 320°C and 500°C. The brown part was sintered at 1000, 1100, 1200 and 1300°C, with three different sintering times of 1, 3 and 5 hours in the furnace. The highest sintered density measured was 95.61% of the theoretical density. The highest hardness and Young’s modulus measured were 150.45HV and 52.61GPa respectively, which is higher than the human bone. The lowest percentage of carbon content was 0.022 wt.% when the sample sintered at 1300°C for 1 hour. Mechanical and physical properties show that the SS316L/HA composite was successfully produced through the PIM process and can be potentially used for medical applications.

Influence of input power in Ar/H2 thermal plasma with silicon powder by numerical simulation

Numerical simulation in inductively coupled thermal plasma was made on the temperature distribution in argon (Ar)+hydrogen (H2) induction thermal plasma torch with silicon (Si) powder injection to obtain the temperature distribution and gas flow fields. The ICTP model was used in this research because it has benefit of good repeatability and no contamination process. Interactions between ICTP and injected powder are very complicated to be understood only by related experiments. Influence of input power in ICTP was numerically investigated on thermal plasma temperature fields and powder evaporation. The temperature distributions of thermal plasma and Si vapor distribution were compared at input powers of 20 kW, 30 kW, and 40 kW. Results indicated that higher input power increases the temperature of the thermal plasma with doughnut shape but it slightly enhances evaporation of the powder at the center axis of the plasma torch.

Real-time wall conditioning by controlled injection of boron and boron nitride powder in full tungsten wall ASDEX Upgrade

Abstract In ASDEX Upgrade with full-tungsten wall, boronization is an important tool to control tungsten sources and allow reliable operation at low collisionality. The duration of the beneficial effects is limited by the erosion of the boron layer, in particular on the tungsten ion-cyclotron antenna limiters. We report results from experiments exploring injection boron-rich powders in tokamak plasmas as a way to replenish boron coating and extend the lifetime of boronization effects. Pure boron and boron nitride powders were introduced gravitationally in plasma discharges at rates up to 60 mg/s for durations up to 3 s. Boron injection with cumulative amounts >100 mg appeared to improve wall conditions similarly to boronization, with indications of reduced influx of oxygen and tungsten from the antenna limiter. Moreover, cumulative injection of 340 mg of B appeared sufficient to enable successful execution of low collisionality scenarios critically relying on freshly boronized walls.

Three-dimensional printing of tungsten structures by directed energy deposition

ABSTRACTAlthough three-dimensional (3D) printing of tungsten parts by Powder Bed Fusion (PBF) has been demonstrated by multiple research groups, a directed energy deposition (DED) process for fabricating pure tungsten structures has never been reported. This work reports successful fabrication of pure tungsten structures by DED, revealing the required process conditions. The effect of laser power, scan speed, powder feed rate and carrier gas velocity on the stability and properties of the structures is first analyzed, based on which the proper process condition for effective 3D printing of tungsten parts is proposed. Fabrication of a rectangular tube of 110 mm in height is demonstrated using an in-house DED printing system. Analyses of the fabricated samples show that the density and the hardness can be as high as 18.9 g/cm3 (98.4% of the theoretical value) and 3.9 GPa, respectively. The results indicate that the optimal condition for 3D printing of tungsten is 400 ~ 530 J/mm2 in terms of specific energy and that high-speed or high-mass injection of powder can induce waviness on the surface. This work suggests that DED can be a promising alternative to produce pure tungsten parts in various applications.

Thermal decomposition behavior and modeling of PMN-PZT ceramic feedstock with varying binder compositions

The thermal debinding process is one of the most crucial steps in powder injection molding because it consumes a great deal of the processing time and may introduce defects into the component. To enhance production efficiency and increase defect avoidance, debinding conditions including maximum temperature, heating rate, and holding time should be determined based on the analysis of thermal decomposition behavior. The thermal decomposition behavior of lead magnesium niobate-lead zirconate titanate (PMN-PZT) ceramic feedstock with varying binder compositions was investigated in this paper using experimental analysis and modeling. In this study, the powder volume fraction in the feedstock was fixed at 45 vol% in order to isolate the effects of binder composition on thermal decomposition behavior. Each feedstock was divided into three groups depending on the variation in the filler binder (first), the backbone binder (second), and the entire binder system (third), respectively. Thermal decomposition behaviors for the feedstocks were analyzed by thermogravimetric analysis experiments at heating rates of 2, 5, and 10 °C min−1. All of the TGA graphs showed two sigmoidal curves due to the difference in the molecular weights of the binders. The apparent activation energy for binder decomposition was calculated based on the Kissinger approach. A remarkable change in activation energy was derived from the variation in the entire binder system. Based on the acquired decomposition parameters, master decomposition curve was constructed and verified experimentally in order to provide a predictive design tool for identifying optimal debinding conditions based on the intrinsic kinetics of binder pyrolysis.

Effect of sintering on the microstructure and mechanical properties of alloy titanium-wollastonite composite fabricated by powder injection moulding process

Abstract Composite biomaterials are in high demand in the medical field of today. The combination of bioactive wollastonite (WA) glass ceramic with the biocompatibility of alloy titanium (Ti6Al4V) could be a good candidate for implant applications. The rheological properties of Ti6Al4V/WA feedstock show a pseudoplastic behaviour with low activation energy. The feedstock was successfully injected as a green part with no defects. The green part was solvent debound for 6 h in heptane and thermal debound in an argon environment for 1 h. The brown part was successfully sintered at 1300 °C for 3 h with 5 °C/min heating and cooling rates. The average sintered density was 4.12 g/cm3; which is 97.5% from the theoretical density. The highest Young's modulus obtained was 18.10 GPa; which is in the range of human bone strength. EDX analysis shows that by increasing sintering temperature, the level of oxygen decreased. Cell viability test shown an absorbance increased with days increasing indicated that the cellular were proliferated on the composite Ti6Al4V/WA composite which also proved that the composite was non-toxic. This indicates that the Ti6Al4V/WA composite is suitable for bone implant applications.