Replication of metal microstructures by micro powder injection molding

In this paper, a study on the production of 316L stainless steel microstructures by μPIM (powder injection molding) is presented. Two types of mold inserts were used and the molding was conducted on a conventional injection molding machine. Based on the characteristics of the mold inserts and the feedstock, suitable processing parameters were selected. Some requirements for the production of the microstructures are discussed. For example, a relatively high mold temperature, high injection pressure and holding pressure were required. The study showed that 316L stainless steel microstructures of φ100 × 200 μm can be injection molded, but there were incomplete filling and demolding problem in the case of smaller microstructures of φ60 × 191 μm. The molded parts were successfully debound and sintered.     

Microstructural evolution of injection molded gas- and water-atomized 316L stainless steel powder during sintering

The present study investigates the microstructural evolution and densification behavior of water- and gas-atomized 316L stainless steel powder. Dilatometry and quenching studies were conducted to determine the extent of densification and corresponding microstructural changes. Results indicate that water-atomized powder could be sintered to 97% of theoretical density, while gas-atomized powders could be sintered to near-full density. The difference in the densification behavior is examined in terms of the particle morphology, initial green density and the particle chemistry.     

Effects of thermal debinding on surface roughness in micro powder injection molding

Micro metal injection molding (μMIM) is a promising process for the replication of metallic microstructures. In the micrometer regime, surface roughness is important in view of the dimensional tolerance and the applications of microstructured parts. In this paper, the effects of debinding on the surface roughness of 316 L stainless steel microstructured parts were investigated. Experimental results showed that using higher heating rates during debinding increased the weight loss of debound parts. The debound parts of higher weight loss gave better surface finish after sintering. Comparing the increase of sintering time and temperature, the surface finish improvement was more significant for increasing temperature.     

Effects of solidification rate on segregation and fluid flow tendency in mushy zone of directionally solidified superalloy Inconel 718

Abstract

The microstructure and composition of the interdendritic liquid along the mushy zone of superalloy Inconel 718 that was directionally solidified at various solidification rates between 2 and 100 μm s^?1 have been investigated by SEM and EDAX techniques. The interdendritic liquid segregation profiles along the mushy zone are presented. The liquid density difference and Rayleigh number in the interdendritic liquid were calculated and analysed as well. It was found that when the solidification rates increased in the range 10–70 μm s^?1, segregation of Nb decreased, but segregation of Mo was most serious at 20 μm s^?1. The liquid density difference increased the most for rates from 20 to 40 μm s^?1 as temperature decreased. The maximum relative Rayleigh number was highest at 10°C below the liquidus temperature at 20 μm s^?1, which indicated the conditions where fluid flow most easily occurred for Inconel 718. The relative Rayleigh number synthetically considers the factors affecting fluid flow and can give a reasonable prediction for fluid flow tendency.     

不同磁性粉末装载量和磁性粉末粒度对粘结NdFeB注射、挤出成型流动性能的影响

利用转矩流变仪和毛细管流变仪，讨论了不同的磁性粉末装载量与磁性粉末粒度对粘结NdFeB熔料流动性能的影响，建立了在不规则的粉末表面形态和复杂的粉末粒度分布下其固相浓度与熔料粘度的物理数学模型。粘结NdFeB熔料流动粘度与其粉末装载量呈现非线性的增长关系；在固定的固相浓度以及所讨论的粉末粒径范围内，熔料体系的粘度与固体粉末粒度呈负相关关系，体系内的作用力主要为液相粘结荆对固相磁性粉末粒子的粘性力；通过粘结Nd—FeB挤出成型时的功率消耗、转矩大小以及挤出物料表观质量等，分析成型设备的流道结构，并比较其与聚合物成型设备的异同。     

粘结剂对注射成型钕铁硼粘结磁体性能的影响

为了制备出高性价比的注射成型粘结钕铁硼永磁材料,系统地研究了粘结剂对注射成型磁体的加工性能、磁性能和力学性能等的影响。用国产的快淬钕铁硼磁粉和尼龙6粘结剂制备出了磁性能为Br:0．5158T,Hcb：321kA／m,Hcj：730kA／m,(BH)m：40kJ／m^3的注射钕铁硼磁体。     

Computer modeling of the heat transfer processes in injection molding

Absract  The results are given of the computer modeling of the heat transfer processes in injection molding. The distribution of temperature in the plant working route and molds for forming ceramic products in the form of nozzles, solid balls, bolls with a hole, and rings have been defined. The initial technological dependences have been calculated of the time of cooling thermoplastic mixtures based on AlN, SiC, and WC to 40°C for products of various shapes and types and sizes. Original Russian Text ? A.A. Leshchuk, T.O. Tsysar’, V.V. Ivzhenko, 2009, published in Sverkhtverdye Materialy, 2009, Vol. 31, No. 2, pp. 34–43.     

注射成形粘结Nd-Fe-N/Nd-Fe-B复合磁体的研究

对注射成形粘结Nd-Fe-N/Nd-Fe-B复合磁体及其复合效应进行了深入的研究,以制备满足市场所需的粘结磁体并扩大Nd-Fe-N的应用.实验结果表明:随着Nd-Fe-B磁粉的加入,复合磁体的抗压强度虽略有降低,但其磁性能及热稳定性均有大幅度改善.特别是由于Nd-Fe-B磁粉对弥散其周围的 Nd-Fe-N磁粉产生了一较强的静磁场作用,使得复合磁体呈现明显的剩磁增强效应.     

Comparative study of nanoparticle effects on feedstock behavior for injection molding

Rheological properties of bimodal feedstocks containing nano- and micro-particles were studied. To examine nanoparticle effects, five feedstocks were prepared with the nanoparticle contents from 0 to 75 vol. %. Each feedstock was formulated with the optimal amounts of the powders, determined from the critical solids loadings of the powders. Viscosity measurement of the feedstocks was performed using a capillary rheometer. From the result, the flow behavior index and flow activation energy were obtained as representative rheological parameters. The moldability index for each feedstock was also calculated and compared. Some bimodal feedstocks showed lower viscosity than microfeedstock due to the roller bearing effect of the nanoparticles. The rheological parameters indicated the bimodal feedstocks were more desirable for mold filling except for 75% nano-bimodal feedstock. The results revealed 25% nano-bimodal feedstock showed the highest moldability index and was the most desirable feedstock to prepare a green body via nano/micro-bimodal powder injection molding.     

Investigation of effects of dibutyltin dilaurate on reaction injection molding polyurethane-urea kinetics, morphology and mechanical properties by in situ FTIR

The bulk catalyst effect of dibutyltin dilaurate (DBTDL) on the reaction of NCO respectively with OH and NH₂ was investigated in detail. The results showed that DBTDL had specific catalyst effect on the reaction of NCO with OH and no measurable effect on the reaction of NCO with NH₂. In situ Fourier transform infrared spectroscopy (FTIR) used in the reaction injection molding (RIM) process showed that with increasing the concentration of DBTDL, the formation rate of the soft segment became fast, and the order degree of urea carbonyls became worse. Meanwhile, more arrange manners of urea carbonyl were present. The bands at 1653, 1647 and 1637 cm⁻¹ were able to be detected at the low conversion. No hydrogen-bonded urea carbonyl available in the spectra at the beginning. The tensile-stress behavior showed that, with the increase of the DBTDL content, the interaction between polar groups became weak, while the virtual crosslinks also became weak. Although the break stress (d), 300‰δ and the hardness of elastomers decreased obviously, however, the tear strength, associated with the morphology of polyurethane-urea (PUU), showed the maximum when the DBTDL content was 2.63‰.     

Experimental validation of post-filling flow in vacuum assisted resin transfer molding processes

In Liquid Composite Molding (LCM) processes with compliant tool, such as Vacuum Assisted Resin Transfer Molding Process (VARTM), resin flow continues even after the inlet is closed due to the preform deformation and pressure gradient developed during infusion. The resin flow and thickness changes continue until the resin pressure becomes uniform or the resin gels. This post-filling behavior is important as it will determine the final thickness and fiber volume fraction distribution in the cured composite. In this paper, a previously proposed one dimensional coupled flow and deformation process model has been compared with the experimental data in which the resin pressure and part thickness at various locations during the post-filling stage is recorded. Two different post-infusion scenarios are examined in order to determine their impact on the final part fiber volume fraction and thickness. The effects of different venting arrangements are demonstrated. The model predictions compare favorably with the experimental data, with the minor discrepancies arising due to the variability of material properties.     

Comparison of modified injection molding and conventional machining in biodegradable behavior of perforated cannulated magnesium hip stents

In this study,perforated cannulated magnesium(Mg)hip stents were fabricated via modified Mg injection molding and conventional machining,respectively.Additionally,the stent canal was filled with paraffin to simulate injection of biomaterials.The microstructure,mechanical performance,corrosion behavior,and biocompatibility were comparably studied.Scanning electron microscopy(SEM)and energy dispersive spectroscopy(EDS)showed higher affinity of interstitial element such as oxygen and carbon as consequences of routine molding process.After immersion in SBF,machining stents showed reduced degradation rate and increased deposition of calcium phosphate compared to molding stents.Corrosion resistance was improved via paraffin-filling.Consistently,the hemolysis and in vitro osteoblast cell culture models showed favourable biocompatibility in machining stents compared to molding ones,which was improved by paraffin-filling treatment as well.These results implied that the feasibility of the prepared machining stents as the potential in vivo orthopaedic application where slower degradation is required,which could be enhanced by designing canal-filling injection of biomaterials as well.     

磁粉表面改性及粒度对注射成形粘结NdFeB磁体性能的影响

注射成形粘结NdFeB磁体满足了市场时磁体小型化、轻型化及高性能化的要求,因而有着广泛的应用前景。本文研究了磁粉特性对注射成形粘结磁体性能的影响,结果表明：采用硅烷对磁粉进行表面改性,能有效提高NdFeB磁粉的抗氧化性及相应粘结磁体的磁学及力学性能;同时NdFeB磁粉粒径太粗太细均不利于磁体性能的提高 其最佳粒径范围是60～100μm。     

粉末冶金TiAl金属间化合物的研究进展

从粉末制备、成形、烧结、热处理等方面综述了粉末冶金方法制备TiAl金属间化合物的最新进展.着重评述了粉末冶金TiAl基合金的几种烧结工艺,其中包括热等静压、自蔓延高温合成、粉末注射成形、放电等离子烧结等,同时论述了上述各方法的优势以及局限性,并指出了今后的研究方向.     

气辅注射成型一维充填过程的最小注射量分析

对气辅注射成型一维充填过程的初始注射量进行了研究,并推导出了熔体最小注射量的计算公式。为气辅注射成型工艺的实际应用起到了指导作用。     

Evaluation of through-thickness permeability and the capillary effect in vacuum assisted liquid molding process

Through-thickness penetration under vacuum assistance is crucial for resin film infusion (RFI) and vacuum assistant resin transfer molding (VARTM) process. In this paper, values of the through-thickness unsaturated permeability (TTUP) and capillary pressure (P_c) are estimated based on the infiltration velocity in preforms of carbon fiber fabric and glass fiber fabric, respectively, measured by a specially designed apparatus. It reveals that, for the through-thickness permeation, the P_c values generally decrease with increasing fiber content. Relatively accurate TTUP can be obtained by counting P_c into the permeation dynamics. If P_c is neglected, liquids with good-wettability, such as silicone oil, tend to result in larger TTUPs. The corrected TTUPs show good agreement according to Carman–Kozeny, Gutowski modified Carman–Kozeny equation, and Gebart model, respectively. The resultant permeability resistance parameters of the preforms indicate that the penetration in carbon fabric bed is slower than in glass fabric bed. However, for fiber volume fraction more than 60%, the corrected TTUPs show no significant difference for all the preforms.     

Regimes of segregation and mixing in combined size and density granular systems: an experimental study

Granular segregation in a rotating tumbler occurs due to differences in either particle size or density, which are often varied individually while the other is held constant. Both cases present theoretical challenges; even more challenging, however, is the case where density and size segregation may compete or reinforce each other. The number of studies addressing this situation is small. Here we present an experimental study of how the combination of size and density of the granular material affects mixing and segregation. Digital images are obtained of experiments performed in a half-filled quasi-2D circular tumbler using a bi-disperse mixture of equal volumes of different sizes of steel and glass beads. For particle size and density combinations where percolation and buoyancy both contribute to segregation, either radial streaks or a “classical” core can occur, depending on the particle size ratio. For particle combinations where percolation and buoyancy oppose one another, there is a transition between a core composed of denser beads to a core composed of smaller beads. Mixing can be achieved instead of segregation if the denser beads are also bigger and if the ratio of particle size is greater than the ratio of particle density. Temporal evolution of these segregated patterns is quantified in terms of a “segregation index” (based on the area of the segregated pattern) and a “shape index” (based on the area and perimeter of the segregated pattern).     

First-principle study on the segregation and strengthening behavior of solute elements at grain boundary in BCC iron

Grain boundary(GB)significantly influences the mechanical properties of metal structural materials,yet the effect of solutes on GB modification and the underlying atomic mechanisms of solute segregation and strengthening in iron-based alloys remain insufficiently explored.To address this research gap,we conducted a comprehensive investigation into the segregation and strengthening effect of 33 commonly occurring solutes in iron-based alloys,with a specific focus on the body-centered cubic(BCC)iron Σ5(310)GB,utilizing first-principle calculations.Our findings reveal a negative linear correlation between solute segregation energy and atomic radius,highlighting the crucial role of atomic radius and electronic structure in determining GB strength.Moreover,through analyzing the relationship between strength-ening energy and segregation energy,it was found that the elements Ni,Co,Ti,V,Mn,Nb,Cr,Mo,W,and Re are significant enhancers of GB strength upon segregation.This study aims to provide theoretical guidance for selecting optimal doping elements in BCC iron-based alloys.     

Load partitioning during creep of powder metallurgy metal matrix composites and Shear-Lag model predictions

It was shown in a previous work that the load transfer mechanism plays a relevant role during the high temperature deformation of discontinuously reinforced metal matrix composites, MMCs. This idea emerged from the comparison of the creep data of a powder metallurgy, PM, 6061Al–15vol%SiC_w composite and the corresponding un-reinforced 6061Al alloy. The idea was further supported by a qualitative analysis of the creep data of MMCs from a number of investigations reported in the literature, particularly of PM composites. In the present work a quantitative and more thorough study of the creep data of these PM composites is presented. Specifically, a well-known Shear-Lag model is used to compare the composites creep strength increment and the predicted load transferred to the reinforcement. These new results sustain more thoroughly the relevance of the load transfer mechanism during creep of MMCs.