Application of a wax-based binder in PIM of WC–TiC–Co cemented carbides

A wax-based binder was developed for powder injection molding of WC–TiC–Co cemented carbides. The critical powder loading and the rheologic behavior of the feedstock were determined. It was found that the critical powder loading could achieve up to 62.5 vol% and the feedstock exhibited a pseudo-plastic flow behavior. The injection molding, debinding and sintering processes were studied. The dimensional deviation of the sintered samples could be controlled in the range of ±0.2% with the optimized processing parameters. The mechanical properties were better than or equivalent to those of the same alloy made by the conventional press-sintering process.     

A new starch-based binder for metal injection molding

A composition of starch and linear low-density polyethylene (LLDPE) was prepared as the binder and a mixture of this binder with 316L stainless steel powder was used to achieve a feedstock with 57% vol. powder loading. Rheological specifications of the binder and the feedstock were observed by means of capillary rheometery. Pseudo-plastic behavior of the binder and feedstock was investigated as a necessity in metal injection molding (MIM) process by proper flow characterization tests and their viscosity as the most significant flow characteristic was obtained in acceptable ranges. Thermogravimetric analysis (TGA) was carried out on feedstock in order to understand decomposition behavior of the binder components. In the next step, injection molding of the components was successfully conducted. Mechanical properties of compacts were then investigated through the triple point flexure test and the results showed that mechanical strength of specimens are very close to established ranges. The density of green parts was measured to assess the compaction of feedstock and it was achieved within the expected range for ferrous-based feedstocks. Debinding process was accomplished on compacted articles at three different temperature ranges including 70, 80 and 90 °C. Sintering process also was successfully accomplished on samples. For observing microstructures, the surface and cross section of specimens were compared before and after debinding as well as after sintering using scanning electron macrograph (SEM). Generally, this newly developed binder demonstrated a good potential for being utilized in MIM process.     

Powder injection molding of pure titanium

An improved wax-based binder was developed for powder injection molding of pure titanium. A critical powder loading of 69 vol.% and a pseudo-plastic flow behavior were obtained by the feedstock based on the binder. The injection molding, debinding, and sintering process were studied. An ideal control of carbon and oxygen contents was achieved by thermal debinding in vacuum atmosphere (10-3 Pa). The mechanical properties of as-sintered specimens were less than those of titanium made by the conventional press-sintering process. Good shape retention and ±0.04 mm dimension deviation were achieved.     

Fabrication and properties of Si3N4 based ceramics using combustion synthesized powders

Silicon nitride (Si₃N₄) based ceramics were fabricated with β-SiAlON and Si₃N₄ powders synthesized by combustion synthesis method via power injection molding (PIM). In the PIM process, the solids loading for each material was first determined from the results of the torque rheometer experiment. The mixing process was repeated to produce the homogeneous feedstock, and homogeneity of feedstocks was evaluated by observing the shear viscosity with time at a constant shear rate. The rheological behavior of feedstocks was investigated using capillary rheometer. It found that both feedstocks have no problem in injection molding. The binder decomposition behavior was also investigated, and a wax-polymer binder system was nearly removed by the optimized solvent and thermal debinding processes. Thereafter, the debound samples were sintered at 1750 and 1800 °C for 4 h in nitrogen atmosphere. Regardless of sintering temperature, the relative density of higher than about 96% was achieved. When comparing mechanical properties including bending strength, Vickers hardness and fracture toughness, Si₃N₄ with 2 wt% Y₂O₃ and 5 wt% Al₂O₃ (Si₃N₄+2Y5A) had higher values than β-SiAlON with 4 wt% Y₂O₃ (β-SiAlON+4Y) regardless of sintering temperature. It was supported by observing the microstructures of the plasma-etched samples.     

Powder injection molding of WC–8%Co tungsten cemented carbide

An improved wax-based multi-component binder was developed for powder injection molding of tungsten cemented carbide. A critical powder loading of 65 vol.% and an ideal rheological properties were obtained by the feedstock based on the binder. An ideal control of carbon content was achieved by thermal debinding in 75 vol.%N₂/25 vol.%H₂ atmosphere, which balanced the decarbonization effect of H₂ and the carburation effect of N₂. Solvent debinding followed by subsequent thermal debinding could substantially increase the debinding rate, and it is more flexible and adjustable to debinding atmosphere. The transverse rupture strength, hardness and density of the as-sintered specimens made by an optimized powder injection molding process were 2500 MPa, HRA90 and 14.72 g cm⁻³ respectively. Good shape retention and ±0.02 mm dimension deviation were achieved.     

Effect of thermo-mechanical properties of PIM feedstock on compacts shape retention during debinding process

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The manufacturing and replication of microfluidic mould inserts by the hot embossing process

In this paper, the manufacturing of metallic microfluidic mould inserts is studied based on the hot embossing process. The feedstocks are prepared and analysed. The quality of the feedstock resulting from the mixing process is found to depend on numerous parameters, such as the mixing time, the mixing temperature, the shear rate and the powder loading. The present mixing study is conducted with copper powders. The thermal and rheological properties of the selected feedstock under various mixing conditions are determined and used to establish the necessary conditions for mixing, hot embossing and debinding to obtain the copper microfluidic mould inserts. Sintering at different temperatures is conducted under vacuum. The effects of the sintering temperatures are evaluated based on the sintered microstructures. In this work, the dimensional variations in the microfluidic samples, in particular the dimensional shrinkage, global warpage and surface roughness at each stage of the process, are quantified and compared in detail.     

YT5硬质合金注射成形

开发了一种适合于硬质合金注射成形的“改进型蜡基粘结剂”和一种称作“高压冷凝溶剂脱脂”的新的脱脂方法。实验结果表明 :使用该粘结剂 ,硬质合金注射混合料流变性能良好 ,临界固体粉末装载量达到 6 5 %。新的脱脂方法脱脂速率快 ,脱脂坯强度高。采用优化的工艺制备了 PIM YT5硬质合金试样 ,其抗弯强度、硬度和密度分别达到2 10 0 MPa、HRA 90 .4和 12 .83g/cm3 ,制品保形性良好 ,尺寸偏差小于± 0 .0 4m m。     

A novel binder and binder extraction method for powder injection molding of tungsten cemented carbide

1　INTRODUCTIONPowderinjectionmolding (PIM ) ,whichisde rivedfromplasticinjectionmolding ,isakindofnet shapepowdermetallurgyformingprocess[13] .Com bininghigh partcomplexitywithhigh productionquantities ,itsupplementstheestablishedprocesseslikediecompaction ,machiningandinvestmentcasting[4 6 ] .Comparingtoconventionalpressing/sinteringprocess,thePIMhasgreattechniqueandcostadvantagesforthepro ductionofcementedcarbidecomponentswithcomplexshapes[7,8] .Sincehydraulicpressureisappliedduringi…     

The effects of nanoparticle addition on SiC and AlN powder–polymer mixtures: Packing and flow behavior

The development of methods to increase sintered density and improve dimensional tolerances is a crucial issue in powder metallurgy and ceramic processing. Increasing the packing density of starting powders is one effective route to achieve high sintered density and dimensional precision. The current paper presents an in-depth study on the effect of nanoparticle addition on the powder content of SiC and AlN powder–polymer mixtures. In particular, bimodal mixtures of nanoscale and sub-micrometer particles were found to have significantly increased powder volume fraction (solids loading) in the mixtures for injection molding. This observation to increasing packing density by using nanoparticles is surprising and novel since nanoparticles are known to inherently exhibit poor packing behavior. Additionally, for a given volume fraction of powder, the bimodal μ-n suspensions had a lower viscosity at any shear rate compared to the monomodal μ-suspensions. The ability to lower the suspension viscosity by adding nanoparticles to micron-sized particles has important implications for processing of particulate suspensions by powder injection molding (PIM), extrusion, slip casting and tape casting. Samples made from bimodal powders exhibited slower polymer removal during debinding and higher densification with lower shrinkage on sintering compared to the corresponding samples made from monomodal powder mixtures.     

金属注射成形的脱脂临界厚度

通过对脱脂动力学的分析，发现在脱脂过程中，存在动力学控制步骤转化的过程，提出了临界厚度的概念。临界厚度越大，意味着脱脂初始阶段升温速率可以较快，脱脂所需时间可以相对缩短。临界厚度越小，那么脱脂初始阶段必须缓慢升温，以免产生鼓泡、裂纹、变形等缺陷。生产实践中临界厚度越大，脱脂处理越容易进行。对脱脂过程中控制步骤的理论计算，得到脱脂临界厚度与粉末大小、脱脂温度和装载量的关系：临界厚度与粉末颗粒大小成正比，粉末颗粒越大，临界厚度也大；临界厚度与保温温度成反比关系，温度越高，临界厚度越小；临界厚度与装载量成反比，装载量越高，临界厚度越小。     

INJECTION MOLDED TUNGSTEN HEAVY ALLOY

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Water soluble Invar 36 feedstock development for μPIM

A water soluble binder system based on cellulose acetate butyrate (CAB) and polyethylene glycol (PEG) is proposed and investigated to carry out a micro powder injection moulding (μPIM) process with an Invar 36 alloy powders. The overall process was optimised with an emphasis on the determination of the optimal solid loading. Several methodologies were evaluated and compared to determine this parameter. A full μPIM was performed with different powder content feedstocks. Dog bone-type micro test parts were fabricated thereof and their mechanical properties were evaluated. Solid loadings up to 65 vol.% resulted to have the most equilibrated properties to successfully fabricate Invar 36 micro parts with the selected powder and binder system.     

Metal injection molding of W-Cu powders prepared by low energy ball milling

Low energy ball milled W/Cu powders were used for metal injection molding (MIM) in order to overcome the low powder volume fraction of MIM parts after debinding as well as the inherently poor sinterability of the W-Cu powder compacts. Ball milling was carried out using commercial fine W and Cu powders to form a powder mixture suitable for injection molding. W powders showed no change in either size or shape during the milling process, but the ductile Cu powders were easily deformed to a three-dimensional equiaxed shape, having a particle size comparable to that of W powders. This modification of powder characteristics by ball milling resulted in an improvement of the solid loading of roughly 58%, maintaining a high and uniform powder packing density in the feedstock. The densification behavior of W-Cu MIM parts is also discussed on the basis of the relationship between Cu composition and W particle size.     

注射成形97W—2Ni—1Fe重合金的研究

制备了几种不同粉末装载量的９７Ｗ－２Ｎｉ－１Ｆｅ重合金注射成形喂料,对这些喂料的流变学行为进行了研究,测量了烧结后产品的力学性能和烧结过程中的收缩。研究结果表明喂料的流变行为可用假塑性体来描述,注射成形所得合金的力学性能优于传统压制／烧结所得合金,当粉末装载量（体积分数,％）为４７时合金力学性能最好。成形坯在烧结过程中的收缩基本各向同性,产品的尺寸偏差小。     

The effects of nanoparticle addition on binder removal from injection molded aluminum nitride

The effects of nanoparticle addition on the multi-step debinding of injection molded aluminum nitride (AlN) samples were studied. Experiments varying the solvent debinding conditions (time, temperature and aspect ratio) were performed on monomodal, microscale (μ) and bimodal, micro-nanoscale (μ-n) AlN samples. Variations in the solvent debinding kinetics as a result of the reduced particle size and increased powder content were examined. The bimodal μ-n AlN samples showed a slower solvent extraction of binder components compared to monomodal μ-AlN samples. The activation energy for solvent extraction estimated from diffusion coefficients (Arrhenius equation) was in close agreement with the value estimated by the master debinding curve (MDC) method. An activation value around 50 kJ/mol was estimated by both the methods for μ and μ-n AlN samples. The thermal debinding behavior of dewaxed samples was also studied and the trends correlated with the solvent debinding behavior.     

粘结剂组成对粘结剂和喂料热性能的影响

研究制备了PW，BO，OP3大系列10种组成的粘结剂及相应10种W-Ni-Fe粉末与粘结剂的混合料。并采用热失重-差热分析(TGA-DTA)分析了粘结剂和喂料的热性能。研究结果表明，粘结剂组成对粘结剂和喂料的热性能如熔点、热分解温度和热分解曲线有很大的影响。通过此变化可以更为准确地确定不同粘结剂组成的喂料中的粘结剂脱除工艺和脱除方式。     

Correlations Between Powder Feedstock Quality,In Situ Porosity Detection,and Fatigue Behavior of Ti-6Al-4V Fabricated by Powder Bed Electron Beam Melting: A Step Towards Qualification

Ti-6Al-4V is the most studied alloy via electron beam melting (EBM) with regards to microstructure and mechanical behavior, but there have been no attempts to correlate in situ porosity detection and fatigue behavior. This is required for widespread adoption of EBM because conventional evaluation is often time-consuming and expensive. This paper presents the use of near-infrared imaging to detect and quantify porosity in Ti-6Al-4V builds fabricated from different powder feedstocks and its correlation to their fatigue response. We report that, for identical processing parameters, the variability in powder feedstock causes variations in porosity and scatter in the respective fatigue response.     

Determination of critical and optimal powder loadings for 316L fine stainless steel feedstocks for micro-powder injection molding

Adapted from powder injection molding (PIM), the micro-PIM technology satisfies the increasing demands for functionalization and miniaturization of micro-parts. Research works in this area have been carried out through micro injection molding tests issued from mixtures consisting in 316L stainless steel fine powders with D₅₀ = 3.4 μm and different thermoplastic polymeric binders. The well appropriate polymer–powder formulations are composed with different binders. The binders have been adapted to micro-injection and tested to find out an optimum feedstock. The rheological characterization of the elaborated feedstock has been carried out according to the selected stainless steel powders and polymers. The critical powder volume loading has been determinated and fixed in the range of 68–70%, and the optimal powder volume loading has been chosen around 66% for 316L stainless steel feedstock (D₅₀ = 3.4 μm). This choice has been confirmed by processing of the micro-components with the retained feedstock loaded up to 66%.     

硬质合金增塑粉末螺杆挤压成形

探讨了用于硬质合金粉末螺杆挤压成形技术的新粘结剂制备及挤压棒的组织形貌。新粘结剂由几种低分子量组元与1种热塑性弹性体高分子组元构成。采用溶剂溶解与加热熔融相结合的办法制备粘结剂。室温下，用合适的剪切力搅拌，能很快将粘结剂与YG8粉末混合均匀，制得组成均一的料浆式挤压用喂料。用扫描电子显微镜观察了挤压毛坯的微观组织及脱脂试样的组织结构与缺陷。用热重(TG)与微分热重(DTG)方法研究了热脱脂机理与动力学，发现了三维扩散控制热脱脂的速率。在脱脂的第1阶段，低分子量组元被脱除掉，挤压毛坯内形成了连通毛细孔。在脱脂的第2阶段，剩下的高分子量组元被完全脱除；第2阶段的热脱脂能以较快的升温速率进行。制备出了φ20mm的硬质合金挤压棒。