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.     

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…     

硬质合金注射成形脱脂过程中的碳含量控制

研究了不同脱脂气氛 (不同比例N2 与H2 的混合气体 )和脱脂方法 (热脱脂、溶剂脱脂 热脱脂、冷凝蒸汽脱脂 热脱脂 )对PIM硬质合金脱脂坯及合金碳含量的影响。结果表明 :N2 热脱脂粘结剂容易以炭黑的形式残留在脱脂坯中 ,造成合金增碳 ;H2 热脱脂导致合金脱碳 ;75 %N2 2 5 %H2 (体积分数 )混合气体热脱脂既能有效地脱除粘结剂 ,又能保证合金碳含量相对稳定 ;溶剂脱脂和冷凝溶剂脱脂能显著缩短脱脂时间 ,而且由于高温保持时间短 ,在后续热脱脂过程中采用H2 作保护气也可获得满意的碳含量 ,说明该方法对工艺条件的适应性强。通过调整热脱脂高温保持时间 ,可在一定范围内对脱脂坯的碳含量进行调整 ,说明过程的可调控性好。与溶剂脱脂相比 ,冷凝蒸气脱脂粘结剂脱除率更高 ,脱脂坯有较高的强度 ,有效地防止了脱脂坯软化变形的现象。     

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

1　ＩＮＴＲＯＤＵＣＴＩＯＮＡｍｏｎｇｃｒｉｔｉｃａｌｉｓｓｕｅｓｉｎｔｈｅｐｏｗｄｅｒｉｎｊｅｃｔｉｏｎ ｍｏｌｄｉｎｇｐｒｏｃｅｓｓｔｈｅｒｅａｒｅｔｈｅｃｏｎｔｒｏｌａｎｄａｖｏｉｄａｎｃｅｏｆｄｉｓｔｏｒｔｉｏｎｄｕｒｉｎｇｔｈｅｒｍａｌｄｅｂｉｎｄｉｎｇａｎｄｔｈｅｍｉｎｉ ｍｉｚａｔｉｏｎｏｆｓｔｒｅｓｓｅｓｉｎｔｈｅｃｏｍｐａｃｔａｆｔｅｒｄｉｅｆｉｌｌｉｎｇ[1] .Ａｆｔｅｒｍｏｌｄｉｎｇｔｈｅｓｔｒｅｎｇｔｈｏｆｔｈｅｃｏｍｐａｃｔｓｉｓｄｅｐｅｎ ｄｅｎｔｏｎｔｈｅｐａｒｔｉｃｌｅ…     

粉末注射成形溶剂脱脂过程的数学模型

从宏观的角度出发 ,仅考虑脱脂预成形坯的体积、粘结剂含量对脱脂过程的影响 ,将预成形坯几何形状等其他因素的影响合理地归结到扩散系数函数中。根据浓度扩散原理建立了描述粉末注射成形溶剂脱脂过程中预成形坯粘结剂含量随时间变化的数学模型 ,避免了求解用Fick第二定律描述的偏微分方程 ,得出了一种预测脱脂量与脱脂时间的有效方法。根据模型求出了脱脂速度函数 ,给出了一种控制溶剂脱脂过程产生缺陷的分段升温优化方法。用该模型对硬质合金注射成形溶剂脱脂过程进行了模拟和预测 ,预测结果与实验结果吻合较好     

Effects of heat treatment on the properties of powder injection molded AlN ceramics

The effects of two different heat-treatment atmospheres,nitrogen atmosphere and reducing nitrogen atmosphere with carbon,on the properties of Y2O3-doped aluminum nitride (AlN) ceramics were investigated.The AlN powder as a raw material was synthesized by self-propagating high-temperature synthesis (SHS) and compacts were fabricated by employing powder injection molding technique.The polymer-wax binder consisted of 60 wt.% paraffin wax (PW),35 wt.% polypropylene (PP),and 5 wt.% stearic acid (SA).After the removal of binder,specimens were sintered at 1850℃ in nitrogen atmosphere under atmospheric pressure.To improve the thermal conductivity,sintered samples were reheated.The result reveals that the heat-treatment atmosphere has significant effect on the properties and secondary phase of AlN ceramics.The thermal conductivity and density of AlN ceramics reheated in nitrogen gas are 180 W·m-1 K-1 and 3.28 g,cm-3 and the secondary phase is yttrium aluminate.For the sample reheated in reducing nitrogen atmosphere with carbon,the thermal conductivity and density are 173 W.m-1.K-1 and 3.23 g·cm-3,respectively,and the secondary phase is YN.     

Development of wax-oil-polyethylene binder for Fe-2Ni powder injection molding

1　ＩＮＴＲＯＤＵＣＴＩＯＮＭｅｔａｌｉｎｊｅｃｔｉｏｎｍｏｌｄｉｎｇ (ＭＩＭ )ｉｓａｎｅｗｌｙｄｅ ｖｅｌｏｐｅｄｔｅｃｈｎｏｌｏｇｙｆｏｒｆｏｒｍｉｎｇｃｏｍｐｌｉｃａｔｅ ｓｈａｐｅｄｍｅｔａｌｓａｎｄａｌｌｏｙｓ[1,2 ] .ＤｅｂｉｎｄｉｎｇｉｓｔｈｅｃｏｎｔｒｏｌｌｅｄｓｔｅｐｉｎＭＩＭ ,ｒｅｓｅａｒｃｈｅｓｏｆｂｉｎｄｅｒｓａｒｅｃｏｒｅｏｆｔｈｉｓｔｅｃｈｎｉｑｕｅ.Ｔｈｅｕｓｕａｌｍｅｔｈｏｄｆｏｒｒｅｍｏｖｉｎｇｂｉｎｄｅｒｉｓｔｈｅｒｍａｌｄｅｂｉｎｄｉｎｇ ,ｈｏｗｅｖｅｒ ,ｔｈｅ …     

聚乙二醇基粘结剂用于Fe—2Ni注射成形的研究

研究了用于Ｆｅ－２Ｎｉ（质量分数,％,下同）注射成形的聚乙二醇－聚甲基丙烯酸甲酯粘结剂的制备。粘结剂混炼时间短,粉末装载量５５（体积分数,％）,Ｈ２Ｏ脱脂速度超过２ｍｍ／ｈ。     

硬质合金挤压成形喂料热脱脂特性

开发出了适用于硬质合金挤压成形的成形剂及相应的热脱脂技术，通过优化配方设计与制备方式及工艺条件，制得了性能优良，分布均匀的成表剂。研究了成形剂及喂料的热脱脂工艺与机遇，发现热脱脂可分为低温区与高温区2个阶段，其脱脂机理均为热扩散，但2阶段热脱脂反应活化能不同；无论是成形剂还是喂料，其它组元的加入起了催化剂的作用，能有产地降低热脱脂反应活化能。     

Atmosphere control during debinding of powder injection molded parts

Atmosphere control during debinding of powder injection molded (PIM) parts is an important parameter to consider. Experimental results have shown that a stagnant atmosphere containing volatiles evolved during debinding can cause slumping of the green samples. Removal of volatiles from the sample zone aids debinding and can reduce cycle times and improve sample quality. Residual carbon and oxygen can be controlled during debinding by adjusting the atmosphere composition. This paper presents the results of PIM 70 vol% spherical copper powder and 30 vol% binder. Debinding atmospheres were altered to determine the effect of debinding on the green body and the sintered sample. This paper was originally presented at the symposium “Paniculate Materials in Rheological Applications,” TMS 1993 Fall meeting, Materials Week Program.     

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.     

YT5硬质合金注射成形新型溶剂脱脂工艺研究

脱脂是整个注射成形工艺中的关键步骤。本文以YT5硬质合金为对象,以正庚烷作为溶剂,系统研究了以多组元聚合物为粘结剂的注射坯样的溶剂脱脂行为。考查了粘结剂体系组成、脱脂温度、脱脂时间、样品厚度、样品形状对坯样脱脂率的影响及其原因。实验结果表明:在本实验所使用的三组粘结剂体系中,改进型蜡基粘结剂溶剂脱脂速度最快,脱脂效果最好,40℃、3h条件下该粘结剂体系中能被溶剂溶解的组元的脱除率达到98%;随脱脂温度的升高、脱脂时间的延长,粘结剂脱除率增大;溶剂脱脂初期为扩散控制,后期为溶解控制;粘结剂平均脱除速率与生坯表面积成正比,与生坯厚度成反比;脱脂完成后,脱脂坯边缘和中心组织均匀一致。     

Fabrication of W–20 wt.%Cu alloys by powder injection molding

W–20 wt.% Cu balls were fabricated by powder injection molding using a binder system consisted of paraffin wax, high density polyethylene, ethylene vinyl acetate and stearic acid. By optimizing the injection molding parameters, defect-free green parts were obtained. A two-step debinding process was employed to extract the binders in the molded samples. All soluble ingredients of the binders in the green parts were extracted during solvent debinding, and the residual binders can be removed in thermal debinding. The debound W–Cu samples were sintered in H₂ atmosphere at temperatures ranging 1050–1150 °C for 2 h. It was shown that relative density of the sintered W–Cu samples increases from 87.37% of the theoretical to 95.58% as sintering temperature rises from 1050 °C to 1150 °C. Microstructures of the molded, the debound and the sintered W–Cu samples were observed by scanning electron microscope, and the sintered W–Cu balls have fine and homogeneous microstructures. Maximum compressive strength of W–Cu balls with 8.5 mm diameter reaches 58 kN.     

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。     

铌合金注射成形脱脂工艺研究

设计了一种适合于铌合金注射成形的低残碳粘结剂体系,为68％PW-5％LDPE-22％PMMA-5％SA（质量分数）,并研究其脱脂工艺。结果表明：脱脂时间、温度及样品厚度对溶剂脱脂率影响显著。采用三氯乙烯为溶剂,在脱脂温度为40℃,溶剂脱脂6h,即可使粘结剂脱除率达到52．8％,使后继热脱脂时间缩短至7．5h。以粘结剂的DSC差热分析结果为指导,可快速制定合理的热脱脂工艺,在真空热脱脂气氛条件下可使脱脂坯残余碳、氧含量得到有效控制,分别为0．18％．0．25％．     

Fabrication of 93W–Ni–Fe alloy large-diameter rods by powder extrusion molding

A powder extrusion molding (PEM) process has been used for the manufacturing of tungsten heavy alloy rods with large length to diameter ratio. An improved wax-based multi-component binder was developed for PEM of 93W–Ni–Fe alloy. The miscibility of its components and the characteristics of the binder were evaluated and good thermal–physical properties were obtained. Also, the feedstock rheological properties, extrusion molding and debinding process were studied. The feedstock exhibited a pseudo-plastic flow behavior. The large length to diameter ratio rods, with diameters up to 36 mm were extruded at 65 °C by optimizing the extrusion process. A two-step debinding process was employed to remove the binder in the extruded rods. Solvent debinding was carried out in n-heptane at 45 °C to extract the soluble components. A process of repeated short time immersion and drying of the extruded rods (called short-period solvent debinding) was developed and using this novel technique the binder removed was raised from 45% to 60%. SEM analyses indicated that a large volume of pores was formed in debound rods, but had not created interpenetrating pore channels yet. The rest of the binder could be thermally extracted at a high heating rate without defects.     

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.     

Rapid debinding of 316L stainless steel injection moulded component

Wax-based binder system is widely used but they suffer from long debinding time and a tendency to slump or distort during debinding. This has been a major obstacle for the economic process for metal injection moulding (MIM). For improving the debinding process, two-step debinding process has been introduced. Gas-atomised 316L stainless steel powder was injection moulded using two types of multi-component binder system comprising (1) a major fraction of paraffin wax and a minor fraction of polyethylene (PE) and stearic acid (SA) as a lubricant, (2) a major fraction of polyethylene glycol (PEG) and a minor fraction of polymethyl methacrylate (PMMA) binder system. Debinding was carried out in two steps; first, the moulded part is immersed in heptane or distilled water at 60 °C to remove the major component of the binder and then heated to remove the remaining binder. The results show that no swelling or distortion was observed on the moulded specimens on both binder systems. Furthermore, the specimens had an adequate strength for handling even after solvent extraction. Large pore were formed from the surface to the interior of the debound part during solvent extraction, allowed easy escape of pyrolysis gases during thermal debinding. Thermal debinding with ramp heating at rates from 3 to 15 °C/min was found to be successful.     

钨基合金增塑粉末挤压成形新技术

采用增塑粉末挤压成形新技术,开发了几种适合钨基合金挤压成形用粘结剂,研究几种配方粘结剂的相容性及挤压、脱脂特性。通过热力学计算和热分析,以及扫描电镜和偏光显微镜观察,发现粘结剂各组元分子间具有较好的相容性。通过优化喂料制备、挤压工艺,分别在60和75℃制备出直径达24mm的大长径比钨基合金棒材。综合采用溶剂-热两步脱脂工艺,实现Ф24mm挤压棒坯的快速无缺陷脱脂。