硬质合金注射成形脱脂工艺与碳含量控制

将传统蜡基粘结剂和油＋蜡改进粘结剂体系分别与粒度为1．97μm的WC-8Co硬质合金粉末混合采用注射成形法制备了全致密高强度的硬质合金。研究了注射坯在Hz中的热脱脂工艺和溶剂脱脂与其后补充热脱脂工艺，和不同脱脂工艺对脱脂坯碳含量的影响。结果表明：油＋蜡改进粘结剂体系具有更好的热脱脂和溶剂脱脂行为。通过工艺优化和碳含量控制，在真空气氛下1400℃烧结80min制备出高抗弯强度的全致密硬质合金烧结制品。     

粉末注射成形热塑-热固粘结剂的开发研制

介绍了硬质合金粉末注射成形用热塑 -热固性粘结剂RG1- 2、RG2 - 3的开发研制过程。结果表明 :在注射完成之前 ,粘结剂和喂料完全表现为热塑性 ,该粘结剂可直接应用于热塑性注射机。喂料的低温流变性能好 ,粉末临界装载量达到 5 9%。RG1- 2、RG2 - 3注射生坯强度分别达到 5 .8MPa和 7.8MPa ,固化后成形坯强度分别达到 17.6MPa和 19.1MPa。采用该粘结剂及相应的注射成形工艺制备的YG8、YT5硬质合金强度分别达到 2 480MPa和 2 10 0MPa ,硬度分别达到HRA89.7和HRA90 .4,制品最小尺寸偏差达到± 0 .0 2mm ,尺寸精度及保形性优于传统蜡基粘结剂。     

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。     

超细WC-6%Co注射坯的脱脂工艺研究

研究了超细硬质合金WC-6%Co注射坯的溶剂脱脂-热脱脂工艺,讨论了脱脂时间、脱脂温度、注射坯形状和固液比等工艺参数对溶剂脱脂速率的影响,通过改善溶剂脱脂-热脱脂工艺,得到了高性能超细硬质合金台阶状圆棒。结果表明:溶剂脱脂速率随着脱脂温度的升高而上升,随时间的延长而降低;溶剂脱脂3 h后,台阶状圆棒中可溶粘结剂基本脱除。溶剂脱脂时,弓形棒和台阶状圆棒的平均脱除速度较快,圆台棒的平均脱除速率较慢,即溶剂脱脂速率与注射坯的S/V(表面积/体积)值成正比。固液比越小,粘结剂平均脱除速率越高;在稳定阶段,残留可溶粘结剂量高的注射坯脱脂速率快。溶剂脱脂时,粘结剂从外向内脱除,内部可溶粘结剂在形成脱除通道后快速脱除。经过DSC分析,溶剂脱脂坯中存在少量高聚物共混物,需改善热脱脂工艺。优化脱脂工艺后,超细WC-6%Co硬质合金台阶状圆棒的碳含量合适,WC晶粒度为0.35μm,硬度HV10为1 828,致密度大于99%,尺寸精度高。     

硬质合金注射成形多组元聚合物粘结剂的溶剂脱脂工艺研究

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。结果表明：在3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。     

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     

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％．     

陶瓷注射成型脱脂方法对ZrO2陶瓷性能的影响

利用超临界CO2流体、溶剂和热处理3种方法对ZrO2陶瓷注射成型坯体进行脱脂,并对试样进行了一系列的性能测试.实验结果显示,脱脂方法对陶瓷性能有较大的影响.超临界流体脱脂克服了热脱脂的开裂、变形等各种缺陷,使烧结件获得较好的力学性能,平均抗弯强度σ为1074MPa，Weibull模数m达到18．93，高于利用溶剂脱脂的烧结件（σ=1038．4MPa，m=13．28）和热脱脂烧结件（σ=983．5MPa，m=7．59）。此外，超临界CO2流体脱脂、溶剂脱脂可使陶瓷注射成型脱脂时间大大减少，脱脂过程约缩短到热脱脂的1／20。     

Fe-Ni-Cu-C合金粗粉注射成形的溶剂-热二步脱脂工艺

对平均粒度为60μm的Fe-Ni-Cu-C合金粗粉进行了注射成形,重点研究了溶剂-热二步脱脂工艺.选用了三氯甲烷、乙醇和花生油混合溶剂体系来进行溶剂脱脂,以粘结剂的差热分析为指导,制定了合适的后续热脱脂工艺.结果表明:利用溶剂脱脂可以除去粘结剂中78%左右的石蜡,缩短了热脱脂时间,热脱脂的升温速率对脱脂坯质量影响显著.     

催化脱脂型粘结剂组分的相容性

对催化脱脂型粘结剂组分的相容性进行研究,对催化脱脂型粘结剂组元的溶解度参数进行热力学计算,采用DSC和扫描电镜分别对粘结剂进行热分析和端口形貌观察来表征粘结剂组元的相容性。结果表明:粘结剂主要组元聚醋酸乙烯(EVA)分别与聚甲醛(POM)和高密度聚乙烯(HDPE)均具有较好的相容性;m(POM)/m(HDPE)/m(EVA)为75/5/1时表现出良好的工艺相容性;设计了以75POM-5HDPE-1EVA(质量分数)为主要组元,同时添加一定量改性剂(石蜡(PW)、邻苯二甲酸二辛醋(DOP)和硬酯酸锌(ZS))的催化脱脂型粘结剂,该粘结剂与93W-Ni-Fe复合粉经混炼制得了均一、稳定的喂料。     

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…     

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.     

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。     

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.     

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.     

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.     

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。     

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。     

氧化锆粉体表面改性及其注射成型水脱脂研究

采用硬脂酸表面改性以改善陶瓷颗粒表面和有机粘结剂的相容性.结果表明,硬脂酸和陶瓷颗粒表面之间发生了稳定的化学结合,提高了注射喂料的流动性和坯体的强度.坯体显微结构分析表明,表面改性促进了粉体在有机粘结剂中的稳定分散.粉体表面改性明显提高了水脱脂速率,坯体7 h脱脂率达到了88%,脱脂过程中水溶性组分在坯体中的表观扩散系数为1.14×10-7cm2/s.