Al_2O_3陶瓷注射成型水基粘结剂喂料组成及脱脂工艺研究

重点研究了Al2O3陶瓷注射成型水基粘结剂喂料的配比及其脱脂工艺.结果表明,当Al2O3粉料质量分数为80%、选用聚乙二醇/聚丙烯/聚乙稀/硬脂酸(m(PEG):m(PP):m(PE):m(SA)=61 : 17 : 17 : 5)水基粘结剂时,Al2O3陶瓷试样性能较好.水脱脂过程中,PEG脱除率随着水温的升高而增大,在50℃去离子水中脱脂4h,PEG脱除率可达74%.     

Al2O3陶瓷注射成型热塑性粘结剂及脱脂工艺研究

重点研究了氧化铝陶瓷注射成型中热塑性粘结剂的选取和对应的热脱脂工艺。结果表明，当Al2O3粉料质量百分含量为70％、选用石蜡／聚丙烯／硬脂酸（mpw：mpp：mSA=79：20：1）热塑性粘结剂时，采用适当的热脱脂工艺，可获得结构缺陷少、性能较高的Al2O3陶瓷材料。     

Ti(C,N)基金属陶瓷注射成形脱脂技术研究

使用传统蜡基粘结剂和改进型蜡基粘结剂分别研究了Ti(C,N)基金属陶瓷粉末注射成形,热脱脂和溶剂脱脂 热脱脂工艺过程,其中包括根据粘结剂TGA制定并优化热脱脂的工艺曲线、不同的溶剂和温度对溶剂脱脂的影响、后续热脱脂工艺路线的确定.结果表明:使用改进型蜡基粘结剂的2#试样热脱脂工艺简单、周期短并易于控制;2#溶剂脱脂率明显高于使用传统蜡基粘结剂的1#试样;经过溶剂脱脂 热脱脂,1#试样脱脂率达到93%,2#试样脱脂率达到96%以上;1#烧结试样的抗弯强度为700 MPa左右,2#则达到1300 MPa,从烧结样品抗弯断口和显微组织的SEM图片得到了验证.Ti(C,N)基金属陶瓷注射成形采用改进型蜡基粘结剂比传统蜡基粘结剂脱脂效果好、力学性能高,改进型蜡基粘结剂更适合Ti(C,N)基金属陶瓷注射成形.     

金属注射成形技术的研究

金属注射成形技术是近年来发展最为迅速的粉末冶金近净成形枝术.从粘结剂、脱脂、烧结、精度及成分控制和计算机模拟等方面阐述了金属注射成形技术(MIM)的研究现状,指出MIM技术的应用领域和材料体系向多方面拓展、粘结剂体系的多样化与脱脂方法的多样化和计算机技术的应用将使MIM技术更加完善.     

Al_2O_3陶瓷注射成型工艺实验研究

采用注射成型的方法制备出了Al2O3陶瓷,根据实验结果分析了陶瓷粉末装载量、混炼温度高低、加料的先后顺序等因素对氧化铝陶瓷喂料性能的影响。并使用热重分析仪分析了粘结剂物料体系的热特性,用扫描电镜分析了成型后的各种胚料的显微结构。     

钛合金粉末注射成形热脱脂工艺的研究

采用粉末注射成形方法制备了钛合金坯体,然后利用溶剂脱脂方法脱除坯体中可溶性粘结剂.在热脱脂速率为2.0℃/min、最高脱脂温度600℃、保温时间为1h和真空脱脂气氛条件下脱除坯体中剩余粘结剂,坯体中残余碳氧含量分别0.092%(质量分数)和0.28%,低于国外报道的PIM钛合金脱脂坯中残余碳氧含量.XRD结果表明,脱脂坯中只存在α相,没有TiC,Ti3Al,TiO和TiN等杂质相存在.N2气氛下脱脂,脱脂坯中残余碳含量较低,但氧含量较高.     

水溶性粘接剂氧化锆粉末注射成形喂料的研究

采用聚乙二醇(PEG)为水溶脱脂粘接剂,聚甲醛(POM)/聚乙烯醇缩丁醛(PVB)为保型粘接剂,混炼制备水溶性粘接剂氧化锆粉末注射成形喂料;通过傅里叶红外光谱和旋转流变测试研究硬脂酸改性氧化锆对注射成形喂料的性能影响,并通过喂料流变行为、注射生坯脱脂率、生坯弯曲强度以及生坯脱脂前后断面形貌扫描电镜分析、烧结体的X射线衍射、硬度及密度表征,研究粘接剂组分配比和喂料粉末装载量对喂料性能的影响.结果表明:硬脂酸可以成功对氧化锆粉末进行改性,并可以明显降低注射成形喂料的黏度;当粉末装载量达到52%(体积分数),粘接剂各组分配比w(PEG)∶w(POM)∶w(PVB)=6∶2∶2时,喂料具有较好的流动性且粉末分散良好,生坯中粘接剂形成网状结构赋予生坯较高的弯曲强度,4 h后水脱脂率超过80%,水脱脂后生坯形成细小且连续脱脂通道;生坯经水脱脂、1 450℃烧结2 h后,烧结体晶型主要由四方相组成,平均晶粒尺寸1μm,密度6.01 g/cm~3,平均维氏硬度达到1 147 HV,与模压成型烧结氧化锆性能相当.     

PVB对玻璃/陶瓷流延生料带结构与烧结性能的影响

用聚乙烯醇缩丁醛作为配制硼硅酸盐玻璃/α-Al2O3流延浆料的粘结剂,流延成型制备玻璃/Al2O3生料带,研究了PVB对玻璃/Al2O3复合料生料带密度、力学性能、微观结构及其烧结性能等的影响。实验结果表明,随着PVB分子量和羟基含量减小,生料带拉伸强度和断裂伸长率降低、体积密度增加、生料带排胶热分解温度降低,对烧结瓷体密度和介电性能的影响较小。     

金属粉末注射成形石蜡-油-聚乙烯粘结剂的研究

本文开发了用于Fe-2Ni粉末注射成形石蜡-油-聚乙烯粘结剂,选择了石蜡和聚乙烯组份,考察了油的加入对组份相容性、生坯强度、粉末装载量、喂料热容、溶剂脱脂速率的影响.该粘结剂用于Fe-2Ni注射成形,粉末装载量达60%(体积分数),生坯强度5.5MPa,溶剂脱脂速率2mm/h以上.     

离心成型法制备无宏观界面的Al2O3/Ni功能梯度材料

采用一种新颖的离心成型法制备了无宏观界面的Al2O3/Ni功能梯度材料, 并研究了浆料调制工艺、离心成型制备机理和梯度材料的力学性能.结果表明, 配制料浆时,粘结剂(聚乙二醇)含量为2%(质量分数)、固相含量为63%(体积分数)、球磨时间为36h,可得到的流动性良好的料浆.经离心成型(3000r/min,40min)得到了无宏观界面的坯体,该坯体在1400℃经2h真空烧结,可以得到致密、组元宏观连续过渡的Al2O3/Ni梯度材料.通过调整固相含量和粘结剂含量,可调控Al2O3/Ni复合材料的成分梯度.     

新型金属注射成形催化脱脂型粘结剂的催化快速分解研究

催化脱脂是目前MIM技术领域新的发展方向,研究了新型金属注射成型催化脱脂型粘结剂的催化快速分解,研究结果表明,该催化脱脂型粘结剂在以HNO3为催化剂进行催化脱脂时,注射成形坯经3－4h催化脱脂后,脱脂坯内部已形成大量的连通孔道,脱脂时间,脱脂温度以及 不同粘结剂组成影响催化脱脂效果。     

金属注射成形蜡基粘结剂的研究

本文研究了综合蜡基和油基粘结剂优点的改进型蜡基粘结剂体系 ,其组成为PP PW 植物油 SA 改性剂。改进型蜡基粘结剂分阶段热解 ,各组元间有较强的相互作用 ,相容性较好。该粘结剂和金属粉末具有较好的混合均匀性 ,改性剂的加入提高了粉末装载量。喂料是一种假塑性流体 ,非牛顿指数n较大 ,粘流活化能ΔEη 较低 ,具有良好的注射填充性。改进型蜡基粘结剂既可热脱脂 ,又可溶剂脱脂 ,溶剂脱脂速度快、维形能力好。     

大尺寸ZrO2注射成型坯体热脱脂缺陷成因探究

采用蜡基ZrO2粉末喂料注射成型获得大尺寸ZrO2陶瓷粉末注射产品（坯体）,并根据喂料热分析曲线的变化特点,系统研究了大尺寸ZrO2坯体的热脱脂过程及规律。通过对热脱脂前后坯体的重量损失、尺寸收缩、外观缺陷和微观组织形貌的分析评估,着重探讨了大尺寸ZrO2坯体热脱脂过程中存在的主要缺陷和成因。研究表明,流蜡、鼓泡和开裂等热脱脂缺陷主要发生在低温脱脂阶段,其主要原因是液态石蜡扩散及分解过程的失衡。为此,结合“失重率控制”的思路和喂料的热失重规律,对热脱脂工艺进行了优化,在不延长总脱脂时间的前提下,显著提高了大尺寸ZrO2坯体的脱脂合格率。     

Influence of the Compacts Homogeneity on the Incidence of Cracks during Thermal Debinding in Ceramic Injection Molding

During thermal debinding in ceramic injection molding, the inhomogeneity of green body is a key origin of cracks. In this study, the impact of low molecular weight binders on the homogeneity of the green body was investigated. Incidence of cracks during thermal debinding indicated that the volume ratio of wax to stearic acid should be out of high viscosity and incompletely wetting region. In these two formulation regions,typical inhomogeneous microstructures were observed. By mercury intrusion method, it was shown that pore size distribution of the debinded compacts was determined by thermal degradation of low molecular weight binders. A particle-rich region model was established to predict the nucleation of cracks caused by solid loading fluctuation. The criterion of cracks nucleation was that local capillary force from solid loading fluctuation was larger than the suction force from the surroundings.     

Scientific and Technological Progress in Binder Burnout from Metal Injection Molded Compacts

A two-component model binder system composed of the low molecular weight component stearic acid (SA) and the polymer polypropylene (PP) was chosen to study the kinetics of long-term conventional thermal debinding of SA from a metal powder compact formed from spherical stainless steel powder. The burnout temperature of the two binder components is widely different, so that the SA-weight loss could be followed in the lower temperature regime independently by thermogravimetric analysis. The experiment provides at constant temperature an exponential decrease of the SA-weight with debinding time. It is suggested that the debinding rate is controlled by diffusion of SA in the thermoplastic to inner surfaces of pores, which develop in the material during debinding. This is in correspondence with previous work on short-term debinding. The kinetics for the PP/SA-system are compared to previous results on binders with other polymer components. The second part of this paper reports about MIM-processing of commercial steel parts with a novel proprietary binder formulation which allows a distortion-free conventional thermal debinding within hours.     

Thermal, Solvent, and Vacuum Debinding Mechanisms of PIM Compacts

The mechanisms of thermal, solvent, and vacuum debinding processes for powder injection molded (PIM) compacts were investigated. Mercury intrusion porosimetry (MIP) and scanning electron microscope (SEM) observations on PIM specimens showed that fine interconnected pores were developed in the early stages of debinding in all three processes. These pores were formed as a result of the decomposition of low temperature binders such as paraffin wax during thermal debinding or arise from the extraction of soluble binder components in solvent debinding. In the later stages of thermal and vacuum debinding, decomposed gases could be trapped in the center region and build up a pressure causing cracking or blistering defects. The solvent debinding process could alleviate these problems, but the penetration of solvent into the binder could still cause cracking or distortion due to swelling of the binder.

It was found that the pore structure evolution was influenced by the heating rate, temperature, pore size, and the amount of existing porosity. From the observed microstructure and mercury porosimetry data, debinding mechanisms were derived and the defects which were frequently seen during debinding were explained with these mechanisms.     

Thermal debinding of Fe3Al-X metal powder compacts

The process of removing a multicomponent binder from a metal powder compact has been investigated. Model experiments of debinding were performed on compounds consisting of less than 40 vol% binders (low molecular weight polyethylene, paraffin and Carnauba waxes) and more than 60 vol% metal content. As typical representatives for injection moulding morphology and meeting all other requirements for optimal powder characteristics, elemental powders of the Fe-Al system were used. Viscosity results over a wide range of shear rates for various plastisols are presented as functions of binder system composition and metal powder content. Based on the rheological response, an optimization of plastisol formulation was performed. Results are reported on three series of debinding modes using heat and fluid wicking in air and in nitrogen. The time dependence of fractional debinding, x(t), during wicking has been estimated using a model. Direct observation by SEM of binder distribution and pore structure evolution at different stages of the debinding process was made. Wick-assisted thermal debinding in nitrogen proved to be an effective debinding method in terms of shape preservation and the absence of defects in the studied material.     

新型陶瓷注射成形喂料催化脱脂过程的研究

陶瓷注射成形是一种受到日益广泛关注的技术 ,但其中脱脂一步传统采用的热脱脂技术脱脂速度慢 ,效率较低。本研究采用以聚甲醛为主要粘结剂制备了可快速脱脂的新型陶瓷注射成形喂料体系 ,并进行催化脱脂工艺的研究 ,记录了该过程中样品失重的情况 ,分析了脱脂阶段不同特征及其原因 ,指出催化脱脂过程速度的控制因素是气态催化剂和气体产物扩散过程。通过脱脂前后样品表面及截断面的扫描电镜分析 ,直观反映了脱脂前后样品微观形貌上的差异及特点。观察了脱脂过程不同时刻样品外围与中心区域的微观形貌 ,证明了脱脂过程是由外围逐渐向内部扩散的 ;记录了经注射成形的试样烧结前后的密度变化     

Pelletization and sintering of New Zealand titanomagnetite ironsand

Direct reduction (DR) of iron ore with hydrogen is a potential route for near-zero CO₂ steelmaking, but vertical shaft DR reactors require that iron ore fines must first be pelletized. This study reports an investigation of the pelletization and subsequent sintering behaviour of titanomagnetite (TTM) ironsand, which is the main iron ore feedstock for New Zealand’s steel industry. Initially green pellets were bound with bentonite and carboxymethyl-cellulose (Peridur), using an average ironsand particle size of 65 µm. The compressive strength of these pellets after sintering at 1200 °C in air for 2 hr was measured to be 976 N, meeting the expected feedstock requirements for a shaft reactor. This strength was attributed to interparticle bonding arising from extensive recrystallisation of titanohematite grains from oxidation of TTM, as well as the formation of a liquid bonding phase due to melting and diffusion of the binders. Building on these results, alternative binders were then explored in order to lower the required sintering temperature. A combination of both organic and inorganic binders was found to deliver optimum performance, wherein carboxymethyl-cellulose based binders provided strength in the green pellets, whilst inorganic binders, such as calcium borate or ground glass, promoted high sintered strengths.     

Development of Novel Binder for Hardmetal Powder Extrusion Molding

A novel binder system for hardmetal powder extrusion moulding(PEM) process has been developed.The binder system comprises a major fraction of a mixture of low molecular weight components (LMWCs) and a minor fraction of very finely dispersed polymer.The feedstocks are mixed as a thick slurry at a suitable temperature and are rapidly homogenized by stirring at an adequate shear force.The binders are removed by thermal debinding.The thermal debinding mechanism has been investigated by thermogravimetry(TG) and differential thermogravimetry(DTG).At the first stage of debinding,the LMWCs are removed.These open up pore channels which allows much faster removal of the remaining polymer component during the subsequent stage.Ihe microtructures of the moulded green parts were observed by scanning microscopy(SEM).The debound samples were sintered at different temperatures,and the sintered samples properties were measured.