【作者】 谭训彦；

【导师】 尹衍升；

【作者基本信息】 山东大学 ， 材料学， 2004， 博士

【摘要】 为了进一步提高ZrO₂陶瓷和Fe-Al/ZrO₂复合材料的性能,改善制备过程中粉体的分散均匀性,并为制备复杂形状的制品打下基础,本文对纳米ZrO₂单一粉体及Fe-Al/ZrO₂复合粉体的分散机制、凝胶注模成型工艺和烧结工艺进行了系统研究。 首先采用氢电弧等离子体法和机械合金化法制备了纳米级的Fe-Al粉体。XRD分析表明:氢电弧等离子体法制备的Fe-Al粉体为B2相Fe₃Al;机械合金化法制备的Fe-Al粉体是一种无序的α-Fe（Al）固溶体,SEM分析表明:随着球磨时间的延长,粉末发生冷焊,当冷焊增加到一定程度之后,粉末的粒度随球磨时间的延长而减小。通过对制备的Fe-Al粉体进行低温退火处理,结合DSC分析了其晶相组织转化的演变规律:用机械合金化法制备的Fe-Al粉体在390℃由无序状态转变为有序DO₃结构,而用氢电弧等离子体法制备的Fe-Al粉体在483℃发生结构的转变。据此采用在750℃焙烧的方法把机械合金化法制备的Fe-Al粉体转化成了有序程度较高的DO₃相Fe-Al粉体。TEM观察表明:制备的粉体粒径小于200 nm。 论文研究了ZrO₂纳米粉体和Fe-Al/ZrO₂复合粉体在水介质和有机液体介质中的分散特性。 当将ZrO₂纳米粉体分散在水中时,以NH₄-PMAA为主要成分的分散剂的加入量和悬浮液的pH值对Zro₂纳米粉体的分散有很大影响。研究结果认为,当悬浮液的pH=10、NH₄-PMAA的加入量为0.6%时,悬浮液的分散效果最好,而且在此条件下可以获得54.33 wt%的高固相含量ZrO₂水悬浮液。采用TEM对分散体系进行了分析,所得到的分散体系中ZrO₂颗粒大小为20～50 nm。 但是,当把Fe-Al粉体加入到已分散好的ZrO₂水悬浮液中时,发现原本耐腐蚀的Fe-Al金属间化合物在变成纳米级的粉体后会与水起化学反应,形成肉眼可见的褐色Fe₂O₃类物质,导致Fe-Al/ZrO₂复合粉体无法直接在水中进行分散。 试验结果说明,Fe-Al/ZrO₂复合粉体在水中不能得到均匀的分散体系,而通过调节pH值和分散剂用量可以使ZrO₂纳米粉体在水中稳定分散。 当将ZrO₂纳米粉体或Fe-Al/ZrO₂复合粉体分散在有机液体中时,采用了丙烯酸（AA）、甲基丙烯酸（MAA）、油酸（OA）、硬脂酸（SA）、Y3000为分散剂,更多还原

【Abstract】 In order to enhance the properties of ZrO₂ and Fe-Al/ZrO₂ composite further, improve the dispersing homogeneity of powders, and lay the foundation for preparing complicated shape parts, studies were carried out in the following respects on the dispersing mechanisms, gelcasting process and sintering process of nano ZrO₂ powder and Fe-Al/ZrO₂ composite powders.Nano sized Fe-Al powders were at first prepared by hydrogen arc-plasma and mechanical alloying. XRD results revealed that the Fe-Al powders prepared by hydrogen arc-plasma were Fe₃Al with B2 structure and the Fe-Al powders prepared by mechanical alloying were a kind of amorphous α-Fe（Al） solid solution. SEM indicated that increasing the milling time led to the occurrence of cold-welding, the increase of which decreased the powder size with the increase of milling time.After being annealed at low temperature, the rules of phase transition of Fe-Al powders were investigated using DSC: at 390℃, Fe-Al powders prepared by mechanical alloying exhibited conversion of disordered structure to DO₃ structure, which occurred in the Fe-Al powders prepared by hydrogen arc-plasma at 483 ℃. Therefore, the Fe-Al powders prepared by mechanical alloying were converted to DO₃ structure by calcinations at 750 ℃. TEM observations revealed that the particle size was less than 200 nm.This paper investigated the dispersion characteristics of nano ZrO₂ powder and Fe-Al/ZrO₂ composite powder in water or organic liquid medium.When ZrO₂ powders were dispersed into water, both the amount of the dispersant NH₄-PMAA and, the pH value of the suspension could affect greatly the dispersion characteristic of nano ZrO₂. The results showed that the optimum content of NH₄-PMAA was 0.6% at pH=10, at which the dispersion effect is optimum and the highest solid content suspension of 54.33 wt% ZrO₂ obtained. TEM observation revealed that the ZrO₂ particle size is 20-50 nm in suspension well-dispersed.However, adding the Fe-Al powders into the well-dispersed ZrC>2 suspension promoted the reaction between the nano-sized Fe-Al intermetallics, which originally possessed high corrosion resistance, and water, with the product of brown Fe2O3-like substance, preventing the dispersion of Fe-Al/ZrC>2 composite powders.Above results indicated that Fe-Al/ZrC^ composite powders couldn’t well-dispersed in water and nano ZrC>2 powder was able to well-dispersed in water by adjusting both the pH value and the amount of dispersant.When ZrC>2 powders or Fe-Al/ZrO2 composite powders were dispersed into the organic liquid using dibutyl phthalate （DBP）, n-octanol or n-butanol as dispersion medium and acrylic acid （AA）, methacrylic acid （MAA）, oleic acid （OA）, stearic acid （SA） or Y3000 being the dispersant, the results of viscosity measurements indicated that: （1） MAA or SA can fairly disperse the nano ZrC>2 powder and Fe-Al/ZrO2 composite powders and obtain 57.28-66.67 wt% suspension in n-butanol or n-octanol. （2） Y3000 has the best dispersion effect for dispersing the nano ZrO2 powder and Fe-Al/ZrC>2 composite powders in n-butanol or n-octanol and 61.9-70.22 wt% suspension obtained.FTIR results indicated that RCOO-Zr or RCOOH HO-Zr coordination bond formed on the surface of ZrC>2 particles or Fe-Al/ZrO2 particles after absorbing dispersant NH^-PMAA, MAA, SA or Y3000, which constituted the chemical absorption. Dispersion mechanisms revealed that （1） adjusting pH value could achieve electrostatic stabilization suspension when dispersing ZrC>2 powders in water and electrosteric stabilization suspension was obtained by both adding polyelectrolyte dispersant NH4-PMAA and adjusting pH value; （2） adding superdispersant Y3000 could attain steric stabilization suspension when dispersing ZrC>2 powders or Fe-Al/ZrCh composite powders in the organic liquid, while the dispersion stabilization should be attributed to the principle that substance is apt to be wetted in similar polarity liquid when incorporating the small molecular weight organic compound MAA or SA; （3） for the high solid content Fe-Al/ZrCh composite powder suspension prepared in this work, the dispersion stabilization was due to rheological stabilization mechanism.The results of dispersion tests showed that the well-dispersed ZrC>2 suspension in water could be prepared by using polyelectrolyte dispersant NH4-PMAA and the superdispersant Y3000 possess the best dispersing effect for Zr(>2 powders or Fe-Al/ZrCh composite powders dispersed in n-butanol or n-octanol.This paper studied the gelcasting process of ZrC>2 or Fe-Al/ZrC^ in aqueous or nonaqueous media on the basis of dispersion tests results.For gelcasting ZrC>2 in water, the influences of the corresponding factors on the strength of ZrC>2 green body were investigated through adjusting the content of main monomer AM, cross-linker monomer MBAM, initiator APS, catalyst TEMED in the acrylamide aqueous gelcasting, the ratio of main monomer to cross-linker monomer and deairing slurry in vacuum. The dry green body prepared on the basis of these parameters exhibited the bending strength of above 20 MPa, which were able to satisfy the requirements of machining on strength fully. The optimal parameters were found to be: the total amount of AM and MBAM in the premix solution is 20 wt%; the ratio of AM to MBAM is 24. In the slurry （50 wt%） containing 50 g ZrC>2 powders, the content of dispersant MN is 6.0 ml, initiator ASP solution is 0.4-0.5 ml and catalyst TEMED is 0.4-1.2 ml.When fabricating ZrC>2 or Fe-Al/ZrO2 by non-aqueous gelcasting, the total amount of monomer in the premix solution is 20 vol%, where the ratio of TMPTA and HDODA is 1:4 and the initiator BPO solution is 1.0 vol%. Green bodies with homogeneous microstructure were prepared by introducing adequate dispersant. EPMA results indicated that the green body obtained by the gelcasting presented more uniform component distribution than that achieved by press molding. SEM analysis showed that gelcasting process enabled the solid particle in the suspension in-situ and consequently reserved the favorable dispersion effects in the green body just as in the suspension.This paper also studied the microstructures and mechanical properties of Fe-Al/ZrC>2 composites.The microstructures of composites were investigated by SEM, TEM, EDS andHREM. The SEM showed that the Fe-Al/ZrO2 composite possessed more uniform microstructure prepared by using dispersed powders than powders milled without liquid. The average grain size of the ZrC>2 and the Fe-Al were 350 nm and 1 urn, respectively. Most of the ZrO2 and Fe-Al grains had an equiaxed morphology and that part of the Fe-Al was clubbed. The The HREM image of Fe-Al/ZrO2 interface along the [001]Fe-Ai/[0H]zrO2 projection shows that the interfaces are very clean, and no reaction phase existed at the interface. The atom arrangement beside interface between Fe-Al and ZrO2 is partly corresponding, existing at semicoherent state. The mismatch is observed at interface.The measurement of mechanical properties indicated that the fracture toughness and bending strength of Fe-Al/ZrO2 composites increase with the increasing of Fe-Al content. The oj, Kic and hardness are 1265MPa, 30.8 MPa ? m1/2 and 87.3HRA respectively when Fe-Al content is 30 vol%. The K/c value of composite is 2.2 times as that of ZrO2, and aj increase 23% compared with ZrO2. the hardness of composites decline slightly with the increasing of Fe-Al content.According to the systematically study, the well-dispersed suspension of Fe-Al/ZrO2 composite powders with high solid content were successfully prepared, and the green body with uniform microstructure had been shaped by gelcasting, and the Fe-Al/ZrO2 composites with uniform microstructure, high fracture toughness, high bending strength and high hardness were sintered. For the excellent properties, the Fe-Al/ZrO2 composites can be applied in some occasions such as high performance ceramic cutting tools and hot-press mould with its high fracture toughness, bending strength and hardness. Now this material has been developing for application by the support of the National Natural Science Fund （No.50242008） and the "863" Program （No.2002AA332100）.更多还原