【作者】 宋杰光；

【导师】 张联盟； 李俊国；

【作者基本信息】 武汉理工大学 ， 材料加工工程， 2008， 博士

【摘要】 硼化锆具有极高的熔点、硬度、化学稳定性、良好的导电导热性等优良特性,因此在航空航天、耐火、切削、电极等领域有广泛的应用前景。但是,ZrB₂难以烧结致密、高温下易氧化及抗热震能力差,使其实用化难以实现。如何获得高致密ZrB₂陶瓷并提高其高温抗氧化性和抗热震性,是当今ZrB₂陶瓷研究的一个热点。本论文提出将烧结致密化和提高抗氧化能力一体化解决的思路:将ZrB₂原料粉体表面改性,制备出具有包覆结构的ZrB₂陶瓷。具体来讲,就是在ZrB₂粉体表面包覆易烧结、不氧化的陶瓷粉体Y₂O₃-Al₂O₃,再通过放电等离子烧结（SPS）制备出具有YAG包覆ZrB₂和YAG-Al₂O₃包覆ZrB₂结构的ZrB₂-YAG和ZrB₂-YAG-Al₂O₃陶瓷。首先,采用化学沉淀法制备Al（OH）₃-Y（OH）₃包覆ZrB₂粉体。对影响ZrB₂分散稳定性的因素和Al（OH）₃-Y（OH）₃包覆ZrB₂效果的因素进行了分析。研究了浆体浓度、分散剂种类及含量、分散方式及时间和pH值对ZrB₂分散稳定性的影响。得出了适宜的分散条件:分散剂为2vol%的PMAA、超声时间为10min和pH值为9。研究了ZrB₂分散稳定性、pH值、溶液浓度、滴定速度和反应时间对ZrB₂包覆效果的影响。得出了适宜的包覆条件:分散剂2vol%-PMAA,超声10min、pH=9、溶液浓度为Al³⁺=0.017mol/L,Y³⁺=0.01mol/L、滴定速度为0.05ml/s、反应时间60min。其次,采用SPS烧结工艺制备了ZrB₂-YAG和ZrB₂-YAG-Al₂O₃陶瓷。研究了ZrB₂-YAG的致密化过程以及工艺参数对致密化和陶瓷性能的影响。ZrB₂-YAG烧结时的收缩主要是由ZrB₂表面包覆的Al₂O₃-Y₂O₃收缩以及反应生成的YAG收缩造成的。通过对烧结温度、烧结压力以及保温时间对陶瓷致密度、弹性模量和断裂韧性的影响研究,得到了优化的制备工艺:烧结温度为1700℃、烧结压力为20MPa和保温时间为4min。由包覆粉体原料烧结的陶瓷致密度明显高于纯ZrB₂陶瓷,所制备的ZrB₂-YAG和ZrB₂-YAG-Al₂O₃陶瓷具有包覆式显微结构。含30%YAG的ZrB₂-YAG陶瓷的相对密度、杨氏模量和断裂韧性分别为98.3%、426GPa和4.15MPam^1/2,表明YAG的加入可以实现ZrB₂在较低的温度（1700℃）下的致密化。YAG-Al₂O₃含量为30wt%时,SPS最优工艺制备ZrB₂-YAG-Al₂O₃陶瓷的相对密度、杨氏模量和断裂韧性分别为98.8%、435GPa和4.23MPam^1/2,表明随着Al₂O₃比例增大,陶瓷不但更容易致密化,而且力学性能也有所提高。此外,为了对比,用机械混合原料采用相同烧结工艺制备了ZrB₂-YAG和ZrB₂-YAG-Al₂O₃陶瓷。结果表明由包覆型原料制备的陶瓷断裂韧性更高,说明了具有包覆结构的材料具有更好的机械性能。研究了ZrB₂-YAG和ZrB₂-YAG-Al₂O₃陶瓷在700—1600℃的高温氧化性能。结果表明:相同SPS条件下制备的纯ZrB₂陶瓷900℃就出现较明显的氧化增重,而ZrB₂-YAG和ZrB₂-YAG-Al₂O₃陶瓷出现明显氧化增重的温度为1200℃。在相同氧化条件下,随陶瓷中不能氧化的相（YAG或YAG-Al₂O₃）含量增大,氧化层越薄。随Al₂O₃含量的增加,陶瓷表现出更好的抗氧化能力,尤其是在更高的温度下（＞1300℃）。此时Al₂O₃与B₂O₃在表面形成较致密的氧化阻挡层(Al₁₈B₄O₃₃)。由包覆粉体原料制备的陶瓷与由机械混合粉体制备的陶瓷相比氧化层变薄,说明包覆结构能够在一定程度上改善陶瓷的抗氧化能力。更多还原

【Abstract】 Zirconium diboride（ZrB₂）is a desirable combination of high melting temperature, resistance to chemical attack,and other physical properties that make it attractive for these applications for aerospace,refractorily,cutting and electrode fields.However, ZrB₂ is hard to sintering densification,easily oxidized and bad thermal shock resistantce in the high-temperature conditions to impact high-temperature properties, which makes it difficultly realize for extensive use.How to achieve the high-density ZrB₂ ceramic,improve oxidation resistance and thermal shock resistantce of ZrB₂ ceramic at high temperature conditions,which already became hot point for researchers of various countries.In this paper,the train of thought that resolving sintering densification and improving oxidation resistance was proposed.Y₂O₃-Al₂O₃ composite powders were coated on the surface of ZrB₂ particles to form Y₂O₃-Al₂O₃/ZrB₂ composite powders with coating structure and easy sintering densification,ZrB₂-YAG and ZrB₂-YAG-Al₂O₃ ceramics with coating structure were prepared through spark plasma sintering（SPS）.First,Al（OH）₃-Y（OH）₃/ZrB₂ composite particles were synthesized by the chemical precipitation method.The dispersibility of ZrB₂ particles and the conditions of synthesizing Al（OH）₃-Y（OH）₃/ZrB₂ composite particles were investigated.Through analysis,the optimum conditions of the dispersibility of ZrB₂ particles in the ZrB₂ suspension are the dispersant（PMAA）content with the 2vol%of ZrB₂ suspension,the ultrasonic dispersion for 10 minutes and pH=9,respectively.The conditions of synthesizing Al（OH）₃-Y（OH）₃/ZrB₂ composite particles with the better coating quality are that ZrB₂ particles is under dispersion conditons（the dispersant（PMAA） content with the 2vol%of ZrB₂ suspension and the ultrasonic dispersion for 10 minutes）,pH=9,the appropriate concentration(Al³⁺=0.017mol/L,Y³⁺=0.01mol/L)of solution,titration speed for 0.05ml/s and reaction time for 60 minutes,respectively.Second,the sintering densification of ZrB₂-YAG and ZrB₂-YAG-Al₂O₃ ceramics were investigated.Through analysis,the optimization sintering technology for preparing ZrB₂-YAG and ZrB₂-YAG-Al₂O₃ ceramics with the SPS is sintering temperature for 1700℃,sintering pressure for 20MPa and holding time for 4min. Relative density of ZrB₂-YAG and ZrB₂-YAG-Al₂O₃ ceramics are increased with increasing YAG and YAG-Al₂O₃ content.Relateive density,Young’s modulus and fracture toughness of 70wt%ZrB₂-YAG ceramics are 98.3%,426GPa and 4.15MPam^1/2,respectively.The results show ZrB₂ ceramics realizes densification under the lower sintering temperature（1700℃）through adding YAG.Relateive density,Young’s modulus and fracture toughness of 70%wtZrB₂-YAG-Al₂O₃ ceramics are 98.8%,435GPa and 4.23MPam^1/2,respectively.Relative density and mechainic properities of ZrB₂-YAG-Al₂O₃ ceramics are increased with increasing Al₂O₃ content.Besides,ZrB₂-YAG ceramics and ZrB₂-YAG-Al₂O₃ ceramics were prepared with mixing raw materials through same conditions,the mechainical properities of sintered ceramics with coated raw materials are higher than that of sintered ceramics for mixed raw materials,which shows ceramics with coated structure possess better mechainical properities.Finally,the oxidation resistances of pure ZrB₂,ZrB₂-YAG and ZrB₂-YAG-Al₂O₃ ceramics from 700℃to 1600℃were studied.Pure ZrB₂ ceramics are shown distinct oxidation weigh gain at 900℃,however,ZrB₂-YAG and ZrB₂-YAG-Al₂O₃ ceramics are shown distinct oxidation weigh gain at 1200℃,which shows oxidation resistance of ZrB₂-YAG and ZrB₂-YAG-Al₂O₃ ceramics are increased with increasing YAG and YAG-Al₂O₃ content.Oxidation resistance of ZrB₂-YAG-Al₂O₃ ceramics is increased with increasing Al₂O₃ proportion,especially for higher temperature（above 1300℃）, because Al₂O₃ react with B₂O₃ to form compacter oxidation resistance layer (Al₁₈B₄O₃₃).Through comparative analysis,oxidation resistance of sintered ceramics with coated raw materials is better than that of sintered ceramics with mixed raw materials,which indicates that ceramics with coated structure improves the high temperature oxidation resistance.更多还原