【作者】 周建民；

【导师】 叶枫；

【作者基本信息】 哈尔滨工业大学 ， 材料学， 2007， 硕士

【摘要】 本文采用热压烧结工艺制备了Nd、Sm、Dy和Yb等四种稀土掺杂的α-Sialon陶瓷材料。利用XRD、SEM、TEM等手段研究了稀土类型及额外添加2wt%稀土氧化物作为助烧剂对Sialon陶瓷材料的致密化、物相组成及显微组织结构的影响;采用三点弯曲、单边缺口测试方法对室温弯曲强度及断裂韧性进行了评定;并着重系统地研究了稀土类型、物相构成及显微组织结构对材料热物理性能、抗热震性能及抗氧化性能的影响。试验结果表明,采用1800℃/30MPa/60min工艺热压烧结,所有材料都获得了大于98%的致密度。通过额外添加2wt.%对应稀土氧化物补充必要的烧结液相,以高纯超细Si₃N₄、AlN、Al₂O₃、RE₂O₃（RE为Nd、Sm、Dy或Yb）粉末为原料,RE_1/3Si₁₀Al₂ON₁₅边界成分的小稀土掺杂的Dy-、Yb-α-Sialon也能够获得全致密的陶瓷材料。XRD物相分析结果显示,对Nd-Sialon材料来说,添加或不添加2wt.%过量稀土氧化物作为助烧剂对物相影响不大,都获得了以α-Sialon为主晶相、同时含有少量β-Sialon和M′(R₂Si_3-xAl_xO_3+xN_4-x)相的陶瓷材料。添加2wt%稀土氧化物助烧剂的Dy-和Yb-sialon材料的XRD物相十分纯净,均由单相α-Sialon组成,并因此保持了很高的硬度（Hv10=21GPa左右）。受稀土类型影响,所得材料的显微组织结构有较大差别。Yb、Dy小稀土掺杂的α-Sialon有较大的化学驱动力,α-Sialon的快速生成尽早地耗尽了高温液相,阻碍α-Sialon晶粒各向异性生长,从而得到了细晶等轴组织;相反Nd、Sm大稀土倾向于延长高温液相的持续时间,有利于获得棒晶组织。本文所得Sialon材料的抗弯强度和断裂韧性分别在300MPa～600MPa和4.0MPa·m^1/2～5.1MPa·m^1/2之间,随棒晶长径比及含量增加而增加。主要的强韧化机制为载荷传递、韧化机制为裂纹的偏转、长棒状晶体的拔出与桥接。所得α-Sialon材料具有较好的抗热震能力,经受1200℃热震温差的剩余强度保持率最低在75%以上;1100℃温差热震,发现材料的剩余强度增加现象。良好的力学与热物理综合性能是其具有较高抗热震能力的主要原因。本文所得的α-Sialon材料具有良好的抗氧化能力。氧化分析结果表明1300℃氧化32h时,NdE2和NdE0单位面积氧化增重为3.5mg/cm²左右,而SmE2、DyE2、YbE2仅仅增重了1.5mg/cm²左右。氧化增重与时间呈抛物线规律。NdE2、NdE0、SmE2、DyE2、YbE2氧化反应活化能计算结果分别为475、488、505、512和515kJ/mol。更多还原

【Abstract】 α-Sialon ceramics composites doped with Nd, Sm, Dy, and Yb rare-earth additives were synt-hesised by hot-pressing. The effects of adding excess 2 wt.% rare earth oxide as sintering aids on the densification, phase components, and microstructure were studied by XRD, SEM and TEM. Room temperature flexure strength and fracture toughness were measured through three-point bending, and single-dege-notch beam bending method. The influence of the rare earth, phase components, and microstructures on the themophysical properties, thermal shock and oxidation resistance of the composites had been investigated.Results showed that all theα-Sialon ceramics achieved densities higher than 98% of their theoretical values after hot pressing at 1800℃for 1h under pressure of 30MPa in a nitrogen atomosphere of 0.1 MPa. The Dy and Yb-dopedα-Sialons were successfully densified by adding 2 wt.% corresponding rare earth oxide as additives, and by using utrafine Si₃N₄、AlN、Al₂O₃ and RE₂O₃（RE= Dy and Yb）as the starting powders.XRD results revealed that the Nd-Sialons hadα-Sialon, trace ofβ-Sialon and M′(R₂Si_3-xAl_xO_3+xN_4-x) in their phase components regardless of the 2 wt.% excess rare earth oxide. On the contrary, the other Sm-, Dy-, and Yb-sialon were pureα-Sialon, and had high hardness (H_v10=21GPa), accordingly.The microstructure of the materials varied with rare earths. Yb and Dy-sialon obtained fine equiaxed grains in their microstructures, because that the smaller rare earths promoted the formation ofα-Sialon. After the transient liquid was depleted, anisotropical growth of theα-Sialon was stunted. This was contrarory to the case of Nd and Sm-Sialon, where elongated grains were presented. The flexure strength and fracture toughness of the materials falled into the range from 300MPa～600MPa and 5.1MPa·m^1/2, depending on their microstructures. Elongated grains of composites impart high toughness and strength to the material throngh energy-absorbing mechanisms of crack bridging,grain pullout,and crack path deflection.The research results show that the composites have excellent thermal shock resistance propertier. The minimum residual strength remained 75% of its original flexural strength at a thermal shock resistance temperature dirrerence （△T） up to1200℃. The residual strength of the composites improved at a thermal shock resistance temperature dirrerence （△T） up to1100℃after water quenching for 14 times.Combination of the excellent mechanical properties together with the good thermophysical properties result in its excellent thermal shock resistance properties.The high temperature oxidation resistance of -Sialon ceramics composites doped with different rare-earth additives was farely good. Weigh gains by area at 1300℃for 32h were 3.5 mg/cm2 for NdE2 and NdE0, but 1.5 mg/cm² for SmE2, DyE2, YbE2 materials. Oxidation activation energies of NdE2, NdE0, SmE2, DyE2,YbE2,were determined to be 475kJ/mol,488kJ/mol,505kJ/mol,512kJ/mol, 515kJ/mol respectively.更多还原