【作者】 郑欣；

【导师】 温广武；

【作者基本信息】 哈尔滨工业大学 ， 材料学， 2007， 博士

【摘要】 本文分别采用熔融法和热压烧结工艺制备了致密的二硅酸锂微晶玻璃及其复合材料。研究了热处理工艺、形核剂含量和烧结温度对微晶玻璃的物相组成、微观组织和力学性能的影响。阐明了晶化处理和热压烧结过程中微晶玻璃的析晶机理以及氧化锆/微晶玻璃复合材料中的强韧化机制。采用熔融法制备二硅酸锂微晶玻璃的研究中,随着P₂O₅含量的增加,玻璃的晶化温度先降低而后又有轻微提高。采用一步法和两步法工艺进行晶化热处理时,Li₂Si₂O₅晶体的相对含量逐渐降低,Li₂SiO₃和Li₃PO₄晶体的相对含量却是增加的趋势。微晶玻璃的组织结构随着P₂O₅含量的增加从片状多晶团聚体转变为无序的棒状晶体甚至是球形晶体。对比发现两步法晶化处理有利于获得较高的析晶度,其中含有1mol%和2mol%P₂O₅的试样经过两步法热处理后具有较好的韧性和强度。另外,根据热力学和结晶学的分析发现Li₂Si₂O₅晶体可能会借助Li₂SiO₃晶体的某些晶面进行外延生长。通过调整SiO₂:Li₂O摩尔比和P₂O₅的含量,采用热压烧结工艺制备了一系列二硅酸锂微晶玻璃。随着SiO₂:Li₂O摩尔比的增加,由于粘度升高,微晶玻璃的致密度不断下降。而Li₂Si₂O₅晶体的含量没有明显变化,但是Li₂SiO₃和SiO₂晶体的含量表现为先降低后增加的趋势。而P₂O₅的含量从1mol%增加到4mol%,由于分相的作用导致玻璃中富-Li区的Li₂O含量减少,体系粘度升高引起致密度下降。而且分相导致Li₂SiO₃和Li₂Si₂O₅晶体的相对含量不断降低。其中Li₂SiO₃晶体在P₂O₅含量为3mol%和4mol%的试样中完全消失。因此认为热压烧结过程中Li₂Si₂O₅晶体的生长是按照反应转化机制不断消耗Li₂SiO₃进行的。在微晶玻璃的组织结构和力学性能的研究中发现,随着SiO₂:Li₂O摩尔比的提高,Li₂Si₂O₅主晶相的形貌从等轴状转变为棒状晶体,然后又有部分等轴状晶体出现。微晶玻璃的力学性能表现为先提高后降低的趋势,其中SiO₂:Li₂O摩尔比为2.0的微晶玻璃具有较好的力学性能。另外,P₂O₅含量的增加一方面促使形核密度提高,微观组织结构得到不断细化,Li₂Si₂O₅晶体的形貌从棒状转变为针状结构。另一方面,由于玻璃体系的分相作用,导致致密度随着P₂O₅含量的增加而降低,因此力学性能也呈现下降的趋势。调整烧结温度的试验结果表明,P₂O₅的含量为1mol%的试样在820℃热压烧结后制备得到的微晶玻璃具有较好的力学性能,其抗弯强度为290MPa,断裂韧性达到3.0MPa·m^1/2。随着烧结温度从780℃提高到840℃,晶体尺寸有所增加,但是对物相组成、晶体相貌和分布状态没有明显影响。对真空热压烧结工艺制备氧化锆/二硅酸锂微晶玻璃复合材料的分析表明,在Li₂O-SiO₂-ZnO-K2O-CaO-1mol%P₂O₅体系中加入不同含量的氧化锆后在800℃下进行真空热压烧结,氧化锆含量从5wt%增加到30wt%,复合材料的析晶度表现为先提高后下降的趋势。微观组织结构与不含氧化锆的微晶玻璃的组织相比得到明显细化。随着氧化锆含量的增加,晶体形貌从棒状转变为球形颗粒,而后又长大为短棒状晶体。力学性能也呈现先提高后下降的趋势,其中含有15wt%ZrO₂的复合材料具有最优的性能,其抗弯强度为333MPa,断裂韧性可以达到3.5MPa·m^1/2。分析证实复合材料中存在残余压应力强化、相变增韧、裂纹偏转和晶粒桥接这些强韧化机制。更多还原

【Abstract】 The lithium disilicate glass-ceramics and their composites with high relative density were prepared by melting method and hot-pressing technology, respectively. The influences of heat treatment processes, content of nucleation agent and sintering temperature on crystalline phase, microstructure and mechanical properties have been studied. Furthermore, the crystallization mechanism of glass-ceramics has been analyzed during heat treatment and hot-pressed sintering. In the glass-ceramics composite systems, strengthen and toughened mechanisms also have been investigated.With regard to lithium disilicate glass-ceramics prepared by melting method, with increasing the content of P₂O₅, the crystallization temperatures increase and followed by a decrease slightly. Meanwhile, the relative content of Li₂Si₂O₅ crystals decrease and those of Li₂SiO₃ and Li₃PO₄ crystals increase in the case of single-stage and two-stage heat treatments. With increasing the content of P₂O₅, the microstructure is transformed from plate-like polycrystalline aggregates to randomly rod-like crystals and even spherical grains. Two-stage heat treatment is favorable to obtain the higher crystallinity and more Li₂Si₂O₅ crystals than single-stage treatment. Moreover, the specimens heat-treated by two-stage treatment with 1mol% and 2mol% P₂O₅ appear the better fracture toughness and flexural strength, respectively. According to the analysis of thermodynamics and crystallography, Li₂Si₂O₅ crystals probable can epitaxial growth on some crystallographic planes of Li₂SiO₃ phase.By varyting the mole ratio of SiO₂:Li₂O and P₂O₅ content, a series of lithium disilicate glass-ceramics are prepared by hot-pressing technology. With increasing the mole ratio of SiO₂:Li₂O, the relative density of glass-ceramics decreases because the viscosity increases. The relative content of Li₂SiO₃ and SiO₂ crystalline phases decrease and followed by an increment. Furthermore, when the content of P₂O₅ increase from 1.0mol% to 4.0mol%, the relative density decreases owning to the phase separation which lead to the increment of viscosity in the Li-rich regions. In addition, the relative contents of Li₂SiO₃ and Li₂Si₂O₅ crystals decrease. Meanwhile, Li₂SiO₃ crystals disappear in the hot-pressed glass-ceramics in which P₂O₅ are 3.0mol% and 4.0mol%, respectively. During hot-pressing sintering, the growth mechanism of Li₂Si₂O₅ crystals is reaction transform which is at the cost of consuming Li₂SiO₃ crystalline phase.With increasing the mole ratio of SiO₂:Li₂O, the crystal morphology is transformed from equiaxed to rod-like grains, and then some equiaxed grains emerge again. Meanwhile, the mechanical properties of glass-ceramics incresase and followed by a decrease, and the specimen whose mole ratio is 2.0 appears better mechanical properties. Additionally, with increasing the content of P₂O₅, the microstructure is refined from rod-like crystals to needle-like structure. On the other hand, because of the phase separation, the relative density and mechanical properties decrease. By varying the sintering temperature, the specimen hot-pressed at 820℃with 1mol% P₂O₅ has the better mechanical properties. The flexural strength and fracture toughness are 290MPa and 3.3MPa·m^1/2, respectively. In addition, with increasing the sintering temperature, the grain size increases slightly. The species of crystalline phases and distribution do not change significantly.Zirconia/lithium disilicate glass-ceramics composites have been prepared according to Li₂O-SiO₂-ZnO-K2O-CaO-1mol%P₂O₅ system with different content of 3Y-TZP by hot-pressing technology at 800℃in vacuum. The crystallinity of the composites increases slightly and followed by a decrement with increasing 3Y-TZP from 5wt% to 30wt%. Furthermore, the microstructure is refined by comparing with that of zirconia-free glass-ceramics. The crystals morphology transforms from rod-like to equiaxial and then converts to short rod-like crystals. In addition, the mechanical properties tend to increase firstly and followed by a decrease. G1P15Z has the best mechanical properties whose flexural strength and fracture toughness are 333MPa and 3.5MPa·m^1/2, respectively. Strengthening and toughening mechanisms, such as strengthening by residual compressive stress, transformation toughening, crack deflection and bridge connection mechanisms are confirmed.更多还原