摘要
氧化铝(Al2O3)是先进结构陶瓷中的典型材料，也是现代社会中应用最广泛的陶瓷材料之一。Al2O3虽具有高强度、耐高温、耐磨损、耐腐蚀性，绝缘性好等优点，但也像其他陶瓷一样，具有致命的弱点，即本身脆性大，对缺陷十分敏感，韧性低。这决定了其使用可靠性和抗破坏能力差，制约了其进一步的
Al2O3陶瓷的韧性和可靠性，避免发生破坏性的脆性断裂，弄清楚其增韧化的物理机制，是结构陶瓷材料研究工作中的一个热点。陶瓷的织构化是提高增韧的主要方式之一，但是制备细晶织构氧化铝陶瓷并系统探讨其对力学性能的影响的研究尚未见报道。本课题以氧化铝为研究对象，采用纳米氧化铝作为基体，结合模板晶粒生长法制备了沿[0001]方向高度择优取向的织构陶瓷，探讨了模板籽晶定向生长的机制，并系统地研究了微观形貌及织构度对氧化铝陶瓷的力学性能的影响规律。
首先采用熔盐法制备形貌可控的、沿[0001]择优取向的片状氧化铝模板，研究了原料种类、熔盐种类、熔盐配比、烧结助剂等因素对片状氧化铝微晶的相结构和微观形貌的影响规律。研究发现，当用Al2(SO4)3作为原料时所得到的产物为团簇状，而γ-Al2O3为原料可制备成分散良好的薄片。氯盐作为熔盐所制备的氧化铝产物为块状团聚，而硫酸盐倾向于产生片状单晶。熔盐比例的增大有利于得到分散性好、粒径大的片状籽晶。当添加SiO2烧结助剂时，随着烧结助剂含量的增加可以促进片状氧化铝的径向
生长，抑制厚度方向生长，从而获得径厚比高达23的片状籽晶。当采用SiO2和CaO作为烧结助剂时，添加少量时有利于径向生长，含量较多时反而抑制了生长。
其次，采用所制备的模板与粒径为30nm的基体进行混合，添加5vol%的片状模板后，采用模板晶粒生长法(TGG)制备出了沿[0001]择优取向生长的氧化铝织构陶瓷，研究发现，随着烧结温度的升高，陶瓷的织构度逐渐提高。当烧结温度为1500°C，烧结时间为4h时，制备了取向度为93.6%的氧化铝织构陶瓷。在织构过程中，基体粉体沿[0001]定向生长，所得的织构陶瓷直径~17μm，厚度~2.3μm。随着样品织构度的增大，样品的断裂模式发生了很大的变化，其裂纹扩展模式由垂直扩展演变为裂纹桥连及偏转，其扩展路径增长。
最后，系统地研究了陶瓷织构度及微观形貌对断裂模式、抗弯强度、断裂韧性、维氏硬度等力学性能的影响规律，并与普通陶瓷做了对比。研究发现，随着样品织构度的从9.62%提高到93.6%，氧化铝陶瓷样品的抗弯强度和断裂韧
性都有上升的趋势。织构度为93.6%的陶瓷样品的硬度、抗弯强度、断裂韧性分别为15.4GPa、589MPa、4.6MPa·m1/2，其断裂韧性是普通陶瓷的1.5倍。此外，织构陶瓷沿[0001]方向的力学性能比垂直于该方向的性能要高，证实了[0001]方向为该陶瓷的优势方向。本研究表明，通过陶瓷织构可使其强度和断裂韧性等产生异向性，依靠裂纹的桥连与偏转机制可在其优势方向上获得比普通陶瓷明
显提高的力学性能，是实现陶瓷增韧的一个有效方法。本研究可为突破高质量的的结构陶瓷的制备技术奠定一定的理论基础，为陶瓷的纳米织构增韧
关键词：氧化铝；模板晶粒生长；织构度；微观形貌；硬度；抗弯强度；断裂韧性
57届格莱美颁奖典礼complimentaryAbstract
Abstract
As a typical advanced structural material,alumina(Al2O3)ceramics are one of the most widely ud industry materials in the modern society.Al2O3has many advantages,such as high strength,high temperature resistance,abrasion resistance, corrosion resistance,and insulation etc.However,the same as other ceramics,Al2O3 ceramics also have fatal weakness,that is,they are brittle and nsitive to defects. Thus,they have bad reliability and poor resistance to damage,restricting its further development and large-scale engineering applications.Therefore,improving the toughness and reliability of Al2O3ceramics and understanding the related toughening mechanism have been a hot topic.Texturing ceramics is one of the most effective method to improve the toughness of cerami
cs.However,there are very limited study on the fabrication and properties of textured alumina ceramics with fine grain sizes.In this work,we fabricated highly[0001]oriented alumina ceramics by templated grain growth via using nano-matrix.The texturing mechanism was explored,and the effects of microstructure and texture fraction on the mechanical properties of alumina ceramics were systematically investigated.
First,alumina platelets were synthesized by molten salt method.The effects of raw materials,molten salts,their ratios,and additives on the morphology development of alumina platelets were studied.Al2(SO4)3raw material produces agglomerations,whileγ-Al2O3yields well-disperd particles.Chloride salts result in overlapping phenomena,but sulfates tend to produce single crystals.Increa molten salt amount is beneficial to fabricate well-disperd platelets with large particle size.Adding SiO2promotes the growth of platelets along the radial direction and prevents the growth along the thickness direction,leading to the large aspect ratio~23.When SiO2and CaO are ud as sintering aids,a small amount of SiO2and CaO sintering is favorable for radial growth,but higher concertation produced the platelets with reduced sizes.
Then,highly[0001]oriented alumina ceramics were textured by templated grain growth via using30nm matrix,and5vol%platelet templates.The results show that with the increa of sintering temperature,t
he textured fraction of ceramics is incread from9.62%to93.6%.When sintered at1500°C for4h,a high texture degree~93.6%was achieved.Highly textured ceramics are consisted of tabular grains with~17μm in diameter and~2.3μm in thickness.With the increa of texture fraction,the fracture mode and path of the samples have changed greatly.The crack propagation mode has been changed from straight expansion to
知足常乐英语Abstract
crack bridging and deflection,and its propagation path is enhanced.
Finally,the effects of texture fraction and orientation on the mechanical properties such as fracture mode,flexural strength,fracture toughness and Vickers hardness were studied and compared with randomly oriented ceramics.It was found that,flexural strength and fracture toughness of alumina ceramics incread with the increa of texture fraction from9.62%to93.6%.The hardness,flexural strength and fracture toughness of the ceramics with the texture degree of93.6% were15.4GPa,589MPa,4.6MPa.m1/2,respectively.Besides,the mechanical properties of the textured ceramics are higher along the[0001]direction than that perpendicular to this direction,confirming that the c-direction is the dominant direction of the ceramics.This work proves that texturing is very effecti
买东西英语
ve to produce ceramics with significantly improved mechanical properties.We believe that this work can lay the foundation for preparing high quality textured structural ceramics,and can add new contributions to the improvement of toughness by nano-texturing,so it is important from both scientific and engineering view points. Keywords:Alumina;Template grain growth;Texture degree;Morphology; Hardness;Flexure strength;Fracture toughness虎翼
目录
摘要........................................................................................................................III 第1章绪论 (1)
摩登大圣1.1引言 (1)
1.2氧化铝陶瓷概述 (1)
个人电脑的英文缩写
狂热爱1.3氧化铝结构陶瓷的增韧方法与机理 (3)
1.3.1晶须/纤维增韧 (4)
1.3.2颗粒增韧 (5)
1.3.3相变增韧 (7)
1.3.4层状增韧 (7)
1.3.5织构增韧 (7)
1.4氧化铝陶瓷的织构化 (8)
1.4.1氧化铝织构陶瓷的研究现状 (9)
1.4.2细晶氧化铝织构陶瓷 (10)
1.5本文的研究目的、意义 (11)
1.6本文的主要研究内容 (11)
第2章片状氧化铝模板籽晶的形貌调控研究 (13)
2.1引言 (13)
2.2沿[0001]取向的模板籽晶的制备技术 (13)
呈报
grelide
2.3[0001]片状氧化铝微晶微观形貌和相结构的调控研究 (14)
2.3.1初始原料对片状氧化铝模板微观形貌的影响 (14)
2.3.2烧结时间对片状氧化铝模板微观形貌的影响 (15)
2.3.3熔盐比例对片状氧化铝模板形貌的影响 (15)
2.3.4熔盐种类对片状氧化铝模板微观形貌的影响 (16)
2.3.5片状氧化铝模板的物相结构分析研究 (17)
2.4生长助剂对片状氧化铝微晶相结构和微观形貌的影响研究 (18)
2.4.1SiO2助剂对片状氧化铝微晶的相结构和微观形貌的影响..18
2.4.2CaO和SiO2混合助剂对片状氧化铝微晶相结构和微观形貌
的影响 (20)
2.5本章小结 (22)
