纳米Al2O3-ZrO2(3Y)复相陶瓷的微波烧结

采用纳米Ａｌ２Ｏ３粉和纳米ＺｒＯ２（３Ｙ）粉为原料,对不同成分配比的Ａｌ２Ｏ３－ＺｒＯ２（３Ｙ）复相陶瓷进行了微波为烧结的研究。实验结果表明微波烧结可获得委肮的致密度,并提高断裂韧性,但晶粒长大倾身大于其它烧结方式;在Ａｌ２Ｏ３－ｚｒ２（３Ｙ）二元系中,随ＺｒＯ２（３Ｙ）含量啬,烧结时的致密化过程加速,且晶粒长大倾向减小。     

谈Al2O3—MgO对氧化锆陶瓷强度的影响

近年来,氧化锆陶瓷作为高温结构陶瓷材料已越来越被人们所重视,其应用范围也日益扩大,且随着各个使用领域的不同,对其强度的要求也越来越高。从而对于如何完善或提高制备工艺,以保证材料或制品微观结构的均匀性,充分发挥各种材料潜在的优异特性已成为广大科技工作者研究的重要课题。     

热压Al2O3—ZrO2（6mol%Y2O3）陶瓷复合材料的组织性能研究

本文考察了全稳定ＺｒＯ２对Ａｌ２Ｏ３陶瓷的组织性能的影响。结果表明，热压Ａｌ２Ｏ３－ＺｒＯ２（６ｍｏｌ％Ｙ２Ｏ３）陶瓷材料的显微形貌与其它Ａｌ２Ｏ３－ＺｒＯ２陶瓷的几乎完全一样，小量ｃ－ＺｒＯ２的存在可促进Ａｌ２Ｏ３陶瓷的烧结并细化晶粒，从而提高材料的力学性能，但其增韧增强能力有限。大量ｃ－ＺｒＯ２的存在因其本身低的力学性能、缺乏相变韧化和存在残余拉应力而使材料的力学性能下降。     

ZrO2—Al2O3系陶瓷复合材料力学性质

本文研究了ZrO_2-Al_2O_3系统陶瓷复合材料的力学性质,发现有两个最佳区域存在:在Al_2O_3基的陶瓷中,添加第二相ZrO_2颗粒可以使Al_2O_3瓷得到增韧和强化;在ZrO_2基的陶瓷中,添加少量Al_2O_3则可以通过Al_2O_3晶粒的裂纹弯曲和分叉增韧,强化ZrO_2的相变增韧,使ZrO_2瓷的强度和断裂韧性得到进一步的提高。适宜地控制YMSZ(Y_2O_3亚稳定ZrO_2)中Y_2O_3和TZP(四方相氧化锆多晶瓷)中的Al_2O_3量,可以获得高韧性和高强度的ZrO_2-Al_2O_3系陶瓷复合材料。     

纳米Al2O3对3Y-ZrO2陶瓷性能的影响

研究了纳米Al2O3添加剂对3Y—ZrO2陶瓷材料烧结和力学性能的影响。实验结果表明：添加纳米Al2O3（0．5mol％～2mol％）可以促进3Y—ZrO2的烧结，并提高材料的抗弯强度和断裂韧性。在1450℃下烧成的添加0．5mol％纳米Al2O3的3Y—ZrO2具有最高的强度和韧性值，分别为620MPa和13．9MPa·m^1/2，比纯3Y-ZrO2的最高强度和韧性（1500℃烧成试样）分别提高了11％和16％。     

Al2O3-ZrO2系熔融材料非平衡态显微结构

含75%质量分数Al2O3的Al2O3-ZrO2系熔融材料在缓慢冷却时,正常的显微结构由粗粒状初晶刚玉和组成少许波动的Al2O3-ZrO2共晶体组成.依冷凝速率梯度不同,该组成样品可以获得显微结构渐变的熔融材料.较快冷凝的同组成样品则呈微细的、均匀的两相结构,间或有少量不定组成的偏共晶.同组成的熔体与水冷钢容器接触激冷时,相当于淬火,只析出尺寸为5～10 μm的立方体和柱状刚玉以及小于2 μm的球状氧化锆晶体,而不存在共晶.以上表明:熔体不沿相图所示析晶路线形成共晶,而是形成了非平衡态的相组合.在激冷的样品中,ZrO2以立方相和四方相为主.缓慢冷凝的自由表面,析出自形刚玉,晶体尺寸达30～40 μm,而＜2 μm ZrO2呈微晶粒填充于其间.     

Al2O3/Fe3Al复合材料的制备及性能

利用热压烧结制备了致密的Al_2O_3/Fe_3Al复合材料。测试表明,该复合材料具有良好的力学性能,其抗弯强度和断裂韧性的最大值分别为832 MPa和7.96 MPa·m~1/2。对试样进行压痕实验,采用SEM对裂纹扩展方式进行观察,结果表明,在复合材料中存在着多种增韧机制,裂纹表现出复杂的扩展方式,这将在较大程度上吸收裂纹扩展能,从而使复合材料的断裂韧性得以提高。     

掺纳米Al2O3的纳米ZrO2(4Y)固体电解质的电性能

以纳米ZrO2(4Y)粉和纳米Al2O3粉为原料, 单轴成型, 1 200, 1 300 ℃无压烧结. 对掺不同质量分数(0.0～5.0%)Al2O3的ZrO2(4Y)烧结体, 用XRD, SEM和TEM研究了相组成和微观结构. 在不同温度下(300～1 000 ℃)测试了交流阻抗谱, 发现掺很少量的纳米Al2O3可降低ZrO2(4Y)的晶粒电阻. 但随着Al2O3掺入量的增加, 晶界电阻增大, 晶粒电阻也有所回升. 晶粒和晶界电导活化能则随Al2O3掺入量的变化不大. 对1 200 ℃,2 h烧结样品, 在1 000 ℃时, 掺0.5% Al2O3的ZrO2(4Y)样品有最大电导率, 为3.8×10-2Ω-1·cm-1.     

Al2O3/ZrO2层状复合陶瓷的结构设计与性能

以ZrO2为基本组成相的层状材料,采用干法的成型工艺,通过对表面层不同组分Al2O3 ZrO2和表面厚度和系统研究和设计,提出设计三层结构复合陶瓷层裂参数λ,当λ小于1．5时,表面层不会出现层裂,整体材料性能较好,研究表明,表面残余压应力的存在,使得三层结构复合陶瓷较单层结构陶瓷表面出更高的强度,硬度,断裂韧性和其他性质,45％Al2O3/ZrO2/45%Al2O3层状复合陶瓷的弯曲强度达682MPa,断裂韧性达16.2Pa.m^1/2;而单层ZrO2陶瓷的弯曲强度和断裂韧性分别仅为450MPa和8.8MPa.m^1/2.     

结构陶瓷弯曲强度的Weibull统计实验研究

本文在强度统计方法的Weibull模数估计及试样数量优化研究基础上,对氧化铝陶瓷进行了弯曲强度统计的大子样模拟母体试验,同时也对碳化硅、氮化硅、氧化铅增韧氧化铝等典型结构陶瓷进行了实验研究。实验结果表明,利用无偏极大似然估计的理论结果及置信度和相对误差双参数可以明确材料强度及其强度统计数据的精度。     

氧化铝/ZTA强夹层层状复合陶瓷的制备和性能

本实验以氧化铝和ZTA为研究对象,制备出ZTA/Al2O3强夹层层状复合陶瓷,复合陶瓷的冲击韧性是单相Al2O3陶瓷的5.6倍,单相ZTA陶瓷的2.8倍;而且复合陶瓷的断裂韧性和维氏硬度在平行于夹层方向和垂直于夹层方向差别不大,克服了弱夹层陶瓷各向异性的缺点.     

High‐temperature Bending Strength of Self‐Healing Ni/Al2O3 Nanocomposites

Bending strength of 5 vol.% Ni/Al₂O₃ composites as a function of testing temperature is investigated at temperatures ranging from room temperature to 1200°C. Self‐healing performance at high temperatures of the composites is evaluated by conducting high‐temperature bending tests for as‐sintered, as‐cracked, and as‐healed specimens. Bending strength of as‐sintered specimens dramatically decreases from 995 MPa at room temperature to 205 MPa at 1200°C. Additionally, the plastic deformation of the as‐sintered specimens occurs when the testing temperature reaches to 1200°C. The values of high‐temperature bending strength of as‐healed specimens are comparable with those of as‐sintered specimens. Similar to that of as‐sintered specimens, bending strength of as‐healed specimens degrades when the testing temperature increases. Results of the present study indicate that the recovery of bending strength by the self‐healing function is able to achieve at temperatures as high as 1200°C. Unlike the mechanical behaviors at high temperatures of as‐sintered and as‐healed specimens, the bending strength of as‐cracked specimens slightly increases with the increase of testing temperature. This phenomenon is attributed to the effect of the self‐healing mechanism during high‐temperature bending tests.     

淀粉燃料对多孔Al_2O_3-ZrO_2(Y_2O_3)陶瓷性能的影响

为了提高多孔Al2O3-ZrO2(Y2O3)陶瓷的强度,以尿素和淀粉为燃料,用低温燃烧法合成活性较高的Al2O3-ZrO2(Y2O3)复合粉体,并用此粉体制备了多孔Al2O3-Zr O2(Y2O3)陶瓷,研究燃烧前驱体中淀粉的外加量(质量分数分别为0、15%、25%、35%、45%、55%)对多孔陶瓷显气孔率、抗折强度和显微结构的影响。结果表明:与尿素为燃料相比,以尿素和淀粉为燃料能提高复合粉体的烧结活性,有效改善多孔陶瓷的显微结构,提高多孔陶瓷的抗折强度。     

(Y,Ce)-ZrO2增韧92Al2O3陶瓷的研究

采用自制均匀分散的(1.5Y,4Ce)-ZrO2微粉,通过适当工艺和92Al2O3复合,提高了92Al2O3陶瓷的韧性和强度.最后采用X-射线衍射分析、扫描电镜分析研究了该样品的机械性能与烧成制度、相组成及微观结构的关系.结果表明:92Al2O3陶瓷性能的提高归因于ZrO2的应力诱导相变增韧,并且当(1.5Y,4Ce)-ZrO2微粉的加入量为20%(质量分数)时,试样在1550℃烧成时,材料的抗弯强度、断裂韧性以及硬度得到了很好的改善.     

CuO/Al2O3-ZrO2催化剂的制备与表征

以溶胶-凝胶加浸渍法制备了CuO/Al2O3-ZrO2催化剂,对催化剂结构与催化性能进行了表征。结果表明以Al2O3稳定的ZrO2做载体制得的CuO/Al2O3-ZrO2催化剂具有较好的NO转化性能和较低的反应温度。     

Microstructure and Bending Strength in the Ternary (Mg,Ca)-Partially-Stabilized Zirconia

Microstructure and bending strength of commercial (MgO,CaO)-partially-stabilized zirconia subjected to heat treatments in the temperature range 900° to 1550°C were characterized. The as-received optimally aged material contained small ellipsoid-shaped tetragonal ( t ) precipitates dispersed homogeneously in the cubic ( c ) grains. Annealing at lower temperatures caused isothermal martensitic transformation to the monoclinic ( m ) phase. Annealing at higher temperatures caused formation of chevronlike and irregularshaped cluster precipitates, due to stress-induced coarsening and precipitate impingement. The loss of bending strength was related to the stored strain energy contributed by each type of precipitate morphology, in addition to decrease in the volume fraction of the t phase.     

Properties of (Y)ZrO2–Al2O3 and (Y)ZrO2–Al2O3–(Ti or Si)C Composites

The effect of Al₂O₃ and (Ti or Si)C additions on various properties of a (Y)TZP (yttria-stabilized tetragonal zirconia polycrystal)–Al₂O₃–(Ti or Si)C ternary composite ceramic were investigated for developing a zirconia-based ceramic stronger than SiC at high temperatures. Adding Al₂O₃ to (Y)TZP improved transverse rupture strength and hardness but decreased fracture toughness. This binary composite ceramic revealed a rapid loss of strength with increasing temperature. Adding TiC to the binary ceramic suppressed the decrease in strength at temperatures above 1573 K. The residual tensile stress induced by the differential thermal expansion between ZrO₂ and TiC therefore must have inhibited the t - → m -ZrO₂ martensitic transformation. It was concluded that a continuous skeleton of TiC prevented grain-boundary sliding between ZrO₂ and Al₂O₃. In contrast, for the ternary material containing β-SiC in place of TiC, the strength decreased substantially with increasing temperature because of incomplete formation of the SiC skeleton.     

Microwave hybrid and conventional sintering of Al2O3 and Al2O3/ZrO2 multilayers fabricated by aqueous tape casting

In this study, microwave hybrid sintering and conventional sintering of Al₂O₃- and Al₂O₃/ZrO₂-laminated structures fabricated via aqueous tape casting were investigated. A combination of process temperature control rings and thermocouples was used to measure the sample surface temperatures more accurately. Microwave hybrid sintering caused higher densification and resulted in higher hardness in Al₂O₃ and Al₂O₃/ZrO₂ than in their conventionally sintered counterparts. The flexural strength of microwave-hybrid-sintered Al₂O₃/ZrO₂ was 70.9% higher than that of the conventionally sintered composite, despite a lower sintering temperature. The fracture toughness of the microwave-hybrid-sintered Al₂O₃ increased remarkably by 107.8% despite a decrease in the relative density when only 3 wt.% t-ZrO₂ was added. The fracture toughness of the microwave-hybrid-sintered Al₂O₃/ZrO₂ was significantly higher (247.7%) than that of the conventionally sintered composite. A higher particle coordination and voids elimination due to the tape casting and the lamination processes, the microwave effect, the stress-induced martensitic phase transformation, and the grain refinement phenomenon are regarded as the main reasons for the mentioned outcomes.     

Microstructure and mechanical properties of Al2O3/ZrO2 composites by two-step sintering

Composites of Al₂O₃/ZrO₂ (containing 25, 50, and 75 vol% ZrO₂) were prepared by mixing Al₂O₃ and ZrO₂ suspensions. The microstructural control via two-step sintering (TSS) was the main objective of this work. For this purpose, different sintering curves were constructed, aiming to achieve the best temperature combination for the sintering steps that provides higher density and finer microstructure. The results were compared with single-step sintering (SSS). Furthermore, microhardness and fracture toughness were measured for the best TSS specimens under each composition. The results showed that the high densities were obtained, and the reduction of grain size was greater than 40% for two-step sintered specimens, compared to SSS ones. Consequently, microhardness values increased. However, fracture toughness values remained unchanged.     

添加Al2O3的Y-TZP基层状陶瓷力学性能

用15%(体积分数)Al2O3/3Y-TZP作为中间层,以20%(体积分数)Al2O3/3Y-TZP作为外层,采用干压、等静压法成型,并通过无压烧结制成了三层复合材料.通过测定材料的收缩率,对烧结收缩引起的应变进行了估算,提出:烧结收缩率也是层状材料设计的主要因素之一.实验结果表明:层状复合材料与15%(体积分数)Al2O3/3Y-TZP单层材料相比,应力方向平行于界面的抗弯强度提高了11.8%,由482MPa提高到539MPa;应力方向垂直于界面的韧性提高了21.2%,由9.9MPa*m1/2提高到12.0MPa*m1/2.