碳化硅晶须对氧化锆陶瓷材料结构的影响

本文研究了不同晶须含量对可相变增韧的ZrO_2(2mol%Y_2O_3)陶瓷及完全稳定的ZrO_2(6mol%Y_2O_3)陶瓷结构的影响。结果表明:晶须的加入使ZrO_2材料的晶料明显细化,但对该类热压复合材料的致密度影响不大;纯ZrO_2(6mol％Y_2O_3)为单一的C相结构,加入晶须后有少量的t相出现;纯ZrO_2(2mol%Y_2O_3)热压材料由t m两相组成,晶须的加入降低了基体中m相的相对含量,但对断裂过程中t→m相交量影响不大。     

ZrO_2增韧陶瓷中四方相氧化锆的相变量、相变区宽度及其增韧机理的研究

利用X射线衍射技术研究了氧化锆增韧氧化铝陶瓷(ZTA)和四方氧化锆多晶陶瓷(TZP)的断裂表面上四方氧化锆ZrO_2(t)的相变量和相变宽度。发现在ZrO_2增韧陶瓷(ZTC)中,ZrO_2(t)相变所需应力σ_T随着稳定剂Y_2O_3含量的增加而增大,断裂面上的ZrO_2(t)的相变量和相变宽度随之减小。在此基础上提出了修正的相变增韧公式: ΔK=0.21E_ce~TV_fh~(1/2)/(1-ν)+1.26V_fh~(1/2)σ_T(1-2ν)/(1-ν) 该式表明:(1)ZrO_2相变增韧存在一定的限制;(2)增加基质材料的强度是进一步提高ZTC的K_(Ic)和σ_f的关键。     

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。     

增韧Z_rO_2陶瓷的研究

以Y_2O_3为固溶剂采用机械粉碎法制备的亚微米级ZrO_2粉末为原料,制造出高强度、高韧性的ZrO_2陶瓷。通过制定合理的配方以及控制烧成工艺条件,可以在坯体中获得大量的亚稳四方ZrO_2。当Y_2O_3加入量为2.5mol％时,抗折强度达978MPa,断裂韧性达15.1MPam~1/2。其增韧机理属于应力诱导相变增韧。     

ZTA陶瓷断裂韧性和强度的研究

通过控制Y_2O_3在YPSZ(Y_2O_3部分稳定氧化锆)的含量以及YPSZ在ZTA(氧化锆增韧氧化铝瓷)中的含量可以最大限度地使基质中的氧化锆以亚稳定四方相形式存在;实验结果表明:上述二值分别为4wt%和18wt%。通过控制YPSZ团聚体尺寸和控制其晶粒尺寸小于基质晶粒尺寸,可以同时较好地使ZTA陶瓷的K_(IC)和σ_f得到提高。     

马氏体相变与ZrO2增韧陶瓷

利用ZrO_2增韧陶瓷机理很大程度上是通过四方相ZrO_2(t—ZrO_2)转变成单斜相ZrO_2(m—ZrO_2)马氏体相变来实现的,而马氏体相变这一概念最早源于金属材料学中.本文旨在通过较深入地了解马氏体相变内容达到有助于研究ZrO_2增韧陶瓷之目的.     

ZrO2增韧Al2O3陶瓷耐磨性的研究

本文对五种不同含量ZrO_2增韧Al_2O_3陶瓷在磨粒磨损条件下的耐磨性进行了试验研究。试验结果表明,ZrO_2增韧Al_2O_3陶瓷的磨损机理不同于金属,它并不是简单的显微切削机理或犁沟机理,其耐磨性与陶瓷的硬度和弹性模量没有单调的依赖关系,而与材料的断裂韧性和抗弯强度呈现比较一致的趋向关系。扫描电镜对摩擦表面和抗弯断口的对比观测表明,ZrO_2增韧Al_2O_3陶瓷磨损破坏机理属于一次性脆性断裂机理。因此,欲提高该陶瓷的耐磨性应当着重于提高陶瓷的韧性和强度。利用ZrO_2的马氏体相变,可望提高陶瓷的韧性和强度,故可望提高Al_2O_3基陶瓷的耐磨性。     

添加Al_2O_3对ZrO_2(Y_2O_3)粉末性能的影响

采用化学共沉淀法制备了ZrO_2(Y_2O_3)和ZrO_2(Y_2O_3)/Al_2O_3超细粉末,研究了添加Al_2O_3对粉末性能的影响.添加Al_2O_3.提高了t—ZrO_2的结晶化温度,抑制了ZrO_2晶粒生长.使ZrO_2粒子得以细化.添加Al_2O_3.还提高了介稳t—ZrO_2的稳定性,有效抑制了t—ZrO_2→m-ZrO_2相变.Al_2O_3添加量超过20wt%时.粉末烧结活性降低,烧结温度提高.     

Y_2O_3对氧化锆陶瓷组织和性能的影响

由于氧化锆陶瓷的脆性特点限制了其自身的发展,所以研究者关注的重点在于如何提高氧化锆陶瓷韧性。氧化锆陶瓷的性能与制备工艺的各个环节息息相关,主要的制备工艺包括粉末的制备、成形和烧结等,每个环节对氧化锆陶瓷的致密度、相结构和力学性能都起着关键性的作用。为此,笔者对氧化锆陶瓷制备工艺进行了深入研究,通过髙能球磨制粉工艺获得超细的ZrO_2、Y_2O_3混合粉末,并经过常压烧结获得高性能的氧化锆陶瓷,这一研究将对超细晶粒增籾,ZrO_2、Y_2O_3机械复合增韧和烧结优化具有理论指导意义,并对氧化锆陶瓷的开发应用具有积极的推动作用。     

细分散ZrO_2的增韧作用及其在Si_3N_4中的应用

本文介绍了ZrO_2(t)(?)ZrO_2(m)的马氏体相变特性及其在陶瓷基质中的相变热力学,归纳了含细分散ZrO_2相的陶瓷增韧机理以及Si_3N_4-ZrO_2系统的研究现状,讨论了利用ZrO_2的相变特性增韧Si_3N_4中的困难所在及共可能的解决途径。     

溶胶-凝胶法制备氧化铝-氧化锆复合粉体

以A1C13·6H2O和ZrOCl2·8H2O为起始原料、NH3·H2O为沉淀剂,采用溶胶一凝胶法制备A12O3含量为51．74％（质量分数,下同）、ZrO2含量为44．95％的A12O3-ZrO2复合粉体。借助X射线荧光分析仪、X射线衍射仪、高温热重仪、激光粒度分析仪和扫描电子显微镜对复合粉体的化学成分、物相组成和粒径分布等进行了表征。结果表明：A12O3-ZrO2复合粉体化学成分均匀性好,粒径较细,粒径小于0．5μm的约为5％,在0．5～5．0μm的约为55％,大于5．0μm的约为40％;随热处理温度升高,复合粉体析晶程度逐渐提高,800℃热处理时t-ZrO2相析出量较少;12O0℃热处理时则析出大量的t-ZrO2相、少量刚玉相和微量c-ZrO2相;1350℃后,刚玉相和c-ZrO2相数量明显增多。     

The role of carbon nanotubes on the stability of tetragonal zirconia polycrystals

The effect of single walled carbon nanotubes (SWNT) at zirconia grain boundaries on the stability of a tetragonal zirconia polycrystalline matrix has been explored in as–sintered composites and after low–temperature hydrothermal degradation (LTD) experiments. For this purpose, highly–dense 3?mol% Y₂O₃–doped tetragonal zirconia polycrystalline (3YTZP) ceramics and SWNT/3YTZP composites were prepared by spark plasma sintering (SPS). Quantitative X–ray diffraction analysis and microstructural observations point out that an increasing amount of well–dispersed SWNT bundles surrounding zirconia grains decreases the metastable tetragonal phase retention in the ceramic matrix after sintering. In contrast, the tetragonal ceramic grains in composites with SWNTs are less sensitive to the presence of water, i.e. to undergo a martensitic transformation under LTD conditions, than monolithic 3YTZP ceramics. The SWNT incorporation diminishes micro–cracking due to tetragonal to monoclinic ZrO₂ phase transformation in the composites.     

Fabrication and characterization of Nb2O5-doped 3Y-TZP materials sintered by microwave technology

The purpose of this research is focused on the manufacture and characterization of a partially stabilized zirconia ceramic with 3 mol% of Yttria and doped with .5 and 1.5 mol% of Nb₂O₅ to analyze the influence of doping, with the purpose of improving the properties before hydrothermal degradation. In the first instance, the microwave sintering process was used for the consolidation of this material, then the physical and mechanical properties were characterized. Together, the results obtained by the conventional sintering process were compared. A low hydrothermal degradation study (LTD) is presented at low temperatures in which possible changes in the mechanical properties of the ceramic materials are analyzed and its influence on the phase transformation that zirconia may present is observed. The mechanical properties were evaluated through hardness, fracture toughness, and Young's modulus tests. Likewise, their density was analyzed, and microstructure was characterized by FESEM. It was found that the microwave-sintered samples at 1200°C exhibited superior properties of toughness than even samples sintered by conventional methods at higher temperatures (1400°C). The sample of 3Y-TZP with 1.5 mol% Nb₂O₅ sintered by microwave with <.2% of porosity achieved a maximum fracture toughness value around 40% higher than the dense monolithic 3Y-TZP material.     

Crystal structure and morphology of CeO2 doped stabilized zirconia ceramics under high-frequency microwave field sintering

Under high-frequency microwave irradiation, zirconia ceramics were prepared by sintering nano-CeO₂ (Ce = 7 mol%) doped zirconia powder. The different effects of temperature environment on the phase structure transformation, surface functional groups, microstructure, growth process, and density of doped zirconia were analyzed, and the optimized microwave sintering process for zirconia was determined. The experimental results reveal that the tetragonal phase of zirconia is positively correlated with the temperature when the temperature reaches about 1100 °C in the studied range. The reason is that the grain grows with the increase of sintering temperature, and the surface energy of grain decreases, which leads to the fluctuation of tetragonal phase content. The density of zirconia reaches 98.03% at 1300 °C, and the growth activation energy is 27.40 kJ/mol. There is no abnormal growth of zirconia particles, and the phase transition temperature decreases, which is attributed to the efficient heating of microwave and the incorporation of nano-ceria stabilizer.     

Development of Ce‐PSZ‐/Y‐PSZ‐Toughened Alumina Inserts for High‐Speed Machining Steel

The nanocomposite CeO₂/Y₂O₃ partially stabilized zirconia (Ce‐PSZ/Y‐PSZ)‐toughened alumina was prepared by wet chemical simultaneous coprecipitation process. The thermal stability of phases and morphology of powders were characterized by TG‐DTA, FTIR, and FESEM. The microstructure, stabilization of phases and compositional analysis with different mol% CeO₂/Y₂O₃‐doped zirconia in alumina are characterized by FESEM, XRD, and EDAX spectra. Significant improvement in fracture toughness and flexural strength has been observed in 10 vol% of partially stabilized zirconia (2.5 mol% Y₂O₃ in ZrO₂/9 mol% CeO₂ in ZrO₂)‐toughened alumina, which is suitable for high‐speed machining applications.     

氧化锆/氧化铝复相陶瓷显微组织缺陷分析

针对5Y-ZrO2/Al2O3复相陶瓷出现的晶粒异常长大和晶粒开裂问题展开研究。以ZrO2和Al2O3为主要原料,采用常压烧结工艺制备陶瓷样品,利用SEM观察显微组织。分析表明:MgO对抑制Al2O3晶粒异常长大有重要影响,MgO的加入量应随着Al2O3加入量的变化而改变;烧结温度的改变将导致异常长大的Al2O3晶粒细化。当烧结温度较低时,Al2O3晶粒将在短轴方向逐渐断开成段;当温度较高时,则沿着长轴方向逐渐开裂成条状。ZrO2晶粒的断裂主要与烧结温度有关:在1630℃以上烧结时,出现裂纹并贯穿晶粒;晶粒开裂的原因是:烧结温度较高时,陶瓷中形成了t-ZrO2,在降温过程中大颗粒的t相发生t→m相变,而小颗粒t相则无法变成m相,引起局部体积变化不均匀,从而产生相变应力导致晶粒穿晶断裂。     

Strength and Phase Stability of Yttria-Ceria-Doped Tetragonal Zirconia/Alumina Composites Sintered and Hot Isostatically Pressed in Argon–Oxygen Gas Atmosphere

Yttria-ceria-doped tetragonal zirconia (Y,Ce)-TZP)/alumina (Al₂O₃) composites were fabricated by hot isostatic pressing at 1400° to 1450°C and 196 MPa in an Ar–O₂ atmosphere using the fine powders prepared by hydrolysis of ZrOCl₂ solution. The composites consisting of 25 wt% Al₂O₃ and tetragonal zirconia with compositions 4 mol% YO_1.5–4 mol% CeO₂–ZrO₂ and 2.5 mol% YO_1.5–5.5 mol% CeO₂–ZrO₂ exhibited mean fracture strength as high as 2000 MPa and were resistant to phase transformation under saturated water vapor pressure at 180°C (1 MPa). Postsintering hot isostatic pressing of (4Y, 4Ce)-TZP/Al₂O₃ and (2.5Y, 5.5Ce)-TZP/Al₂O₃ composites was useful to enhance the phase stability under hydrothermal conditions and strength.     

Manipulating microstructure and mechanical properties of CuO doped 3Y-TZP nano-ceramics using spark-plasma sintering

Nano-powder composites of 3Y-TZP doped with 8 mol% CuO were processed by spark-plasma sintering (SPS). A 96% dense composite ceramic with an average grain size of 70 nm was obtained by applying the SPS process at 1100 °C and 100 MPa for 1 min. In contrast to normal, pressureless, sintering during SPS reactions between CuO and 3Y-TZP were suppressed, the CuO phase was reduced to metallic Cu, while the 3Y-TZP phase remained almost purely tetragonal. Annealing after SPS results in grain growth and tetragonal to monoclinic zirconia phase transformation. The grain size and monoclinic zirconia phase content are strongly dependent on the annealing temperature. By combining the processing techniques studied in this work, including traditional pressureless sintering, properties of the composite ceramic can be tuned via manipulation of microstructure. Tuning the mechanical properties of dense 8 mol% CuO doped 3Y-TZP composite ceramic by utilising different processing techniques is given as an example.     

Preparation, sintering, microstructure, and thermal stability of Y2O3- and CeO2-doped tetragonal zirconia ceramics

Yttria- and ceria-doped tetragonal zirconia polycrystals ((Y, Ce)-TZP) with compositions 2·5 mol% YO_1·5-4 mol% CeO₂---ZrO₂, 4 mol% YO_1·5-4 mol% CeO₂---ZrO₂, and 2·5 mol% YO_1·5-5·5 mol% CeO₂---ZrO₂ were prepared from zirconia sols obtained hy hydrolysis of ZrOCl₂ solution, and their sintering, microstructure and thermal stability were studied. Sintered bodies with 99% TD were obtained by firing at 1400°C for 2 h in air. The grain size of (Y, Ce)-TZP increased with decreasing Y₂O₃ content in Y₂O₃---CeO₂---ZrO₂. (Y, Ce)-TZP was resistant to tetragonal-to-monoclinic (t → m) phase transformation during low temperature ageing as compared with 3Y-TZP.     

Yb2O3 and Y2O3 co-doped zirconia ceramics

A suspension stabilizer-coating technique was employed to prepare x mol% Yb₂O₃ (x = 1.0, 2.0, 3.0 and 4.0) and 1.0 mol% Y₂O₃ co-doped ZrO₂ powder. A systematic study was conducted on the sintering behaviour, phase assemblage, microstructural development and mechanical properties of Yb₂O₃ and Y₂O₃ co-doped zirconia ceramics. Fully dense ZrO₂ ceramics were obtained by means of pressureless sintering in air for 1 h at 1450 °C. The phase composition of the ceramics could be controlled by tuning the Yb₂O₃ content and the sintering parameters. Polycrystalline tetragonal ZrO₂ (TZP) and fully stabilised cubic ZrO₂ (FSZ) were achieved in the 1.0 mol% Y₂O₃ stabilised ceramic, co-doped with 1.0 mol% Yb₂O₃ and 4.0 mol% Yb₂O₃, respectively. The amount of stabilizer needed to form cubic ZrO₂ phase in the Yb₂O₃ and Y₂O₃ co-doped ZrO₂ ceramics was lower than that of single phase Y₂O₃-doped materials. The indentation fracture toughness could be tailored up to 8.5 MPa m^1/2 in combination with a hardness of 12 GPa by sintering a 1.0 mol% Yb₂O₃ and 1.0 mol% Y₂O₃ ceramic at 1450 °C for 1 h.