Ce-TZP材料形状记忆效应的研究

本文对相变增韧氧化锆陶瓷Ce-TZP材料的形状记忆效应进行了研究。研究结果表明:在张应力作用下,含有10mol％CeO_2的Ce-TZP陶瓷具有形状记忆效应。材料的形状记忆效应,由材料内稳定剂的含量及材料的显微结构所决定。记忆量与材料的变形量和环境的温度有关。本文还在理论上对产生形状记忆的条件及其机理作了初步分析和探讨。     

不同晶型ZrO_2纳米粉对氧化镁陶瓷烧结和抗热震性的影响

为提高氧化镁陶瓷的抗热震性,以高纯氧化镁粉为主原料,分别加入14%(w)的m-ZrO_2纳米粉、t-ZrO_2纳米粉、c-ZrO_2纳米粉为添加剂,经配料、成型、1 550℃保温2 h烧结制备氧化镁陶瓷试样,并研究加入不同晶型ZrO_2纳米粉对氧化镁陶瓷的烧结性和抗热震性的影响。结果表明:加入的ZrO_2弥散分布于方镁石晶粒晶界处,提高了试样的致密度;加入m-ZrO_2的试样中,ZrO_2与Mg O形成了固溶体,活化了方镁石晶体的晶格,大幅度促进了试样的烧结;加入t-ZrO_2和c-ZrO_2的试样中,ZrO_2以第二相增韧机制提高了抗热震性;加入m-ZrO_2的试样中,ZrO_2以相变增韧和第二相增韧的复合增韧机制提高了抗热震性。     

Ce—TZP陶瓷的压缩应力应变特性

本文采用宏微观相结合的方法,对12mol％Ce-TZP+10wt％Al_2O_3陶瓷材料的压缩应力应变特性进行了研究。通过实验首次发现该材料在室温下应力应变关系的伪弹性行为,证实了在加卸载过程中材料内部发生的可逆马氏体相变机理,并同时讨论了室温下材料内部出现可逆铁弹性畴转的可能性。最后就上述两种机理对静止与扩展裂纹的增韧效应进行了分析,提出了可逆相变条件下的增韧计算公式。     

Mg—PSZ陶瓷热处理与四方析体马氏体相变温度关系的研究

采用带有液氮负温裝置的LK-02型高速淬火膨胀仪对已获得工业应用的、含10mol％MgO的Mg-PSZ陶瓷的热处理条件与其中t-ZrO_2的马氏体相变温度(M_4、M_6)及可相变t-ZrO_7析体量的关系进行了研究,认为:t-ZrO_2析体的粒径及其热处理过程中的应力应变状态是决定或影响马氏体相变温度高低和在应力诱导下可相变t-ZrO_2量的两个基本因素;采取1420℃和1100℃的综合热处理,与在1420℃或1100℃进行单一温度热处理相比,易于控制M、和M_4值,且能保证较高的可相变t-ZrO_7析体量,是优化Mg-PSZ结构和性能的一种值得进一步进行研究的热处理工艺。经1100℃、4b热处理的Mg-PSZ试样的“Δl-T”曲线的低温端未观察到明显的表征马氏体相变的膨胀效应。     

氧化铈稳定氧化锆四方多晶体的制备及其力学性能研究

选用价格便宜的CeO_2作稳定剂,制备了高性能的四方氧化锆增韧陶瓷Ce-TZP。与Y-TZP相比,这种新材料晶粒尺寸较为粗大,t-ZrO_2→m-ZrO_2相变临界尺寸较大,从而不需用超细粉末做原料即可制得性能较好的增韧ZrO_2陶瓷。试验发现,添加适量的Al_2O_3和TiO_2可使烧结温度明显降低,同时力学性能得到大幅度提高。本文对此进行了初步探讨并利用XRD、SEM及EDAX等实验手段对力学性能与显微结构的关系进行了初步的理论分析。本研究取得最高Vickers硬度值约9GPa,最高抗弯强度约为2.1GPa(标准离差0.63GPa),最高断裂韧性约14MPa·m~(1/2)(标准离差1MPa·m~(1/2))。     

（Ce—TZP）—Al2O3陶瓷力学性能及其增韧机理的研究

本文研究了不同Al2O_3含量对(Ce-TZP)-Al_2O_3陶瓷强度、硬度及断裂韧性的影响。结果表明:Al_2O_3含量在10—20wt%时,具有明显的增强效果,较大幅度地提高了硬度及强度,并保留较高的韧性。借助于磨损试验和X射线衍射分析,研究了Ce-TZP材料的增韧机理。结果表明:材料的磨损抗力与磨损面上单斜相增量呈一致增加的关系。可以认为,该材料的增韧以相变增韧为主要机制。     

陶瓷的脆性与增韧

改善陶瓷材料的脆性是陶瓷学家们所长期关注的问题。纤维补强及氧化锆相变增韧在实践中被证实对改善陶瓷材料的脆性以及强化陶瓷是两条有效的途径。本文将就以上两条途径的研究中的某些问题进行简要的讨论。在纤维补强陶瓷复合材料的研究中指出纤维与基体之间在化学上的相容性的重要,在两者间的热膨胀和弹性模量上的匹配亦是不可忽视的以及认为西者的界面结合以适宜为度。在氧化锆相变增韧的研究中讨论了四方氧化锆(t-ZrO_2)的保持,应力诱导的可相变的t-ZrO_2以及对增韧作用有贡献的可相变的t-ZrO_2等问题。文中亦列举了Y-TZP和ZTA的有关性能。     

ZrO2陶瓷的微波烧结制备及其性能

以微波热解制备的氧化锆粉体为原料、氧化钇为烧结助剂,采用微波烧结方式制备氧化锆陶瓷,研究了不同氧化钇含量对氧化锆陶瓷的微波烧结行为、物相组成、显微结构及致密化的影响。结果表明:在微波烧结过程中,随着Y_2O_3含量的增加,ZrO_2陶瓷的物相从m-ZrO_2逐渐转变为m-ZrO_2与t-ZrO_2(c-ZrO_2)并存,且ZrO_2陶瓷的晶粒随着烧结助剂含量的增加而逐渐变小,样品致密度下降。当烧结温度为1 450℃时,微波烧结获得的未添加烧结助剂的样品致密度达到99%,远远高于传统电阻烧结所获得样品的致密度。     

冷却方式对Y_2O_3-ZrO_3陶瓷相变及力学性能的影响

研究了常压烧结Y_2O_3-ZrO_2陶瓷不同冷却方式对其力学性能及t—m相变的影响。试验结果表明;冷却方式不同可以使材料中t-ZrO_2相含量不同,这与t—m相变的成核有关,成核过程是温度和时间的函数。随冷却速度增大,相变开始点温度(M_s)降低,相变终了点温度(M_f)则不受冷却速度的影响。     

不同晶相结构ZrO2负载铜基催化剂用于二乙醇胺脱氢反应

通过制备不同晶相结构〔单斜相(m-ZrO_2)、四方相(t-ZrO_2)和无定型(a-ZrO_2)〕ZrO_2载体,再通过沉积沉淀法制得Cu/m-ZrO_2、Cu/t-ZrO_2和Cu/a-ZrO_2催化剂,分别用于催化二乙醇胺脱氢合成亚氨基二乙酸反应。采用XRD、氮气物理吸附脱附、XPS、H_2-TPR、CO_2-TPD对催化剂的结构进行了表征。结果表明,Cu/m-ZrO_2催化剂界面更加有利于Cu~+/Cu~0稳定存在,具有更多的碱性位点,且抗氧化性较好。在二乙醇胺脱氢反应中,Cu/m-ZrO_2催化剂性能最好,反应时间为2.5 h,亚氨基二乙酸收率为97.64%。     

干摩擦及水润滑下氧化锆-氧化铝层状复合陶瓷的摩擦学行为

研究了氧化锆氧化铝三层结构层状复合陶瓷在干摩擦和水润滑下的摩擦学性能和磨损机制，并比较了氧化锆-氧化铝单层陶瓷在相同条件下的摩擦学性能。结果表明：相同条件下，层状陶瓷的摩擦系数和磨损率均低于单层陶瓷，根本原因在于层状陶瓷表面的压应力导致的韧性提高和磨损表面剪切应力的降低。水润滑可以有效地降低复合陶瓷的摩擦磨损，主要原因是由于水引起主导磨损机制发生变化，由干摩擦时的磨粒磨损和粘着磨损转变为摩擦化学磨损和疲劳磨损。     

Spark assisted chemical engraving (SACE) mechanism on ZrO2 ceramics by analyzing processed products

Traditional machining processes are usually unworkable for ZrO₂ ceramics due to the mechanical properties of fragility, high hardness and high-temperature resistance. The process of spark assisted chemical engraving (SACE) has been explored for machining ZrO₂ ceramics, but up to now the processing mechanism has not been clearly understood yet. To understand the microscopic mechanism, the phase transition paths of ZrO₂ ceramics under various physical and chemical conditions were analyzed. A backstepping approach based on structures and components of SACE processed products was proposed to verify the physical and chemical mechanisms. According to the crystal phase composition of the processed debris resulting from Raman spectrum analysis, it was found that the debris exhibited crystalline and amorphous forms which provided the evidence of physical crushing and chemical reactions. Furthermore, the chemical removal mechanism was proven by the nearly saturated concentration of Zr ion in the processed solution according to the ICP-OES assay of SACE electrolyte. The quantitative proportion of physical and chemical effect can be successfully determined by distinguishing and analyzing two kinds of debris with different crystal phase compositions which yield distinctly identifiable appearances under an optical microscope.     

五价钽、锂掺杂对Y-TZP微观结构和性能的影响

在前人工作的基础上,本文作者进一步深入细致地分析了总结了Ｎｂ２Ｏ５和Ｔａ２Ｏ５对Ｙ－ＴＺＰ微观结构和宏观性能的影响并提出了自己的见解,研究发现Ｎｂ２Ｏ５和Ｔａ２Ｏ５的添加使得Ｙ－ＴＺＰ轴比及热膨胀各向异性增大,马氏体相变起努温度升高,可相变,ｔ－ＺｒＯ２含量上升有利于材料机械性能的提高。     

Comparative studies of dynamic hysteresis responses in hard and soft PZT ceramics

Lead zirconate titanate (PZT) is a ferroelectric material with very interesting and useful dynamic hysteresis properties. Normally, PZT is doped with donors or acceptors to yield better electrical properties. Soft and hard PZT ceramics are respectively donor- and acceptor-doped PZT, which are commercially available and widely employed in various applications. Previous investigations have mainly been focused on the dynamic hysteresis at room temperature and under stress-free condition. However, when used, these ceramics are normally subjected to stress. More importantly, the ambient temperature is usually not at room temperature. Therefore, this study was to investigate dynamic hysteresis behavior of both hard and soft PZT ceramics with varying compressive stress and temperature. The results clearly revealed the influence of external stress and temperature on the dynamic hysteresis of both types of PZT ceramics. Increasing stress and temperature resulted in a decrease of the hysteresis area of the two types of PZT ceramics.     

Grain-Boundary-Phase Identification of a Lead-Based Relaxor by X-ray Photoelectron Spectroscopy

X-ray photoelectron spectroscopy was used to study a lead-based relaxor dielectric ceramic to identify the grain-boundary phase most likely to be responsible for the insulation degradation of relaxor dielectric ceramics under humid loading conditions. The grain-boundary phase consisted mainly of lead and oxygen. The binding energies of Pb4f_7/2 and O1s in the grain-boundary phase were found to be 137.3 eV and 528.8 eV, respectively, and these values agreed well with those for Pb₃O₄ and PbO₂. In addition, the broadness of the Pb4f_7/2 peak suggested the presence of PbO. Measurements were made of lead dissolution from dielectric ceramics in hot water; specimens with a grain-boundary phase gave a 30 to 50 times greater lead concentration in the hot water than specimens without a grain-boundary phase. This demonstrated that the grain-boundary phase easily dissolved in hot water. Thus, it was concluded that the grain-boundary phase contained water-soluble PbO₂ and PbO. The results strongly supported the resistance degradation mechanism of relaxor dielectric ceramics under humid loading conditions as previously proposed by the authors.     

Wear properties of Y–α/β composite sialon ceramics

The tribological properties of yttrium containing α/β composite sialon ceramics have been studied under non-lubricated conditions by means of block-on-ring and ball-on-disk type experiments against a commercial silicon nitride material. The sialon ceramics were produced by hot pressing powder mixtures of Si₃N₄, AlN, Al₂O₃ and Y₂O₃, resulting in composite ceramics containing different amounts of the α/β phases. The effects of microstructural differences on the mechanical properties of the ceramics, and their wear characteristics under a range of testing conditions have been assessed. It was found that Vickers hardness decreased whilst both fracture toughness and bending strength increased with increasing amount of β phase in the composite. Under mild testing conditions, material removal was considered to occur by polishing of the surface, and in this case the high α-sialon composites exhibited the highest wear resistance, reflecting their higher hardness. Under severe testing conditions, the wear behaviour was characterised as microcracking caused by the higher Hertzian stress levels, and resulted in grain removal or “dropping” from the surface of the materials. Under these conditions, the elongated microstructure and higher fracture toughness of the low α-sialon composites hinder the crack propagation and result in better wear characteristics when compared to the fine equiaxed α-sialon materials.     

Influence of corrosion and mechanical loads on advanced ceramic components

Advanced oxide ceramics are prospective materials for severe application conditions, including corrosion, particularly, in oxygen-rich environments, combined with the action of mechanical loads. The corrosion behavior and mechanical strength decrease of oxide ceramics, such as high alumina, alumina–mullite and zirconia-based ceramics, were studied in water steam supercritical conditions (elevated temperatures and pressures). The strength decrease under the action of the studied aggressive environment is mostly dealt with the glassy phase dissolution and intergranular corrosion for alumina–mullite and high alumina ceramics, while degradation of zirconia-based ceramics is also dealt with the phase transformation. The influence of structure defects related to processing of the ceramics on corrosion is considered.     

氧化锆增韧陶瓷的室温动态疲劳

用动态疲劳试验法研究了３Ｙ－ＴＺＰ和３Ｙ－ＴＺＰ／Ａｌ_２Ｏ_３（２０ｗｔ％）陶瓷在空气中的室温动态疲劳，并讨论了疲劳慢裂纹扩展特性。另外利用动态疲劳数据对两种陶瓷的平均寿命进行了预测。两种陶瓷材料在室温下均存在着慢裂纹扩展，主要是由空气中水蒸汽的应力腐蚀所造成的，且裂纹是沿晶界玻璃相扩展的。相变诱发的表面压应力和裂纹尖端的正应变可提高疲劳抗力。在８００ＭＰａ应力作用下，３Ｙ－ＴＺＰ和３Ｙ－ＴＺＰ／Ａｌ_２Ｏ_３（２０ｗｔ％）的平均寿命分别为２４ｍｉｎ和７２ｈ，平均寿命随应力的增大而缩短．     

(1-x)NBT-xBaTiO3系陶瓷材料弛豫特性的研究

测量了各样品在1kHz、10kHz、100kHz频率下从室温至500℃的介电温谱,表明材料为弛豫铁电体,Ba2+的掺入使其弛豫特性有所降低。当x≥0.10时,材料在低温下具有正常铁电体的特征,高温下具有弛豫铁电体的特征。两个介电反常峰的存在表明在此温度区间材料发生了两次相变。     

Strength Evaluation of Piezoelectric Ceramics under Transient Thermal Environments

The strength of piezoelectric ceramics is analyzed for a plate suddenly exposed to an environmental medium of different temperatures. The admissible temperature jump the material can sustain is studied using the stress- and fracture-toughness-based failure criteria. The critical parameters governing the level of the transient thermal stress in piezoelectric ceramics are identified. Solutions are obtained for the maximum thermal shock that the plate can sustain without failure, under the conditions that (i) maximum local tensile stress equals the tensile strength of the ceramic, and (ii) maximum stress intensity factor for representative pre-existing cracks equals the fracture toughness of the ceramic.