部分稳定氧化锆在低温共烧微晶玻璃基板中的作用研究

利用氧化锆的相变能够提高材料韧性的作用,在MgO-Al2O3-SiO2微晶玻璃中添加部分稳定超细氧化锆,用烧结法制得微晶玻璃基板。使用AKASHI压痕法测试材料增韧前后的韧性,利用FESEM观察微晶玻璃断口形貌,用XRD测试样品中的晶体组成,并在多芯片基板上初步得到满意的使用效果。实验证明,添加一定量的超细氧化锆后微晶玻璃的韧性有很大的提高,基板的破损率有较大的降低。     

Micromechanical properties and microstructure evolution of magnesia partially stabilized zirconia prepared by spark plasma sintering

Magnesia partially stabilized zirconia (Mg-PSZ) is a widely used engineering ceramic owing to its high hardness and exceptional toughness. It is usually processed by conventional firing followed by subeutectoid aging. In this work, Mg-PSZ was prepared by spark plasma sintering (SPS) followed by sequential subeutectoid aging to fine-tune its mechanical properties. Mg-PSZ prepared by SPS with the rapid heating capability presents much smaller grains than conventionally prepared counterparts. After aging, a significant fraction of the matrix cubic phase transforms into tetragonal, orthorhombic, and monoclinic zirconia. Microindentation and in-situ microcompression tests reveal that aging Mg-PSZ for 4 h leads to maximum fracture toughness and fracture strain due to the tetragonal-to-monoclinic transformation toughening. Post compression TEM analyses show dominant monoclinic ZrO₂ decorated by a high density of twin boundaries and stacking faults formed to accommodate the shear deformation. Preparation of Mg-PSZ by SPS offers rapid and effective approaches in finetuning the phases and mechanical properties.     

Zirconia matrix composite dispersed with stainless steel particles: Processing and oxidation behavior

Materials with non uniform properties are being developed to optimize several functions of industrial components in severe atmospheres at high temperature. These composites called M(p)-CMC(s): “ceramic matrix composites dispersed with metal particles” are candidates for high-temperature structure materials as functionally graded materials (FGMs) such as intermediate components between electrolyte and interconnecting components in SOFC.Preparation of a model composite M(p)-CMC(s) is described. Powder metallurgy process is used to obtain a dense composite (98% of the theoretical density) based on yttrium stabilized zirconia for the ceramic part and on 304L stainless steel for the metallic part. The characteristics of this material as well as its behavior under oxidation at high temperature are reported.     

High‐temperature fracture toughness of mullite with monoclinic zirconia

Reactive sintering of zircon and alumina and zirconia additions to mullite are well‐established methods for improving the poor fracture toughness of mullite. While it is clear that transformation toughening is responsible for the improved toughness by addition of partially stabilized zirconia, it is not clear why adding unstabilized zirconia increases the toughness although microcracking and crack deflection have been suggested. Therefore, the fracture toughness of a mullite composite with 20 vol% unstabilized zirconia and a monolithic mullite were investigated at ambient conditions and at temperatures up to 1225°C. It was found that monoclinic zirconia increases the toughness at ambient conditions from the monolithic mullite value of 1.9 to 3.9 MPa·m^1/2. The toughness of the composite with zirconia remains relatively constant from ambient to 600°C but then decreases rapidly. The mechanism for the toughness enhancement as well as the reason for its variation with temperature are explained using changes in residual stress state as deduced using the sphere in shell model from the measured thermal expansion behavior.     

Transformation Toughening and Fracture Behavior of Molybdenum Disilicide Composites Reinforced with Partially Stabilized Zirconia

The effects of yttria stabilization (0–6 mol%) on the fracture toughness of molybdenum disilicide composites reinforced with 20-vol%-yttria-stabilized zirconia particles are elucidated. Fracture toughness tests were conducted under three-point bend loading using single-edge-notched specimens. The stress-assisted martensitic phase transformation of zirconia associated with the fracture process was then studied using optical interference microscopy and laser Raman spectroscopy. Stress-induced martensitic transformation from tetragonal to monoclinic phase was observed only in the plastic wake of the material stabilized with 2 mol % yttria. The degree of toughening in this composite was also predicted using micromechanical models that assess the combined effects of transformation toughening and crack deflection. However, the fracture toughness of the 2-mol%-yttria-stabilized composite was in the same range as those of the other composites that did not exhibit evidence of transformation toughening. The toughening in the other composites is explained by considering the effects of crack deflection, residual stresses, and microcracking induced by residual stresses that occur as a result of the thermal expansion mismatch between the matrix and the reinforcements.     

Investigation of Toughening and Resistance-Curve Behavior in Hybrid Molybdenum Disilicide

This paper presents the results of a study of the toughening and resistance-curve behavior in a hybrid molybdenum disilicide (MoSi₂) composite that has been reinforced with 2 mol% yttria partially stabilized zirconia particles (TZ-2Y) and niobium layers. Toughening and resistance-curve behavior occur as a result of the combined effects of crack bridging and transformation toughening. Crack-tip shielding that is due to large-scale crack bridging and transformation toughening also is modeled using micromechanics concepts. The models show that the overall crack-tip shielding from transformation toughening is very limited. However, large-scale bridging by the ductile niobium layers promotes significant levels of toughening and resistance-curve behavior.     

四方氧化锆陶瓷复合材料评述

四方氧化锆陶瓷（ＴＺＰ）通过相变增韧具有很高的强度和断裂韧性，但在中高温下由于相变增韧作用的逐渐消失，力学性能迅速下降。在ＴＺＰ基体中加入第二相粒子成为复合材料，是提高ＴＺＰ韧性和高温力学性能的有效方法。本文综述了晶须、颗粒和片晶增强ＴＺＰ复合材料的增韧机理、性能改善的效果、以及存在的问题，展望了今后的研究方向。     

New Development of the J-Based Fracture Testing Technique for Ceramic-Matrix Composites

The J -based fracture testing technique is newly extended to experimentally determine the tension-softening (σ–δ) relations in ceramic-matrix composites. The J -based technique originally proposed for concrete has been well established for quasi-brittle materials where the fracture process is primarily dominated by the formation of a fracture process zone and the contribution of the crack tip toughness is negligibly small. In this study, the J -based technique is further developed to cover a more general case, i.e., a material in which the crack tip stress singularity coexists with the fracture process zone. This is the case, in particular, for modern fiber-reinforced ceramic composites and coarse-grained ceramics. The newly derived testing technique has been applied to foam glass composites reinforced with SIC and stainless steel short fibers. The validity of the deduced tension-softening relations has been examined by microscopy observations and by comparing with other conventional testing methods: the fracture energy method and the R- curve approach. It is suggested that the J -based fracture testing technique can provide reasonable tension-softening relationships and fracture parameters in modern ceramics and ceramic-matrix composites.     

Electroconductive composite of zirconia and hybrid graphene/alumina nanofibers

Novel type of hybrid nanofillers representing graphene encapsulated alumina nanofibres was selected as an additive to develop toughened electroconductive partially stabilized zirconia. The sinterability, mechanical and electrical properties of the produced nanocomposites were studied as function of the filler/graphene content. Composites containing just 0.6 vol.% of graphene corresponding to 3 vol.% of hybrid nanofibres exhibited high electroconductivity of 58 S/m without deterioration of mechanical properties. They also showed a slight toughening effect that is reflected by an increase in the indentation fracture toughness by 20% as compared to monolithic zirconia.     

Using macroporous graphene networks to toughen ZrC–SiC ceramic

Graphene is one of the important candidates in ceramic toughening due to its outstanding physical and chemical properties. For the weak interface toughening of large-diameter graphene sheet and alleviation of the interfacial reaction between ceramic precursors and graphene sheets during high-temperature pyrolysis, ZrC–SiC?Graphene composite was synthesized via a facile technology of infiltrating ceramic slurry instead of ceramic precursor into macroporous graphene network and spark plasma sintering. The incorporation of the graphene network improved fracture toughness, critical crack size, and fracture energy of ZrC–SiC ceramic. The multiple length-scale toughening mechanisms of ZrC–SiC?Graphene composite include the macroscopic toughening mechanism of crack deflection and bifurcation and the micro toughening mechanism of graphene bridging, ceramic micro zone tearing, graphene pull-out, graphene and ceramic brick slipping.     

R-curve behavior and flexural strength of zirconia-toughened alumina and partially stabilized zirconia composite laminates

A composite-laminate formed by thick layers (~ 320?µm) of zirconia-toughened alumina (ZTA) with thin (~ 50?µm) interlayers of zirconia partially stabilized (Y-PSZ) has been fabricated by tape casting and pressureless sintering. Fracture behavior and strength has been investigated and compared to a “monolithic” reference, e.g. a stack of zirconia-toughened alumina (ZTA) without interlayers. The fracture behavior has been analysed using stable crack growth in V-notched specimens loaded in 3-point bending. The ZTA+Y-PSZ composite laminate presented a rising crack resistance with maximum values between 6 and 14?MPa?m^1/2. In contrast, the “monolithic” ZTA laminate shows a plateau R-curve behavior at 2.7?MPa?m^1/2. Several toughening mechanisms were identified in the ZTA+Y-PSZ composite laminate, such as, crack arrest/slow down, micro cracking and bifurcation. These toughening mechanisms are most likely caused by high tensile residual stresses that were estimated theoretically.     

Introduction to a tough,strong and stable Ce-TZP/MgAl2O4 composite for biomedical applications

The processing of a new ceria-doped tetragonal zirconia polycrystal-based (Ce-TZP) composite and its microstructural and mechanical features are presented. Slip casting and die pressing were used to process commercially available Ce-TZP and MgAl₂O₄ powders into a dense ceramic composite. The absence of tetragonal to monoclinic transformation under hydrothermal conditions was assessed during accelerated aging tests. Biaxial flexural strength and fracture toughness values of more than 900 MPa and 15 MPa √m, respectively were measured, showing that phase transformation toughening of zirconia is maintained in the composite, while the inter/intragranular dispersion of nano-scaled magnesia spinel leads to strengthening of the Ce-TZP matrix. Flaw tolerance is attained, since the strength appears to be transformation dependent. These properties allow the composite to be used in the fabrication of various load-bearing components by employing conventional processing methods and sintering, for example for structural biomedical applications.     

Microstructural Characterization of ZrO2/O'-SiAION Composites

Zirconia has demonstrated a very moderate toughening effect in nitrogen-based ceramic composites because the reaction between tetragonal zirconia ( t -ZrO₂) and nitrogen results in additional zirconia stabilization to a nontrans-formable t ' or cubic structure. In O'-SiAlON matrices, the oxygen concentration increases and the oxygen-rich inter-granular glassy phase prevents zirconia from nitridation. As a result, tetragonal ZrO₂ is maintained and is transformable in the O'-SiAlON materials. The present study has provided transmission electron microscopy (TEM) evidence of the zirconia transformation and the associated toughening effect in a ZrO₂/O'-SiAlON composite. The implications and limitations of the transformation on toughening of the material are discussed.     

微波处理条件下含氧化钇稳定氧化锆增韧氧化铝陶瓷中的相变行为研究

本文采用XRD方法对微波热处理前后具有不同含量的氧化钇稳定氧化锆增韧氧化铝陶瓷的相变行为进行了研究。实验结果表明微波处理过程中,低含量Y_2O_3稳定ZTA陶瓷表面几乎皆为单斜相,当Y_2O_3含量超过2mol％时则四方相含量剧增,其原因在于ZTA陶瓷微波处理引起体积性加热造成较大的内外温差,使得内应力缓解了基质对ZrO_2的约束而发生t—ZrO_2=m—ZrO_2相变。同时如果调节稳定剂含量适中(如2mol％Y_2O_3),并对瓷体进行微波特殊处理后可获得较高的断裂相变量,有利于相变增韧陶瓷力学性能改善及损伤部件的性能自回复。     

SiC_w/莫来石和SiC_w/Y-TZP/莫来石复合材料的力学性能与显微结构

以莫来石为基体,SiC晶须(SiC_w)和Y-TZP(Y_2O_3稳定的四方ZrO_2多晶)为两种补强剂,采用热压烧结工艺,制备SIC_w/莫来石和SIC_w/Y-TZP/英来石复合材料。研究了复合材料的力学性能与显微结构,并对强化增韧机制进行了分析。结果表明,SiC晶须补强莫来石,可以改善其强度和断裂韧性。若SiC晶须和Y-TZP共同补强英来石,则可以进一步提高其强度和断裂韧性。晶须引起裂纹偏转,晶须拔出以及由ZrO_2相变引起的微裂纹增韧是该复合材料的主要增韧机制。SiC晶须和Y-TZP两种补强剂的共同作用,对莫来石强度和断裂韧性的提高具有叠加或协同效应。     

The Influence of Platelet‐Like LaMgAl11O19 on the Toughness of 3 mol% Yttria Partially Stabilized Zirconia Ceramic

LaMgAl₁₁O₁₉‐3 mol% yttria partially stabilized zirconia ceramics were successfully prepared by pressureless sintering at 1550°C for 3 h. The ceramic's mechanical properties were measured, and the phase composition and microstructure observed using X‐ray diffraction and scanning electron microscopy. The results show that the mechanical properties of the ceramic were initially improved on addition of LaMgAl₁₁O_19, but further additions were detrimental. When the amount of LMA added was equal to 2 wt.%, the bending strength and fracture toughness reached 812 ± 37 MPa and 14.0 ± 0.3 MPa·m^1/2. This equates to an increase of 8.0% and 6.9% compared with untreated 3 mol% yttria partially stabilized zirconia (3YSZ) ceramic, respectively. However, the bending strength and fracture toughness both decreased when the amount of LaMgAl₁₁O₁₉ added was 4 and 6 wt.%. A crack propagation and force analysis of the crack tips in LaMgAl₁₁O₁₉‐platelet‐reinforced 3YSZ ceramic were also carried out. The results indicate that phase transformation and crack deflection were the dominant toughening mechanisms in the LaMgAl₁₁O₁₉‐3YSZ ceramic. At the same time, energy dissipation by the LaMgAl₁₁O₁₉ platelets also helps to restrain crack propagation in the matrix, which improves toughness more effectively.     

Effect of Zirconia Concentration on the Growth of Nanowires in Bioactive Glass–Ceramic Coatings

Bioactive glass–ceramic with various zirconia concentrations was applied on stainless steel (SS) by the sol–gel method. Bioactive glass powder was prepared by the sol–gel method, and thermal properties of the prepared powders were studied by differential thermal analysis (DTA). The effects of zirconia were investigated to explore the growth of nanowires. The growth model of nanowires, in this study, is proposed in terms of the surface diffusion. The coatings showed the hardness values to be in the range of 3000–4500 MPa. The hardness values of prepared composite coatings increased with an increase in zirconia amounts.     

Potassium sodium niobate (KNN)‐based lead‐free piezoelectric ceramic coatings on steel structure by thermal spray method

For the first time, potassium sodium niobate (KNN)‐based lead‐free piezoelectric ceramic coating with strong piezoelectric response was fabricated on stainless steel substrates by thermal spray process, after introducing NiCrAlY and yttria‐stabilized zirconia (YSZ) intermediate layers. A large effective piezoelectric coefficient (d₃₃) of 125 pm/V was obtained with the thermal‐sprayed KNN‐based ceramic coating on the steel substrates. The mechanisms of improving the structure and enhancing the properties of the KNN‐based piezoelectric ceramic coatings by introducing the intermediate layers were analyzed. Ultrasonic transducers were designed and fabricated from the KNN‐based coatings directly formed on a steel plate structure, and the feasibility for generation and detection of ultrasonic waves for structural health monitoring using the thermal‐sprayed lead‐free piezoelectric ceramic coating was demonstrated.     

氧化锆相变稳定机制的研究进展及应用

综述了氧化锆相变的机理及相变稳定的影响因素,认为空位是影响氧化锆相稳定性最重要因素;对ZrO2相变增韧增强陶瓷材料的作用及作为固体电解材料、催化剂及催化剂载体方面的应用也作了简单阐述;并对今后的研究工作做了展望.     

Low-Pressure Injection Molding of Ceramic Springs

Injection molding has important advantages over other methods for the production of advanced ceramic parts with complex shapes. In this work, low-pressure injection molding was used to produce helical ceramic springs using two different kinds of molds. The ceramic powders used were submicrometer-sized alumina and partially stabilized zirconia. Sintered alumina and zirconia springs were obtained free of defects, with densities from 96% to 99% of the theoretical value. In preliminary mechanical tests, these ceramic springs supported axial deformations up to 10% before failure.