ZTA陶瓷ZrO3的韧化机制与断裂特征

选用无压烧结和热压烧结两种系列不同成分配比的ＺｒＯ２韧化Ａｌ２Ｏ３（ＺＴＡ）陶瓷，在较宽的力学性能范围内研究ＺｒＯ２的韧化机制对材料强度、韧性的贡献及其与断裂特征之间的关系。压痕裂纹揭示出ＺｒＯ２的不同韧化机制有不同的开裂特征：微裂纹韧化的材料，压痕裂纹弯曲行进，并且沿着ｍ－ＺｒＯ２颗粒与基体的交界面扩展；相变韧化的材料，压痕裂纹穿越ｔ－ＺｒＯ２颗粒。此特征能很好地解释：微裂纹韧化可以提高材料的断     

β″－Al_2O_3陶瓷的强化和韧化

研究了稳定ＺｒＯ＿２和部份稳定ＺｒＯ＿２对β″－Ａｌ＿２Ｏ＿３陶瓷的强化和韧化作用，观察了不同种类、不同含量的ＺｒＯ＿２对β″－Ａｌ＿２Ｏ＿３陶瓷的显微结构、力学性能和电导率的影响，探讨了β″－Ａｌ＿２Ｏ＿３的韧化机理。     

Si_3N_4－ZrO_2陶瓷中ZrN的生成及其对性能的影响

研究了ＺｒＮ在Ｓｉ＿３Ｎ＿４－ＺｒＯ＿２复相陶瓷中的形成及其对材料性能的影响，结果表明：在１．５ＭＰａＮ２气压烧结条件下，ＺｒＮ的形成温度约为１６００℃，提高Ｎ＿２的压力有利于抑制ＺｒＮ的生成，以稳定的ｔ－ＺｒＯ＿２加Ｓｉ＿３Ｎ＿４基体中，对抑制ＺｒＮ的生成有明显作用。当复相陶瓷中生成一定量的ＺｒＮ时，力学性能明显下降，而ＺｒＯ＿２分布均匀且以ｔ－ＺｒＯ＿２，ｃ－ＺｒＯ＿２形式存在时，复相陶瓷具有较高的强度（７４０ＭＰａ）和断裂韧性（８．８ＭＰａ·ｍ￣（１／２））。     

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。     

GPSZrO_2-Si_3N_4复合材料性能的研究

本文研究了ＧＰＳＺｒＯ２－Ｓｉ３Ｎ４复合材料的烧结性能、相组成、显微结构和力学性能。ＺｒＯ２－Ｓｉ３Ｎ４复合材料在１７７０～１８００℃,氮气压力分别为１ＭＰａ,２ＭＰａ,３ＭＰａ下烧成,获得相对密度＞９５％烧结体。实验结果表明：少量的工业ＺｒＯ２对氮化硅有助烧作用,增大氮气压力有利于改善氮化硅陶瓷材料的烧结性能和力学性能;ＺｒＯ２可提高氮化硅基体的断裂韧性,在３ＭＰａ下烧成条件下,添加１５％ＺｒＯ２的Ｓｉ３Ｎ４复合材料断裂韧性可达８．０８ＭＰａ．ｍ１／２,与基体相比提高２１．５％,第二相粒子增韧和微裂纹增韧为主要增韧机理。     

铝锆复合材料的增韧机理

在氧化铝陶瓷基质中,四方氧化锆（ｔＺｒＯ２）转变为单斜锆（ｍＺｒＯ２）,同时颗粒周围产生微裂纹,故复合材料的增韧机理主要为相变增韧和微裂纹增韧。为了测定这两种增韧作用的大小,进行了如下的实验：试样配比为８５Ａｌ２Ｏ３·１５ＺｒＯ２,分别加入不同量的纯ＺｒＯ２、Ｙ２Ｏ３部分稳定ＺｒＯ２及ＭｏＯ２部分稳定ＺｒＯ２,在３０ＭＰａ下热压成型,１４００～１５００℃,１ｈ,通Ｎ２条件下烧成,制成含ｍＺｒＯ２１０％、４５％和６７％的试样。实验结果表明：含纯ＺｒＯ２的合成料断裂韧性最高,Ｙ２Ｏ３部分稳定Ｚ…     

添加Al2O2对ZrO2（Y2O3）粉末性能的影响

采用化学共沉淀法制备了ＺｒＯ２（Ｙ２Ｏ３）和ＺｒＯ２（Ｙ２Ｏ３）／Ａｌ２Ｏ３超细粉末，研究了添加Ａｌ２Ｏ３对粉末性能的影响。添加Ａｌ２Ｏ３提高了ｔ－ＺｒＯ２的结晶化温度，抑制了ＺｒＯ２－ｍ－ＺｒＯ２相变。Ａｌ２Ｏ３相变。Ａｌ２Ｏ３添加量超过２０ｗｔ％时，粉末烧结活性降低，烧结温度提高。     

Y2O3改性的MgO—ZrO2共析陶瓷

共析ＭｇＯ－ＺｒＯ２陶瓷添加Ｙ２Ｏ３可以获得高温热稳定性和较佳的力学性能，添加２％Ｙ２Ｏ３时断裂韧性为７．６ＭＰａ．ｍ＾１／２，弯曲强度为６１８ＭＰａ，用透射电子显微镜详细研究和讨论了上述材料的时效显微组织和韧化的原因。     

β“—Al2O3陶瓷的强化和韧化

研究了稳定ＺｒＯ２和部份稳定ＺｒＯ２对β”－Ａｌ２Ｏ３陶瓷的强化和韧化作用，观察了不同种类、不同含量的ＺｒＯ２对β”－Ａｌ２Ｏ３陶瓷的显微结构、力学性能和电导率的影响，探讨了β”－Ａｌ２Ｏ３的韧化机理。     

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。     

Microstructure and toughening mechanisms of Al2O3/(W,Ti)C/graphene composite ceramic tool material

To toughen the Al₂O₃ matrix ceramic materials, Al₂O₃/(W, Ti)C/graphene multi-phase composite ceramic materials were fabricated via hot pressing. The effects of the graphene nanoplates (GNPs) content on microstructure and mechanical properties were investigated. Results showed that the fracture toughness and flexural strength of the composite added with just 0.2?wt% GNPs were markedly improved by about 35.3% (~ 7.78?MPa?m^1/2) and 49% (~ 608.54?MPa) respectively compared with the specimens without GNPs while the hardness was kept about 24.22?GPa. However, the mechanical properties degrade with the further increase of GNPs’ content owing to the increased defects caused by agglomeration of GNPs. Synergistic toughening effects of (W, Ti)C and GNPs played an essential role in improving the fracture toughness of composites. By analyzing the microstructures of fractured surface and indentation cracks, besides GNPs pull-out, crack deflection, crack bridging, crack branching and crack arrest, new toughening mechanisms such as break of GNPs and crack guiding were also identified. Furthermore, interface stress can be controlled by means of stagger distributed strong and weak bonding interfaces correlated with the distribution of GNPs.     

Fabrication and properties of in situ reduced graphene oxide‐toughened zirconia composite ceramics

Graphene oxide and zirconia powders were mixed using a colloidal coating route. In situ reduced graphene oxide‐toughened zirconia ceramics were prepared by spark plasma sintering. Their microstructure, mechanical properties, and toughening mechanisms were investigated. The results show that graphene oxide can be easily reduced in situ during sintering and that it disperses homogeneously within the zirconia substrate. Compared with the toughness of 3 mol.% yttria‐stabilized zirconia, the fracture toughness of in situ reduced graphene oxide‐toughened zirconia increased by up to 175% (from ~6.07 to ~10.64 MPa·m^1/2) at 0.09 wt.% graphene oxide with a small increase in hardness. The improvement is more significant than that of prereduced graphene oxide‐toughened cases, and it is associated with the formation of a C‐O‐Zr bond at the interface in addition to conventional toughening mechanisms.     

钇补强颗粒弥散陶瓷复合材料增韧机制的微观结构表征

在Al2O3/（W,Ti）C陶瓷复合材料中适量添加稀土元素钇能显著提高其断裂韧性。本文运用SEM与TEM技术,从微观结构的角度探讨了其增韧机制。表明,由于稀土钇的添加,使材料内部形成不同程度的强弱界面,它们与扩展中的裂纹相互作用,使得裂纹桥联、裂纹分支、裂纹偏转以及微裂纹增韧机制得到明显增加和加强,从而以多种增韧机制及其协同作用共同提高稀土补强Al2O3/（W,Ti）C陶瓷复合材料的断裂韧性。     

K R -Curve Behavior of Duplex Ceramics

The fracture toughness behavior during crack growth ( K ^R -curve behavior) of duplex ceramics is investigated. Different types of K ^R -curves can be distinguished depending on the microstructural designs of these materials which are characterized by the volume fraction and size of the dispersed pressure zones, and by their effective volume expansion. According to their K ^R -curve behavior, duplex ceramics can be subdivided into two groups consisting of "short-range" and "long-range" toughened materials. The experimental results are discussed regarding the appearance of different toughening mechanisms which are documented by crack path micrographs. An unusual toughening effect, a "crackbranching chain reaction," is documented by in situ observations. The critical stress to nucleate the observed process zone development is calculated and compared with the internal stress intensity factor K _i which has been previously proposed for these materials and with the material strength.     

Interaction of toughening mechanisms in a hybrid epoxy system

Interaction between different toughening mechanisms is studied using a heat treated hybrid system, consisting of carboxyl‐terminated butadiene acrylonitrile (CTBN) rubber and EXPANCEL (expandable hollow microspheres) as modifiers for an epoxy resin. It was found that the fracture toughness of the hybrid system is higher than that of either individually EXPANCEL‐ or CTBN‐modified system for a given content of modifier, although the maximum toughness was not substantially high compared with maxima of single modifier systems. Microscopic examination revealed that damage zone due to CTBN particles ahead of the crack reduces due to the presence of EXPANCEL particles and nevertheless its fracture toughness increased. A possibility was deduced that the cavitation due to CTBN assists with promoting compressive stresses around EXPANCEL particles ahead of the crack tip, resulting in increase in fracture toughness. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4470–4475, 2006     

Microstructural Design of Toughened Ceramics

The fracture toughness of ceramics can be improved by the incorporation of a variety of discontinuous, elastic reinforcing phases that generate a crack-bridging zone. Recent models of toughening by crack-bridging processes are discussed and used to describe the behavior observed in whisker-reinforced ceramics. The toughening response in ceramics reinforced with other types of discontinuous reinforcements is then considered (e.g., matrix and second-phase platelike grains, elongated matrix grains, and grain-size effects in noncubic matrices). It is shown that crack-bridging toughening processes can be combined with other bridging mechanisms and with other toughening mechanisms (e.g., transformation toughening) to achieve synergistic effects. From these discussions, it is shown that the design of the toughened materials relies heavily on the control of the material properties and microstructural components influencing the toughening behavior to optimize the contributions of both the reinforcing phase and the matrix.     

Microstructure and fracture toughness of SiAlCN ceramics toughened by SiCw or GNPs

Mechanical alloying and spark plasma sintering (SPS) were used to prepare dense SiAlCN ceramic and SiAlCN ceramic toughened by SiC whiskers (SiC_w) or graphene nanoplatelets (GNPs). The influences of different reinforcements on the microstructure and fracture toughness were investigated. The SiAlCN ceramic exhibited a fracture toughness of 4.4 MPa m^1/2 and the fracture characteristics of grain bridging, alternative intergranular and transgranular fracture. The fracture toughness of SiC_w/SiAlCN ceramic increased to 5.8 MPa m^1/2 and toughening mechanisms were crack deflection, SiC_w bridging and pull-out. The fracture toughness of GNP/SiAlCN ceramic increased significantly, which was up to 6.6 MPa m^1/2. GNPs played an important role in grain refinement, which resulted in the smallest grain size. Multiple toughening mechanisms, including crack deflection, crack branch, GNP bridging and pull-out could be found. The better toughening effect could be attributed to the larger specific surface area of GNPs and the appropriate interface bonding between GNPs and matrix.     

Effect of crosslink density on fracture behavior of model epoxies containing block copolymer nanoparticles

Model diglycidyl ether of bisphenol-A based epoxy resins containing well-dispersed 15 nm block copolymer (BCP) nanoparticles were prepared to study the effect of matrix crosslink density on their fracture behavior. The crosslink density of the model epoxies was varied via the controlled epoxy thermoset technology and estimated experimentally. As expected, it was found that the fracture toughness of the BCP-toughened epoxy is strongly influenced by the crosslink density of the epoxy matrix, with higher toughenability for lower crosslink density epoxies. Key operative toughening mechanisms of the above model BCP-toughened epoxies were found to be nanoparticle cavitation-induced matrix shear banding for the low crosslink density epoxies. The toughening effect from BCP nanoparticles was also compared with core-shell rubber-toughened epoxies having different levels of crosslink density. The usefulness of the present findings for designing toughened thermosetting materials with desirable properties is discussed.     

Fabrication and properties of monolayer graphene reinforced Al2O3/TiN ceramic tool material

Al₂O₃/TiN/graphene ceramic tool materials were prepared by spark plasma sintering technology and the strengthening and toughening mechanisms were studied. The influence of monolayer graphene content on the mechanical properties and microstructure of the composite material were analyzed and the strengthening and toughening mechanisms were researched. The results showed that with an addition of .5 vol.% graphene the mechanical properties of the material reached the best. The bending strength, hardness, and fracture toughness were 624 MPa, 23.24 GPa, and 6.53 MPa·m^1/2, respectively. Graphene existed in the forms of few-layer and multilayer. The toughening mechanism of few-layer graphene was mainly graphene breaking, and that of multilayer graphene included graphene breaking and pulling-out. Graphene could contribute to the uniform growth of grains due to the excellent electrical conductivity and the high thermal conductivity. The addition of nano-TiN introduced many endocrystalline structures and graphene promoted this phenomenon. Micro-TiN grains made the crack extension show a combination of transgranular fracture, intergranular fracture, crack bridging, and crack deflection, while graphene introduced weak grain interfaces and made the crack appear more branches. The layered graphene made the material fracture change from two-dimension to three-dimension.     

TiB2／SiCw复合材料增韧机理的微观分析

在ＴｉＢ２／ＳｉＣｗ基体中加入适量的ＳｉＣｗ可以明显地提高其断裂韧 性ＫＩＣ，其它机械性能也有不同程度的改善。ＳＥＭ、ＴＥＭ微观分析表明：在具有较高ＫＩＣ值的ＴｉＢ２／ＢｉＣｗ陶瓷复合材料中，ＳｉＣｗ与ＴｉＢ２晶粒之间有较适宜的界面结合，两相之间未发现有明显的界面化学反应用，当该复合材料发生断裂时，其内部出现晶须拔出，裂纹桥连，裂纹偏转三种增韧机制。