陶瓷材料的超塑性

虽然陶瓷材料在本质上是一种脆性材料；然而研究已表明细晶陶瓷材料具有超塑性，在高温下能产生很大的拉伸形变．本文综述了超塑性的特征和Y2O3稳定四方ZrO2多晶体这种典型的超塑性陶瓷材料的形变机理，形变特征以及动态晶粒生长、玻璃相和产生孔穴对其超塑性形变的影响，此外，还总结了其他陶瓷材料，包括Al2O3、Al2O3－Y2O3稳定四方ZrO2、纳米陶瓷和玻璃陶瓷的超塑性行为和特征．     

陶瓷材料超塑性研究进展

超塑性是细晶陶瓷在高温下的固有属性。本文综述了陶瓷材料超塑性的一般特征和氧化钇稳定四方相氧化锆多晶陶瓷(Y-TZP)的形变机理及最新研究进展。解释了不同纯度Y-TZP陶瓷在Ⅰ区存在巨大差异的原因以及杂质特征对应力指数的影响。从能量的观点进一步分析了陶瓷材料超塑变形过程中的控速机制。对共价键陶瓷Si₃N₄、SiC的超塑性特征以及晶间玻璃相在超塑变形中的作用进行了概括。此外,还总结了其它陶瓷材料,包括Al₂O₃及其复合陶瓷、纳米陶瓷的研究进展及发展方向。     

超塑性合金

所谓超塑性是指某种金属或陶瓷，在高温低应力拉伸变形时呈现出异常高的延伸率的一种现象。将这一现象应用于实际便可形成一种低成本省能源的零部件制造方法。超塑性具有下列特征：对于通常不可能进行塑性加工的难加工材料，如果能使晶粒细化就能显示其超塑性；可按接近所需形状和尺寸进行成形；成形之后的切削加工很少。因此，研究人员努力开发这种对众多难以近净成形的高强度材料和新型材料进行塑性加工的方法。     

搅拌摩擦加工镁合金超塑性最新研究进展

搅拌摩擦加工是制备细晶材料的有效手段,可使镁合金获得超塑性,进而提高镁合金的塑性加工能力,扩大镁合金的应用范围。搅拌摩擦加工制备细晶镁合金的超塑性已经成为国内外的研究热点。在介绍搅拌摩擦加工技术原理的基础上,综述了搅拌摩擦加工镁合金超塑性最新研究进展,介绍了镁合金超塑性变形机理,并提出了研究方向。     

先进陶瓷最新研发动向

日本名古屋工业技术研究所是国家级的研发机构，它的研发很大程度上带有试验性和前瞻性。该所在高技术陶瓷研究的动向是：具有协同结构的陶瓷材料；具有纳米晶粒的超级金属，具有清洁环境减少污染的陶瓷材料；生物陶瓷；具有超塑性的陶瓷；电子工业应用的氧化物陶瓷；与能源相关的陶瓷；轻质材料等。     

超塑性材料研究的新进展

介绍了超塑性的基本概念和超塑性材料的研究历史,叙述了金属、精细陶瓷的超塑性及其加工方法。     

Mg-Li系合金超塑性研究进展

超塑性是材料在一定温度和应变速率下表现出异常高塑性的能力。Mg-Li合金具有超轻的密度、高比刚度和良好的电磁屏蔽能力,可望在航天、军事、汽车、3C电子等领域获得应用。综述了国内外Mg-Li合金超塑性研究现状,介绍了轧制、挤压、等通道转角挤压、搅拌摩擦加工、差速轧制、高压扭转和多向锻造方法获得的超塑性。指出了Mg-Li合金超塑性存在的问题和今后进一步研究的方向。     

日本最新高技术陶瓷战略研发动向

日本名古屋工业技术研究所是其国家级的研发机构，它的研发很大程度上带有试验性和前瞻性。该所在高技术陶瓷研究的动向是：具有协同结构的陶瓷材料；具有纳米晶粒的超级金属，具有清洁环境减少污染的陶瓷材料；生物陶瓷；具有超塑性的陶瓷；电子工业应用的氧化物陶瓷；与能源相关的陶瓷；轻质材料等。生物陶瓷方面，该所研究开发的重点方向之一是人工合成陶瓷关节材料。     

金属间合物超塑性的研究进展

金属间化合物超塑性是近十几年开展的研究课题。超塑性加工技术是解决金属间化合物加工成型难题最可行的方法之一。综述了金属间化合物及其合金的超塑性研究进展,并着重介绍了热点研究的铝化物的情况。     

绝缘陶瓷材料电火花加工技术的研究进展

陶瓷材料特性鲜明，有着广阔的应用前景。辅助电极法电火花加工绝缘陶瓷是一种新兴的加工工艺，介绍了陶瓷材料电火花加工技术的基本原理及研究进展。     

Superplastic microstructures

Abstract

The production of fine, stable equiaxed grains, having disordered high angle boundaries, is a prerequisite for superplastic behaviour in crystalline solids. The way that superplastic microstructures can be achieved in pseudo-single-phase and duplex materials by thermomechanical processing is discussed for a number of commercially significant materials. The resulting superplastic deformation characteristics are outlined, as are the factors that influence cavitation during superplastic flow. Alloys based on aluminium, titanium, copper, iron, and nickel are considered, and also aluminium based metal-matrix composites, intermetallic phases, and crystalline ceramic materials. Recent work on markedly enhanced superplastic behaviour in aluminium and copper alloys and in stainless steels is reported, and the similarities between superplasticity in crystalline ceramics and metallic materials is discussed. The development of superplastic microstructures in metal-matrix composites, intermetallic phases, and ceramics has enhanced their formability and their potential as high temperature structural materials.

MST/1298     

Superplastic ductility of oxide and nonoxide ceramics

The superplastic ductility of oxide and nonoxide SHS ceramics is considered. It is established that with certain temperature-rate dependences these ceramic materials manifest features typical of superplastic flow. It is shown that the ceramics undergo some specific microstructural changes under strain conditions.Institute of Problems of Metal Superductility, Russian Academy of Sciences, Ufa. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 65, No. 5, pp. 617–622, November, 1993.     

Ceramics superplasticity: Deformation mechanisms and microstructures

The superplasticity shall be generally achieved by grain refinement of various ceramics (ionic polycrystals and covalent polycrystals). This nature can be utilized for novel deformation processing in ceramic industy, for example, superplastic forming and superplastic forging. The superplasticity is a macroscopic phenomena that is very sensitive to slight difference in atomistic structure, and nature and chemical bonding of grain boundary. The mechanism of superplasticity is grain boundary sliding accommodated by matter transport through grain boundary. The models developed for superplasticity are classified by the structure of grain boundary. The experimental results on superplasticity of Zro₂ and Si₃N₄ were reviewed and compared to the predictions from the theories.     

Superplasticity in ceramics

It is now recognized that superplasticity is a potential deformation process in ceramics. This review summarizes the major characteristics of superplasticity and examines the reports of both transformation and structural superplasticity in ceramic and other non-metallic materials. It is shown that there are both similarities to and differences from metals. Similarities include the variation of strain rate with stress and grain size, but an important difference is the necessity to consider the role of intergranular glassy phases in ceramics. Superplasticity is also important in intermetallic compounds, and in geological materials where there is evidence for superplastic deformation both in laboratory experiments and in natural deformation.     

陶瓷超塑性的研究进展

本文综述了氧化锆及其复相陶瓷超塑性的研究现状，论述了陶瓷超塑性的变形机理，微观特征和断裂特性。同时，分析和对比了陶瓷超塑性与金属超塑性的特点。目前，对于正确理解超塑性陶瓷的变形机理，还需进行大量工作。     

多孔陶瓷材料的发展状况

评述了多孔材料的类型、结构、性质,对目前应用比较成功的几种制备技术进行了分析,并介绍了多孔陶瓷广阔的应用前景、研究进展和未来的研究方向。     

Seventy-five years of superplasticity: historic developments and new opportunities

On this seventy-fifth anniversary of the first scientific report of true superplastic flow, it is appropriate both to look back and examine the major developments that established the present understanding of superplasticity and to look to the future to the new opportunities that are made possible by new processing techniques, based on the application of severe plastic deformation, that permit the production of fully dense bulk materials with submicrometer or nanometer grain sizes. This review proposes a minor modification to the present definition of superplasticity, it provides an overview of the current understanding of the flow of superplastic metals and ceramics and then it examines, and gives examples of, the new possibilities that are now available for achieving exceptional superplastic behavior.     

High-temperature deformation of fully-dense fine-grained boron carbide ceramics: Experimental facts and modeling

Boron carbide ceramics are the hardest material in Nature after diamond and the cubic phase of boron nitride. Due to this fact, their room-temperature fracture properties are the object of intense research. Paradoxically, high-temperature deformation is essentially unknown, because very high temperatures and stresses are necessarily required and high-quality specimens have not been available until recently. In this paper, the high-temperature compressive creep of fine-grained boron carbide polycrystals is reported. The breakdown of the classical power-law for high-temperature plasticity in ceramics is found. An analytical model is proposed. The model assumes that deformation is produced by dislocation glide. However, since the formation of twins is energetically favorable in this material and they act as strong barriers for dislocation glide, their motion turns to become progressively more difficult as elongation proceeds. The combination of increasing twin barriers and dislocations in mutual interaction is proposed to be the mechanism for high-temperature plasticity in this material. The model is validated with the experimental results. Final elongation of boron carbide specimens is reported to be over 100%, although this material cannot be described as a superplastic ceramic.     

Composites in context

The large scale social changes which influence the development of new materials are reviewed and the new materials and processing methods being developed in response to these are described and contrasted with some recent advances in composite materials science.The particular technologies described are injection casting and superplastic forming, high temperature reinforcement by in situ composites and mechanical alloying. Aluminium lithium alloys are compared with carbon fibre reinforced plastics and with SiC reinforced aluminium. The reasons for the interest in new ceramic materials are reviewed and methods used to toughen ceramics are explained. Fibretoughening i is the most effective. Finally the properties of the newest composites containing carbon fibres in thermoplastic matrices are reviewed.