Bonding strength and fatigue strength tests of SPF/DB joints in 7475 aluminum alloy and Ti-6Al-4V alloy were carried out. Their strengths of the joints using cryogenic rolled sheet were higher than those using conventional cold rolled sheet. Surface finish for removing oxide film was essential to obtain high-quality bond in aluminum alloy.

The term “superplasticity” is taken as meaning high-strain-rate-sensitivity flow when it is used in geological contexts involving predominantly compressive stress states. Such flow has been observed in calcite and olivine polycrystalline aggregates in laboratory tests and the mechanism deduced to be diffusion-controlled granular flow. From microstructural observations, similar deformation processes are inferred to have occurred in a number of geological situations. On the basis of extrapolation from experiment to geology, superplastic flow might be expected under some geological conditions in calcite and olivine rocks at grain sizes approaching the order of one millimetre, while there are indications that the grain size limit for quartzites may be rather smaller. However, the knowledge of superplasticity in most rocks is still very fragmentary, especially in regard to mechanisms where a fluid phase may be involved, as in porous rocks.

Deformation studies in compression and in tension have clearly shown evidence for superplasticity for a wide range of fine grained ceramics from both macroscopic and microscopic points of view. The main purpose of this paper is to focus attention on chemical effects in ceramic grain boundaries which can lead to a great variety of behavior. Grain boundary segregation or precipitation, residual impurities or doping elements, and glassy or liquid phases at grain boundaries can strongly affect the macroscopic flow properties of superplastic fine grained ceramics. Some microstructural and grain boundary features, mainly in two oxide materials (alumina and yttria doped zirconia), are analyzed, compared, and discussed in connection with their observed superplastic behavior. Special attention is devoted to the relation between the overall chemistry of the materials (impurities and doping elements) and to the grain boundary structure and chemistry (segregation, precipitation, intergranular phases). Some consequences and implications on the tailoring of ceramic microstructures for superplasticity are discussed. In addition, some recent hot forming and hot bonding experiments are also reported.

Experiments were conducted to determine the mechanical characteristics of an yttria-stabilized tetragonal zirconia containing 3 mol % Y2O3. Specimens were pulled in tension at elevated temperatures over a range of strain rates. It is demonstrated that this material exhibits good superplastic ductility, with tensile elongations >100% when the tests are conducted at low strain rates. Internal cavities are formed during deformation and it is shown that the cavitated area decreases with decreasing strain rate. At fast strain rates, of the order of 10−3 s−1, the cavities tend to link preferentially in a direction perpendicular to the tensile axis.

Concurrent grain growth, and in particular, dynamic grain growth, was observed to take place during superplastic deformation of Y-TZP. As a result of this concurrent grain growth, the measured strain rate sensitivity was found to be lower than that measured under constantstructure conditions. In the present paper, data obtained from the superplastic deformation of YTZP under constant-structure conditions are presented. It is demonstrated that the strain rate sensitivity values are generally higher than 0.5, when measured from the grain size-compensated data; this result suggests a grain boundary sliding mechanism. Microstructures from samples prior to and after superplastic deformation reveal grains which are essentially equiaxed; this observation is also consistent with a grain boundary sliding mechanism. Both high-resolution images of grain boundary triple points using transmission electron microscopy, and fracture surface studies using Auger electron spectroscopy and X-ray photoelectron spectroscopy indicate that there is no evidence for the presence of glassy phases at grain boundaries in Y-TZP.

The new class of high-transition-temperature ceramic superconductors (e.g. Y-Ba-Cu-O) show a fine grain size polycrystalline structure, similar to that shown by the superplastic metals. The material behaves in a brittle manner with a strain to fracture below 0.5 % at room temperature. One of the reasons for this mechanical behavior is that the grain boundaries are easily separated when a stress is applied. It was found in this work that a deformation of the superconductor ceramic (scc) in superplastic metal (spin) matrix reduces the separation of the grain boundaries in such materials so that they can be deformed at room temperature. The spin matrixes used in this work were Zn-Cd, Bi-Sn and Cd-Sn. It was found that the highest the yield point of the matrix the highest the deformation induced in the scc. The Cd-Zn alloy was the most effective in avoiding the separation of the grain boundaries during the deformation of a composite formed by a cylinder of scc embedded in a spin matrix. Meissner effect was observed in the scc, after more than 160 % of plastic deformation. SEM observations show that deformation takes place by grain boundary sliding and some grain refinement was observed.

Both static and dynamic grain growth have been studied during superplastic deformation of fine-grained yttria-stabilized tetragonal zirconia (Y-TZP) and alumina reinforced yttria-stabilized tetragonal zirconia (Al2O3/YTZ). Grain growth was observed in both materials at temperatures above 1350° C. In the case of Y-TZP, both static and dynamic grain growth were found to obey a similar equation of the form: where D is the instantaneous grain size, Do is the initial grain size, t is the time, and k is a kinetic constant which depends primarily on temperature and grain boundary energy. The activation energies for Y-TZP were approximately 580 and 520 kJ/mol, for static and dynamic grain growth, respectively. In the case of Al2O3/YTZ, it was found that the grain growth rate for the Al2O3 phase was slower than that for the ZrO2 phase. The growth rate of the ZrO2 phase in Al2O3/YTZ is, however, similar to that in monolithic ZrO2, i.e., Y-TZP.

Superplasticity is a mode of deformation for fine-grained polycrystalline solids at elevated temperatures: included are metals, ionic polycrystals (e.g. oxides) and covalent polycrystals (e.g. non-oxide ceramics). Plastic deformation of covalent crystals by dislocation glide is not easy because of their high Peierls force. This paper describes high ductilities in Si3N4 and SiC, and also reports superplastic elongations in Si3N4/SiC composite.

Fine-grained Si3N4/SiC composites (20 wt% SiC) were fabricated by hot-pressing amorphous Si-C-N powder with 6 wt% Y2O3 and 2 wt% A12O3 as sintering aids. The composites were composed of equiaxed grains (<200 nm) and elongated grains. A composite exhibited a superplastic elongation larger than 150 % at 1600 °C and at an initial strain rate of 4 × 10−5 s−1. The superplasticity of the composite is probably related to the presence of an intergranular liquid phase.

Hipped and extruded materials were prepared from atomized-powders containing 5.25C, 1.5Cr and balance Fe. The materials consist of a matrix of 80 volume percent of iron carbide and 20 volume percent of a discontinous iron base phase. Both processed materials were reduced in thickness (6:1) at 720°C. The grain size was about 2 μm for the hipped-and-pressed material and about 4 μm for the extruded-and-pressed material. Compression tests were used to evaluate the strain-rate-sensitivity exponent, m, in the temperature range from 725°C to 950°C, over the strain rate range of 10−5 to 2 × 10−2 s−1. The as-hipped material does not exhibit superplastic behavior because the grain shape is not equiaxed. At low stresses, in the superplastic range (m≈0.5), the hipped-and-pressed material was weaker than the extruded-and-pressed material as a result of the fine grain size. At high stresses, when slip dominates the deformation process, m is about 0.2 and a reversal in the relative strength is obtained. Tensile tests were performed and elongations in excess of 600% were achieved. The hipped-and-pressed material was shown to be more ductile than the extruded-and pressed-material which is attributed to its fine grain size.

In this paper, the superplastic and isothermal hobbing process for manufacturing die cavities is described. The technical parameters, the design method of the set-up and the lubrication are also mentioned. Recently, these technologies have been applied in hobbing automobile link rod dies and other parts. By means of finite element analysis and experiments, the deformation paramaters for superplastic hobbing are obtained. They can be used in determining the process and choosing the blank sizes.

The fractal dimensions of cavities during superplastic deformation of high strength aluminium alloy 7475 were measured with different strain, temperature, strain rate, and grain size. The results show that the fractal dimension of cavities increases with the increase of strain. Deformation under lower temperature, higher strain rates, or for larger grain sizes corresponds to higher fractal dimensions of cavities. The higher the fractal dimension of cavities, the more complex the cavities' shapes and the more possible it is for the specimen to rupture.

A fine grained yttria stabilized zirconia and a zirconia composite containing 20% alumina exhibit superplastic characteristics, with optimum elongations to failure of ≥500%. There is microstructural evidence for deformation enhanced grain growth and concurrent cavitation in both of these superplastic ceramics. Grain sizes after superplastic deformation may be several times larger than the initial grain size, and the level of cavitation can attain values as high as ≥30% under some experimental conditions. This report presents in a comparative format some recent experimental results on the microstructural aspects of superplastic deformation and concurrent cavitation in these superplastic ceramics.

Recent advances in the technologies of powder metallurgy lead to the development of some superplastic aluminium alloys containing a deliberate addition of a large amount of Zr and /or Cr and Mn that exhibit the high strain rates superplasticity. For a few alloy systems, the large elongation more than 500% has been observed over the strain rates of 1×10−1s−1, which rates are two or three orders of magnitude faster than those at which superplasticity is found in conventional superplastic aluminium alloys produced by ingot metallurgy. The high strain-rates superplasticity obtained in both type of fully static recrystallized and dynamic recrystallized P/M aluminium alloys. The decreasing of initial size of grains and/or sub-grains leads to the increasing the strain-rates for superplastic flow in both types of alloys. The refinement of grains or sub-grains size is one of necessary and important to obtain the high strain-rates superplasticity.

The superplastic deformation behavior and mechanisms of commercial Al-4cu-1.6 Mg-0.0Mn have been studied, using tensile tests with microstructuraL observations being carried out by optical and transmission etectronmicroscopy. The results of tensile tests show that considerable superplasticflow can be obtained without any pretreatment to this atloy.The maximum elongaton achieved is 42096 and the strain rate sensitivity index, m, is 0.49. Microstructural analysis reveals that the dominant mechanism in the early stage of deformation is diffusion. As strain increases, grain-borundary sliding and grain rearrangment take the dominant part in thedeformation process, and diffusion becomes an accommodation mechanism. Second phase particles effectively restrict grain growth during deformation. Cavity initiation and growth during deformation are the direct cause of specimen failure.