Superplasticity in Advanced Materials - ICSAM 2006

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Authors: W.L. Lu, Y. Wang, Jin Tao Hai
Abstract: Sandglass extrusion is an ultrafine grain size method. Due to the repetitive and multiple extrusions, large strain can be accumulated and ultrafine grain size can be obtained. Some factors can affect the experimental results of sandglass extrusion, such as extrusion ratio, number of extrusion, extrusion temperature, friction and free space in mould cavity etc. These factors have different effects on material microstructures, properties and defects. In this paper, the effects of extrusion ratio and friction on material microstructures during sandglass extrusion process have been discussed and theory analysis and experimental results have been reported.
383
Authors: Wen Juan Zhao, Hua Ding, D. Song, F.R. Cao, Hong Liang Hou
Abstract: In this study, superplastic tensile tests were carried out for Ti-6Al-4V alloy using different initial grain sizes (2.6 μm, 6.5μm and 16.2 μm) at a temperature of 920°C with an initial strain rate of 1×10-3 s-1. To get an insight into the effect of grain size on the superplastic deformation mechanisms, the microstructures of deformed alloy were investigated by using an optical microscope and transmission electron microscope (TEM). The results indicate that there is dramatic difference in the superplastic deformation mode of fine and coarse grained Ti-6Al-4V alloy. Meanwhile, grain growth induced by superplastic deformation has also been clearly observed during deformation process, and the grain growth model including the static and strain induced part during superplastic deformation was utilized to analyze the data of Ti-6Al-4V alloy.
387
Authors: Yao Zong Zhang, Jian Bo Huang, H.P. Wang, X. Lin
Abstract: This paper discusses the issues about the incorruptibility of industrial dies, mainly researches the G111WC and G112WC mixed alloy layer sprays fusing on the surface of industrial dies under the vacuum condition and the solid phase welding-on mechanism of the mixed alloy layer under superplastic state. It points out that when W≈1 ( W is strain ratio of coating and substrate ) and within the range of the generatrix’s superplasticity, the layer and the generatrix will realize the solid state diffusion joining by superplastic coordinate deformation, which leads to an effective welding.
399
Authors: Yong Qing Zhao, Heng Lei Qu, L.Y. Zeng
Abstract: The superplastic tensile deformation behavior and structural evolution of two kinds of α+β titanium alloys were investigated in this paper, one is a new high strength high toughness Ti alloy with damage tolerance called TC21, and the other is a new superplastic Ti alloy so called Ti-SP2500. The results indicated that TC21 alloy has good superplasticity at the temperature from 720 to 960 and with the strain rate of 5.510-5s-1∼1.110-2s-1. On the optimal superplastic condition, the maximum elongation is over 1300%. During the superplastic tensile deformation, the dynamic recrystallization occurs in deformation zone of the specimens and the superplasticity is improved. Ti-SP2500 alloy has good superplasticity at the temperature from 720°C to 800°C and with the strain rate of 6.67 10-4s-1∼1.1110-2s-1. The maximum elongation for Ti-SP2500 alloy will exceed 2200% at 780°C with the strain rate of 5.5610-3s-1. Its superplastic deformation mechanism is controlled by grain boundary sliding, and the grain deformation and dislocation creep has the coordinating action.
405
Authors: G. Wang, Kai Feng Zhang, Wen Bo Han, D.Z. Wu, C.W. Wang
Abstract: The superplastic bulging capabilities of Ti-6Al-4V butt-welded plates with 0.8mm in thickness with high energy beam welding methods namely plasma arc welding (PAW), electron beam welding (EBW) and laser beam welding (LBW) are studied in virtue of superplastic bulging tests. Superplastic bulging tests are performed at the superplastic forming temperature 925°C under 1MPa gas pressure. The superplastic bulging capability is represented by the maximum relative bulging height h after fracture. Experimental results suggest that all of butt-welded plates with high energy beam welding methods possess good superplastic bulging capability. Among them, the maximum relative bulge height of LBW is the highest, that of EBW is slightly lower and that of PAW is the lowest. The higher the input energy density is, the bigger the bulge height will be. Furthermore their microstructure evolutions of various weld metals during superplastic bulging were systematically analyzed via metallographical tests. The relation between the microstructure of weld metal and its superplasticity is found. Metallographical analysis shows that the microstructure of Ti-6Al-4V weld metal with high energy beam welding methods is composed of fine acicular martensite. The higher the input energy density is, the finer the martensite structure will be. Upon heating, this martensite changes to a basketweave-like structure and upon bulging, the martensite structure have the trend of transforming to fine equiaxed grain. This can explained the reason why the Ti-6Al-4V butt-welded plates with high energy beam welding methods have excellent superplastic bulging capability.
411
Authors: Ying Ying Lin, Miao Quan Li, Y. Niu, W.F. Zhang
Abstract: Isothermal compression tests were carried out on the Ti-5.6Al-4.8Sn-2.0Zr-1.0Mo alloy with and without hydrogen. A series of experiments including the optical microstructure and TEM (Transmission Electron Microscope) were performed to the compressed samples. The results show that hydrogenation not only increases the fraction ofβ phase, but also activates the propagation of the dislocation and formation of the twins, which are benefit for plastic or superplastic formability.
417
Authors: Min Wang, Hong Zhen Guo
Abstract: According to accommodate-state and big bulk 18-8 type austenitic stainless steel has the weakness of coarse-grained and low strength. Optical microscopy,electron microscopy and X-ray diffraction were used to analyze microstructure and grain size of austenitic stainless steel specimens after deformation heat treatment. The paper investigates the influence of recrystallization annealing on the ultra-fine structure of cold deformation austenitic stainless steel. The results show that austenitic stainless steel can produce deformation-induced martensite by cold rolling deformation, and that the content of martensite increases with deformation degree. During the annealing, ultra-fine grains can be obtained by the reversal transformation-induced martensite(M′→ γ ). After severe cold deformation, inside austenitic grains imported austenitic-martensite(γ /M) phase boundaries shall serve to add a great deal of forming nucleus location for recrystallization, to enhance forming nucleus ratio and refine grain. 1Cr18Ni9Ti austenitic stainless steel by severe cold deformation and recrystallization annealing can acquire ultra-fine grains.
421
Authors: S.S. Jiang, Kai Feng Zhang
Abstract: In this paper, the process is divided into two steps. (1) First, the ceramic die used to fabricate the denture base was made by mixing the green of ZrO2 and TiO2 with PVA and press them into the oral cavity model to get the ceramic die before sintered. Then it was sintered to be the ceramic die after sintered in the atmosphere. (2) Second, the 0.8mm Ti-6Al-4V plate covered with BN was fabricated to be denture base by blow forming at the optimal superplastic forming temperature using nitrogen gas. The pattern of the Ti6Al4V denture base was the same as the detail of the ceramic die.(3) Third, the thickness of Ti-6Al-4V alloy denture base was investigated and the accuracy was measured by compared the distance between the marked points of the framework against the ceramic die. Although the thickness of denture base was reduced by superplastic forming, the framework had about 78.5% of the original plate thickness. Differences in the thickness did not significantly affect the gap discrepancy and the accuracy of fit of the denture base would satisfy ordinary clinical requirements.
427
Authors: H.Y. Xu, Zhi Qiang Li, He Ping Guo
Abstract: Tensile testing was performed on fine-grained GH4169 superalloy sheet at elevated temperatures (920°C~980°C) and at different initial strain rates (10-4~10-2s-1). The maximum elongation obtained was 280%. By TEM, active dislocation movement was observed and compared at different strain level and strain rate. Dynamic recovery and recrystallization was also found during superplastic deformation that played an important role of softening. At last the superplastic deformation mechanism of GH4169 alloy was discussed.
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