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Creep and superplasticity of the fine-grained Sn-1wt.% Bi alloy, processed by conventional rolling (CNR), cryorolling (CRR) and equal channel angular pressing (ECAP) routes, were investigated by indentation testing at room temperature (T > 0.6T_m). Based on the steady-state power law creep relationship, the stress exponents of 4.1, 2.8 and 2.5 were obtained for the CNR, CRR and ECAP routes, respectively. The corresponding strain rate sensitivity (SRS) indices of 0.24, 0.36 and 0.40, corresponding respectively to the grain sizes of 2.8, 2.1 and 1.2 μm, indicate that the materials processed by ECAP and CRR exhibit superplastic deformation behavior for which, grain boundary sliding is the possible creep mechanism.

The crack propagation properties for ultrafine-grained Zn-22wt%Al alloy during low cycle fatigue (LCF) in the superplastic region and the non-superplastic region were investigated and compared with the corresponding results for several other materials. With the Zn- 22wt%Al alloy, it was possible to conduct LCF tests even at high strain amplitudes of more than ±5%, and the alloy appeared to exhibit a longer LCF lifetime than the other materials examined. The fatigue life is higher in the superplastic region than in the non-superplastic region. The rate of fatigue crack propagation in the superplastic region is lower than that in the other materials in the high J-integral range. In addition, the formation of cavities and crack branching were observed around a crack tip in the supereplastic region. We therefore conclude that the formation of cavities and secondary cracks as a result of the relaxation of stress concentration around the crack tip results in a reduction in the rate of fatigue crack propagation and results in a longer fatigue lifetime.

The objective of this study was to experimentally determine the properties of magnesium alloys during plastic deformation under various temperature regimes. Proportional loading tests combining both axial and torsional loads were performed on cylindrical AZ31 Mg alloys in a range from room temperature to 673 K, where superplasticity has a high probability of occurrence, and the crystalline structures of the samples were observed after these tests. The above observations indicate that the deformation mechanisms in AZ31 Mg alloy are dominated by twinning deformation at 300 K and 423 K, and by grain boundary sliding promoted by dynamic recrystallization at 523 K and higher temperatures.

The grain size of as-extruded AZ31 magnesium alloy was refined by isothermal annealing pretreatment through orthogonal experiment. By using the Gleeble-3800 thermal simulator, the compression superplasticity of as-extruded AZ31 magnesium alloy was studied. The high strain rate superplastic compression was realized. The process parameters of the superplastic compression were established and the mechanism of the superplastic deformation was analyzed. The effects of deformation temperature and strain rate on the superplastic flow were investigated. The results indicated that at 250°C–300°C and strain rate at 1×10^-2s^-1, the true strain values were all more than 2.03. As the temperature was 300°C and the strain rate was 1×10^-2s^-1–1×10 s^-1, the true strain values were all more than 2.18. The results showed that the as-extruded AZ31 magnesium alloy being refined presented good compression superplasticity. The main mechanism for the superplastic compressive deformation of the as-extruded AZ31 magnesium alloy was grain-boundary sliding, meanwhile, dynamic recrystallization also played a harmonious role during the superplastic deformation.

This paper provides a comprehensive review on the methodological development and technical applications of in situ microscopy, including transmission electron microscopy (TEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM), developed in the last decade for investigating the structure-mechanical-property relationship of a single one-dimensional nanomaterial, such as nanotube, nanowire and nanobelt. The paper covers both the fundamental methods and detailed applications, including AFM-based static elastic and plastic measurements of a carbon nanotube, external field-induced resonance dynamic measurement of elastic modulus of a nanotube/nanowire, nano-indentation, and in situ plastic deformation process of a nanowire. Details are presented on the elastic property measurements and direct imaging of plastic to superplastic behavior of semiconductor nanowires at atomic resolution, providing quantitative information on the mechanical behavior of nanomaterials. The studies on the Si and SiC nanowires clearly demonstrated their distinct, "unexpected" and superior plastic mechanical properties. Finally, a perspective is given on the future of nanomechanics.

Processing through the application of severe plastic deformation (SPD) provides a very attractive tool for the production of bulk ultrafine-grained materials. These materials typically have grain sizes in the submicrometer or nanometer ranges and they exhibit high strength at ambient temperature and, if the ultrafine grains are reasonably stable at elevated temperatures, they have a potential for use in superplastic forming operations. Several procedures are now available for applying SPD to metal samples but the most promising are Equal-Channel Angular Pressing (ECAP) and High-Pressure Torsion (HPT). This paper examines the basic principles of ECAP and HPT and describes some of the properties that may be achieved using these processing techniques.

This paper concentrates on the study of the superplastic response of coarse-grained Al-Mg alloys under uniaxial tension at different temperatures (ranging from 400°C to 525°C) and strain rates (10^-2 S^-1, 10^-3 S^-1 & 10^-4 S^-1). The microstructures have been analyzed using optical (OM) and transmission electron microscopy (TEM). It has been observed that continuous re-crystallization occurs during hot deformation of the alloy at the temperature of 425°C and strain rate of 10^-2S^-1. At the temperature of 425°C and strain rate of 3.78×10^-3S^-1, this Al-Mg alloy has the maximum elongation to failure of 181%, which is sufficient for manufacturing of extremely complex shapes using superplastic forming technology. The constant strain rate sensitivity index m and TEM observations show that in this case deformation mechanism involved is dislocation glide. Recrystallization during the hot tension greatly enhanced the plasticity of the coarse-grained material at a strain rate of about 10^-2S^-1 and the maximum elongation changes as a function of the strain rate.

The fine-grained as-rolled Mg-7.83Li alloy demonstrated the elongations to failure ranging from 500 to 600% at temperatures of 473-623 K at an initial strain rate of 1.67×10^-3 s^-1. The sample for temperature-strain-rate-changing tension exhibited a taper appearance and induced considerable dynamic grain growth. Observation by scanning electron microscope revealed that there are many dimples on the fracture surface and the fracture mode is intergranular fracture. The models of number of dislocations and dislocation density inside the grain and at the grain boundary were incorporated into the calculation of constitutive equations and four modified Ruano-Wadsworth-Sherby deformation mechanism maps (DMMs) were constructed. The new DMMs gave the distribution and the variation of dislocation parameters. It was shown that grain boundary sliding accommodated by slip controlled by lattice diffusion is the dominant superplastic mechanism of the present alloy at 573 K.

The crack propagation properties for ultrafine-grained Zn–22wt%Al alloy during low cycle fatigue (LCF) in the superplastic region and the non-superplastic region were investigated and compared with the corresponding results for several other materials. With the Zn–22wt%Al alloy, it was possible to conduct LCF tests even at high strain amplitudes of more than ±5%, and the alloy appeared to exhibit a longer LCF lifetime than the other materials examined. The fatigue life is higher in the superplastic region than in the non-superplastic region. The rate of fatigue crack propagation in the superplastic region is lower than that in the other materials in the high J-integral range. In addition, the formation of cavities and crack branching were observed around a crack tip in the supereplastic region. We therefore conclude that the formation of cavities and secondary cracks as a result of the relaxation of stress concentration around the crack tip results in a reduction in the rate of fatigue crack propagation and results in a longer fatigue lifetime.

The objective of this study was to experimentally determine the properties of magnesium alloys during plastic deformation under various temperature regimes. Proportional loading tests combining both axial and torsional loads were performed on cylindrical AZ31 Mg alloys in a range from room temperature to 673 K, where superplasticity has a high probability of occurrence, and the crystalline structures of the samples were observed after these tests. The above observations indicate that the deformation mechanisms in AZ31 Mg alloy are dominated by twinning deformation at 300 K and 423 K, and by grain boundary sliding promoted by dynamic recrystallization at 523 K and higher temperatures.

This paper proposes a forming technology of AZ80A magnesium alloy automotive wheel, which collects the superplastic compound extrusion and the bulging technology of rigid die. By using dynamic recrystallization superplasticity, the new method completes the forming for complex auto wheel successfully. It has the advantages of simple process, high forming efficiency and compact structure.