High Strain Rate Superplasticity in Microcrystalline and Nanocrystalline Materials

Superplasticity has evolved to become a significant industrial forming process. The phenomenon of superplasticity is explored at high strain rates where it is economically more attractive. True tensile superplasticity has been demonstrated in nanocrystalline materials. The difference in the details of superplasticity between the nanocrystalline and microcrystalline state is emphasised

Laminated Metal Composites—high Temperature Deformation Behavior

A constitutive model for deformation of a novel laminated metal composite (LMC) which is comprised of 21 alternating layers of Al 5182 alloy and Al 6090/SiC/25p metal matrix composite (MMC) has been proposed. The LMC as well as the constituent or neat structures have been deformed in uniaxial tension within a broad range of strain-rates (i.e. 10−6 to 10+1 s−1) and moderate to high homologous temperatures (i.e. 0.85 ≥ 0.95 Tm). The stress exponent, n, of the Al 5182 layers increases from 3 to 5 with increasing strain-rate (i.e. \u3e10−3 s−1). The MMC layer\u27s apparent n value decreases from 7 to 5 with increasing temperature. Furthermore, at low strain-rates (i.e. \u3c10−3 s−1) an apparent threshold stress dominates the MMC\u27s observed mechanical behavior. The LMC structure exhibits a behavior somewhat closer to the MMC layers. The results of these experiments have lead to a characterization of the neat layer\u27s mechanical behavior and a subsequent semi-empirical constitutive rate equation for both the Al 5182 and Al 6090/SiC/25p. These predictive relations for the neat layers have been coupled with a proposed model, which takes into account the dynamic load sharing between the elastically stiffer and softer layers when loaded axially during isostrain deformation of the LMC. This deformation model has led to the development of a constitutive relationship between flow stress and applied strain-rate for the laminated structure, which has been compared with experimental data

Deformation behavior of nanostructured aluminum alloy processed by severe plastic deformation

Microstructure and deformation behavior of the commercial aluminum-based Al7.5%Zn&ndash;2.7%Mg&ndash;2.3%Cu&ndash;0.15%Zr alloy subjected to high pressure torsion (HPT) were studied in the present work. A small grain size less than 100 nm, high level of internal stresses and presence of second phase nanoparticles were revealed by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The nanostructured alloy processed by HPT exhibits tensile strength of 800 MPa and ductility of 20% at optimal temperature-strain rate conditions. Unusual influence of a short pre-annealing on tensile strength and ductility of as-processed alloy is discussed.<br /

Altered cytokine profiles in patients with Chuvash polycythemia

Chuvash polycythemia results from a homozygous 598C\u3eT mutation in exon 3 of the von Hippel-Lindau (VHL) gene. This disrupts the normoxia pathway for degrading hypoxia inducible factor (HIF)-1α and HIF-2α causing altered expression of HIF-1 and HIF-2 inducible genes. As hypoxia induces expression of proinflammatory cytokines, we hypothesized that there might be an elevation of Th1 cytokines in the setting of Chuvash polycythemia. We analyzed plasma concentrations of Th1 (interleukins-2 and 12, interferon-γ, granulocyte-monocyte colony-stimulating factor, tumor necrosis factor-α) and Th2 cytokines (interleukins-4, 5, 10, and 13) using the Bio-Plex multiplex suspension array system in 34 VHL598C\u3eT homozygotes and 32 VHL wild-type participants from Chuvashia. Concentrations of all the Th1 and Th2 cytokines measured were elevated in the VHL598C\u3eT homozygotes compared with the control wild-type participants, but the ratios of Th1 to Th2 cytokines did not differ by genotype. In parallel, peripheral blood concentrations of CD4 positive T-helper cells and CD4/CD8 ratio were lower in the VHL598C\u3eT homozygotes. In conclusion, the up-regulated hypoxic response in Chuvash polycythemia is associated with increased plasma products of both the Th1 and Th2 pathways, but the balance between the two pathways seems to be preserved. Am. J. Hematol. © 2008 Wiley-Liss, Inc