High-temperature deformation and environment-induced degradation of Waspaloy

The tensile properties of Waspaloy, a candidate structural material to be used in nuclear hydrogen generation, were evaluated at temperatures up to 1000°C. The results indicate that this alloy was capable of maintaining appreciably high tensile strength up to 600°C, followed by a substantial drop beyond this temperature. Between ambient temperature and 300°C, the failure strain was lowest at 300°C due to a maximum dislocation density, as determined by transmission electron microscopy. The lowest ductility was, however, observed at 800°C, possibly due to the formation of brittle sigma phase. The cracking susceptibility of Waspaloy in an acidic solution was enhanced at a higher temperature when tested by the slow strain rate (SSR) technique. Slight variations in ductility parameters, true failure stress and time to failure were observed under anodic controlled potentials in SSR testing. The magnitudes of critical potentials, determined by an electrochemical method, became more active (negative) with increasing temperature. The general corrosion rate was gradually reduced with the longer exposure period. Combinations of ductile and brittle failures were observed depending on the testing temperature

Implications of the polymorphism of HLA-G on its function, regulation, evolution and disease association

The HLA-G gene displays several peculiarities that are distinct from those of classical HLA class I genes. The unique structure of the HLA-G molecule permits a restricted peptide presentation and allows the modulation of the cells of the immune system. Although polymorphic sites may potentially influence all biological functions of HLA-G, those present at the promoter and 3′ untranslated regions have been particularly studied in experimental and pathological conditions. The relatively low polymorphism observed in the MHC-G coding region both in humans and apes may represent a strong selective pressure for invariance, whereas, in regulatory regions several lines of evidence support the role of balancing selection. Since HLA-G has immunomodulatory properties, the understanding of gene regulation and the role of polymorphic sites on gene function may permit an individualized approach for the future use of HLA-G for therapeutic purposes

Use of Alloy 800H as a Heat-Exchanger Material

Identification and characterization of structural materials for high-temperature heat exchangers to be used in nuclear hydrogen generation pose severe challenge to scientists and engineers. However, Alloy 800H has been widely used for high-temperature applications in the presence of hostile environments in view of its superior metallurgical and corrosion properties documented in the published literature (1-5). The tensile properties of Alloy 800 H have been determined at temperatures ranging from ambient to 600°C. The tensile strength of this alloy was gradually reduced with increasing temperature, as expected. However, some reduction in failure strain was noted at temperatures up to 200°C, which can be attributed to the dynamic stain ageing effect. The results of stress-corrosion-cracking (SCC) testing performed in a simulated acidic solution at constant-load (CL) did not exhibit any failure. The magnitude of true failure stress was gradually reduced in SCC testing under a slow-strain-rate (SSR) condition without showing any significant variation in ductility parameters. The localized corrosion study conducted in a similar environment by a polarization technique revealed more active (negative) critical potentials at elevated temperatures. The fractographic evaluations of the tested specimens showed dimpled microstructures indicating ductile failures