Solid-state diffusion bonding of superalloys for aerospace applications

With a view of furthering the application of diffusion bonding in aerospace applications, the influences of processing parameters on the joining of nickel-based superalloy, ferritic ODS (Oxide Dispersion Strengthened) alloy and PH (Precipitation Hardened) stainless steel have been carried out and joints of good quality have been produced. The effect of bonding temperature, time, pressure and PBHT (Post Bonding Heat Treatment) on the bonding of Inconel 718 to itself was assessed. A post bonding heat treatment (PBHT) is helpful and crucial to produce a sound joint. The influence of pressure was studied for the bonding of Inconel 718 to 17-4 PH stainless steel. FEM (Finite Element Method) was carried out to assess the residual thermal stress. For the bonding of ODS alloy - Incoloy MA 956, in addition to the influence of bonding pressure, temperature and time, the influence of surface roughness was examined.Doctor of Philosophy (SME

Phase diagram and density of SiO2–H2O fluid across critical conditions

Abstract The SiO2–H2O binary system serves as a basis for understanding complex silicate-water systems. In this study, based on limited existing experimental data of solubility, we propose a new thermodynamic model for SiO2–H2O fluid by modifying the traditional non-random two-liquid model with a simplified polymerization reaction. This model is applicable from 773 K to the anhydrous quartz melting temperature and from 0.5 GPa to at least 2 GPa across the critical conditions. It can predict solid–liquid equilibrium and vapor–liquid equilibrium in good agreement with available experiments. The upper critical endpoint of the SiO2–H2O system is predicted to be at ~ 1.14 ± 0.18 GPa and 1344 ± 87 K. With the new model, we obtain a quantitative three-dimensional pressure–temperature–composition phase diagram of the SiO2–H2O fluid, which greatly facilitates the understanding of the complex phase behavior of this binary around the upper critical endpoint. In addition, since the model is based on the Gibbs free energy foundation, we further discuss the derived density variations of SiO2–H2O fluid along with its complex phase changes in typical geochemical processes

Highly ordered nanoporous TiO2 and its photocatalytic properties

Hexagonally packed nanoporous TiO2 has been developed by a self-templating electrochemical anodization method on titanium foil. The template is made by a two-step anodization process, where highly ordered hexagonally packed dimples are formed on titanium surface through self-organization. The template is then subjected to a third anodization process with a fast voltage ramp rate, from which a highly ordered porous structure is obtained. Such a material with an ordered structure shows enhanced photocatalytic activity as compared to titania nanotube. Keywords: Titanium dioxide, Highly ordered, Nanoporous, Anodization, Photocatalyti

Additional file 1 of Phase diagram and density of SiO2–H2O fluid across critical conditions

Additional file 1: Appendix A. Introduction to the NRTL model. Appendix B. Workflow and derivation of the two-step model

Effects of Fumed and Mesoporous Silica Nanoparticles on the Properties of Sylgard 184 Polydimethylsiloxane

The effects of silica nanoparticles on the properties of a commonly used Sylgard 184 polydimethylsiloxane (PDMS) in microfluidics were systemically studied. Two kinds of silica nanoparticles, A380 fumed silica nanoparticles and MCM-41 mesoporous silica nanoparticles, were individually doped into PDMS, and the properties of PDMS with these two different silica nanoparticles were separately tested and compared. The thermal and mechanical stabilities of PDMS were significantly enhanced, and the swelling characteristics were also improved by doping these two kinds of nanoparticles. However, the transparency of PDMS was decreased due to the light scattering by nanoparticles. By contrast, PDMS/MCM-41 nanocomposites showed a lower coefficient of thermal expansion (CTE) owing to the mesoporous structure of MCM-41 nanoparticles, while PDMS/A380 nanocomposites showed a larger elastic modulus and better transparency due to the smaller size of A380 nanoparticles. In addition, A380 and MCM-41 nanoparticles had the similar effects on the swelling characteristics of PDMS. The swelling ratio of PDMS in toluene was decreased to 0.68 when the concentration of nanoparticles was 10 wt %

Effects of Matrix Silicon Content on the Plasma Electrolytic Oxidation of Al-Si Alloys Using Different Power Modes

The plasma electrolytic oxidation (PEO) of pure Al and Al alloys containing 4, 9, 12, or 15 wt.% Si were investigated under pulsed bipolar current and pulsed bipolar voltage modes, respectively. It was determined that the discharge sparks preferentially occurred on the SiO2 relative to the Al2O3 during the initial stage of PEO processing regardless of the power mode. Following 30 min of PEO treatment under the two modes, the thicknesses of the layers decreased, whereas their specific energy consumption increased with increasing Si content in the matrix. The presence of primary Si in the alloy with 15 wt.% Si had a significantly negative effect on the PEO process in the pulsed bipolar current mode: The layer thickness decreased by 45%, and its specific energy consumption increased by 52%, compared with those on pure Al. However, in the pulsed bipolar voltage mode, the layer thickness on the evaluated samples only decreased slightly, and it became much more similar after treatment