TY - JOUR A1 - Epishin, A. A1 - Camin, B. A1 - Hansen, L. A1 - Heuser, M. A1 - Lopez-Galilea, I. A1 - Ruttert, B. A1 - Theisen, W. A1 - Fedelich, Bernard T1 - Refinement and Experimental Validation of a Vacancy Model of Pore Annihilation in Single-Crystal Nickel-Base Superalloys during Hot Isostatic Pressing JF - Advanced Engineering Materials N2 - Initially, as-cast and homogenized single crystals of nickel-base superalloy CMSX-4 are subjected to hot isostatic pressing at 1288 °C. Two series of experiments are conducted: under the same pressure of 103 MPa but with different durations, between 0.5 and 6 h, and under different pressures, between 15 and 150 MPa, but for the same time of 0.5 h. The porosity annihilation is investigated metallographically and by high-resolution synchrotron X-ray tomography. The obtained experimental results are compared with the predictions of the vacancy model proposed recently in the group. Herein, the model is further refined by coupling with X-ray tomography. The model describes the evolution of the pore arrays enclosed in the 3D synchrotron tomograms during hot isostatic pressing and properly predicts the time and stress dependences of the pore annihilation kinetics. The validated model and the obtained experimental results are used for selecting the optimal technological parameters such as applied pressure and processing time KW - Superalloys KW - HIP KW - Single-Crystal KW - Diffusion PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-526859 DO - https://doi.org/10.1002/adem.202100211 VL - 23 IS - 7 SP - 211 AN - OPUS4-52685 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schmidt, C. A1 - Hensen, C. A1 - Wallmann, K. A1 - Liebetrau, V. A1 - Tatzel, Michael A1 - Schurr, S. L. A1 - Kutterolf, S. A1 - Haffert, L. A1 - Geilert, Sonja A1 - Hübscher, C. A1 - Lebas, E. A1 - Heuser, A. A1 - Schmidt, M. A1 - Strauss, H. A1 - Vogl, Jochen A1 - Hansteen, T. T1 - Origin of High Mg and SO4 Fluids in Sediments of the Terceira Rift, Azores‐Indications for Caminite Dissolution in a Waning Hydrothermal System JF - Geochemistry, Geophysics, Geosystems N2 - During R/V Meteor cruise 141/1, pore fluids of near surface sediments were investigated to find indications for hydrothermal activity in the Terceira Rift (TR), a hyperslow spreading center in the Central North Atlantic Ocean. To date, submarine hydrothermal fluid venting in the TR has only been reported for the D. João de Castro seamount, which presently seems to be inactive. Pore fluids sampled close to a volcanic cone at 2,800‐m water depth show an anomalous composition with Mg, SO4, and total alkalinity concentrations significantly higher than seawater and a nearby reference core. The most straightforward way of interpreting these deviations is the dissolution of the hydrothermally formed mineral caminite (MgSO4 0.25 Mg (OH)2 0.2H2O). This interpretation is corroborated by a thorough investigation of fluid isotope systems (δ26Mg, δ30Si, δ34S, δ44/42Ca, and 87Sr/86Sr). Caminite is known from mineral assemblages with anhydrite and forms in hydrothermal recharge zones only under specific conditions such as high fluid temperatures and in altered oceanic crust, which are conditions generally met at the TR. We hypothesize that caminite was formed during hydrothermal activity and is now dissolving during the waning state of the hydrothermal system, so that caminite mineralization is shifted out of its stability zone. Ongoing fluid circulation through the basement is transporting the geochemical signal via slow advection toward the seafloor. KW - Isotope ratio KW - Delta value KW - Pore fluids KW - Magnesium KW - Hydrothermal fluid PY - 2019 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-503430 DO - https://doi.org/10.1029/2019GC008525 VL - 20 IS - 12 SP - 6078 EP - 6094 PB - Wiley AN - OPUS4-50343 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -