Microstructure, deformation and lifetime of alloy 617B - experiences from different heat treatments and heats

The present work summarizes experiences with Alloy 617B from different heat treatments and heats investigated at Fraunhofer IWM. For this purpose, different batches of Alloy 617B are compared with respect to chemical composition, grain size, and precipitation state. Moreover, results from low cycle fatigue tests at different strain rates with and without hold times are presented, giving impressions about the viscoplastic material properties and lifetime as a function of the material condition. Further investigations comprise fatigue crack growth measurements and fractographic analysis for the characterization of the prevailing damage mechanisms

Experimental investigations and numerical simulation accompanying the HWT test loop operation

A material test loop has been installed at GKM Mannheim, which enables thick-walled components of future highly-efficient power plants to be exposed to steam temperatures of up to 725 °C. The project goal was to demonstrate the feasibility of a 700 °C power plant. Based on the experience with materials and component manufacturing, operational experience and scientific investigations, fundamental knowledge of material behavior was determined which allows an assessment of the behavior of key components, such as headers, tubes, bends and valves. For this purpose, in addition to the test loop construction and its operation, extensive material characterizations and numerical analyses were carried out at the participating research institutes Materials Testing Institute (MPA) University of Stuttgart, the Fraunhofer Institute for Mechanics of Materials IWM in Freiburg and the Institute of Materials Technology (IfW) at the Technical University Darmstadt. The determination and evaluation of material properties, which also comprise microstructural investigations, was aimed at gaining a deeper understanding of the Nickel base Alloy 617B and Alloy C263 and their welded joints. For basic material qualification and qualification of manufactured components an extensive experimental investigation program as well as tests to ensure quality of materials, welds and repair welds was initiated. The operating parameters of the test loop were first optimized by numerical simulations of component loading and lifetime with existing models [1]. An adaptation of the models to the experimental data of the project material enabled a more precise confirmation of the predictions carried out during regular operation of the test loop. To quantify service experience, numerous measuring results and findings regarding damage evolution were evaluated and compared to results from material tests and predictions from numerical analyses

Reversible phosphocholination of Rab proteins by Legionella pneumophila effector proteins

The Legionella pneumophila protein AnkX that is injected into infected cells by a Type IV secretion system transfers a phosphocholine group from CDP-choline to a serine in the Rab1 and Rab35 GTPase Switch II regions. We show here that the consequences of phosphocholination on the interaction of Rab1/Rab35 with various partner proteins are quite distinct. Activation of phosphocholinated Rabs by GTP/GDP exchange factors (GEFs) and binding to the GDP dissociation inhibitor (GDI) are strongly inhibited, whereas deactivation by GTPase activating proteins (GAPs) and interactions with Rab-effector proteins (such as LidA and MICAL-3) are only slightly inhibited. We show that the Legionella protein lpg0696 has the ability to remove the phosphocholine group from Rab1. We present a model in which the action of AnkX occurs as an alternative to GTP/GDP exchange, stabilizing phosphocholinated Rabs in membranes in the GDP form because of loss of GDI binding ability, preventing interactions with cellular GTPase effectors, which require the GTP-bound form. Generation of the GTP form of phosphocholinated Rab proteins cannot occur due to loss of interaction with cellular GEFs