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In this presentation tribological investigations on steels, polymers and coatings in gaseous and liquid hydrogen are shown. For steels the results of show that although martensitic steel may suffer from hydrogen embrittlement, application e.g. in roller bearings is possible. On the other hand, martensitic transformation of austenitic steels may cause problems in the application of these materials. Furthermore, the tribological performance of polymer composites with and without solid lubricant fillers in gaseous and liquid hydrogen was investigated. In particular, PEEK- and PTFE-matrix compounds showed low friction and sufficient low wear under these conditions. Among the solid lubricants, carbon-based materials are appropriate for hydrogen applications. Several variants of DLC and ta-C materials were tested. Beside the results for hydrogen, also a comparison with CH4-environment is shown.
Chemical composition of the welding seam and HAZ has significant effect on weld quality. Current inspection methods for weld seams measure and investigate post factum and cannot prevent weld defects. Element burn-off may significantly affect solidification leading to embrittlement or cracking Control of weld chemical compositions insures a controlled solidification and resistance to related weld defects.
TIG welding process was monitored using LIBS for the in situ measurement of chemical compositions in austenitic stainless steels. This research aims to prototype a real-time chemical composition analysis system for welding applications and prove the feasibility of such a quality control loop.
The chemical compositions of the weld pool, considering the welding metallurgy, is the most critical parameter for any occurring weld defects, e.g. hot cracking. Hence, controlling the weld pool chemical composition allows governing of the weld pool solidification behavior by monitoring and adjusting the respective welding parameters, e.g. welding current.
LIBS measurements were conducted during a TIG-welding process. The effect of the welding plasma on the LIBS signal was thoroughly investigated by varying various LIBS settings, e.g. delay and exposure time. Quantification of the main alloying elements Cr and Ni in the weld pool during welding was achieved by univariate calibration procedure.
Chemical compositions of the welds have significant effect on weld quality. Current inspection methods for the weld seams employ mostly post factum methods and cannot prevent weld defects.Elemental burn offs may significantly affect solidification leading to embrittlement or cracking. Control of weld chemical compositions insures a controlled solidification and resistance to related weld defects.
Chemical composition of the welding seam and HAZ has significant effect on weld quality.
Current inspection methods for weld seams measure and investigate post factum and cannot prevent weld defects. Element burn-off may significantly affect solidification leading to embrittlement or cracking. Control of weld chemical compositions insures a controlled solidification and resistance to related weld defects. “Industry 4.0” is the current trend of automation and data exchange in manufacturing technologies. With this trend “intelligent” welding machines will be developed. LIBS can provide significantly important online data for such systems.
Chemical compositions of a weld can be varying locally as a result of the welding process. These local variations can be due to the vaporization of individual alloying elements. In this work, tungsten inert gas (TIG) bead-on-plate stainless steel welds of EN grade 1.4404 and 1.4435 were investigated using laser-induced breakdown spectroscopy (LIBS) on the completed welds. This study aims to reveal the welding parameters’ influence on the resulting local chemical compositions of the stainless steel welds. We demonstrated Mn vaporize before Cr due to its lower latent enthalpy of vaporization. Hence, Mn accumulates on the heat-affected zone (HAZ) both sides across the weld bead by being swept away through the circulation flow of the welding plasma. Additionally, increasing the heat input tends to enhance the accumulated Mn content on the HAZ as well as increasing the shielding gas flow rate. The results are in good agreement with the literature and proved that LIBS is an effective method to inspect completed welds.