WELDMECS

Welding Metallurgy and Cracking in Superalloys

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 Obiettivo del progetto (Objective)

'Predictive, metallurgy informed crack criteria will be developed within the WELDMECS project. These crack criteria are developed in a format appropriate for implementation to finite element software. It will be useful for general thermo-mechanical simulations estimating the risk for various crack formations. The primary target in current topic description (JTI-CS-2012-3-SAGE-02-029) is to utilize the crack criteria for both welding and heat treatment simulations. Since cracking during welding or heat treatment is a many-faceted problem, care has been taken to strongly incorporate fundamental metallurgical understanding and testing into the models. The model will be based on actual failure mechanisms, metallurgical changes and their relations to the material response and prevailing thermo-mechanical conditions. Up to date – simulations have focused on geometric tolerances and/or prediction of residual stresses. Only simpler, limited defect criteria have been used in this context. The current project is expected to further the modeling of manufacturing processes in the area of predicting crack formations.'

Introduzione (Teaser)

Cracking associated with welding or heat treatment is a serious problem in metal forming and a safety-critical one when it comes to fabrication of jet engine components. The EU is supporting research to ensure that cracking is under control.

Descrizione progetto (Article)

The project 'Welding metallurgy and cracking in superalloys' (WELDMECS) is developing hot cracking criteria for superalloys that will be used to develop finite element (FE) simulation software to support aircraft manufacture. Hot cracking occurs during solidification due to different melting points of various materials or impurities in an alloy. The software will include thermomechanical simulations estimating the risk for crack formation. Fundamental metallurgical foundations and extensive testing are supporting model development.

Scientists are exploiting two common test protocols as well as thermomechanical simulation to determine the criteria. Gleeble testing exploits machine systems by the same name that heat a sample and mechanically work it while measuring various parameters of interest. After testing, the microstructure of the materials can also be examined. The Varestraint test applies a selected strain (bending) parallel to the welding location to a sample during welding. The extent of cracking is observed as an indication of sensitivity to hot cracking.

The first period was focused largely on preparation for Gleeble and Varestraint testing. Scientists characterised the material microstructure and prepared samples. Gleeble experiments have begun and the team is working on the code to simulate both types of tests.

Hot cracking produces serious defects in welded or heat-treated parts. WELDMECS is filling an important need with FE models simulating two of the most important experimental tests to evaluate effects of heating and forming. This will minimise the need for extensive testing campaigns, supporting more rapid and less costly identification of the proper manufacturing conditions for safer aircraft.