Project insituLIBS - In situ investigation of phase distribution and melt pool solidification of duplex stainless steels using laser-induced breakdown spectroscopy (LIBS)

17/01/2022

• Challenge
• Objectives
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Modern steels exhibit microstructural changes during welding that result to uneven phase ratios and changes in chemical composition. Microstructural changes can lead to solidification cracks, increase in susceptibility to corrosion, lower ductility and critical strength values. Laser-induced breakdown spectroscopy (LIBS) enables time- and spatially-resolved in situ measurement of both temperature and chemical composition during welding.

The aim is to increase the accuracy of the prediction of the weld microstructure of modern steels. Especially regarding modern wind turbines, it is necessary to monitor the welding processes with high precision. For this purpose, measurements of the chemical composition as well as electron temperature calculations are realized by means of LIBS. With electron temp. data, it is possible for the first time to calculate the cooling rate without an additional measuring device and to analyze the cooling curves of the solidifying weld metal in the weld pool.

LIBS is a spectroscopic method that can be used to determine elemental compositions. Short, high-energy laser pulses ablate a small volume (< 0.1 mm³) of the bombarded material and ionise it to form a plasma. The decayed plasma emits element-specific light. The simple experimental set-up and the fast, non-destructive analysis procedure characterize the LIBS analysis. Elemental analyses can be performed without contact and without pretreatment of the samples. Liquid as well as solid and gaseous substances can be analyzed.

Funding

The project is funded by the German Research Foundation (DFG), project number 442001176.

insituLIBS - In situ investigation of phase distribution and melt pool solidification of duplex stainless steels using laser-induced breakdown spectroscopy (LIBS)

Weld seam monitoring

Laser-induced breakdown spectroscopy (LIBS) offers a promising option for in situ weld monitoring. In LIBS analysis, a high-energy pulsed laser generates a plasma on the material surface. The expansion of the plasma causes electromagnetic radiation. This radiation is element specific and can be used to chemically characterize the tested material after a reference analysis. The solidification sequence of the material correlates directly with the temperature in the molten bath. Therefore, it is necessary to monitor this temperature in the welding process to make immediate parameter adjustments. By calculating electron temperatures in the laser plasma, the temperature can be determined with time and spatial resolution without additional measuring equipment. Following the measurement process, spectra are generated and evaluated for each individual measurement point. After subtraction of the background radiation, the intensities of the elements of interest can be filtered out.

Project coordination

Bundesanstalt für Materialforschung und -prüfung (BAM)
Division Weld Mechanics

Funding

The project is funded by the German Research Foundation (DFG), project number 442001176.