Reduction of hot cracking by magnetofluiddynamic modification of the laser-induced melt pool convection during powder-based generative laser cladding

热裂纹的产生是高耐热镍基高温合金焊接过程中的一个重要问题。热裂纹通常与沿熔合区和部分熔化区中的晶界沿着存在的液膜有关，并且只能被抑制到非常有限的程度。尽管对这一现象进行了大量的研究和分析，但情况仍然如此。值得注意的措施是材料改进和热机械处理，这些措施只能在特定的安排下应用。在本建议中，提出了一种新的方法，它抑制了热裂纹的原因，通过使用非接触的方法来影响凝固过程。它是基于激光诱导修改的熔池对流（马兰戈尼对流），使用定制的磁场。与经由电子束或电弧的能量输入相反，激光束不与所施加的磁场相互作用。这限制了对流动熔池的影响。这种限制是一个独特的功能，并提供了潜在的表面应用，是独立于基板的几何形状。除了大量的理论分析，第一个实验结果。后者巩固了最初的工作假设。因此，一个广泛的实验研究计划将得到解决。这尤其包括熔池与时间和/或空间变化或恒定磁场的相互作用以及通过系统地调节激光功率、焦距和/或相互作用时间来改变熔池。识别与熔池对流的相互作用需要目前在激光材料加工、流体动力学以及材料工程和表征方面具有相当专业知识和知识的合作。

The occurrence of hot cracking is a significant problem during welding processing of highly heat resistant nickel base superalloys. Hot cracking is most often associated with liquid films that are present along grain boundaries in the fusion zone and the partially melted zone and can only be suppressed to a very limited extent. Latter is the case despite remarkable studies and analyses of the phenomenon. Notable measures are material improvements and thermomechanical treatment which can only be applied with particular arrangements. In the present proposal a new approach is presented which suppresses the cause of hot cracking by using a non-contact method to influence the solidification process. It is based on the laser-induced modification of the melt pool convection (Marangoni convection) using customized magnetic fields. In contrast to an energy input via electron beam or electric arc the laser beam is not interacting with the applied magnetic field. This limits the influence on the flowing melt pool. This limitation is a unique feature and offers the potential for surface applications that are independent from the geometry of the substrate. Besides the substantial theoretical analysis, first experimental results are presented. Latter consolidate the initial working hypothesis. Consequently, an extensive experimental research program will be addressed. This includes in particular the interaction of the melt pool with temporal and/or spatial varying or constant magnetic fields as well as the variation of the melt pool through the systematic adjustment of laser power, focal distance and/or the time of interaction. Identifying the interaction with the melt pool convection requires the present collaboration with considerable expertise and knowledge in laser material processing, fluid dynamics as well as materials engineering and characterization.