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

热裂的发生是高耐热镍基高温合金焊接过程中的一个重要问题。热裂最常与在熔合区和部分熔化区沿晶界出现的液膜有关，并且只能在非常有限的程度上被抑制。尽管对这一现象进行了大量的研究和分析，但情况仍然是后者。值得注意的措施是材料改进和热处理，这些措施只能在特殊安排下使用。本文提出了一种通过非接触方法影响凝固过程来抑制热裂原因的新方法。它是基于使用定制磁场对熔池对流（马兰戈尼对流）的激光诱导修正。与通过电子束或电弧输入的能量相比，激光束不与外加磁场相互作用。这限制了对流动熔池的影响。这种限制是一种独特的特性，为独立于基板几何形状的表面应用提供了潜力。除了大量的理论分析外，还给出了初步的实验结果。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被处理。这特别包括熔池与时间和/或空间变化或恒定磁场的相互作用，以及通过系统调整激光功率、焦距和/或相互作用时间而引起熔池的变化。确定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多的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.