Eutectic Al alloys with tailored solidification path to probe fundamental aspects of solidification in laser-based AM II

我们的项目目标是评估Al-Ni-Ce体系在其耦合共晶生长区域附近是否适合于PBF-LB/M。特别是具有优异力学性能的超细共晶组织最初是目标。在第一阶段，我们已经验证了我们的两个研究假设，即在Al-Ni中，通过选择过共晶合金成分和特定的工艺条件，可以设计出材料的微观组织，特别是超细的二元共晶。事实上，虽然间距被证明在共晶耦合生长的情况下可以有效地描述凝固速度，但从实验和数值(相场法)都已经证明了广泛的其他微观结构，说明了共晶生长的强烈不对称耦合区域。此外，工艺参数和材料参数也影响熔池动力学，并建立了熔池尺寸与孔洞形成之间的联系。在SPP2122的第二阶段中，将更详细地研究这种联系。特别是，为了更好地理解小孔起始与合金成分的关系，从而拓宽工艺窗口，特别是在低激光扫描速度下，我们将关注孔口距离和激光光斑大小的影响。将进行熔池模拟以及三元Al-Ni-Ce合金的实验。减少孔隙率与产生适当的微结构是齐头并进的。在这方面，三元合金系统中可能的组织结构的多样性将比二元合金系统中的更广泛。将特别关注三相共晶耦合生长，以产生超细的三元共晶以及两相纳米晶结构，在第一阶段证明了大扫描速度，两相的晶粒度都在50 nm范围内。这种纳米晶结构是固有的，具有很大的硬度，没有凝固裂纹，但似乎很容易产生冷裂纹。当气孔率较低，组织有希望时，我们将对所生产的样品进行系统的力学测试(硬度、拉伸测试)。然后，我们的项目应该在第二阶段结束时提供一种程序，以建立致密的样品，甚至可能是局部优化的性能。

Our project goal is to evaluate the Al-Ni-Ce system around its zone of coupled eutectic growth for its suitability for PBF-LB/M. In particular, ultra-fine eutectic structures with superior mechanical properties are originally targeted. In phase 1, we have already verified two of our research hypotheses, namely that in Al-Ni the material microstructures, in particular an ultra-fine binary eutectic, can be designed by selecting hypereutectic alloy compositions and specific processing conditions. Indeed, while the spacing has proven efficient to apprehend the solidification velocity in the case of a eutectic coupled growth, a broad range of other microstructures have been evidenced, both experimentally and numerically (phase-field method), illustrating the strong asymmetric coupled zone of eutectic growth. Moreover, the process and material parameters also influence the melt pool dynamics, and a link between its dimensions and the porosity formation via keyholing has been established. In phase 2 of SPP2122, this link will be investigated in more detail. Especially, the influence of the hatch distance and the laser spot size will receive our attention in order to better understand the keyholing onset dependent on alloy composition and thereby broaden the process window, particularly at low laser scanning speed. Melt pool simulations, as well as experiments with the ternary Al-Ni-Ce alloy, will be performed. Reducing porosity goes hand in hand with generating appropriate microstructures. In this respect, the variety of possible microstructures is expected to become even broader in the ternary alloy system than for binary alloys. A particular focus will be put on the three-phase eutectic coupled growth in order to produce ultra-fine ternary eutectics as well as on a two-phase nanocrystalline structure, evidenced during phase 1 for large scanning speeds, with grain sizes in the range of 50 nm for both phases. This nanocrystalline structure emerges intrinsically, shows remarkably large hardness values and no solidification cracks, however, it seems to be prone to cold cracks.We will systematically perform mechanical testing (hardness, tensile tests) on the produced samples when porosity is low and the microstructure is promising. Our project should then provide, at the end of phase 2, a procedure to build dense specimens with, possibly even locally, optimized properties.