Design of microstructure and degradation behavior of oxide-particle modified Fe-based alloys processed by selective electron beam melting

第一阶段的资助重点是纯铁的可加工性，以及通过电子粉末床熔合（E-PBF，也称为PBF-EB/M）改性的CeO2和Fe2O3粉末。微观结构、机械性能和腐蚀性能受微量氧化颗粒添加的影响。准静态和循环力学研究表明，这是完全可能的，并且由于具有意想不到的高损伤容限，可以实现明显优于热轧铁的疲劳强度。尽管在这些条件下存在与工艺相关的高缺陷密度，但这些影响在CeO2修饰中尤为明显。因此，假定这些氧化物能有效地提高硬度。补充研究还表明，孔隙中的局部酸性环境会阻碍表层的形成，从而导致材料的更高腐蚀速率。由于CeO2颗粒的积极影响被观察到，并且由于材料也提供了对缺陷的高损伤容错，因此选择性引入的孔可以用作进一步的自由度来调节腐蚀速率。因此，在资助期间，必须建立两个E-PBF工艺路线，以允许具有更高的CeO2含量的铁粉的稳健加工。为了促进即时的工艺稳定性，将考虑粉末的导电性。当致密材料可以重复加工时，样品将在形状、尺寸和分布方面具有专门定制的孔隙度。这代表了调整材料性能的进一步自由度，并且只有通过增材制造工艺才能实现。此外，在材料方面，需要非常高的损伤容忍度。加载过程中的计算机断层扫描可用于扩展和分析孔隙，否则太小而无法检测。孔隙中的腐蚀过程将通过专门设计的装置进行研究。除了高周疲劳和腐蚀载荷外，还将进行低周疲劳和断裂力学研究，以表征从孔隙开始的裂纹扩展。最后，建立疲劳寿命模型，以评估和预测裂纹扩展作为材料常数、裂纹长度和腐蚀因子的函数。基于所阐述的模型，预测其他材料在高度复杂载荷情景下的行为也将成为可能，因此增材制造的生物可吸收植入物最终可以根据预期的应用进行个性化定制。

Funding period one focused on the processability of pure iron as well as powders modified by CeO2 and Fe2O3 via electron powder bed fusion (E-PBF, also PBF-EB/M). The microstructure and the mechanical and corrosive properties were intended to be influenced by minimal additions of the oxide particles. Quasi-static and cyclic mechanical investigations showed that this is robustly possible and that, due to an unexpectedly high damage tolerance, fatigue strengths significantly superior to those of hot-rolled iron can be achieved. Despite a process-related high defect density present in these conditions, these effects were particularly evident in the CeO2 modifications. Therefore, an effective increase in hardness as a result of these oxides is assumed. Complementary investigations also showed that a local acidic environment in pores can impede the formation of surface layers, leading in turn to higher corrosion rates of the material. Since positive effects were observed as a result of the CeO2 particles and since the material also offers a high damage tolerance to defects, selectively introduced pores can thus be used as a further degree of freedom to adjust the corrosion rate. Consequently, in funding period two E-PBF process routes must be established to allow for robust processing of iron powders with even higher CeO2 contents. In order to promote immediate process stability, the electrical conductivity of the powder will be considered. When dense material can be processed reproducibly, samples will be manufactured with porosity specifically tailored in terms of shape, size and distribution. This represents a further degree of freedom for adjusting the material properties, and is only possible by additive manufacturing processes. Furthermore, on the material side the very high damage tolerance is required. Computed tomography investigations during loading can be used to expand and analyse pores that otherwise are too small for detection. The corrosive processes in the pores are to be investigated by means of a specifically designed setup. Complementing to high-cycle fatigue and corrosive loading, low-cycle fatigue and fracture mechanics investigations will be conducted to characterize crack advance starting from the pores. Finally, a fatigue life model will be established to assess and predict crack propagation as a function of material constants, the crack length and a corrosion factor. Based on the model elaborated, a prediction of the behavior of other materials under highly complex loading scenarios shall be possible as well, so that additively manufactured, bioresorbable implants can finally be individually tailored for the intended application.