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

第一阶段的资金重点是纯铁以及通过电子粉末床熔融（E-PBF，也称为PBF-EB/M）由CeO 2和Fe 2 O3改性的粉末的加工性。微观结构以及机械和腐蚀性能旨在受到氧化物颗粒的最小添加的影响。准静态和循环机械调查表明，这是强大的可能性，由于意外的高损伤容限，疲劳强度显着上级热轧铁可以实现。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CeO 2改性中特别明显。因此，假设这些氧化物有效地增加了硬度。补充研究还表明，孔隙中的局部酸性环境会阻碍表面层的形成，进而导致材料的腐蚀速率更高。由于观察到CeO 2颗粒的积极效果，并且由于该材料还提供了对缺陷的高损伤容限，因此选择性引入的孔可以用作调节腐蚀速率的另一自由度。因此，在资助期间，必须建立两条E-PBF工艺路线，以允许对具有更高CeO 2含量的铁粉进行稳健的加工。为了促进即时工艺稳定性，将考虑粉末的导电性。当致密材料可以重复加工时，将根据形状、尺寸和分布专门定制孔隙率来制造样品。这代表了调整材料特性的更大自由度，并且只有通过增材制造工艺才有可能。此外，在材料方面，需要非常高的损伤容限。在加载过程中的计算机断层扫描研究可以用于扩展和分析孔，否则太小，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。作为对高周疲劳和腐蚀载荷的补充，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进展。最后，将建立疲劳寿命模型，以评估和预测作为材料常数、裂纹长度和腐蚀因子的函数的裂纹扩展。基于所阐述的模型，还可以预测其他材料在高度复杂的负载情况下的行为，以便最终可以针对预期应用单独定制增材制造的生物可吸收植入物。

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.