In-situ synthesis of ß-NiAl based alloys by means of laser metal deposition

由于高温航天应用对材料的要求越来越高，目前最先进的镍基高温合金需要进一步发展或替代。- nial的密度较低，仅为同类镍基超级合金的三分之二。此外，1638°C的高熔点、优异的导热性和在高温下优异的抗氧化性使nial基合金成为未来涡轮发动机高温应用的有前途的材料。然而，室温下有限的延展性和断裂韧性以及高温下较差的强度等问题尚未解决，迄今为止阻碍了该技术向工业领域的转移。基于已经收集的知识，增材制造（AM）技术激光金属沉积（LMD）被确定为一种能够克服这些挑战的技术。在拟议的研究活动中，将详细研究近净形状制造，定制热处理条件和原位合金改性的优势，以加工二元和三元- nial基合金。首先，将使用LMD加工一个参考预合金Ni50Al50粉末，以收集有关- nial合金加工的基本知识。在此基础上，对复杂的ß-NiAl-Ta-Cr合金的原位合金化进行了深入的研究。通过处理预合金Ni50Al50以及三元元素Ta和Cr，可以实现第二相增韧。关键方面是形成金属间相和难熔二次相，从而提高高温强度和室温断裂韧性。通过参数变化（如激光功率、进料速率），分析焊接工艺与沉积材料微观结构之间的相互关系。最后，所获得的知识将用于开发渐变的ß-NiAl-Ta-Cr结构，该结构具有空间可分辨的laves相量。通过这种方法，将分析制造具有本地定制材料特性的ß-NiAl-Ta-Cr组件的可能性。在这些研究中，将对材料微观结构进行深入分析，并对制造样品的机械性能进行表征，以检测和理解工艺参数、创建的微观结构和最终材料性能之间的相关性。通过高速成像，对加工区内现象的分析，如不同材料对激光辐射的特定吸收，将被纳入调查。总体目标是深入了解LMD原位合金化过程、二元和三元ß-NiAl基合金的微观结构和材料性能之间的相关性和相互依赖性。

Due to increasing material requirements of high temperature aerospace applications current state-of-the-art Ni-based superalloys need to be further developed or replaced. ß-NiAl exhibits a low density of only two thirds of comparable Ni-based super alloys. Moreover, the high melting temperature of 1638 °C, a superior thermal conductivity and an outstanding oxidation resistance at elevated temperatures of ß-NiAl make NiAl-based alloys a promising material for high temperature applications in future turbine engines. However, the unsolved issues of a limited ductility and fracture toughness at room temperature as well as a poor strength at high temperatures have prevented the transfer to industry so far. Based on already gathered knowledge the Additive Manufacturing (AM) technique laser metal deposition (LMD) was identified as a technology, which is capable of overcoming these challenges. Within the proposed research activity the advantages of near net shape manufacturing, tailored thermal process conditions and in-situ alloy modification will be investigated in detail for the processing of binary and ternary ß-NiAl based alloys.Firstly a reference pre-alloyed Ni50Al50 powder will be processed by LMD in order to gather basic knowledge about the processing of ß-NiAl alloys. Based on this the in-situ alloying of complex ß-NiAl-Ta-Cr alloys will be investigated profoundly.By processing pre-alloyed Ni50Al50 as well as the ternary elements Ta and Cr a second phase toughening shall be achieved. Key aspect is the formation of intermetallic and refractory secondary phases, which yield increased high temperature strength and improved room temperature fracture toughness. By parameter variation (e.g. laser power, feeding rate) interdependencies between the welding process and the microstructure of the deposited material will be analysed. Finally, the obtained knowledge will be used to develop graded ß-NiAl-Ta-Cr structures, which exhibit a spatially resolved amount of Laves-Phase. By this the possibility of manufacturing ß-NiAl-Ta-Cr components with locally tailored material properties will be analyzed.Within these investigations a profound analysis of the material microstructure as well as a characterization of the mechanical properties of manufactured samples will be conducted for detecting and understanding correlations between process parameters, the created microstructure and the resulting material properties. By means of high-speed imaging an analysis of phenomena within the process zone, such as a varying material specific absorption of the laser radiation will be incorporated into investigations.The overall goal is to obtain an in-depth understanding of correlations and interdependencies between the LMD in-situ alloying process, the microstructure and the material properties of binary and ternary ß-NiAl based alloys.