The development of Nb Si core-shell powders for Laser-based Powder Bed Fusion

Kurzfassung

Aircraft engine materials are constantly evolving to meet new requirements. One example is the goal of increasing engine efficiency. This can be achieved by increasing the turbine inlet temperature. As the turbine inlet temperature is increased, the materials used need to be able to withstand higher temperatures. Nb and Si which forms Nb-Si precipitates within a Nb matrix. Such a Nb-Si alloy exhibits a high level of strength and good creep behavior at high temperatures. By using this alloy the maximum possible the turbine inlet temperature could be increased to 1350 °C, which is 200 °C above the current limit of Ni-based alloys [1]. However, due to the high melting point and the reac-tivity of the melt, Nb-Si alloys are hard to process by fine casting [2]. Therefore, laser-based powder bed fusion (PBF/LB or LPBF) can be a suitable processing route for the production of Nb-Si parts since the prevailing temperatures exceed those of conventional processing techniques. In this work, a Nb-Si core-shell powder was additively manufactured by LPBF. The powder was manufactured by coating a pure Nb core with Si (by pack-cementation). This manufacturing route was chosen because of the aforementioned challenges in processing intermetallic Nb-Si (alloy) and since pure Nb is prone to oxidation, which occurs at high process temperatures even in extremely good gas atmospheres. Therefore, Nb powder is coated with Si in order to increase the oxidation resistance allowing for longer reuse in LPBF. Although the first built samples still exhibited a crack network and porosity, general trends can be associated with the building parameters. The micro-structure consists mainly of intermetallic phases which explained the brittle behavior even at 1000 °C built platform temperature. Thus, further development of the core-shell powder and LPBF parameters are necessary. However, the results are promising and provide a good foundation for the future production of dense parts from Nb-Si Core-shell powders by LPBF.