Development of Nickel-base superalloys for additive manufacturing (AM) is a time intensive and costly process. The large number of alloying elements complicates the development of the alloy itself and the production of powder, to assess the processability, is very expensive. In our work, we speed up the development of Nickel-base superalloys for additive manufacturing by using computational alloy development, electron beam remelting (EBR) and local mechanical testing.

For computational alloy design, the in-house developed PyMultOpt algorithm is applied. This algorithm calculates promising alloy compositions within a predefined design space. Via optimization, the algorithm identifies compositions with the best combination of properties according to goals (properties that should be maximized) and constraints (property values that must be fulfilled). We use electron beam remelting to address processability in terms of crack susceptibility by measuring the crack density in the remolten zone. At first, a flat bulk sample of the alloy, as calculated by PyMultOpt, is arc-melted and homogenized. Afterwards the sample is remolten several times with a Selective Electron Beam Melting machine. By decreasing the remelting depth with each step, starting from deep to shallow meltpools, a layer-wise structure is obtained. Thermal simulations are employed a priori to estimate meltpool depth and geometry as a function of thermophysical material properties and processing parameters. First experiments with the crack-prone Alloy 247 using this approach show promising results. The layered structure and elongated grains which are typical for many AM process parameters is clearly visible. Furthermore, cracking can be observed within the remolten zone which indicates that the evaluation of crack susceptibility with this method is possible. We successfully produced remolten surface regions of up to 1 mm in thickness. This allows local mechanical testing of the mimicked AM microstructure. For this purpose, we employ profilometry-based indentation plastometry at temperatures of up to 800 °C to obtain the material’s yield strength. The results are in good agreement with what is derived on bulk tensile tests.

Using this workflow incl. the EBR method, we can quickly identify promising alloy compositions and evaluate their processability and susceptibility to cracking. Subsequent mechanical testing of the remolten zone allows us to evaluate the mechanical properties of new developed alloys.