Designing an Fe-Ni-Ti maraging steel tailormade for laser additive manufacturing

Kurzfassung

Laser additive manufacturing (LAM) offers high flexibility in the production of customized and geometrically complex parts. The technique receives great interest from industry and academia but faces substantial challenges regarding processability and insufficient mechanical properties of LAM-produced material. One reason is that currently mainly conventional alloys are being used in LAM, which were developed for different processes such as casting. Since these alloys are not optimized for the specific process conditions encountered in LAM such as fast cooling and cyclic re-heating, they cannot be expected to perform ideally in such processes regarding processability and resulting mechanical properties. Here we present the development of a new, simple ternary Fe-Ni-Ti maraging-type alloy tailor-made for LAM. We used compositionally graded samples to screen Ti compositions from 0 to 21 at. % and efficiently identify promising microstructures and mechanical properties. Under LAM solidification conditions the desired mainly martensitic microstructure needed for a maraging steel formed at Ti compositions ranging from 0 to 7 at. %. Within this composition range, the intended microstructure is formed and additionally some unique process conditions of LAM such as cyclic re-heating can be exploited. Specifically, in-situ phase transformations can be controlled during LAM, via the thermal history. At higher Ti compositions two different eutectic microstructures with different primary phases were found that show a high hardness of up to 700 HV.