Abstract

A key differentiator for additive manufacturing is spatially resolved functional grading, which enables a level of control not possible with conventional methods. Utilizing the solid-state austenite-martensite phase transformation, we create an in-situ microstructurally and magnetically graded single-composition material by utilizing the rapid solidification and thermal strain associated with selective laser melting. The thermal martensite start temperature is lowered by the fine grain sizes produced by high cooling rates, thereby increasing the proportion of retained austenite. Then, martensitic transformation driven by in-situ deformation is caused by the thermal strain that was added during the construction. We have been able to control the final ratio of austenite to martensite by controlling the thermal strain and the build parameters and geometry. Partially austenitic regions exhibit paramagnetic behavior, whereas dual-phase regions with an increasing proportion of martensite exhibit ferromagnetic behavior. This enables us to construct a magnetically graded rotor that is successfully utilized in a synchronous motor.