Investigating the microstructure of an additively manufactured FeCo alloy: an electron microscopy study

Abstract The objective of the present investigation is to correlate mechanical properties with microstructure for FeCo alloy using electron microscopy. A short parameter adaption is conducted to determine the optimum laser powder bed fusion parameters, which lead to the highest sample density. Subsequently, FeCo alloy samples are produced to address the evolving microstructure and mechanical properties. A high build rate is also attained along with the high density. X-ray micro-tomography of the samples revealed a remaining porosity of 0.02%. Electropolishing and subsequent microstructural examinations are undertaken by electron backscatter diffraction employing scanning electron microscopy. Elongated columnar grains are observed on the side of the samples, which is characteristic of selective laser melting. Based on transmission electron microscopy, the composition of Fe and Co at the submicron scale is homogeneous. The dislocation density near the grain boundaries measured by transmission electron microscopy is ≈ 2.2 × 1013 m−2. Unresolved lattice fringes due to dislocation strain fields are observed in high-resolution transmission electron microscopy images. Different tensile properties are obtained with loading parallel as well as perpendicular to the build direction. This is due to different Schmid factors of the grains during loading parallel and perpendicular to the build direction. A mixture of cleavage and dimple fracture is noticed upon loading parallel to the build direction. Whereas loading perpendicular to the build direction shows only cleavage fracture.