Grain size assessment using EBSD on heterogeneous additively manufactured microstructures

Grain microstructures are important for a whole range of materials properties. With the widespread use of additive manufacturing (AM), current standards for grain boundary evaluation, such as ASTM E2627-13, may not be fit for purpose due to their microstructural complexity. They are notoriously anisotropic across a range of length scales due to the non-equilibrium nature of the solidification process and the tracking of the heat source. In this work we examine the grain microstructure of a nickel superalloy produced by laser powder bed AM by electron back scatter diffraction. We find that the guidelines provided by the ASTM E2627-13 are not suitable for such heterogeneous and anisotropic materials and some modified guidelines are provided on the field of view and EBSD step size that should be used to characterise such materials.