Advanced quantification of the site-occupancy in ordered multi-component intermetallics using atom probe tomography

Abstract

A new experimental method is proposed to quantify the site-occupancy of substitutional solute elements in multi-component intermetallics from atom probe tomography data and is applied to the L12 ordered γʹ phase in the top, middle and bottom regions of an electron powder bed fusion produced IN-738LC build. Ti, W and Ta are found to substitute almost exclusively for the β sites. Cr and Mo show mixed behaviour with a higher proportion substituting for the β sites. Co also shows mixed behaviour but with a higher proportion substituting for the α sites. While γʹ maintains an almost constant chemistry and site-preference behaviour throughout the build, the relative site-occupancy ratio is observed to change, particularly for Co and Mo. The results suggest that local changes in thermal history inherent to metal additive manufacturing processes may induce changes to the resultant site-occupancy of γʹ. The method described here improves the experimental quantification of the local atomic site-occupancy, enabling an assessment of the substitutional solute element fractions occurring at the α and β sites in L12 ordered structures. This is important in multi-component intermetallics because of the burgeoning interest in relating the elastic and plastic properties of these structures to their site-occupancy.