Microstructure-mechanical property correlation in electron beam-powder bed fusion Inconel 718 superalloys: Role of build angle on defect formation, γʺ precipitation, and creep resistance

The correlation between microstructure and mechanical properties in additively manufactured Inconel 718 superalloys fabricated by electron beam-powder bed fusion (EB-PBF) with four build angles was systematically investigated. Although all as-built specimens achieved relative densities above 99%, the volumetric defect density increased monotonically from 4.59 × 10 -1 % to 9.49 × 10 -1 % with increasing build angle, with the dominant defect population shifting from gas-entrapped pores and micro-cracks at low angles to lack-of-fusion defects at 90°. All specimens developed columnar grains parallel to the build direction, with coarse Laves phase and MC particles along grain boundaries. The 0° and 90° specimens exhibited γʺ volume fractions exceeding 15%, delivering superior high-temperature tensile strength and good uniform elongation, whereas the 15° and 45° specimens showed γʺ fractions below 8% due to enhanced heat dissipation into the powder bed. Notably, the 0° as-built alloy achieved a creep rupture life approximately twice that of fully heat-treated wrought Inconel 718, owing to the synergistic combination of a strong (0 0 1) γ texture, low defect density, and high γʺ fraction. In contrast, the 90° specimen showed a markedly shortened creep life due to strain localization at defects along high-angle grain boundaries, indicating that creep resistance is governed by coupled effects of texture, defects, grain-boundary characteristics, and precipitation rather than any single factor. These findings establish build angle as a primary processing variable controlling defect formation, γʺ precipitation, and high-temperature performance of EB-PBF Inconel 718.