Correlation of Microstructure to Creep Response of Hot Isostatically Pressed and Aged Electron Beam Melted Inconel 718

Creep rupture samples were fabricated by additive manufacturing (AM) via electron beam melting (EBM) to study the effects of grain morphology (equiaxed/columnar grains) and loading direction (longitudinal/transverse) with respect to build direction on creep deformation at 923 K (650 °C) with applied stresses of 580 and 600 MPa. The observed minimum creep rates and creep rupture lives of EBM Inconel 718 after post-processing by hot isostatic pressing (HIP) were found to be comparable to wrought material. The material with equiaxed grains exhibited low creep strain (2 pct) and short creep lifetimes (800 hours), whereas longer times (approximately 4500 hours) and high creep strain (up to 23 pct) were observed for material with columnar grains. The high stress exponent (n > 14) reflected the resistance to dislocation motion by γ” particles during creep. A precipitate-free zone (PFZ) was observed around the grain boundary δ phase. Creep damage occurred as voids and cracks in the PFZ. Optimal post-processing of EBM Inconel 718 material should be explored to prevent δ phase embrittlement.