Microstructure and mechanical properties of nickel-based superalloy MAR-M247 fabricated via electron beam powder bed fusion (EPBF)

MAR-M247, a nickel-based superalloy, offers excellent mechanical properties at elevated temperatures but suffers from poor printability due to severe cracking. This study demonstrates the successful fabrication of MAR-M247 using electron-beam powder bed fusion (EPBF) with pre-heating at 1000 degrees C, achieving a high relative density (>99.5 %). Pre-heating suppressed the typical solidification microstructures observed in AM-fabricated alloys and minimised residual stress, resulting in reduced cracking. The as-printed alloy exhibited superior mechanical properties, with yield strengths of 820 MPa at room temperature and 640 MPa at 871 degrees C, outperforming conventionally cast MAR-M247. Atom probe tomography (APT) confirmed a high volume fraction (73.1 %) of gamma' precipitates, including fine secondary precipitates near grain boundaries, enhancing mechanical strength by restricting dislocation motion. However, ductility decreased at elevated temperatures due to liquation cracking along grain boundaries, driven by solute segregation (Mo, B, and Cr). Creep behaviour analysis using the Larson-Miller Parameter (LMP) indicated that the as-printed alloy exhibited a rupture life comparable to post-processed cast alloys despite the presence of liquation cracks. Primary gamma' precipitates (0.2-1 mu m) were the main contributors to creep resistance, while fine secondary precipitates (similar to 30 nm) near grain boundaries provided additional resistance.