Microstructure of nickel-base superalloy MAR-M247 additively manufactured through scanning laser epitaxy (SLE)

Scanning laser epitaxy (SLE) is a laser powder bed fusion (LPBF) based additive manufacturing (AM) process developed for the repair and manufacture of gas turbine hot-section components made of nickel-base superalloys. In the present study, the single-pass fabrication of more than 1500 μm thick deposits of MAR-M247, a non-weldable superalloy atop similar chemistry substrates using a high-power laser beam is demonstrated. Metallurgical continuity is achieved across the entire deposit-substrate interface and the samples show little or no warpage across a broad range of processing parameters. In order to relieve the residual stresses and enable precipitation of the strengthening phases, the SLE-deposited MAR-M247 samples are subjected to a commercially available heat treatment process. Microstructures of the as-deposited and the heat-treated MAR-M247 samples are investigated using optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and Vickers microhardness measurements. The crack-free deposits obtained here for MAR-M247 represent one of the first few successes reported for a non-weldable alloy of its kind. The results demonstrate that the SLE process has significant potential for the AM-based repair of existing and fabrication of entirely new gas turbine hot-section components utilizing feedstocks of high γ′ content nickel-base superalloy powders. The results also establish that MAR-M247 is an attractive material for the LPBF-based AM processes.