Microstructure and selected properties of the solution heat-treated MAR-M247 Ni-based superalloy fabricated via directional solidification

Abstract

This work focuses on MAR-M247 Ni-based superalloy manufactured via directional solidification at various withdrawal rates (3.4 or 5.0 mm/min) and shell mold temperatures (1510 °C or 1566 °C) after solution heat-treatment (SHT). Observations and analyses of four casting variants were carried out using thermodynamic simulations, differential scanning calorimetry (DSC), X-ray diffraction (XRD), light microscopy (LM), scanning electron microscopy (SEM), X-ray spectroscopy (EDX), and tensile tests at ambient temperature. The solidus and liquidus temperatures were very similar for all variants and were in the range of 1263–1264 °C and 1356–1359 °C, respectively. The presence of the γ, γ′, MC carbides, and M5B3 phases was confirmed. Microstructure differences were observed depending on the manufacturing parameters. The castings’ dendritic regions consisted of γ′ precipitates surrounded by the matrix, with a mean size ranging from 0.203 to 0.250 μm, depending on the casting parameters. The amount of the MC carbides in the interdendritic spaces was in the range of 1.87–1.92%. The tensile tests determined that castings produced with preheat temperature of 1566 °C were characterized by higher elongation and slightly lower yield strength in comparison to 1510 °C.