Effect of boron addition on microstructure and mechanical properties of an additively manufactured superalloy

The effect of boron addition (0.010, 0.015, and 0.020 wt.%) on the microstructure and mechanical properties of an additively manufactured superalloy was examined. The as-built microstructure was investigated by scanning electron microscopy and transmission electron microscopy. The results demonstrate that boron precipitates as M₃B₂ boride at the grain boundary. The increase in boron content increases the amount of γ/γ′ eutectic and the size and fraction of M₃B₂ boride. Boron creates nanoscale fine borides at grain boundaries, which significantly reinforces grain boundaries. The mechanical property analysis indicated that the addition of boron improved the tensile ductility at 760 °C and stress rupture properties at 760 °C/780 MPa. However, with the excessive addition of boron, the mechanical property was reduced.