Influence of the TiB2 content on the processability, microstructure and high-temperature tensile performance of a Ni-based superalloy by laser powder bed fusion

Abstract

The nickel-based GH3230 (Haynes 230) superalloy is widely used in the aerospace and power industries because of its excellent high-temperature strength and thermal stability. Owing to the crack susceptibility, however, GH3230 alloy offers poor processability processed by the laser powder bed fusion (LPBF) process. This paper systematically studies the processability, microstructure and high-temperature tensile performance of LPBF-fabricated GH3230 material modified by the addition of sub-micrometre TiB 2 particles. The results reveal that the addition of TiB 2 particles contributed to improving the processability of this alloy during the LPBF process. Also, the microcracking in LPBF-fabricated pure-GH3230 was addressed in the present study by introducing 1 wt% or 2 wt% sub-micrometre TiB 2 particles to GH3230 powder. When the addition of TiB 2 was up to 3 wt%, however, micro-cracks formed again. The micro-CT results confirmed that micro-cracks were the primary defects in the fabricated pure-GH3230 specimen, while only a limited number of open pores were detected in GH3230–1 wt% TiB 2 and GH3230–2 wt% TiB 2 specimens. The micro-cracks were categorised to solidification and solid-state cracking in terms of their formation mechanisms and characteristics. The yield-strength values of LPBF-fabricated GH3230–1 wt% TiB 2 and GH3230–2 wt% TiB 2 at 850 °C were examined to 254 MPa and 311 MPa, respectively, which were 29% and 59% higher than pure-GH3230. Compared to pure-GH3230, the elongation values of GH3230–1 wt% TiB 2 and GH3230–2 wt% TiB 2 were also significantly improved because of the elimination of micro-cracks. This work provides an effective route to eliminate cracks and to improve mechanical properties for Ni-based superalloys. • Microcracks categorised to solidification cracking and solid-state cracking. • Microcracking elimination achieved by introducing 1 wt% and 2 wt% TiB 2 . • The addition of 3 wt% TiB 2 enabled the formation of microcracks. • TiB 2 improved both laser absorption and thermal conductivity of the powder bed.