Influence of Nb content on phase precipitation behavior of new Ni–Co-based superalloys by selective laser melting

Abstract

In this paper, the evolution of the γ′ and η phases of new Ni–Co-based superalloy with different Nb contents was investigated using a combination of thermodynamic calculations and high-throughput selective laser melting (SLM). Thermodynamic calculations show that the increase of Nb content lowered the solubility temperature of the γ′ phase and caused the precipitation of the η phase. The alloys with the Nb gradient content prepared by SLM during aging at 800 °C for 100h indicated that the maximum volume fraction and size of the γ′ phase reach the maximum at 3.0–3.5% Nb. The elongated η phases enrichment in Ni, Ti, and Nb atoms precipitate for the Nb content higher than 2.2% Nb and prefer to grow longitudinally at the expense of the γ′ precipitates. Combining the influence of the Al/(Nb + Ta + Ti) ratio on the η precipitates, the addition of Nb content in the Ni–Co-based superalloys is less than 2.2%, which increases the high-temperature yield strength and tensile strength.

Keywords

• Ni-Co-based superalloys
• High-throughput preparation
• Selective laser melting
• Microstructure
• Precipitation