γ′ Precipitation Study of a Co-Ni-Based Alloy

Abstract

A Co-Ni-based alloy strengthened by '-(L1 2) precipitates was utilized to investigate the precipitation evolution after various cooling rates and several aging conditions. In this study, the precipitate size and volume fraction have been studied via scanning electron microscopy and transmission electron microscopy. The influence of the precipitation evolution was measured via microhardness tests. The cooling rate study shows a more sluggish ' precipitation reaction compared with that observed in a Ni-based superalloy. Following a rapid cooling rate, the application of appropriate double aging treatments allows the increase of the ' volume fraction as well as the control of the size and distribution of the precipitates. The highest hardness values reach those measured on supersolvus cast and wrought Ni-based superalloys. The observed ' precipitation behavior should have implications for the production, the heat treatment, the welding or the additive manufacturing of this new class of high temperature materials.

Microstructure and compression strength of Co-based superalloys hardened by γ′ and carbide precipitation

“…Besides, the eutectic formation under the oxidation line during the heat treatment activate the oxygen reaction. Following this idea, the oxidation behaviour is being studied in alloys with Ni, where the addition of Cr, Si and Al improve the oxide protect line [61,62].…”

Interplay between solidification microsegregation and complex precipitation in a γ/γ’ cobalt-based superalloy elaborated by directed energy deposition

“…In high γ'-phase fraction nickelbased superalloys as in Udimet 720LI, CM247LC or IN939, intergranular solid state cracks are observed following subsolvus temperature holding [2][3][4][5]. In the case of cobaltbased superalloys, they exhibit slower γ'-phase precipitation kinetics even with a high γ'-phase volume fraction that causes less hardening at high cooling rates than nickelbased superalloys [6]. This feature is expected to preserve them from strain-age cracking, making them particularly attractive in AM as substitutes for nickel-based superalloys with a high γ'-phase fraction.…”