Niobium Base Superalloys: Achievement of a Coherent Ordered Precipitate Structure in the Nb Solid-Solution

Abstract

In a previous work, the chemical elements necessary for the achievement of Niobium base superalloys were defined in order to get a structure equivalent to that of Nickel base superalloys, which contain ordered precipitates within a disordered solid-solution. It was especially emphasized that precipitation hardening in the Niobium matrix would be possible with the addition of Ni. The remaining question about the design of such Niobium superalloys concerned the achievement of ordered precipitates in crystalline coherence with the Nb matrix i.e., with a crystalline structure equivalent to the Nb crystal prototype and with a lattice parameter in coherency with that of the Nb matrix. In order to reduce the trial/error experimental work, a reasoning based on various data for the achievement of coherency is presented. Then, starting from the Nb-Hf-Ni ternary alloy thus defined, this paper demonstrates that the precipitation of an ordered Nb phase within a disordered Nb matrix can be achieved with lattice parameter coherency between the ordered precipitates and the disordered matrix. The chemistry and the crystallographic structure of the precipitates were characterized using Transmission Electron Microscopy and Atom Probe Tomography. These results can help to conceive a new family of Nb base superalloys.

Preparation of VZrHfNbTa High-Entropy Alloy-Based High-Temperature Oxidation-Resistant Coating and Its Bonding Mechanism

“…Therefore, niobium-based alloys have received attention due to the lower liquid-phase line temperature and the limitation of their melting point, but their limit service temperature [8] can no longer meet the temperature-bearing capacity required for advanced aero-engines [9]. Although niobium-based alloys have ideal high-temperature mechanical properties [10,11], they suffer from serious oxidation problems at high temperatures [12,13], for example, niobium-silicon-based alloys. The alloys currently used in industry have problems in the high-temperature oxidation environment such as pulverization and mechanical property imbalance.…”

Additive manufacturing of high-strength multiphase nanostructures in the binary Ni–Nb system for the discovery of new types of superalloys

“…However, processability of alloys with large fractions of intermetallic phases, which can have extraordinary strength at high temperature but are typically brittle at low temperature, remains a significant obstacle [11]. Refractory-based superalloys, with significantly higher melting temperatures and higher specific strengths (i.e., ratio of strength-to-density), are a tantalizing prospect, though processing is extremely challenging or simply impractical using traditional methods like casting and hot-and cold-working processes [12][13][14][15][16][17][18].…”