Development of a Refractory High Entropy Superalloy

Oleg Senkov,Dieter Isheim,David Seidman,Adam Pilchak

doi:10.3390/e18030102

Oleg Senkov, Dieter Isheim + Show 2 more

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https://doi.org/10.3390/e18030102

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Abstract

Microstructure, phase composition and mechanical properties of a refractory high entropy superalloy, AlMo0.5NbTa0.5TiZr, are reported in this work. The alloy consists of a nano-scale mixture of two phases produced by the decomposition from a high temperature body-centered cubic (BCC) phase. The first phase is present in the form of cuboidal-shaped nano-precipitates aligned in rows along <100>-type directions, has a disordered BCC crystal structure with the lattice parameter a1 = 326.9 ± 0.5 pm and is rich in Mo, Nb and Ta. The second phase is present in the form of channels between the cuboidal nano-precipitates, has an ordered B2 crystal structure with the lattice parameter a2 = 330.4 ± 0.5 pm and is rich in Al, Ti and Zr. Both phases are coherent and have the same crystallographic orientation within the former grains. The formation of this modulated nano-phase structure is discussed in the framework of nucleation-and-growth and spinodal decomposition mechanisms. The yield strength of this refractory high entropy superalloy is superior to the yield strength of Ni-based superalloys in the temperature range of 20 °C to 1200 °C.

Highlights

Future hypersonic vehicles and turbine engines will require revolutionary new structural alloys, which can survive extreme temperature and loading conditions, are simultaneously ductile and tough, and are able to meet unusually demanding design requirements [1]
Current high-temperature ceramics and intermetallics are incapable of meeting these requirements due to low toughness, while advanced
Microstructural analyses indicate that the AlMo0.5NbTa0.5TiZr refractory high entropy alloys (RHEAs) was essentially a single-phase body-centered cubic (BCC) structure at the annealing temperature, 1400 °C

Summary

Introduction

Future hypersonic vehicles and turbine engines will require revolutionary new structural alloys, which can survive extreme temperature and loading conditions, are simultaneously ductile and tough, and are able to meet unusually demanding design requirements [1]. Ni-based superalloys are approaching possible extreme property combinations with respect to their evolution and development; i.e., they still suffer from high density and their maximum temperature use is limited by melting at ~1250–1300 ̋ C. New metallic materials with higher melting points, such as. The concept of high entropy alloys (HEAs) is one of the most recent developments in material science [6]. Depending on their compositions and microstructures, HEAs offer a diverse range of attractive properties, such as high microhardness and wear resistance, exceptional mechanical properties and oxidation resistance [7,8,9].

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