Development of a Refractory High Entropy Superalloy (Postprint)
AFRL Materials and Manufacturing Directorate Wright Patterson Air Force Base United States
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Microstructure, phase composition and mechanical properties of a refractory high entropy super alloy, AlMosub 0.5NbTasub 0.5TiZr, 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 asub 1 326.9 plus or minus 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 asub 2 330.4 plus or minus 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 super alloy is superior to the yield strength of Ni-based super alloys in the temperature range of 20 degrees C to 1200 degrees C.
- Metallurgy and Metallography