Influence of cooling rate on the microstructure and room temperature mechanical properties in the refractory AlMo0.5NbTa0.5TiZr superalloy

Refractory chemically complex alloys with bcc-based microstructures show great potential for high-tem-perature applications but most of them exhibit limited room-temperature ductility, which remains a challenge. One such example is the AlMo0.5NbTa0.5TiZr alloy, mainly consisting of a nano-scaled structure with an ordered B2 matrix and a high-volume fraction of aligned cuboidal and coherently embedded A2 precipitates. This work aims to investigate how the cooling rate after hot isostatic pressing of the AlMo0.5NbTa0.5TiZr alloy affects its microstructure and its resulting hardness and fracture toughness at room temperature. A slow cooling rate of 5 degrees C/min leads to a coarse microstructure consisting of aligned slabs (mean A2 precipitate approximate to 25 nm) with a nanohardness of about 8 GPa. In contrast, after the fastest cooling rate (30 degrees C/min), the A2 precipitates become more cubic with an edge length of approximate to 16 nm, resulting in an increase in nanohardness by 10 %. The fracture toughness is roughly independent of the cooling rate and its mean value (approximate to 4.2 MPa center dot m1/2) resembles that of some B2 intermetallics and other A2/B2 alloys. As the lattice misfit between the A2 and B2 phases is known to play a key role in microstructure formation and evolution, its temperature dependence between 20 and 900 degrees C was investigated. These findings offer in-sights into the evolution of the microstructure and room-temperature mechanical properties of the AlMo0.5NbTa0.5TiZr alloy, which could help the development of advanced chemically complex alloys.(c) 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http:// creativecommons.org/licenses/by/4.0/).