Phase Decomposition of a Single‐Phase AlTiVNb High‐Entropy Alloy after Severe Plastic Deformation and Annealing

Abstract

An equiatomic AlTiVNb high-entropy alloy is deformed by high pressure torsion inducing a nanocrystalline microstructure. The samples then are subjected to isochronal heat treatments between 300 C and 1000 C. The hardness increase from %7.4 GPa for the as-processed state to 10.4 GPa for an annealing temperature of 700 C, while for higher temperatures the hardness starts to decrease. Furthermore, the reduced modulus increases after annealing treatments as well. It will be shown that the unusual annealing response can be related to the formation of intermetallic phases creating a multi-phase nanocomposite material during annealing. The results give new insights into the thermodynamic stability of this alloy, which are also relevant for coarser-grained microstructures.

Phase Engineering of High‐Entropy Alloys

“…The transformation between solid‐solution phase and intermetallic‐compound phase can be achieved by heat treatment. Schuh et al found that the internal friction and defect structure of equiatomic AlTiVNb nanocrystalline HEA were reduced under the annealing treatment, making the reduced modulus close to the modulus of coarse grains 111. Once the modulus getting closed to saturation, the HEA began to form intermetallic‐compound phase.…”

“…Schuh et al found that the internal friction and defect structure of equiatomic AlTiVNb nanocrystalline HEA were reduced under the annealing treatment, making the reduced modulus close to the modulus of coarse grains. [111] Once the modulus getting closed to saturation, the HEA began to form intermetalliccompound phase. Similarly, Dai et al found that the abundant grain boundaries in nanocrystalline HEA provided a pathway for the rapid diffusion of elements along the grain boundary at a low-temperature annealing condition.…”

Nanostructured high-entropy materials

“…Compared with 3d transition HEAs, the grain sizes that can be achieved in these alloys are much larger, typically in the range of 40-50 nm. Processing via HPT does not affect this average grain size range and has been used to produce singlephase BCC HEAs by Schuh et al [42,43].…”

Metastability in high-entropy alloys: A review

“…An abundance of investigations have emerged in the literature focusing on microstructural characteristics, defect evolution as well as mechanical properties for HEAs after SPD. [99][100][101][102][103][104][105][106][107][108][109] A recent work by Bhattacharjee et al 106 reported that the nanolamellar AlCoCrFeNi 2.1 HEA, which was achieved by cryorolling and annealing processes, exhibited a remarkable increase in both the yield strength and the ultimate tensile strength (UTS) without sacrificing too much ductility [ Fig. 8(a)].…”