Structural evolution and magnetic properties of high-entropy CuCrFeTiNi alloys prepared by high-energy ball milling and spark plasma sintering

A powder of equiatomic CuCrFeTiNi high-entropy alloy (HEA) was prepared by short-term (30 min) high-energy ball milling (HEBM). Our structural and chemical analysis showed that micron sized particles of bcc CuCrFeTiNi consisting of nanosized crystalline grains (similar to 6 nm) could be obtained after 30 min of HEBM. The influence of milling time (30 divided by 240 min) on structural and magnetic transformations of CuCrFeTiNi powder mixture was investigated. The HEA powders were thermally stable up to 500 degrees C based on DSC results. The HEA powder was subsequently consolidated by spark plasma sintering at 700 degrees C resulting in a consolidated bulk HEA with co-existing bcc and fcc phases. The as-milled CuCrFeTiNi powder blend contained a solid solution with bcc (Imam) structure. Annealing at 600 degrees C (t = 180 min) increased the crystallinity of the alpha-phase (bcc) and gave rise to formation of the gamma-phase (fcc, Fm3m) whose amount grew with increasing dwell time. Between 800 and 1000 degrees C, a tetragonal intermetallic phase - most likely FeCr - appeared and subsequently vanished. At 1000 degrees C, the final product was found to contain two solid solutions based on the gamma-phase (fcc). The Vickers hardness H-v(HEBM) = 7.7 GPa of the SPS consolidated CuCrFeTiNi alloy (milled for t = 180 min) was markedly higher than the one of SPS-produced ones without HEBM (H-v = 2.1 GPa). Paramagnetic behavior at room temperature with a small ferromagnetic contribution at low fields was observed for as-milled powder after 180 min of HEBM. A small magnetic hysteresis was observed at 5 K and 300 K with a coercive field of around 16 kA/m. Above 100 K, the inverse susceptibility of a HEA powder ball-milled for t = 240 min showed a clear paramagnetic response. The Curie temperature T-c similar to 50 K was found. (C) 2019 Elsevier B.V. All rights reserved.