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 (∼6 nm) could be obtained after 30 min of HEBM. The influence of milling time (30 ÷ 240 min) on structural and magnetic transformations of CuCrFeTiNi powder mixture was investigated. The HEA powders were thermally stable up to 500°С based on DSC results. The HEA powder was subsequently consolidated by spark plasma sintering at 700 °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 (Im3m) structure. Annealing at 600°С (t = 180 min) increased the crystallinity of the α-phase (bcc) and gave rise to formation of the γ-phase (fcc, Fm3m) whose amount grew with increasing dwell time. Between 800 and 1000°С, a tetragonal intermetallic σ-phase – most likely FeCr - appeared and subsequently vanished. At 1000°С, the final product was found to contain two solid solutions based on the γ-phase (fcc). The Vickers hardness HvHEBM = 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 (Hv = 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 TC ∼50 K was found.