Effect of matrix reversible transition on mechanical and tribological properties of a novel Co-free high-entropy alloy

A novel Co-free Al0.7CrFeMnNi1.3 high-entropy alloy (HEA) was prepared and followed by annealing treatment at 400-1000degree celsius for 2 h to investigate the effect of microstructure evolution on compression and tribological properties. The results reveal that as-cast/annealed alloy exhibits the dendrite structure, and trimodal distribution of B2 precipitates along with inverse precipitated BCC phase is also observed before and after annealing. However, the matrix is firstly transformed from BCC to a phase, and then reversed back to BCC phase due to an increasing of annealing temperature. The element distribution of as-cast/annealed alloy indicates the reversible transition between BCC and a phase is achieved by local rearrangement of atom, instead of conventional diffusion nucleation and growth. The trimodal distribution of B2 precipitates on BCC matrix results in excellent compression property (the yield strength of 1023-1164 MPa, and the total ductility of 45-52 %), and the strengthening increments are mainly attributed to precipitation strengthening of nanoscale B2 and spherical B2 precipitates, and grain-boundary strengthening mechanism of rod-shaped B2 precipitates. Compared with the traditional form of precipitation phase formed by diffusion nucleation and growth, the non-diffusion formation mechanism of a phase makes the hardening effect show a characteristic of fast response and non-overaging, which significantly improving wear resistance of alloy. The formation of a phase does not change the dominant abrasive wear mechanism, but which is transformed into delamination wear mechanism due to the coarsening of B2 precipitates.