Effects of the phase content on dynamic damage evolution in Fe50Mn30Co10Cr10 high entropy alloy

The Fe50Mn30Co10Cr10 high entropy alloy with different martensite phase content were dynamic loaded at 190 m/s and 420 m/s impact velocity respectively by one-stage light gas gun. The effect of phase content on dynamic damage evolution in this alloy was firstly studied. Results showed that after hot-rolling and quenching (HRQ), the mass percentage of martensite in the HRQ sample was 28.3 wt%, and the size of martensite aggregated area (M area) was large (∼49 μm). The sample cold-rolled and quenched (CRQ) after HRQ treatment had more martensite (46 wt%), and M areas in the CRQ sample were uniformly distributed and relatively smaller (∼10 μm) than that of the HRQ sample. Voids nucleated in the matrix where the impact impedance was lower than the martensite. The compressive residual stress in the M area and tensile residual stress in the matrix induced by the martensitic transformation inhibited and promoted nucleation of voids. The uniform distributed tensile residual stress areas with smaller size in the CRQ sample was more, which led to the more nucleation sites, higher nucleation density, and higher initial damage rate. Meanwhile, voids were difficult to coalesce due to larger space between voids and limit of growth by the small-sized M areas, thus the damage evolution rate of the CRQ sample was relatively lower. Therefore, the spall strength of the CRQ sample (1.89 GPa) was smaller than that of the HRQ sample (2.21 GPa) under the impact velocity of 190 m/s. Microcrack propagation “avoided” the small-sized and uniformly distributed M area, so the turning path and direction deviation of microcrack were shorter and smaller. Then the microcracks in the CRQ sample tended to coalesced into a large-sized crack, which lead to a higher crack propagation rate and lower spall strength of the CRQ sample (1.98 GPa) under higher impact velocity of 420 m/s. Furthermore, the microcrack in the CRQ sample could propagate along a “coalescence path” that formed at the interface of the adjacent M areas, which may have further increased the rate of crack propagation, and resulted in the lower spall strength of the CRQ samples.