UC San Diego

High entropy alloys are newly discovered class of metal alloys. It gains many researchers’ attention due to their good and exceptional mechanical properties. This work aims to examine CoCrFeMnNi mechanical response at different strain rates and temperatures. In addition, to studying the adiabatic shear band evolution and the mechanism of grains refinement inside the shear band. Microhardness were also measured inside and outside the shear band. The microstructure was examined by optical microscopy, SEM, EBSD and TEM.

CoCrFeMnNi improve its strength with lowering temperature and increasing the strain rate. In addition, adiabatic shear bands were clearly overserved in CoCrFeMnNi hat shape specimens at 153K and 300K. The grains inside the shear band were extremely refined to equiaxed nanograins at 153K while grains were refined to ultrafine equiaxed grains at the test conducted at 300K.

There were dual refinement mechanisms; the deformation twinning and rotational dynamic recrystallization. The initial average grain size was 10 µm while the refined equiaxed nanograins were between 0.05-0.2 µm for 153K test while between 0.25-0.35 µm for 300K test. TEM images shows evidence that the difference in the refinement factor for these tests is due to the increase of twinning density at lower temperature for specimen tested at 153K. CoCrFeMnNi show excellent microharndess inside the shear band and superior property compared with 316L austenitic stainless steel.

Adiabatic shear band was also observed in finite element model. The numerical model shows good approximation with the actual results and also used to validate the developed Johnson Cook plasticity model.