Semi-solid Thixotropic Behavior and Microstructure Evolution of Cold Deformed CoCrCu1.2FeNi High-Entropy Alloy

The high entropy alloys (HEAs) of dual FCC have great potential for semi-solid processing. Therefore, at tem-peratures of 1130-1225 degrees C and strain rates of 0.1-10 s ? 1 isothermal deformation, semi-solid thixotropic behavior and microstructure evolution of the deformed CoCrCu1.2FeNi HEA were investigated by scanning electron mi-croscopy (SEM), differential scanning calorimetry (DSC), optical microscopy (OM), and electron backscattered diffraction (EBSD). The results show that the original billet is a deformed microstructure consisting of dual FCC structure. The alloy exhibits a typical stress-strain curve at the low strain rate. When the strain rate is larger than 0.5 s- 1, the stress-strain curves show two peaks. The apparent viscosity decreases with an increase of shear rate and deformation temperature, indicating that the shear thinning effect occurs. Semi-solid compression leads to uneven plastic deformation. According to the degree of plastic deformation, the sample is divided into hard deformation zone, large deformation zone, transition deformation zone and free deformation zone. The flow stresses, liquid phase fraction and deformation mechanisms of the solid particles can lead to variations in the microstructure of the different zones. The roundness of the grains increases and then decreases as the temper-ature rises, while the grain size fluctuates in the large deformation zone. Phase structure is not changed during semi-solid deformation, but it can weaken the segregation of Cu at low temperatures and low strain rates during isothermal deformation. The strain rate is the main factor affecting recrystallization, the degree of recrystalli-zation increases with increasing temperature at low strain rates, and a large amount of deformation micro-structure is produced at high strain rates.