Effects of Annealing Temperatures on Mechanical Behavior and Penetration Characteristics of FeNiCoCr High-Entropy Alloys

In this paper, the mechanical properties, penetration characteristics, and deformation behaviors of FeNiCoCr high-entropy alloys (HEAs) annealed at different temperatures were investigated. The quasi-static and dynamic compression tests were conducted by a universal testing machine and Split Hopkinson Pressure Bar (SHPB) system, respectively. Furthermore, the penetration experiments of long rod projectiles (LRPs) of FeNiCoCr HEAs into semi-infinite steel targets launched by a small caliber ballistic gun with velocities ranging from 650 m/s to 1500 m/s were carried out, in comparison with that of steel LRPs. The microstructures of recovered projectiles were observed by the X-ray diffraction, optical microscope, and transmission electron microscope, which were used to further analyze the deformation behaviors of FeNiCoCr HEAs. The results showed that FeNiCoCr HEAs owned a single face-centered cubic structure. Annealing twins and grain refinement were detected, affecting the yield strength of the alloys. The strength of the alloy annealed at 600 degrees C was the highest and then decreased with the increasing annealing temperature. At higher strain rates, special adiabatic shear characteristics occurred in the alloys, while twins dominated the whole deformation process of the projectiles. Compared to other annealed alloys, the alloy annealed at 600 degrees C performed the best penetration performance. While the impact velocity had significant effects on the penetration performance of the alloy annealed at 1000 degrees C, the penetration performance of the alloy annealed at 850 degrees C on steel targets was almost the same as that of the steel LRPs.