Microstructures, mechanical properties and corrosion resistances of FCC CoCrFeNiTi high-entropy alloys prepared by pre-alloyed powder mixing and vacuum laser-directed energy deposition

In this study, vacuum laser-engineered directed energy deposition (V-LDED) was employed to fabricate CoCrFeNiTi_x (x = 0.1, 0.2, 0.3) high-entropy alloys (HEAs) by strategically mixing equiatomic pre-alloyed CoCrFeNi and CoCrFeNiTi powders. With increasing Ti content, the lattice distortion of the HEAs intensified, grains were refined, and precipitate content increased; however, the face-centered cubic (FCC) structure remained the predominant structure. The strength and plasticity of the HEAs initially increased and then decreased with the addition of Ti. The CoCrFeNiTi_0.3 (Ti0.3) alloy exhibited the best mechanical properties, with a tensile yield strength (TYS) of 604 MPa, an ultimate tensile strength (UTS) of 882 MPa, and a plastic elongation of 13.5%. Compared to the Ti-free alloy, the TYS and UTS were increased by 124% and 83%, respectively. The CoCrFeNiTi_0.2 (Ti0.2) alloy showed the best corrosion resistance with the corrosion potential (E_corr), corrosion current density (I_corr), passivated film resistor (R_c), and charge transfer resistance (R_ct) values of –0.208 V, 4.889 × 10^–7 A/cm², 7.03 × 10³ Ω/cm², and 8.50 × 10⁵ Ω/cm², respectively. The addition of Ti increased the Cr and Ti contents in the passive film, which are easily passivated elements. The multiple effects of Ti on the corrosion resistance were mainly attributed to the formation and composition of the passive film and density of the precipitates.