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

This study employed vacuum laser-engineered directed energy deposition (V-LDED) to fabricate CoCrFeNiTix (x = 0.1, 0.2, 0.3) high-entropy alloys (HEAs) through strategic mixing of equiatomic CoCrFeNi and CoCrFeNiTi pre-alloy powders. With the increase of Ti content, the lattice distortion of the HEAs was intensified, the grains were refined and the precipitates content were increased, but the face-centered cubic (FCC) structure remained the predominant structure. Both of the strength and plasticity of the HEAs increased first and then decreased as the addition of Ti. Ti0.3 alloy exhibited the best mechanical properties with a tensile yield strength (TYS) of 604 MPa, a ultimate tensile strength (UTS) of 882 MPa and a plasticity elongation of 13.5%. Compared with Ti-free alloy, the TYS and UTS were reinforced by 124% and 83%, respectively. Ti0.2 alloy showed the best corrosion resistance with an Ecoor of -0.208 V, an Icoor of 4.889×10-7 A/cm², a Rc of 7.03*103 /cm2 and a Rct of 8.50*105 /cm2. The addition of Ti could increase Cr and Ti content in the passive film, which are easily passivated elements such as. The multi-effect of Ti on corrosion resistance was mainly attributed to the formation and composition of the passive film, and the density of precipitates.