Titanium doping levels and their effects on FeCoCrNi high-entropy alloys: From microstructure to performance

FeCoCrNi High-entropy alloys (HEAs) are renowned for their exceptional ductility and corrosion resistance but often lack sufficient strength and wear resistance. Introducing of titanium (Ti) into HEAs is a recognized strategy to enhance overall performance. This study systematically investigates the effects of varying Ti doping levels (1, 3, 7, and 9 at. %) on the microstructure and performance of FeCoCrNi HEAs. The results indicate that Ti doping induces significant lattice distortion, leading to a heterogeneous microstructure and precipitations. Mechanical tests reveal that hardness, yield strength, and ultimate tensile strength increase with Ti doping, though at the expense of ductility. Specifically, the alloy with 7 at. % Ti doping demonstrates the most balanced mechanical properties, achieving a product of strength and elongation (UTS x delta) of 35,742 MPa%. This balance is attributed to the synergistic effects of solid solution strengthening, grain boundary strengthening, and precipitation strengthening. Furthermore, this alloy also exhibits the lowest coefficient of friction and wear rate. However, due to a more pronounced tendency for galvanic corrosion in alloys with higher Ti doping levels, electrochemical corrosion tests show that the alloy with 1 at. % Ti doping has superior corrosion resistance. This study highlights that the appropriate incorporation of Ti into FeCoCrNi-based HEAs can significantly enhance overall performance. Nevertheless, selecting the optimal Ti content requires careful consideration of specific usage scenarios to balance improved mechanical and tribological properties with potential impacts on corrosion resistance.