Microstructures and Mechanical Properties of AlCrFeNiMo_0.5Ti_x High Entropy Alloys

Effects of Ti addition on the microstructures and mechanical properties of AlCrFeNiMo_0.5Ti_x (x=0, 0.25, 0.4, 0.5, 0.6, 0.75) high entropy alloys (HEAs) are investigated. All these HEAs of various Ti contents possess dual BCC structures, indicating that Ti addition does not induce the formation of any new phase in these alloys. As Ti addition x varies from 0 to 0.75, the Vickers hardness (HV) of the alloy system increases from 623.7 HV to 766.2 HV, whereas the compressive yield stress firstly increases and then decreases with increasing x above 0.5. Meanwhile, the compressive ductility of the alloy system decreases with Ti addition. The AlCrFeNiMo_0.5Ti_0.6 and AlCrFeNiMo_0.5Ti_0.75 HEAs become brittle and fracture with very limited plasticity. In the AlCrFeNiMo_0.5Ti_x HEAs, the AlCrFeNiMo_0.5 HEA possesses the highest compressive fracture strength of 4027 MPa and the largest compressive plastic strain of 27.9%, while the AlCrFeNiMo_0.5Ti_0.5 HEA has the highest compressive yield strength of 2229 MPa and a compressive plastic strain of 10.1%. The combination of high strength and large plasticity of the AlCrFeNiMo_0.5Ti_x (x=0, 0.25, 0.4, 0.5) HEAs demonstrates that this alloy system is very promising for engineering applications.