Studies on the microstructure and properties of AlxCoCrFeNiTi1-x high entropy alloys

Highlights: • The influence of Al being replaced partially by Ti on Al_xCoCrFeNiTi_1-x is discussed. • Al_xCoCrFeNiTi_1-x (x = 1.0, 0.8, 0.5) alloys have good mechanical properties. • Al_xCoCrFeNiTi_1-x (x = 1.0, 0.8, 0.5) alloys present excellent corrosion resistance. • Increased Ti-content in Al_xCoCrFeNiTi_1-x promotes the formation of the FCC phase. • Ti's small substitution to Al cannot improve the corrosion resistance. Al_xCoCrFeNiTi_1-x (x = 1.0, 0.8, 0.5 in molar ratio) high entropy alloys (abbreviated as Al-1.0, Al-0.8, Al-0.5 in the paper) were fabricated by repeated arc-melting and casting under vacuum. the effects of Al being replaced partially by Ti on the microstructure, mechanical properties and corrosion resistance in the solutions of 3.5 wt% NaCl, 0.5 mol/L NaOH and 0.5 mol/L H₂SO₄ were studied. The microstructure analysis showed that the Al-1.0 is mainly composed of single-phase BCC solid solution, while the Al-0.8 and the Al-0.5 consist of BCC and FCC biphasic solid solutions. With the increase of Ti atomic content, the elemental segregation intensifies, the FCC phase increases, and the BCC phase decreases. The results of hardness test and compressive test showed that all of the three alloys have good comprehensive mechanical properties, especially the Al-0.8. In the NaCl and NaOH solutions, the Al-1.0 and the Al-0.5 have similar corrosion resistance, but the Al-1.0 is a better choice out of economic consideration. In the H₂SO₄ solution, the Al-0.5 has the best corrosion resistance, followed by the A1-1.0 and the Al-0.8. A small amount of Ti addition in Al_xCoCrFeNiTi_1-x cannot offset the negative effects of the biphasic structure and the intense elemental segregation on the corrosion resistance and the corrosion resistance can be improved obviously Only when the atomic percentage of Ti exceeds that of Al.