The Study Of Microstructures And Tribological Properties Of Al_xCrCuFeNi₂ High Entropy Alloys

Since the concept of high entropy alloys formally put forward in 1995, high entropy alloys had attracted wide attention of many scholars both at home and abroad with follow-up research and reports, due to the advanced concept, simple crystal structure and excellent properties. Based on the widely reported Al-Co-Cr-Cu-Fe-Ni alloys, the new Al-Cr-Cu-Fe-Ni₂ alloys were designed. This paper mainly studied the microstructure and tribological properties of Al_xCrCuFeNi₂ high entropy alloys with different content of Al element.The high entropy alloys were prepared using the WKFEI non-consumable vacuum arc furnace. The phase composition and microstructure of high entropy alloys were analysed by the metallographic microscope, Ricoh D/MAx-RB X-ray diffractometer, and JEOL JMS-6390 scanning electron microscopy（SEM） analysed. The hardness was calculated by HVS-1000 Vickers hardness test. The tribological performances of high entropy alloys under dry sliding condition, deionized water and simulated rainwater were conducted on the reciprocating friction and wear testing machine（MFT-R4000）. High temperature pin-disk friction and wear rig was selected for high temperature sliding text. The effect of meterial structure, test environment and load on the tribological properties of the alloys was investigated in detail. The results showed that:For Al_xCrCuFeNi₂（x = 1.0, 1.3, 1.8） high entropy alloy system, with the increase of Al element content, the crystalline structure of the alloy system was transformed from simple face-centered cubic（FCC） structure to the body centered cubic（BCC） structural, and the hardness presented a tendency of increasing. When x = 1.8, the Fcc structure was completely replaced by Bcc, and the hardness reached the highest at the same time.The high entropy alloy with 1.3 mole ratio of Al possessed the highest wear resistance, and the lowest wear rate. The friction coefficient fluctuation tended to be decreased, and wear rate was lower with the increase of load. The main wear mechanism was abrasive wear for the alloy. As the AlCrCuFeNi2 alloy had lowest hardness and severe element segregation, the friction surface produced many cracks and ferice plastic deformation. The main wear mechanism is adhesion, oxidation and fatigue. Besides, the wear resistance was the lowest.In the deionized water, the friction coefficient curves of high entropy alloys showed significantly flat. The wear traces were smooth level off with slight wear and tear, and the wear rate was lower an order of magnitude than that in the dry grinding. In addition, in the same conditions, for high content of aluminum alloy（x = 1.3, 1.8）, the wear rate was much lower than that of AlCrCuFeNi₂ alloy whose aluminum content was low, which was lowed by more than 75%.In the simulate rainwater, the wear surface was left much tiny corrosion mud, illustrating that the corrosion wear took place. Electrochemical tests in the simulated rainwater were conducted to further testify the alloys corrosion property. It was showed that the corrosion potential of the three kinds of alloys was similar, while the corrosion current density of Al_1.3CrCuFeNi₂ alloy was the lowest. In addition, two high entropy alloys with high aluminum content occured twice passivation with a long second passivation time over 750 mV. During the time, the effective protective membrane was formed on the surface to improve the corrosion resistance of alloy. In the process of sliding friction, Al1.3CrCuFeNi2 alloy showed the higher corrosion resistance and wear resistance.