The Research On Structure And Properties Of FeCoCrNiCu_0.5Al（Si）_X High Entropy Alloys

The design of traditional alloy is based on some main performances to select a principal component (the general content is more than50%) and through the alloying process to improve primary properties and satisfy the secondary performance requirement, such as iron-based iron and steel materials, Mg-based magnesium alloy and Al-based aluminium alloy. High entropy alloy is a new concept of the alloy which was put forward in nineteen ninties, and it has a number of excellent properties incomparable to traditional alloys, such as high strength, high hardness, high wear and corrosion resistance, high electrical resistivity. Therefore, the high entropy alloy becomes a new research focus in the materials science.In this paper, the FeCoNiCrCu0.5Alx high entropy alloys (x values in molar ratio, x=0.5,1.0,1.5, denoted by Al0.5, Al1.0, Al1.5, respectively) were prepared by vacuum arc melt casting. The effects of Al content and heat treatment on structure, hardness, electrochemical properties and magnetic properties of FeCoNiCrCu01.5Alx high entropy alloys were studied. The thermal stability of FeCoNiCrCu0.5Alx high entropy alloys decreased, and the stable structure of alloys transform from FCC structure to FCC+BCC duplex structures with increasing of Al content. The microstructure of as-cast alloys was dendrite structure. The hardness, corrosion resistance and saturation magnetization (Ms) of BCC phase was better than that of FCC phase. The hardness of Al1.0as-cast alloy was the highest, and the compressive of Al1.5as-cast alloy was above3500MPa. The hardness of Al1.0reached to665.0HV, however, it decreased after heat treatment. The corrosion resistance of Al1.0as-cast alloy was the strongest and better than321stainless steel. The corrosion resistance of alloys decreased after heat treatment. The alloy which was quenched after homogenization treated at1100℃and then aged at700℃had the best comprehensive corrosion resistance. The Ms of Al1.0as-cast alloy was the highest, and reached to64.8emu/g. High entropy alloys with single BCC phase had the best comprehensive properties.The FeCoCrNiCu0.5Six high entropy alloys (x values in molar ratio, x=0,1.0,1.5, denoted by Si0, Si1.0,Si1.5, respectively) were synthesized by vacuum arc melting by adding non metallic element Si instead of the metal element Al. The effects of Si content and cooling rate after heat treatment on structure, hardness and corrosion resistance of alloys were investigated. The FeCoCrNiCu0.5Six high entropy alloys were formed with simple crystal structure and the as-cast alloys was dendrite structure. The intensity of diffraction peaks decreased with the increase of silicon content. The hardness of Sio alloy reached to997.4HV, and the hardness of FeCoCrNiCu0.5Six alloys decreased with the addition of Si, however, it improved after heat treatment. The hardness of furnace colded Si1.5alloy increased by18.67%, and the hardness of quenched Si1.5alloy increased by29.74%after heat treatment, so they had good softening resistance at high temperature. The corrosion resistance of Si1.0alloy was the best and better than321stainless steel, however, it decreased after heat treatment. The softening resistance at high temperature and the corrosion resistance of the high entropy alloys improved with the addition of Si element.Used SGTE database and combined with the contribution of magnetic properties on the free energy, calculated the stable crystal structure of the FeCoNiCrCu0.5Alx alloy on the basis of the characteristic crystal theory. The calculation results were consistent with the experimental results, and this method has a guiding significance on the prediction of stable structure of high entropy alloy with other components.