Structural Control And Properties Of FeSiBAlNiM(M=C,Co_x,Ce,Gd) High Entropy Alloys

High entropy alloys(HEAs) are defined as equi-atomic alloys that contain at least five principal elements in equal or near equal atomic percent. The coming of the concept of HEAs provides an effective design idea for exploring advanced materials with unique properties. The intensive study will supply the very important theoretical guiding and practical application. In this paper, we select the equi-atomic Fe Si BAl Ni HEAs possessing a certain glass forming ability(GFA) as the based alloy. On this basis, C, Ce, Gd and Co_x(x=0.2~0.8) with different radius, are selected and added as the sixth element in order to systematically investigate the effect of the intrinsic properties and size effect on the microstructure and performances of the based HEAs. Moreover, we selected moderate annealing treatment at different temperatures to investigate the effects of annealing temperature on microstructure and properties. Additionally, bulk FeSiBAlNiM(M=C, Co_x, Ce) alloys were fabricated by Spark Plasma Sintering(SPS) technique and the correlation between compositions and performances is studied.In this thesis, HEA powders and bulks are fabricated by mechanical alloying(MA) and SPS, respectively. They are investigated by X-ray diffraction, differential scanning calorimetry, field emission scanning electron microscopy, transmission electron microscopy, alternating gradient magnetometer, Vickers' microhardness and electrochemical workstation. The detailed results are shown below:1. Amorphous HEA powders of FeSiBAlNiM(M= Co_x, Ce, Gd) were fabricated by mechanically alloying, while the structure of FeSiBAlNiC contains main amorphous structure and some Si phase. In addition, additional Co_x, Ce and Gd shortens the formation time of amorphous phase and thus enhances GFA of based alloy effectively. From the point of thermal property, C and Ce additions also remarkably promote the thermal stability of amorphous structure in HEA powders. By calculating the radius ratio(Ri) between additional atoms and the based atoms, it can be found that higher Ri values promote the enhanced GFA.It has been found that the obtained FeSiBAlNiM(M=Co_x, Ce, Gd) HEA powders exhibit semi-hard magnetic performance by testing the hysteresis loops, while transformation from semihard-magnetism to soft-magnetis happens in the HEA with C addition after 140 h MA. The saturation magnetization(Ms) values of MAed 140 h FeSiBAlNiC HEA powders is the largest, while it is the smallest for FeSiBAlNiCe. This means C addition promotes the semi-hard magnetism while Ce addition exhibits a decreased effect.2. Annealing the HEA powders(140 h) at different temperatures, it is found that the products are mainly the solid solutions and a small amount of intermetallics. Additionally, annealing makes the soft-magnetism of 140 h milled FeSiBAlNiC HEA transforms to semihard-magnetis, and shows a dedrimental effect on the magnetism. While a higher annealing temperature is beneficial for the semi-hard magnetism of FeSiBAlNiM(M=Ce, Gd). Annealing FeSiBAlNiCo_x HEA powders at 800? effectively increases the Ms, and it becomes enhanced with increasing Co contents, which is attributed to the transformation from body-centered cubic(BCC) solid solution to face-centered cubic(FCC) solid solution.3. FeSiBAlNiM(M=C, Co_x, Ce) bulk HEAs are fabricated by SPS technique, and the microstructure of SPSed bulks contains mainly BCC solid solutions and a little amount of intermetallics. What's more, the SPS-ed bulks possess high hardness, with most HV values more than 1000 HV. The SPS-ed bulk HEAs possess semi-hard magnetism except for 850? SPS-ed W6-Co HEA, which shows excellent soft magnetism. What's more, the semi-hard magnetism of the bulks exhibits an increasing effect compared with milling product. Moreover, the show. Additionaly, excellent passive region can be observed in 3.5% Na Cl aqua and the FeSiBAlNiCe bulk HEA shows the best corrosion resistance.