Effect Of Alloying Elements On The Microstructure And Mechanical Properties Of High-entropy Alloys

High-entropy alloys (HEAs) take up five or more than five principal elements in equiatomic or close-to-equiatomic ratios. Simple crystal structures, FCC and/or BCC solid solution phases, instead of complicated intermetallic compounds tend to be formed in HEAs during solidification due to the significantly high entropy effect. Nanocrystallines or amorphous could be formed in the as-cast alloys due to the sluggish diffusion and highly crystal distortion. These specific microstructures lead to excellent properties, such as high strength/hardness, outstanding wear resistance, exceptional high-temperature strength, good structural stability, good corrosion and oxidation resistance and combinations of aforementioned properties, by solid solution strengthening, precipitation strengthening and dispersion strengthening. HEAs have many advantages over the traditional alloys and become an attractive field in metallic materials.The Al0.5CoCrCuFeNiBx, Alo.sCoCrCuFeNiSiy, Al0.5CoCrCuFeNiBxSix, Co1.5CrFeNi1.5Ti0.5AlxMoy and Al0.2Co1.5CrFeNi1.5TiNbxVy alloys were designed and the alloys ingots were prepared by vacuum arc melting and casting. The crystalline structures were characterized by using X-ray diffraction (XRD). The microstructure and chemical compositions were studied by using SEM equipped with EDS. The hardness and wear properties of alloys were tested.It is indicated that these five series of HEAs are all composed of simple solid solution structures, i.e. FCC, BCC and mixtures of both FCC and BCC solid solutions. The formation of simple solid solution structures is attributed to the effect of high mixing entropy which inhibits the formation of intermetallic phases.In the Al0.5CoCrCuFeNiBx alloys, the alloy without B addition consists of only FCC phases and the alloys with B additions consist of FCC phases and borides including Cr2B and (Cr,Fe)B-type borides the volume fraction of which increased with increasing B content. There were no distinct differences in the lattice constants of FCC phases indicating that B mainly precipitated as borides instead of entering the crystal structures. The hardness of the alloys increased with increasing B content. The hardness of the alloy with x=0,607 HV, is 2.31 times that of the alloy with x=0,263 HV. The of Al0.5CoCrCuFeNiBx exhibited excellent wear resistance which also increase with increasing B content, particularly for the alloys with x≥0.4.For the Al0.5CoCrCuFeNiSiy alloys, the BCC phases started to appear with the addition of Si addition. The alloys with x≤0.4 were composed of both FCC and BCC phases and those with x≥0.6 were composed of BCC phases. The lattice constants of both FCC and BCC phases decreased with the addition of Si. The hardness of the alloy with x=1.0,727 HV, is 2.76 times that of the alloy without Si addition. The wear resistance of the alloys increased with increasing Si content.With the addition of both B and Si, the alloys were composed of FCC, BCC, borides and silicides. The addition of B and Si decreased the lattice constants of both the FCC and BCC phases. The hardness of the alloys increased with increasing B and Si content. The hardness of the alloy with x=0.8,784HV, is 2.98 times that of the alloy without B and Si additions. The wear resistance of the alloys increased with the increase of B and Si content.In Co1.5CrFeNi1.5Ti0.5AlxMoy alloys, FCC structured simple solid solution were formed. The changes of the lattice constants of the alloys with Al and Mo additions were minor. There are no distinct differences in the hardness and the wear resistance of the alloys with Al and Mo additions.In Al0.2Co1.5CrFeNi1.5TiNbxVy alloys, the microstructures were composed of FCC structured solid solution η phases. The changes in the lattice constants of the alloys with Nb and V additions were minor. The hardness and wear resistance of the alloys increased with the additions of Nb and V. The wear resistance increased with increasing hardness and exhibited strong correlation to the hardness.These five series high-entropy alloys all showed good properties and were expected to have a great application potential for industrial materials.