Structure and physical-mechanical properties of cast heat-resistant FeNiCrCuAl high-entropy alloys

The crystal lattice of high-entropy alloys (HEAs) undergoes significant deformation, that is why HEAs have high strength, significant wear resistance and corrosion resistance in environments with high chemical activity [1]. This work was aimed at creating new heat-resistant high-entropy alloys, based on inexpensive elements and prepared from common master-alloys, studying their phase composition and structure, as well as determining their physical-mechanical properties. FeNiCrCuAl alloys do not contain such an expensive element as cobalt (Co), which is usually present in similar metallic systems. FeNiCrCuAl high-entropy alloys were made from a mixture of pure metals (Cu, Ni, Al), low-carbon ferrochromium (FeCr70C1), stainless steel (GX10CrNiMn-18-9-1) and cast iron (content, wt.%: C = 2.60, Si =1.80, Mn = 1.30, Ni = 17.00, Cr = 2.30, Cu = 3.60, S = 0.05, P = 0.07). The investigated alloys were prepared by lost foam and sand mold casting methods. The phase composition of the as-cast FeNiCrCuAl alloys is represented by three phases: BCC-ordered solid solution of type B2, FCC solid solution and complex carbides (FeCr)₇C₃. Carbides were formed due to the presence of carbon in the charge materials such as cast iron (C = 2.6 wt. %) and stainless steel (C = 0.1 wt. %). A wide number of different meltings were performed therefore the chemical composition of the alloys fluctuated and the period of the BCC lattice parameter varied from 2.8859 Å to 2.8983 Å, and the FCC lattice parameter was from 3.6406 Å to 3.6666 Å. The microstructural analysis of the optical photographs revealed that the structure of the alloys was heterogeneous and consisted of granular and lamellar dendrites and interdendritic space. The HEAs of the FeNiCrCuAl system are characterized by relatively high hardness and samples suffered brittle failure during tensile tests due to the presence of carbides and BCC phase. The Brinell hardness and tensile strength in the as-cast alloys were in the range of 275 HB to 415 HB and from 300 MPa to 748 MPa, respectively.