The Mechanical and Corrosion Behaviors of As-cast and Re-melted AlCrCuFeMnNi Multi-Component High-Entropy Alloy VASILE SOARE, DUMITRU MITRICA, IONUT CONSTANTIN, GABRIELA POPESCU, IOANA CSAKI, MIHAI TARCOLEA, and IOAN CARCEA A multi-component AlCrCuFeMnNi high-entropy alloy, prepared by vacuum induction melt- ing, was investigated for structural, mechanical, and corrosion characteristics, before and after the re-melting process. Optical microscopy analysis revealed a dendritic solidification behavior. The interdendritic area contains two main phases and occasionally small hard phases. The re-melting process produced a finer dendritic structure, with rounded dendrites and reduced interdendritic hard phases. The SEM-EDAX analysis showed that the dendrite region contains a Widmanstatten type of structure and are composed of Cr-Fe rich phases, whereas the inter- dendrite region contains Cu and Mn rich phases. XRD analysis revealed two disordered BCC type A2 structures with high Cr and Fe content and an FCC A12 type of structure for the Cu and Mn rich interdendritic phase. The lattice constants, determined by X-ray diffraction, are 2.87 and 2.91 A ˚ for the A2 phases and 3.67 A ˚ for A1 phase. The Vickers micro hardness increased with the homogeneity of the alloy, having a maximum value of 4370 MPa for the re-melted sample. Corrosion tests carried out in 3.5 wt pct sodium chloride aerated solution indicated that the corrosion resistance improved with the re-melting process, being 1.5 to 2 times better than that of 304 stainless steel. DOI: 10.1007/s11661-014-2523-7 Ó The Minerals, Metals & Materials Society and ASM International 2014 I. INTRODUCTION HIGH-ENTROPY alloys (HEAs), discovered in 1995 by Yeh, [1] emerged as a new type of advanced metallic materials and have received increasing attention from the materials science community. HEAs exhibit a wide range of excellent mechanical and physical prop- erties, such as high strength and toughness, high stiffness, improved corrosion resistance, hydrophobicity, high hardness and good temperature stability, super- plasticity and high-strain-rate superplasticity and there- fore provide a number of promising applications. [1,2] Due to the high mixing entropy, HEAs are prone to have simplified microstructures with solid solution phases, often consisting of a single phase characterized by a simple crystal structure. In addition to the high- entropy effect, sluggish diffusion and severe lattice distortions have a significant effect on the structures and properties of high-entropy alloys. A comprehensive understanding of the thermody- namics of these alloys is important in order to develop stable simple phase multi-component equiatomic alloys, as genuine high-entropy alloys. In the estimation of the entropy of metallic alloy formation, Boltzmann’s hypothesis states that the maximum entropy of mixing is obtained at equiatomic compositions, and the follow- ing equation can be used: DS ¼ k ln w ¼R 1 n ln 1=n þ 1 n ln 1=n þ  þ 1 n ln 1=n ¼R ln 1 n ¼ R ln n ½1 where R is the ideal gas constant and n the number of mixed elements. From n = 6, DS becomes higher than the mixing entropy of most intermetallic compounds, which leads to the preferential formation of solid solutions. From n = 5 to n = 13 elements, alloys have entropies between 1.61 and 2.56 R and belong to the high entropy domain. The limit of thirteen elements is arbitrary. It has been shown that once this value is surpassed, the benefit brought by element addition would be insignificant. [3,4] Previous research work on high-entropy alloys is based on various systems, [5–10] Al-Co-Cr-Fe-Ni repre- senting the most studied system. [11–15] Aluminum con- tent has a strong influence over the structural configurations and mechanical properties of high-en- tropy alloys. In Al x CoCrCuFeNi, [5,11] Al x FeCo NiCrMn, [16] and AlCrFeCuNi x [17] alloys a small Al content (x < 1.3) forms a malleable FCC structure and a higher Al content generates a more resistant and brittle VASILE SOARE, Head of New Materials and Technologies Laboratory, and DUMITRU MITRICA and IONUT CONSTANTIN, Experienced Researchers, are with the National R&D Institute for Nonferrous and Rare Metals – IMNR 102 Biruintei Blvd., 077145 Pantelimon, Ilfov County, Romania. Contact e-mails: vivisoare@imnr.ro, soarevivi@gmail.com GABRIELA POPESCU and MIHAI TARCOLEA, Professors, and IOANA CSAKI, Assistant Professor, are with the Polytechnic University of Bucharest, Faculty of Materials Science and Engineering, 313 Splaiul Independentei, 060032 Bucharest, Romania. IOAN CARCEA, Professor, is with Gheorghe Asachi Technical University of Iasi, Faculty of Materials Science and Engineering, 67A Prof. Dr. Doc. Dimitrie Mangeron Blvd., 700050 Iasi, Romania. Manuscript submitted April 16, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS A