The Mechanical and Corrosion Behaviors of As-cast and Re-melted AlCrCuFeMnNi Multi-Component High-Entropy Alloy
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TRODUCTION
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 properties, such as high strength and toughness, high stiffness, improved corrosion resistance, hydrophobicity, high hardness and good temperature stability, superplasticity and high-strain-rate superplasticity and therefore 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 highentropy effect, sluggish diffusion and severe lattice distortions have a significant effect on the structures and properties of high-entropy alloys.
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: [email protected], [email protected] 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
A comprehensive understanding of the thermodynamics 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 following equation can be used: 1 1 þ þ DS ¼ k ln w ¼ R n ln 1=n n ln 1=n ½1 1 1 þ ¼ R ln ¼ R ln n n ln 1=n n 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 representing the most studied system.[11–15] Aluminum content has a strong influence over the structural configurations and mechanical properties of high-entropy alloys. In AlxCoCrCuFeNi,[5,11] AlxFeCo NiCrMn,[16] and AlCrFeCuNix[17] alloys a small Al content (x < 1.
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