Processing and Properties of Nanocrystalline CoCrFeNiCuAlTiXVMo High Entropy Alloys by Mechanical Alloying

Fabrication of nanocrystalline equiatomic high entropy alloys is a crucial aspect for the product of many tools. The present study describes the synthesis of nanocrystalline equiatomic CoCrFeNiCuAlTiXVMo (X？=？Zn, Mn) high entropy alloys by mechanical alloying and their characterization by XRD and SEM. The CoCrFeNiCuAlTiXVMo (X？=？Zn, Mn) high entropy alloys have BCC solid solution with crystallite size less than 10？nm. These alloys are stable even after annealing at 600°C for 1？h. The hardness of the high entropy alloys is found to be 7.6 and 6.2？GPa, respectively. 1. Introduction High entropy alloys are equiatomic or near-equiatomic multicomponent alloys, wherein configurational entropy is maximized to obtain single-phase solid solution [1]. These new generation alloys are quite different from the traditional ones, which are based on one or two major elements. Solid solutions with multiprincipal elements have been generally found to be stable at elevated temperatures due to their large entropies of mixing, which lead to the sluggish diffusion of atoms [2–6], preventing the precipitation of intermetallic compounds. The formation of solid solutions in high entropy alloys by melting is facilitated by small atomic size difference and small enthalpy of mixing between the constituent elements. It is expected that the same conditions facilitate the formation of solid state solution state when the alloy is formed by mechanical alloying as well. Mechanical alloying is a widely used solid state processing route for the synthesis of materials out of equilibrium with good homogeneity [7]. 2. Experimental The present study was taken up to prepare a new ten-element equiatomic multicomponent HEA alloy system with composition CoCrFeNiCuAlTiXVMo (X = Zn, Mn), starting from elemental powders. Co, Cr, Fe, Ni, Cu, Al, Ti, Zn, V, Mo, and Mn powders with purity higher than 99.5% and particle size of 44？μm were used as starting materials. The elemental powders with a total mass of 5？g were milled in a planetary ball mill (Fritsch planetary ball mill) with tungsten carbide can and balls. The powder-to-ball weight ratio is 1？:？15, and 300？rpm speed was used. In order to confirm the alloy formation during milling, several mg samples were taken out after 5, 10, and 20？h. After 20？h of milling the powder sample was removed from the vial for further characterization and consolidation. The powders were compacted using cold compaction at 800？MPa for 5 minutes followed by sintering at 600°C for 1？h. The phase structure and stability of the as-milled and annealed (600°C for 1？h)