SCANNING VOL. 00, 1–7 (2012) C  Wiley Periodicals, Inc. Evaluation of Tribological Behavior of Al-Co-Cr-Fe-Ni High Entropy Alloy Using Molecular Dynamics Simulation JEN-CHING HUANG 1,2 1 Department of Mechanical Engineering, Tungnan University, Taiwan 2 Research Center for Micro/Nanotechnology, Tungnan University, Taiwan Summary: High-entropy alloys have been studied extensively for their excellent properties and perfor- mance, including outstanding strength and resistance to oxidation at high temperatures. This study em- ployed molecular dynamics simulation to produce a high-entropy alloy containing an equal molar ratio of Al, Co, Cr, Fe, and Ni and investigated the tribolog- ical behavior of the material using a diamond tool in a vacuum environment. We also simulated a AlCoCr- FeNi high-entropy alloy cooled from a high temper- ature molten state to 300 K in a high-speed quench- ing process to produce an amorphous microstructure. In a simulation of nanoscratching, the cutting force– distance curve of high-entropy alloys was used to evaluate work hardening and stick–slip. An increase in temperature was shown to reduce the scratching force and scratching resistance. Nanoscratching the high-entropy alloy at elevated temperatures provided evidence of work hardening; however, the degree of work hardening decreased with an increase in tem- perature. And it can also be found that when the tem- perature is higher, the fluctuation of the cutting force curve is greater. SCANNING 00: 1–7, 2012. C  2012 Wiley Periodicals, Inc. Key words: high entropy alloy, tribological behavior, nanoscratching, molecular dynamics simulation , PACS: 81.05.Bx, 82.20.Wt Contract grant sponsor: National Science Council; Contract grant number: NSC 99-2221-E-236-001. Address: Jen-Ching Huang, Associate Professor, Department of Mechanical Engineering, Tungnan University, No. 152, Sec. 3, PeiShen Rd., ShenKeng, New Taipei City 222, Taiwan E-mail: jc-huang@mail.tnu.edu.tw Received 4 August 2011; Accepted with revision 22 November 2011 DOI 10.1002/sca.21006 Published online in Wiley Online Library (wileyonlinelibrary.com) Introduction In recent years, an entirely new field of high- entropy alloys, containing multiple principal elements in equimolar or near-equimolar ratios, has been de- veloped by researchers such as Yeh et al. (2004a,b, 2007). High-entropy alloys contain at least five prin- cipal elements at concentrations of between 5 and 35 in percentage. Solid solutions with multiprincipal ele- ments tend to be more stable at elevated temperatures due to the high degree of entropy associated with such mixing. In previous studies, high-entropy alloys have demonstrated simple crystal structures, ease of nanoprecipitation, a promising degree of hardness, and resistance to temper softening, wear, oxidation, and corrosion (Tung et al., 2007; Huang et al., 2007). Among these alloys, AlCoCrFeNi has shown partic- ular promise for applications in structural and tool industries, making it an ideal candidate material for nanomolds. The next obvious step in the develop- ment of this technology is to evaluate the tribological properties. Alloys based on a single principal element have been widely investigated, and factors influencing the friction curve of metallic materials have been shown to include hardness, plastic deformation, work hard- ening, and the evolution of crystallographic texture, all of which take place during the wearprocess (Yeh et al., 2004a,b, 2007). Among the many techniques based on atomic force microscopy (AFM), mechanical scratching, also known as scratch nanolithography, is emerging as a simple, reliable, and versatile scheme with which to fabricate a wide range of nanoscale devices (Huang et al. 2009, 2010; Tseng et al. 2009, 2010). The AFM- based scratch technique can also be used with a dia- mond probe to test the tribological properties of hard materials (Huang et al., 2011a,b). A better understanding of the properties and mechanisms associated with nanoscale process- ing requires further theoretical analysis. Over the past decades, numerous molecular dynamics (MD)