TECHNICAL PAPER TP 2675 Effect of Zr Addition on Microstructure and Properties of FeCrNiMnCoZr x and Al 0.5 FeCrNiMnCoZr x High Entropy Alloys Siti Sarah Mohd Pauzi • Widyani Darham • R. Ramli • M. K. Harun • Mahesh Kumar Talari Received: 15 November 2012 / Accepted: 7 March 2013 / Published online: 22 May 2013 Ó Indian Institute of Metals 2013 Abstract In this study, the effect of Zr addition on phase formation, microstructure, and hardness of FeCrNiMn- CoZr x and Al 0.5 FeCrNiMnCoZr x were investigated. High entropy alloys (HEA) were synthesized using arc melting technique in argon (Ar) atmosphere (x = 0, 0.1, 0.2, 0.3). Ingots were homogenized for 24 h at 900 °C in Ar atmo- sphere. Phase formation, microstructure and hardness of HEAs were investigated using field emission scanning electron microscope (FESEM), X-ray diffraction (XRD) and vickers microhardness tester. Electron micrographs of HEAs showed majorly dendritic(DR) and interdendrit- ic(ID) phases. For both FeCrNiMnCoZr x and Al 0.5 FeCr- NiMnCoZr x alloys, amount of ID phases is seen to increase with increased Zr content. Aluminium containing HEAs showed fine needle-shaped precipitates dispersed through- out the matrix phase. XRD results confirmed the presence of mixed FCC/BCC phases in FeCrNiMnCoZr x alloys and BCC as majority phase in Al 0.5 FeCrNiMnCoZr x alloys. As the Zr content increased, hardness of HEA increased. Keywords High entropy alloys Á Microstructure Á Hardness Á Alloying elements 1 Introduction Intermetallic compound formation in the alloys at higher alloying additions could lead to embrittlement, difficulty in microstructure tailoring and deterioration of mechanical properties [1, 2]. High entropy alloy (HEA) is a new approach for alloy design, proposed to overcome the lim- itations of traditional alloys [3]. Yeh et al. [4] have defined that HEA is composed of at least five principal metallic elements in near equimolar ratios with each element con- centration between 5 to 35 at %. It is reported that addition of alloying elements with larger atomic sizes, tend to form secondary phases and also aid in solid solution strength- ening [5]. Recently, Hsu et al. [6] have found that a new HEA, AlCoCrFe x Mo 0.5 Ni, derived from the AlCoCrCuF- eNi system by replacing Cu with Mo, which has bigger ionic radius, displayed markedly higher hardness and wear resistance. Li et al. [1] has synthesized FeNiCrCuCo and FeNiCrCuMo alloys and reported that they formed single phase FCC solid solution. When Al substituted the Cu or Co in these alloys, the microstructure of the alloys changed to BCC solid solution or BCC ? FCC solid solution. Zhang et al. [7] have investigated the effect of Al addition on microstructure and mechanical properties of CoCr- FeNiTi alloy and obtained compressive strength and elastic modulus as high as 2.28 and 147.6 GPa, respectively. According to Guo et al. [8], valance electron concentration (VEC) of HEA can be determined from the VEC of indi- vidual elements in the HEA. Furthermore they have sug- gested that higher VEC values (C 8) promote FCC phase formation where as lower VEC ( \ 6.87) values stabilize BCC phases. Thus low VEC value of Al (VEC = 3) can effectively stabilize BCC structure in HEA. Zr addition to the FeNiCrCu alloy system caused the intermetallics (ZrFe 3 Al) in microstructure due to the stronger compound formation tendency between Zr and other components [1]. Minor additions of Zr to HEA can form small quantities of compounds which could aid in improving hardness. In this study, a new HEA FeCrNiMnCoZr x and Al 0.5 FeCrNiMn- CoZr x alloys (x = 0, 0.1, 0.2 and 0.3) were prepared and S. S. M. Pauzi Á W. Darham Á R. Ramli Á M. K. Harun Á M. K. Talari (&) Faculty of Applied Sciences, Universiti Teknologi MARA, Shah Alam, Malaysia e-mail: talari@gmail.com 123 Trans Indian Inst Met (August 2013) 66(4):305–308 DOI 10.1007/s12666-013-0264-8