Vol.:(0123456789) 1 3 Metals and Materials International https://doi.org/10.1007/s12540-019-00332-0 Efects of Al on the Phase Volume Fractions and Wear Properties in the Al x CoCrFeMoNi High Entropy Alloy System Hakan Gasan 1  · Ersu Lökçü 1  · Akin Ozcan 2  · Osman Nuri Celik 3  · Ibrahim Celikyurek 1  · Mustafa Ulutan 3  · Yavuz Kurtulus 2 Received: 14 February 2019 / Accepted: 10 June 2019 © The Korean Institute of Metals and Materials 2019 Abstract A detailed investigation was carried out to study the efect of Al on the phase volume fractions and wear properties in the Al x CoCrFeMoNi high entropy alloy (HEA) system. The analysis of phases was studied by X-ray difraction for further Riet- veld refnement was performed to determine the volume fraction of phases. In order to accomplish experimental studies, the volume fraction of phases has been analyzed by CALPHAD based simulations. The wear behavior of HEAs were studied under dry sliding conditions using a ball-on-disc geometry. The alloy system includes FCC, σ, B2 and BCC phases and exhibits a broad range of phase transformations with varying Al content. The wear behavior of HEAs, in the present work, is correlated with their volume fraction of phases and hardnesses. The minimum wear rate, 3.04 × 10 −5  mm 3 /(Nm), is observed in A 1.5 CoCrFeMoNi alloy containing relatively hard σ, B2 and BCC phases, which has a maximum hardness 829.8 HV. Keywords High entropy alloys · Wear · Rietveld analysis · CALPHAD 1 Introduction High Entropy Alloys (HEAs), including more than fve major elements in equi-atomic or near equi-atomic compo- sitions are proposed as a new alloy system [1]. These alloys have superior properties such as high strength, hardness, wear and corrosion resistance [2–4] due to the high confgu- rational entropy of mixing [5, 6]. The key concept of HEAs is to maximize the confgurational entropy to achieve a sin- gle phase disordered solid solution. These disordered sin- gle phases have been shown to present on the face centered cubic (FCC), body centered cubic (BCC) and hexagonal closed-packed (HCP) crystal structures [7–9]. On the other hand, it has been shown that, the ordered solid solutions and/or intermetallic phases can also exist in HEAs [10–12]. Although the formation of the ordered solid solutions and/ or intermetallic phases is controversial to the concept of HEAs, controlling the formation and the fraction of phases can bring signifcant advantages to the design of HEAs for the desired applications. In this light, under the name of second generation HEAs, which contain features of dual or complex phases, have been referred in detail [12]. The Al–Co–Cr–Fe–Mo–Ni HEA system ofers attractive mechanical properties, due to the presence of soft FCC phase and with relatively hard BCC, ordered body-centered cubic (B2) and body-centered tetragonal (σ) phases for the various contents [13–17]. The efects of Co [13], Fe [14], Cr [15], Al [16] and Ni [17] contents on the phase formation and micro- structure of the base AlCoCrFeMo 0.5 Ni HEAs have been studied extensively by Hsu et al. Moreover, Hsu et al. [18] constructed approximate phase diagrams from experimental studies for this alloy system to guide efcient alloy design. Among the various mechanical properties, wear is one of the most important issue for industrial applications such as punches, dies, molds, etc. Chuang et al. [19] explored the wear properties of the Al x Co 1.5 CrFeNi 1.5 Ti y HEAs which were similar hardness and better wear resistance to commer- cial wear-resistant steels SUJ2 and SKH51. It was found that the amounts of Al and Ti strongly afect the microstructure and existing phases. Closely related to our system, the wear properties of AlCoCrFe x Mo 0.5 Ni HEAs was investigated by * Ersu Lökçü elokcu@ogu.edu.tr 1 Department of Metallurgical and Materials Engineering, Eskisehir Osmangazi University, 26480 Eskisehir, Turkey 2 Institute of Science, Eskisehir Osmangazi University, 26480 Eskisehir, Turkey 3 Department of Mechanical Engineering, Eskisehir Osmangazi University, 26480 Eskisehir, Turkey