Effect of Nb addition on the microstructural, mechanical and electrochemical characteristics of AlCrFeNiCu high-entropy
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Effect of Nb addition on the microstructural, mechanical and electrochemical characteristics of AlCrFeNiCu high-entropy alloy N. Malatji 1), A.P.I. Popoola 1), T. Lengopeng 2), and S. Pityana 2) 1) Tshwane University of Technology, Pretoria, South Africa 2) Council for Scientific and Industrial Research, Pretoria, South Africa (Received: 6 April 2020; revised: 18 August 2020; accepted: 31 August 2020)
Abstract: AlCrFeNiCuNbx (x = 0.05, 0.15, and 0.26) high-entropy alloys (HEAs) were successfully fabricated using the laser metal deposition technique. The laser power of 1600 W and scanning speed of 1.2 m/min were used during laser processing of the alloys. The microstructural, mechanical, and electrochemical characteristics of the alloys were evaluated using various advanced characterization techniques. Results showed that the alloys exhibited a dual-phase structure with dendritic grains. The inclusion of Nb in the AlCrFeNiCu alloy matrix promoted the formation of fine eutectic structures and changed the shape of the grains from columnar to equiaxed. The Cu content decreased with the increase in the content of Nb, whereas the Al content increased with the increase in the content of Nb. The findings indicated that the presence of Nb in the alloy promoted the formation and enhanced the stability of the body-centered cubic (bcc) phase. All of the alloys that contained Nb also exhibited high hardness, compressive strength, and wear resistance. Furthermore, the low current density and positive shift in potential exhibited by HEAs with appropriate addition of Nb highlighted the superior anticorrosive properties. Keywords: high-entropy alloys; microstructure; microhardness; friction; wear loss; corrosion resistance
1. Introduction The development of high-entropy alloy (HEA) systems with high aluminum (Al) content is an area of considerable interest in the materials science community [1–3]. These alloys are characterized by dual-phase solid solution structures (i.e., body-centered cubic (bcc) + face-centered cubic (fcc) phases) that have excellent mechanical properties [4–6]. The Al content of the alloy matrix determines the strength and ductility that will be exhibited by the alloys. The incorporation of Al in HEA matrices not only reduces the density of the alloys but also induces the formation of a strong bcc phase, which improves the mechanical strength of the alloys [7–8]. However, the high Al content increases the mechanical strength of the alloys at the expense of their ductility. The variation of Al in CoCrCuFeNi HEA from 0 to 2 mol improved the hardness of the alloy from HV 45 to 78. Alloys with 2 mol Al were also observed to have a low coefficient of friction (CoF) [9]. The highest elastic modulus of >200 GPa was observed in AlCoCrFeNi HEAs with the Al stoichiometric fraction between 0.3 and 0.4. Increasing the Al stoichiometric fraction beyond 0.4 yielded hard alloys with a high proportion of bcc phase to fcc phase and low elasti
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