Microstructure, Phase Occurrence, and Corrosion Behavior of As-Solidified and As-Annealed Al-Pd Alloys Libor D ˇ uris ˇka , Maria ´ n Palcut, Martin S ˇ pota ´k, Ivona C ˇ ernic ˇ kova ´, Ja ´ n Gondek, Pavol Priputen, Roman C ˇ ic ˇ ka, Dus ˇ an Janic ˇ kovic ˇ, and Jozef Janovec (Submitted September 20, 2017; in revised form December 7, 2017) In the present work, we studied the microstructure, phase constitution, and corrosion performance of Al 88 Pd 12 , Al 77 Pd 23 , Al 72 Pd 28 , and Al 67 Pd 33 alloys (metal concentrations are given in at.%). The alloys were prepared by repeated arc melting of Al and Pd granules in argon atmosphere. The as-solidified samples were further annealed at 700 °C for 500 h. The microstructure and phase constitution of the as-solidified and as-annealed alloys were studied by scanning electron microscopy, energy-dispersive x-ray spectroscopy, and x-ray diffraction. The alloys were found to consist of (Al), e n ( Al 3 Pd), and d (Al 3 Pd 2 ) in various fractions. The corrosion testing of the alloys was performed in aqueous NaCl (0.6 M) using a standard 3- electrode cell monitored by potentiostat. The corrosion current densities and corrosion potentials were determined by Tafel extrapolation. The corrosion potentials of the alloys were found between 2 763 and 2 841 mV versus Ag/AgCl. An active alloy dissolution has been observed, and it has been found that (Al) was excavated, whereas Al in e n was de-alloyed. The effects of bulk chemical composition, phase occurrence and microstructure on the corrosion behavior are evaluated. The local nobilities of e n and d are discussed. Finally, the conclusions about the alloyÕs corrosion resistance in saline solutions are provided. Keywords Al-Pd alloys, corrosion resistance, intermetallic, mi- crostructure characterization, potentiodynamic polar- ization 1. Introduction Among metallic systems comprising structurally complex phases (SCPs), the Al-TM systems (TM stands for one or more transition metals) have been the most widely studied (Ref 1-7). The SCPs have specific transport properties, e.g., an anomalous relation between electrical and thermal conductivities has been found (Ref 7-10). Moreover, surfaces of complex metallic alloys (CMAs) provide a rich variety of different adsorption sites (Ref 11-13). As such, potential applications of Al-based CMAs are reported in catalysis (Ref 14), solar light absorption (Ref 15), polymer–matrix (Ref 2), and metal–matrix (Ref 16) composites. Some of the applications are now commercialized. For instance, the Al-based coatings comprising SCPs have been used as scratch-resistant films, offering a lowered adhesion to some polymers or food (Ref 2). The maraging steel comprising nano-sized quasicrystalline particles has also been used in electric shavers (Ref 2). The Al-based alloys exposed to corrosive environments form a compact protection layer composed of Al 2 O 3 and AlO(OH) (Ref 17, 18). Chlorine anions, often present in aqueous solutions, weaken the passive films. As such, these materials are susceptible to pitting corrosion (Ref 19-22). By adding TM elements (e.g., Cr, W, Mo, Ta), the Al pitting potential can be increased (Ref 23-25). Nevertheless, electro- chemically noble intermetallic phases formed in these alloys may play the role of cathodes during electrochemical corrosion. As such, their corrosion stability may result in an anodic dissolution of the surrounding metal matrix. The matrix depletion may have fatal consequences for the materials integrity. The electrochemical properties of SCPs were reported to be different from those of Al (Ref 26-38). It has been argued that metal composition of CMAs plays a major role in determining the alloyÕs corrosion resistance (Ref 26). In corrosion protection, the Al-based CMAs could be utilized as coatings to coat either Al alloys or low-alloyed steels. The passivation stability of classical Al alloys is often very poor when a pH is increased above 8-9. Since the alloying elements, such as Cr or Cu, are passivating at different pH, a mixed passivation layer can be formed on these materials. The chemical composition of the passive layer could be further modified by specific TM elements. The recent study of Al-Cr- Fe CMAs (Ref 30) revealed a high stability of these materials in alkaline solutions. The corrosion resistance of these alloys thus could make them attractive for technologically important applications taking place in alkaline environments. Al-Pd alloys have been studied for their catalytic properties (Ref 39). Pd exhibits a strong interaction with Al resulting in the formation of noble metal-like electronic structure of Al-Pd alloys. In the Al-Pd system, a number of SCPs have been found. Altogether five structures of e-phases (binary e 6 , e 28 (Ref 40-42), ternary e 16 , e 22 , and e 34 ) were found and classified as approximants of decagonal quasicrystal (Ref 5, 7). The structures differ in the length of lattice parameter c. The CMAs comprising e-phases are diamagnetic. Their electrical resistivity is moderate and shows a weak temperature dependence at 4- Libor D ˇ uris ˇka, Maria ´n Palcut, Martin S ˇ pota ´k, Ivona C ˇ ernic ˇkova ´, Ja ´n Gondek, Pavol Priputen, and Roman C ˇ ic ˇka, Faculty of Materials Science and Technology in Trnava, Slovak University of Technology in Bratislava, Ja ´na Bottu 2781/25, 917 24 Trnava, Slovak Republic; Dus ˇan Janic ˇkovic ˇ , Institute of Physics, Slovak Academy of Sciences, Du ´ bravska ´ 9, 845 11 Bratislava, Slovak Republic; and Jozef Janovec, Slovak University of Technology in Bratislava, University Science Park, Vazovova 5, 812 43 Bratislava, Slovak Republic. Contact e-mail: libor.duriska@gmail.com. JMEPEG ÓASM International https://doi.org/10.1007/s11665-018-3245-6 1059-9495/$19.00 Journal of Materials Engineering and Performance