Communication Evolution of Bimodal Microstructure and High-Temperature Wear Resistance of Al-Cu-Ni Alloys SHUBHADEEP MAITY, DIPAK KR. CHANDA, PARTHIBAN RAMASAMY, BIJAY KUMAR SHOW, JU ¨ RGEN ECKERT, and SUPRIYA BERA We report excellent high-temperature (300 °C) wear resistance of copper mold-cast Al 80 Cu 15 Ni 5 and Al 75 Cu 15 Ni 10 alloys. The evolution of a novel bimodal microstructure consisting of a-Al, eutectic a-Al + Al 2 Cu, and a vacancy ordered phase (Al 3 Ni 2 type) restricts severe adhesive and abrasive wear at high temperature. Particularly, the Al 75 Cu 15 Ni 10 alloy shows a low wear rate at 300 °C. In-depth microstructural characterization of the as-cast alloys and the worn samples elucidate the wear mechanism. https://doi.org/10.1007/s11661-019-05518-0 Ó The Minerals, Metals & Materials Society and ASM International 2019 INTRODUCTION A superior material index (strength/density ratio) at room and elevated temperatures are essential for struc- tural materials in the aerospace and automotive indus- try. In comparison to steels, aluminum (Al) alloys are superior in density (four times lower than steels) but have lower yield strength (three times lower than steels). [1–3] Hence, a lot of work has been carried out to improve the strength of Al alloys at elevated temperatures ( < 400 °C). [4–6] Several Al-based high- temperature phases like ordered phases (NiAl, Al 3 Ni 2 , and AlNi 3 ) and in situ grown metal-intermetallic com- posites (e.g., eutectic Al-Al 2 Cu, Al-Al 3 Ni, Al-Al 3 Sc, Al 3 Zr, and Al-Al 3 Fe phases) play a crucial role to accomplish the requirements. [3,7–10] It is well known that application of Al-based high-temperature materials is restricted due to inadequate room-temperature ductil- ity. [11,12] Recent studies have proven that a high-volume fraction of ordered phases, intermetallics, or eutectics with nano-/ultrafine length-scale combined with soft primary dendrites enhances the strength while main- taining moderate ductility due to enhanced dislocation activity. [3,8,13,14] Furthermore, the addition of ternary alloying elements can improve ductility. [3,8] Such ternary additions either yield a combination of two types of eutectics with different length-scale or refine the eutec- tics and form colonies. Several types of alloys, for example, Al-Cu-Ni, Al-Ni-Cr, Al-Cu-Ag, Al-Ni-Fe, and Al-Ni-Zr, [3,8,15–18] have been developed based on the above considerations. Mainly, Al-Cu-Ni alloys are attractive due to the formation of high-temperature ordered phases and intermetallics (e.g., NiAl, Al 3 Ni 2 , AlNi 3 , and Al 7 Cu 4 Ni) and in situ grown metal-inter- metallic eutectics (Al-Al 2 Cu, Al-Al 3 Ni). [3,7,8,10,18] How- ever, limited data are available on the mechanical property analysis of Al-Cu-Ni alloys. [3,25] Furthermore, vacancy ordered phases (VOPs) is formed in Al-Cu-Ni systems which have a high potential for high-tempera- ture applications due to their high melting point and a high degree of ordering. [19] So far, studies are restricted to fundamental phase analysis of VOPs in Al-Cu-Ni alloys [19–24] due to their monolithic structure. However, it is also interesting to engineer structures to utilize VOPs for high-temperature applications because of their promising mechanical properties. On a different perspective, the deformation behavior of Al alloys under extreme conditions has a high impact on aerospace and defense applications. [26–28] Al alloys face severe deformation under wear in most aerospace and automotive applications. [29–31] Generally, deforma- tion of Al at high temperatures occurs through the formation and movement of dislocations and shear bands. [26,27,32] Al-Cu-Ni alloys are also very useful in spray coating technology due to strong interfacial reactions between the constituents. [22,33,34] Thus, it is essential to study the wear behavior of such alloys at room and elevated temperatures. The present investigation deals with the synthesis of a bimodal microstructure of ordered and eutectic phases of different length-scale in Al-Cu-Ni alloys and the wear behavior at room and elevated temperature (300 °C). SHUBHADEEP MAITY, BIJAY KUMAR SHOW, and SUPRIYA BERA are with the Department of Metallurgical and Materials Engineering, National Institute of Technology, Durgapur 713209, India. Contact e-mail: supriyabera@mme.nitdgp.ac.in DIPAK KR. CHANDA is with the School of Materials Science and Nano Technology, Jadavpur University, Kolkata 700032, India. PARTHIBAN RAMASAMY is with the Erich Schmid Institute of Materials Science, Austrian Academy of Sciences, Jahnstraße 12, 8700 Leoben, Austria. JU ¨ RGEN ECKERT is with the Erich Schmid Institute of Materials Science, Austrian Academy of Sciences and also with the Department of Materials Science, Montanuniversita¨t Leoben, Jahnstraße 12, 8700 Leoben, Austria. Manuscript submitted May 3, 2019. METALLURGICAL AND MATERIALS TRANSACTIONS A