Analysis of Splitting and Martensitic Transformation of AlNi Intermetallic Obtained by Transient Liquid Phase Bonding
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This study investigates the characteristics of the AlNi intermetallic formed in a Ni/Al/Ni couple obtained by the Transient Liquid Phase Bonding (TLPB) process. The crystal structure and orientation of the AlNi intermetallic phase were evaluated through SEM-EDS EBSD and its mechanical properties were analyzed by means of instrumented hardness. The results showed that AlNi intermetallic splits into two layers, with different Al content and the same crystal structure and orientation. EBSD mapping revealed that there is no grain boundary along the split line, suggesting that a chemical partition takes place without the need of nucleation, like in a spinodal decomposition. A martensitic layer formed at the Ni-rich AlNi split side was identified by indexing the measured Kikuchi patterns. Instrumented hardness showed that the mechanical properties of AlNi phase change markedly depending on its chemical composition. These results provide experimental data that contribute to the understanding of the solid-state transformations occurring in the central portion of the Al-Ni phase diagram under isothermal conditions. https://doi.org/10.1007/s11663-020-01832-w Ó The Minerals, Metals & Materials Society and ASM International 2020
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INTRODUCTION
THE development of low density and high strength alloys for the aerospace industry has been the aim of countless investigations.[1] In this context, the alloys belonging to the Al-Ni system, Figure 1, were extensively studied since the intermetallic phases are attractive for high-temperature applications.[1–7] The Al-Ni equilibrium diagram shows five intermetallic phases (IPs): Al3Ni, Al3Ni2, AlNi, Al3Ni5, and AlNi3.[1] Depending on the technique used to prepare the Al-Ni alloy, the resulting microstructure can show not only a combination of the IPs shown in Figure 1, but also a metastable Al4Ni3 and a martensitic phase.[8–19] The AlNi intermetallic phase is particularly
MARIANA POLISERPI and SILVANA SOMMADOSSI, are with the Materials Characterization, IITCI CONICET-UNCo, Buenos Aires 1400, 8300 Neuque´n, Argentina. Contact e-mail: [email protected] ROBERTO BOERI is with the Metallurgy Division, INTEMA CONICET-UNMdP, Av. Juan B. Justo 4302, B7608FDQ Mar del Plata, Argentina RICARDO BUZOLIN and CECILIA POLETTI are with the Institute of Materials Science, Joining and Forming, TU-Graz, Kopernikusgasse 24/I, 8010 Graz, Austria and also with the Christian Doppler Laboratory for Design of High-Performance Alloys by Thermomechanical Processing, Kopernikusgasse 24/I, 8010 Graz, Austria. Manuscript submitted September 19, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS B
attractive since it exhibits the highest melting point (1638 °C) and is stable at room temperature. Another distinctive feature of this phase is the wide range of composition (45 to 56 at. pct Ni) under which it remains stable. Combining low density (5.86 g/cm3) and high oxidation resistance, the AlNi phase has a great potential for its application as high-temperature protective coatings.[7] Nevertheless, this phase shows
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