Al-Ti Particulate Composite: Processing and Studies on Particle Twinning, Microstructure, and Thermal Stability
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ALUMINUM and its alloys are one of the most important classes of lightweight materials which find their applications in structural, automotive, and aerospace industry owing to their high specific strength, high toughness, and good corrosion-resistant properties. The ever-increasing demands of higher strength-to-weight ratio led to the development of new techniques and technologies to improve the mechanical properties of aluminum by various means. Some of the methods widely adopted to achieve this include grain refinement, strain hardening, precipitation hardening, solid solution strengthening, and thermo-mechanical treatments. Metal matrix composite (MMC) technology is another widely used method for strength improvement of Al alloys.[1] However, although the strength is increased,
DEVINDER YADAV, Research Associate, and RANJIT BAURI, Associate Professor, are with the Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras, Chennai 600036, India. Contact e-mail: [email protected] ALEXANDER KAUFFMANN, Research Associate, is with the Institute for Applied Materials, Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany. JENS FREUDENBERGER, Professor, is with the Institute for Metallic Materials, IFW Dresden, PO Box 270117, 01171 Dresden, Germany, and also with the Institute of Materials Science, Technische Universita¨t Bergakademie Freiberg, Gustav-Zeuner-Str. 5, 09599 Freiberg, Germany. Manuscript submitted September 10, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS A
retaining the ductility is a major challenge in most of the above processes. In the MMC technology, high-strength and high-modulus ceramic particles such as Al2O3, SiC, B4C, AlN, TiB2, and TiC are added to aluminum to improve its mechanical properties. These particles are inherently brittle and hence the improvement of strength is accompanied by a large drop in the ductility.[2–5] Poor wetting, particle clustering, and interfacial debonding are the other main reasons attributed to the drop in ductility in MMCs.[6–9] Harder metallic particles can be used as reinforcements in an aluminum matrix as an alternative approach to retain the ductility of the composite. The issues of residual stress and wettability can be minimized, too. However, retaining metallic particles as reinforcement is difficult. Metals with low solid solubility such as Ni, Fe, and Ti readily react with Al by means of the formation of brittle aluminides (NiAl, Al3Ni, Al3Fe, Al3Ti, etc.) with rapid kinetics.[10–15] On the other hand, high-solid solubility metals such as Cu, Zn, Mg, and Li easily dissolve into Al to form solid solutions. Hence, the main challenge here is to incorporate metallic particles and retain them in elemental state as reinforcements. In other words, the reaction or dissolution of the metallic particles during processing is to be prevented which is a difficult task in conventional composite processing routes. Ti is an attractive choice for reinforcement because of its high specific strength, high modulus, and good fatigue
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