In Situ Al-TiC Composites Fabricated by Self-propagating High-Temperature Reaction: Insights on Reaction Pathways and Th
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INTRODUCTION
IN recent years, much attention has been given to the concept of light weighting, particularly in the automotive and aerospace industries, in order to meet stringent guidelines for fuel economy. This trend toward light weighting has led to an increased use of and interest in aluminum alloys due to their high strength-to-weight ratio, low cost, and ability to be work- or precipitaHowever, aluminum alloys tion-hardened.[1–5] C.W. REESE, A. GLADSTEIN, and A.J. SHAHANI are with the Materials Science & Engineering, University of Michigan, Ann Arbor, MI 48109. J.M. FEDORS is with the Materials Science & Engineering, Worcester Polytechnic Institute, Worcester, MA 01609. V. DE ANDRADE is with the Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439. B. MISHRA is with the Materials Science & Engineering, Worcester Polytechnic Institute and also with the Mechanical Engineering, Worcester Polytechnic Institute, Worcester, MA 01609. A.I. TAUB is with the Materials Science & Engineering, University of Michigan and also with the Mechanical Engineering, University of Michigan, Ann Arbor, MI 48104. Contact e-mail: [email protected] Manuscript submitted October 14, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
commonly suffer from poor mechanical properties at elevated temperature, making their use in many industrial applications limited. Metal matrix nanocomposites (MMNCs) offer a potential pathway toward improving the high-temperature performance of Al-based materials via the incorporation of small amounts of refractory reinforcement particles. MMNCs are typically manufactured via ex situ processing, wherein precursor particles are added to a melt during processing.[6] However, ex situ MMNCs can suffer from the high precursor cost, poor wetting between matrix/reinforcement, and contamination of reinforcement powders.[7] Alternatively, particles can also be created directly in the melt via in situ reactions during processing. Previous work has demonstrated the possibility of particle formation through direct reaction between the constituent elements (e.g., solid–liquid reaction[8,9] or liquid–gas reaction[10,11]), as well as through solid-state diffusion-mediated reactions between compounds and individual elements (e.g., displacement reaction[12–18]). In situ MMNCs exhibit reduced particle agglomeration and stronger particle-matrix interfacial bonding.[19,20] Of the in situ methods, the self-propagating high-temperature synthesis (SHS) approach has proven to be
attractive for its ability to fabricate MMNCs in a wide variety of material systems and its potential compatibility with existing commercial equipment. A very promising approach utilizes a small amount of thermite (2.7 mol pct CuO) allowing for the SHS processing of TiC/Al MMNCs at relatively low bulk temperatures (750 C to 920 C).[9,21] However, the underlying mechanisms of the particle formation are not well understood which limits the ability to optimize the process for large-scale production. The SHS reaction pathways for TiC format
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