Scandium on the formation of in situ TiB 2 particulates in an aluminum matrix
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ARTICLE Scandium on the formation of in situ TiB2 particulates in an aluminum matrix Dan Huang School of Engineering Technology, Purdue University, West Lafayette, Indiana 47906, USA
David Yan Department of Aviation and Technology, San Jose State University, San Jose, California 95192, USA
Siming Ma and Xiaoming Wanga) School of Engineering Technology, Purdue University, West Lafayette, Indiana 47906, USA (Received 9 May 2018; accepted 5 June 2018)
TiB2 particulates were formed in situ in an aluminum matrix via chemical reactions between an aluminum melt and the mixture of K2TiF6 and KBF4 salts. Different effects of Sc addition on the formation of the TiB2 particulates were revealed depending on the participation of Sc at different stages of the formation of the particulates. The metal–salt reactions resulted in boride layers along the a-Al grain boundaries in the presence of Sc, while the addition of Sc after the metal–salt reactions broke up the boride layers improving the dispersion of the TiB2 particulates to a limited degree. Sc promoted the growth of the TiB2 particulates, resulting in the coarsening of TiB2 particulates. The participation of Sc in the formation of TiB2 particulates altered the coarsening of the TiB2 particulates, resulting in different morphologies of the TiB2 particulates depending on the participation of Sc in the formation of the TiB2 particulates at different stages.
I. INTRODUCTION
Aluminum alloys reinforced with ceramic particulates, aluminum metal matrix composites (MMCs),1,2 show a high potential in meeting the ever-increasing demand for property improvement, such as high strength and high modulus, from the fast growing aerospace, electronics, and automotive industries.1–4 Aluminum alloys, as matrices, are featured with low density, high thermal conductivity, and plasticity. Meanwhile, the ceramic particulates offer high strength and moduli. Among various ceramic reinforcements, TiB2 particulates have attracted a great deal of attention due to their high strength, hardness, and strong covalent bonding with the aluminum matrix.5–15 The most attractive property of TiB2 as reinforcement is its good wettability by an aluminum melt, resulting in strong bonding to the aluminum matrix, which transfers stress from the matrix to the reinforcing particulates effectively in service with improved strength. A good wettability is also a key factor for obtaining uniform dispersion of the reinforcing particulates and therefore homogeneous properties of the composites. In comparison, other ceramic particulates, such as Al2O3, SiC, etc., are not wetted by an aluminum melt, causing difficulties in dispersion into an aluminum melt
and therefore weak matrix/reinforcement interfacial bonding and possible premature failure.1,2,16–19 TiB2 particulates can be introduced into an aluminum matrix as preformed particulates (ex situ) or formed in situ in the matrix. In situ fabrication eliminates possible oxygen contamination, producing a clean TiB2/Al interface and, therefore, strong TiB2/Al interfacial bon
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