Microstructure Formation and Micropillar Compression of Al-TiC Nanocomposite Manufactured by Solidification Nanoprocessi
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OWING to their well-balanced specific strength, plasticity and thermal stability, metal matrix nanocomposites (MMNCs) are expected to be utilized as structural materials in the aerospace, defense industries and micro-electro-mechanical-system (MEMS).[1] Among the various routes hitherto developed to fabricate MMNCs, solidification processing is one of the most widespread techniques owing to its simplicity, cost-effectiveness, and the potential for scalable
manufacturing.[2] However, nanoparticles (NPs) tend to agglomerate owing to their low wettability within the melts, and therefore, uniform dispersion of NPs is a long-standing challenge. Recently, two dispersion mechanisms have been proposed[3]: self- and pseudo-dispersion, which were determined using the relationship between the Van der Waals attraction (Wvdw), Brownian motion (Eb), and energy barrier (Wbarrier) in the reinforcement matrix system: (i)
ZUQI HU is with the Department of Materials Science and Engineering, University of California, Los Angeles, CA 90095, and also with the Institute of Materials, China Academy of Engineering Physics, P.O. Box 9071-2, Jiangyou, Sichuan, China. Contact e-mail: [email protected] CHEZHENG CAO and MAXIMILIAN SOKOLUK are with the Department of Mechanical and Aerospace Engineering, University of California, Los Angeles, CA 90095. MARTA POZUELO and JENN-MING YANG are with the Department of Materials Science and Engineering, University of California. XIAOCHUN LI is with the Department of Materials Science and Engineering, University of California, and also with the Department of Mechanical and Aerospace Engineering, University of California. Manuscript submitted December 22, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS A
(ii)
If Wvdw < Eb Wbarrier, NPs could overcome the Wvdw, and could, therefore, freely move and self-stabilize in the melt, i.e., self-dispersion. Chen et al.[3] reported the self-dispersion of 14 vol pct SiC NPs in the Mg-6Zn alloy, which simultaneously enhanced the strength, stiffness, plasticity, and high-temperature stability of the alloy, and yielded a specific strength superior to that of most structural metals. Adding 10 vol pct WC NPs to a Ag-Cu alloy increased its tensile strength by 74 pct without scarifying its plasticity.[4] Self-dispersion has also been achieved in Mg-30 pct TiC and Al-30 pct TiB2 systems.[5] If Eb < Wvdw Wbarrier, NPs could be kinetically trapped by Wvdw and could form a
separate NPs’ domain within melt, i.e., pseudodispersion. Then, the NPs’ domains would be pushed and squeezed by the growing dendrites during the solidification, and the NPs would distribute along the last solidified locations. Liu et al.[6] observed pseudo-dispersion in Al-9 vol pct TiC MMNCs and reported that the TiC domains, where dense NPs were loaded and separated by a few layers of Al atoms, were distributed along grain boundaries. Furthermore, state-of-the-art structural materials exhibiting inhomogeneous microstructures, such as architectures, ‘sandwich’ structures, and nanotwin/laminate),[7
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