Citation: Tahani, M.; Postek, E.; Sadowski, T. Molecular Dynamics Study of Interdiffusion for Cubic and Hexagonal SiC/Al Interfaces. Crystals 2023, 13, 46. https:// doi.org/10.3390/cryst13010046 Academic Editor: Bolv Xiao Received: 19 November 2022 Revised: 19 December 2022 Accepted: 22 December 2022 Published: 27 December 2022 Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). crystals Article Molecular Dynamics Study of Interdiffusion for Cubic and Hexagonal SiC/Al Interfaces Masoud Tahani 1,2, * , Eligiusz Postek 2, * and Tomasz Sadowski 3, * 1 Department of Mechanical Engineering, Ferdowsi University of Mashhad, Mashhad 91779-48974, Iran 2 Institute of Fundamental Technological Research, Polish Academy of Sciences, Pawi´ nskiego 5B, 02-106 Warsaw, Poland 3 Department of Solid Mechanics, Lublin University of Technology, 20-618 Lublin, Poland * Correspondence: mtahani@um.ac.ir or mtahani@ippt.pan.pl (M.T.); epostek@ippt.pan.pl (E.P.); t.sadowski@pollub.pl (T.S.) Abstract: The mechanical properties of the SiC/Al interface are crucial in estimating the overall strength of this ceramic-metal composite. The present work investigates the interdiffusion at the SiC/Al interface using molecular dynamics simulations. One cubic and one hexagonal SiC with a higher probability of orientations in contact with Al are examined as two samples of metal-matrix nanocomposites with whisker and particulate reinforcements. These reinforcements with the Si- and C-terminated surfaces of the SiC/Al interfaces are also studied. The average main and cross- interdiffusion coefficients are evaluated using a single diffusion couple for each system. The effect of temperature and annealing time are analysed on the self- and interdiffusion coefficients. It is found that the diffusion of Al in SiC is similar in cubic and hexagonal SiC and as expected, the interdiffusion coefficient increases as the temperature and annealing time increase. The model after diffusion can be used to evaluate the overall mechanical properties of the interface region in future studies. Keywords: interdiffusion; metal-matrix composites; silicon carbide/aluminium interface; molecular dynamics 1. Introduction In recent decades, the use of ceramics in various engineering applications such as aerospace and automobile industries, cutting tools, and gas turbines has increased sig- nificantly. The advantages of ceramics are their excellent high-temperature, outstanding wear, and great corrosion resistance. However, they possess some disadvantages including brittleness, relatively low thermal conductivity, low fracture toughness and strength, poor resistance to creep, fatigue, and thermal shock. The disadvantages of ceramics can be overcome by microstructural engineering such as the development of metal-matrix com- posites (MMCs). They are usually used under extreme loading conditions such as impacts, high dynamic loads, elevated temperatures, and thermal shocks. To this end, accurate determination of the mechanical properties of MMCs is of great importance. Silicon carbide (SiC), alumina (Al 2 O 3 ), and tungsten carbide (WC) are the popular reinforcements, and aluminium, magnesium and titanium are the most common metal matrix materials. The SiC/Al metal-matrix nanocomposites have extensive applications due to their excellent properties, such as high strength, high fatigue, high toughness, excellent mechanical damping, good wear resistance, low density, and low coefficient of thermal expansion [1,2]. The SiC/Al MMC is mainly used in microelectronics as a substrate for power semi- conductor devices and high-density multi-chip modules, where it aids in the removal of waste heat. It can be used as heatsinks, substrates for power electronics, heat spreaders, housings for electronics, and lids for chips (e.g., microprocessors). Crystals 2023, 13, 46. https://doi.org/10.3390/cryst13010046 https://www.mdpi.com/journal/crystals