Molecular simulation of interfacial reaction between TiAl alloy melts and different coatings

Abstract

T iAl alloys exhibit many excellent properties such as low density, high melting temperature, good elevatedtemperature strength, Young's modulus, high resistance to oxidation, and excellent creep properties [1][2] . Thus, TiAl alloys are extensively applied in the gas turbine and automotive industries [3][4] . However, the poor ductility at room temperature hinders the development of TiAl alloys [5] . Some research results showed that TiAl alloys with fully lamellar structure, which could be obtained by controlling the crystallographic orientation using the directional solidification technique [6] , have a well-balanced combination of strength, ductility and other properties. Nevertheless, during the directional solidification of TiAl alloys, the high reactivity between the molten alloy and the ceramic crucible materials such as graphite and alumina brings in defects and contamination, which contributes to the poor mechanical properties [7] . Zhang et al. [8][9] [10][11][12] . But, so far, no crucible materials have been found to be absolutely inert to TiAl melts, and some interactions between the crucibles and the molten metal always occur during melting and casting [13][14] . Molecular modeling techniques have been widely applied to materials as a way to better understand the structure of materials and their interactions on the atomic scale. Simulation-derived diffusion rates can be used to evaluate the interfacial reaction processes. Molecular dynamics (MD) simulations may be adopted to calculate the diffusion coefficient for a variety of structures more accurately, and the diffusion coefficients of oxygen and oxide molecules in simulated systems were verified by many researchers [15] . The reaction between TiAl alloys and coatings are accompanied by the diffusion of oxygen atoms and the change of energy [16] . This research was focused on the modeling of the oxygen diffusion. In addition, there are no relevant reports on computational energy which applied molecular dynamics methods to the interaction. Thus, the diffusion process of oxygen and the binding energy of coatings are studied through molecular dynamics simulations, so as to provide a new understanding of the