First-principles And Experimental Study On The Effect Of Alloying Element And Interface Phase Al₄C₃ On The SiC/Al Interface

In this thesis, the effects of alloying elements（Mg, Si, Cu） and interface phase Al₄C₃ on the interfacial bonding of Si C/Al were studied. The effect of three temperature 800℃, 900℃ and 1000℃ on the wettability of Si C/Al system was investigated using a dispensed sessile drop method. Besides, the effect of the addition of alloying elements（Mg, Si, Cu） on the wettability of the Si C/Al system at 900℃ was also studied. The interface morphology was observed by SEM-EDS. An ideal model of Si C/Al was established by CASTEP module of Materials Studio based on density functional theory, discussing the effect of addition of alloying elements（Mg, Si, Cu）on Si C/Al interface through the electronic structure, the bonding strength of the interface was characterized by the adhesion power. The thermodynamics of Al₄C₃ formation will be studied. The process of Al film adsorbing carbon atom is investigated by the first-principles method. The Si C+Al₄C₃/Al model is constructed by Materials Studio, the effect of generation of partial Al₄C₃ at the interface on interface bonding is analysed. The Al₄C₃/Al model is also constructed, and the nature of Al₄C₃/Al bonding was analyzed by electronic structure.The results show that: the wetting dynamics of Si C/Al system is mainly divided into three stages. At 800-1000 the temperature range, the initial contact angle and final contact angle of the Si C/Al system decrease with the increase of temperature, the initial contact angle decreases from 131° to 109°, and the final contact angle decreases from 90° to 50°. With the temperature increases, the interfacial reaction of Si C/Al system is more intense, the geberation of Al₄C₃ phase is more, and the Al₄C₃ phase is favorable for the wetting of Si C/Al system. In the process of Si C/Al reaction, the wetting property of the whole system is a dynamic process, the true wettability may change from Si O2/Al to Si C/Al, and then change to Si C+ Al₄C₃/Al, and finally change to Al₄C₃/Al.Al（111） surface and Si C（001） surface are the smallest energy surface of the low index surface. In the Si C（001） surface, the surface energy of Si-terminated is less than C-terminated, and the work of adhesion of Si C/Al system of Si-terminated is less than that of C-terminated. Brigde structure of Si-terminated surface is the main bonding method of Si C/Al system. The doping of three alloying element make the interface adhesion energy and electron population between interface atoms increase resulting instrengthen the interaction with each other, the Si C/Al system is more stable, the combination effects of microalloys from large to small are Mg>Cu>Si. As the number of doped alloy atoms increase, the work of adhesion Si C/Al system was increased first and then decreased. The addition of three elements will increase the initial contact angle, but the final contact angle is less than that of the pure Al/Si C system. The final contact angle is changed from 73° to 61°, 67° and 63° respectively, indicating that three elements（Mg, Si, Cu） can improve the wettability of the Si C/Al system.According to the calculation of the thermodynamic model of Al₄C₃, the six groups of experiments in this paper will produce Al₄C₃ phase. The simulation result of Al（111）film adsorb carbon atoms by first principles show that: the most stable position which adsorb carbon atom is on the bridge; With the increase of the coverage rate of carbon atom, the adsorption energy of carbon atoms decreases gradually,thecovalent and ionic bonds are formed between aluminum atom and carbon atom; The adhesion energy of Si C+Al₄C₃/Al interface is 1231 m J/m2 by first principle calculation. The adsorption of carbon atoms on the aluminum surface will form a covalent bond and ionic bond between the carbon atom and the aluminum atom, and the silicon atoms at the interface also form a covalent bond, which promotes the interface bonding. In the Al₄C₃（001）surface, the surface energy of Al-terminated is less than C-terminated, and the work of adhesion of Al₄C₃ /Al system of Al-terminated is less than that of C-terminated. By comparing with the the adhesive energy of experimental measurements, HCP structure of Al-terminated surface is the main bonding method of Al₄C₃/Al system. By comparing the work of adhesion of hree kinds system, it can be seen that the generation of Al₄C₃ phase will enhance interface bonding of Si C/Al system.