First-principles calculations of the effects of the interface microstructure on the wettability of a Cu–Ti/AlN system

The active element Ti is always added to Cu-, Ag-, or Sn-based fillers used to join ceramics, because it promotes the wetting of the fillers on ceramics. However, different mechanisms have been proposed on the mode of action of the active element Ti in promoting the wetting of the filler alloy. In this study, in order to gain a better understanding of the two controversial wetting mechanisms, which are based on adsorption and interfacial reaction, density functional theory (DFT) calculations were performed to investigate the role of the active element on the interfacial properties of the Cu–Ti/AlN wetting system. The following three typical wetting interface models were constructed: (1) the original interface of Cu/AlN, (2) adsorption interface of Cu/AlN(Ti), and (3) reaction interface of Cu/TiN. First, according to the convergence of the surface energy, a four-atom-layer Cu (111) slab, an eight-atom-layer AlN (001) slab, and a five-atom-layer TiN (001) slab were used to represent the Cu bulk, AlN bulk, and TiN bulk, respectively. Then, interface models were constructed and the work of adhesion, Bader charges, differential charge density, and density of states were analyzed, and the theoretical contact angles were calculated. The results indicate that both the adsorption of Ti at the interface and its reaction with AlN to form a TiN layer remarkably improve the wetting of Cu on AlN, and the contact angle decreased from 173° to 74° and then to 119°. This study constitutes a modest step toward clarifying the wetting mechanism of Ti-added active fillers on ceramics.