Interfacial reactions related to the TiN layer growth process between nanocrystalline epitaxial layers of AlN deposited on c-plane sapphire and a Ti–containing metal brazing or sintering layer using Ag–Cu–TiH2, Ag–TiH2 and Cu–TiH2 pastes have been investigated. The brazed/sintered samples were heated in vacuum at 850 °C for 30 min. The TiN layer produced at the metal/AlN interfaces consists of TiN particles < 50 nm in size and grain boundary phases including Al-containing Ag and Al-containing Cu. The Al concentration within the TiN layer decreases as the distance increases from the AlN epitaxial layer. These experimental observations all suggest that when AlN is used as a starting material in the active metal bonding method, interfacial reaction processes take place with the generation of a local Al-based eutectic liquid phase and elemental transport through this eutectic liquid phase.