Diffusion couples of aluminum nitride (AlN) and Ti were annealed under an argon atmosphere at temperatures ranging from 1300 degrees to 1500 degrees C for 0.5-36 h. The morphologies, crystal structures, and chemical compositions of the reaction zones at AlN/Ti interfaces were characterized using analytical scanning electron microscopy and analytical transmission electron microscopy. An interfacial reaction zone, consisting of TiN, tau(2)-Ti2AlN, tau(1)-Ti3AlN, alpha(2)-Ti3Al, and a two-phase (alpha(2)-Ti3Al+alpha-Ti) region in sequence, was observed in between AlN and Ti after annealing at 1300 degrees C. The alpha(2)-Ti3Al region revealed equiaxed and elongated morphologies with [0001](equiaxed)//[1100](elongated) and (1010)(equiaxed)//(1122)(elongated). In the two-phase (alpha(2)-Ti3Al+alpha-Ti) region, alpha(2)-Ti3Al and alpha-Ti were found to satisfy the following orientation relationship: [0001](alpha-Ti)//[0001](Ti3Al) and (1100)(alpha-Ti)//(1100)(Ti3Al). The gamma-TiAl and a lamellar two-phase (gamma-TiAl+alpha(2)-Ti3Al) structure, instead of tau(1)-Ti3AlN, were found in between tau(2)-Ti2AlN and alpha(2)-Ti3Al after annealing at 1400 degrees C. The orientation relationship of gamma-TiAl and alpha(2)-Ti3Al in the lamellar structure was identified to be as follows: [011](TiAL)//[2110](Ti3Al) and (111)(TiAl)//(010)(Ti3Al). Compared with the reaction zone after annealing at 1400 degrees C, the gamma-TiAl was not found at the interface after annealing at 1500 degrees C. The microstructural development resulting from isothermal diffusion at 1300 degrees C and subsequent cooling at the interface are explained with the aid of the Ti-Al-N ternary phase diagram and a modified Ti-Al binary phase diagram.