Production of intermetallic compounds from Ti/Al and Ni/Al multilayer thin films—A comparative study

This paper details a study of Me/Al (Me = Ti or Ni) multilayer thin films with equiatomic average chemical composition and different nanometric periods. The nanomultilayers were deposited by magnetron sputtering onto stainless steel substrates. The as-deposited Me/Al multilayer films are constituted by Ti- or Ni- and Al-rich layers. Transmission electron microscopy analysis reveals columnar growth and nanometric grains, whose size increases with the period and heat treatment. The nanostructural characterisation also reveals well-defined layered structures along the entire thickness of the multilayer films. In the as-deposited films the Me- and Al-rich layers are perfectly identified, even for short periods. Heat treatment leads to a disruption of the nanolayered structure by interdiffusion followed by chemical reaction to form intermetallic compounds. Whatever the system and the period, after heat treatment the films always evolve to the equilibrium intermetallic compound—γ-TiAl or B2-NiAl.