Diffusion of sputtered inconel 617 coatings in titanium

INCONEL 617 coatings 10-to 13-μm thick were radio frequency (RF) magnetron sputtered onto commercially pureα-titanium substrates and heat-treated at 800 °C for 2 hours. The resulting structures were examined in cross section by scanning electron microscopy (SEM) and analytical transmission electron microscopy (TEM). Scanning electron microscopy of polished and etched cross sections showed that the coating remained continuous, and as a result of inter-diffusion, a layer66-μn thick had formed below the coating. Examination of the coating near the free surface by TEM showed it contained both M₂₃C₆ and M₆C carbide precipitates, while several micron-thick layers containing intermetallic phases such as σ,γ′, and Ti₂Ni were found near the substrate. Kirkendall voids 75 to 300 Å in diameter were present near the original INCONEL 617/α-titanium interface. The microstructure further below that interface contained a thin layer of titanium martensite and Widmanstätten α + Ti₂Ni. No TiNi or TiNi₃ was found. The diffusivity of nickel and titanium was reduced several orders of magnitude and is attributed primarily to the formation of intermetallic compounds in the coating and substrate.