The effect of oxygen on the grain boundary and void structure of titanium films

Abstract

Titanium films 5000 nm thick were deposited onto steel substrates by electron beam evaporation over a range of substrate temperatures and oxygen partial pressures. The film structure was examined by X-ray diffraction and transmission electron microscopy. At substrate temperatures below 625 K the structure changes with distance from the substrate. Near the surface the films consist of elongated titanium grains, each surrounded by an amorphous oxide layer. At substrate temperatures above 625 K the grains are equiaxially oriented in the plane of the film and only the α-Ti phase is found. Voids exist in the interior of the grains for substrate temperatures between 625 and 775 K and at the triple points of grain boundaries for temperatures above 775 K. It is proposed that oxygen is located only within the oxide film at low temperatures, at the void surface at intermediate temperatures and within the α-Ti lattice at the highest temperatures.