Structural formation of aluminide phases on titanium substrate

Abstract

An aluminum layer on titanium substrate has been formed by thermal deposition. The structural formation of aluminide phases on the Ti substrate has been studied. The sequence of structural transformations at the Ti/Al interface is limited by the reaction temperature and time. Kinetics of these transformations are defined by a factor of concentration. At the initial stages at the Ti/Al interface the Al 3Ti alloy starts forming as a result of interdiffusion, and gradually the whole aluminum film is spent on the formation of this layer. The Al 3Ti layer decomposes with increasing temperature (>600 °C). At 800 °C the two-phase (Ti 3Al+TiAl) layer is formed on the titanium surface. The TiAl compound is unstable and later on with the increase of the exposure time at 800 °C gradually transforms into the Ti 3Al. The chain of these successive transformations leads to the formation of the continuous homogeneous layer consisting of the Ti 3Al compound on the titanium surface. At temperatures exceeding the allotropic transformation temperature (>900 °C) the Ti 3Al compound starts decomposing, aluminum atoms diffuse to the substrate and are uniformly distributed within the surface volume. All structural changes taking place at the Ti/Al interface are accompanied by considerable changes in microhardness. Due to the Ti 3Al layer being formed on the titanium surface, its microhardness increased practically by 2.5 times.