Sputtered Hf-Ti nanostructures: A segregation and high-temperature stability study

High-temperature stability and segregation tendency of a Hf-Ti alloy is investigated using specimens sputtered in monolithic and multilayer configurations. Upon annealing at 800 degrees C for 96 h, the alloy shows segregation of Hf and Ti at the nanoscale even though the bulk Hf-Ti phase diagram predicts a homogeneous solid solution. The length scale of segregation is found to depend upon the initial as deposited structure, with the monolithic film showing Ti segregation at grain boundaries, and the multilayered specimens showing a nanostructure of Hf-rich grains and Ti-rich intergranular amorphous regions. The multilayer specimens exhibit similar post-annealing grain diameters even when the initial layer thickness is varied. Thermodynamic Monte Carlo simulations show a solid solution when the bulk constraint is imposed, in line with the phase diagram expectation, and a polycrystalline nanostructure with solute segregated intergranular regions with full equilibration, in general agreement with the experimental observations. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.