The effect of creep on the residual stress in vapour-deposited thin films

The residual stress state of coatings can be critically important in dictating their performance. When the residual stress in the coating is compressive the substrate is put into tension and, as the temperature increases, it can reduce this tensile stress by creep processes, which in turn will reduce the stress in the coating. A model has been developed to characterize this process by predicting how stress is generated and relaxed during coating deposition or scale growth. The output from the model has been validated by experimental measurements on vapour-deposited TiN on stainless steel and shows excellent agreement with experimental data measured by X-ray diffraction. The amount of stress relaxation by creep depends on the thickness of the substrate and coating, the time of exposure and temperature and, to a lesser extent, the cooling rate and the creep properties of the substrate material. (C) 1998 Published by Elsevier Science S.A. All rights reserved.