RESIDUAL STRESS IN TiN COATINGS ON Ti-6Al-4V

摘要

Residual stresses in TiN coatings deposited by a reactive ion process on Ti-6A1-4V sheet were determined over the temperature range from 20-700 ℃, using the sin~2ψX-ray diffraction method. Calculations based on the relative thermal expansion coefficients of the coating and substrate showed that the magnitude of the thermal stress at room temperature was only -0.04 GPa, so hat the observed compressive stress of the order of-2 GPa could be attributed almost entirely to microstresses generated during the deposition of the TiN coating. The observed stress remained approximately constant after heating for 1 h periods at temperatures up to 500℃ and then reduced irreversibly to―0.6 GPa over the temperature range from 500 to 700℃. The reduction in compressive stress was accompanied by a decrease in peak breadth and an increase the perfection of the [111] texture of the TiN coating, confirming that the stress relief was associated with recovery processes involving point defects and dislocations. A simultaneous decrease in the d-spacings of planes parallel to the surface of the coating over the temperature range from 500― 700℃ is attributed to the relief of the ε33 Poisson generated strain, rather than a loss of nitrogen from the TiN structure.