Temperature Dependence of Residual Stress in Titanium Nitride Coatings on Haynes 188 Superalloy

Residual stresses in TiN coatings deposited by a reactive ion process on Haynes 188 superalloy, for potential application in jet engines, were determined over the temperature range from 30–800 °C, using high temperature X-ray diffraction. In the as-coated condition the TiN films have a pronounced [111] orientation texture and a compressive room temperature stress of -10.5 GPa. After heating for periods of 1h between 450 and 800 °C, the compressive residual stress was irreversibly decreased to -8.3 GPa and the widths of the diffraction peaks were reduced, confirming that the stress recovery is due to the removal of crystalline defects generated during the deposition of the coating. The crystallinity of the texture and the hardness of the TiN coating were not significantly changed after progressively heating for 1 h periods between 30-800°C. It was concluded that the associated stress recovery is not detrimental to the basic erosion and abrasion properties of the coating. An anomalous increase in compressive residual stress observed on re-heating from 30-800 °C is attributed the presence of nitrogen gas pockets within the TiN coating.