Residual stress, hardness and chemical stability of TiN coatings

The residual stress in TiN coatings deposited on 316 stainless steel sheet by a reactive ion PVD process was determined over the temperature range from 15-800°C, using the sin 2 ψ X-ray diffraction method. A compressive stress of -4 GPa, observed in the TiN films at room temperature, decreased progressively on heating and reduced to zero at the deposition temperature of 475°C. At higher temperatures, the residual stress became tensile in form and increased to +6.8 GPa at 800°C. After the treatment at 800°C, the room temperature compressive stress was decreased to -3 MPa, which is the order of residual stress due to differential thermal contraction between the film and substrate. The breadth of the X-ray diffraction profiles was also significantly reduced after this heat treatment, confirming that microstresses introduced during film growth were annealed out by heating to 800°C. A darkening of the sample surface, combined with a reduction in indentation hardness and lattice parameter indicated that a nitrogen loss of 0.025% occurred during the heat treatments used in the residual stress determinations.