Temperature Dependence of Residual Stress in Tin Films on 316 Stainless Steel

The residual stresses in a TiN film deposited by a reactive ion coating process on a 316 stainless steel sheet were determined by the sin$ X-ray diffraction method, at temperatures from 15-800 “C. Using specially designed nickel clips, the coated strip was heated by the passage of a resistive current, in conjunction with a surround heater, and the temperature was measured by a Pt/Pt-lO%Rh thermocouple welded to the under surface of the strip. Compressive stresses of the order of -4 GPa were observed at room temperature. On heating to 475 “C, the compressive residual stresses were progressively reduced to zero. On further heating, the stresses became tensile in form, and increased to 6.8 GPa at 800 “C. The deviation from linearity of the Ad/dn versus si&$ plots indicated that microstresses were also present in the deposited film and this effect was confirmed by profile breadth measurements. These microstresses were relieved by heating to 800°C. After this treatment the compressive residual stress at room temperature was reduced to -3 GPa, confirming the relief of point defects introduced during the growth of the coating. Surface discolouration and lattice parameter changes also indicated that nitrogen loss occurred from the TiN film during the high temperature treatment.